Home « Gardening News « August 1, 2007

Yard and Garden News

Featured this issue:

• What's Up With That?!
• Seasonal Watering Guide For Trees and Shrubs – Deciduous and Evergreen
• Biological Control of Invasive Plants in Minnesota, A Collaborative Effort
• Switchgrass, Wonder Grass of the Future?
• Something Strange in the Garden
• Trouble Shooting for Nutrient Disorders of Plants
• Sphecid Wasps Are Common Now
• Entomology Shorts
• Summertime Lawn Stresses Still Causing Concerns
• Aster Yellows
• August Gardening To-Dos

What is the most important “secret” to keeping landscape trees and shrubs healthy? It's not fertilizers, nor growth regulators, nor biological soil inoculants. It's not herbicides, fungicides or insecticides, either. It is water management, the art and science of maintaining soil moisture at an optimum level for trees and shrubs, young to ancient. When water management is ignored or otherwise goes wrong, trees and shrubs languish, suffer and die.

Part One: Water Management Tools

At a minimum, invest in several good soaker hoses or “drip” watering tapes. Most hardware stores, home improvement centers or garden centers have soaker hoses. Watering tape is usually something that is special ordered, and costs about the same as a soaker hose, often a bit less. One brand, T-Tape, has been used extensively in commercial nurseries and has an excellent track record for performance and ease of use. Access the T-Tape web site for more information: http://www.dripworksusa.com/farm.html .

Regardless of whether a soaker hose or a watering tape is used to provide irrigation water, they are more efficient than lawn sprinklers. Little water is lost to evaporation when soaker hoses or watering tapes are used, and if they are used to water boulevard trees, sidewalk pedestrians won't be shocked by a curtain of sprinkler water!

Another basic “tool” would be a soil probe. With a probe, a 6 to 18 inch core of soil can be pulled from the rhizosphere (the root environment) of the landscape's trees and shrubs. Checking this soil core will eliminate the need for guessing if you've watered enough or investing in more expensive soil water monitoring equipment. Again, these can be found in many good garden centers, or on-line. Just type in “soil probe” in any search engine and a variety of resources will pop up, prices ranging from $30 to $200. If you want my opinion, expect to invest about $75 for a good one for home use. If you get the cheaper ones, expect to buy several over the span of a year or two.

You are now armed to begin managing the soil moisture requirements of your trees and shrubs. Note that no mention was made of underground irrigation systems. They're wonderful for turf grass and sometimes flowers. No mention was made of deep root watering devices, either.

Part Two: Young and Old

Newly Planted Trees and Shrubs : Water where the roots are, not where they will end up. Water should be supplied by either you or the clouds twice a week for the first growing season (which ends when the soil is frozen). As a rule of thumb, supply 1.5 to 2.5 gallons of water per inch of stem diameter (the higher rate for fast-draining, sandy soils) per irrigation. Consider investing in tree watering bags…they're wonderful and can be found at: www.treegator.com/ . For the next two to three years (depending on the size of the transplant), supply water at least once per week. Thoroughly water a root area with a radius of 3 to 6 feet (6 feet for larger transplants – 3” caliper and above) around the plant's stem. Soaker hoses or watering tapes are the best choices for supplying water.

Established Young Trees and Shrubs : This would be defined as after the transplant shock period when the characteristic root-to-shoot balance is reestablished. Generally, the transplant shock period for trees is 1 year per 1 inch of stem caliper. So, for example, a 2 inch caliper tree normally takes at least two years to get through transplant shock. No such formula exists for shrubs.

Provide (via clouds or hoses) a thorough soaking in the *critical root zone once per week as a normal course of action. Forget about that “one inch of water per week.” It's sure not based on woody plant research. With the soil probe, check the soil moisture. As a minimum, the top 8 to 12 inches of soil should be moist – but not saturated. There are a lot of fancy gadgets and electronic widgets that can set you back a lot of money and not do as good of a job as a soil probe. Get in touch with the rhizosphere! Feel the soil and develop a sense of what's enough, what's dry, how long did it take to moisten the soil to that depth and if the hoses are in the right position.

[*The critical root zone can be calculated by measuring the diameter of the plant's stem (in inches) and then multiplying that number by at least 1 foot. Don't multiply inches times feet, just the number of inches because it's a ratio that determines the critical root area. This product (for instance, a 5 inch diameter plant stem x 1 foot = 5 feet) is the radius of the rooting area measured out from the plant's stem.]

Established Trees and Shrubs : Would you stop feeding and watering your pets just because they're no longer puppies, kittens or colts? NO! So don't treat trees and shrubs that way! For the life of the trees and shrubs, and for the life of the trees and shrubs, make certain that the rhizosphere is moist to a depth of at least 12 inches throughout the growing season, which includes the autumn until the soil freezes.

Place the watering devices within the canopy or critical root zone of the landscape trees and shrubs. For “normal” trees and shrubs, the edge of the canopy is a fine place to stop the irrigation, even though there will be roots beyond that point. For more columnar growing plants, using the formula for calculating the critical root zone is a more accurate estimation of the extent of the critical root system. Generally, there's no need to irrigate closer than 3 feet or so to the trunks of trees since there are few fine roots in that area.

Don't guess if you've watered enough or long enough. Use the soil probe. Don't believe weather reports…they're only semi-accurate and quite honestly, most rains don't provide enough moisture for the rhizosphere. It usually takes an extended rainy period to thoroughly moisten the soil.

Part Three: Mulch Madness!!!

The single-most effective way to moderate soil moisture fluctuations and reduce the frequency and amount of irrigation is the application of a generous layer of mulch (preferably organic) over as much of the root system as can be tolerated. It is astonishing how long the soil below a generous mulch layer remains moist, even in droughty periods. In addition to moderating soil moisture extremes, organic mulches break down and continuously add organic matter to the soil horizon.

Use a minimum of 3 to 4 inches of coarse organic mulches (e.g., wood chips, but not redwood nuggets), or 2 to 4 inches of finer mulches (shredded bark, hulls, composted leaves). Don't pile the mulch against the stems of plants. If you annually add a fresh topping of mulch, DO NOT REMOVE THE OLD MULCH! BAD GARDENER!!! When old mulch is removed, all of the wonderful fine roots of the trees and shrubs are removed, too. Treat your trees and shrubs as a forest or prairie does with annual, light applications of organic materials. (Natural areas do this with their old leaves, dead roots, dead branches, thatch, etc.).

Mulches don't make water…they conserve water. Make certain that the rhizosphere is thoroughly moistened (break out that soil probe again) before the mulch is applied. If there is turf around the plants, place 5 to10 layers of newspapers over the turf, soak the newspapers and then apply the mulch. If you don't read newspapers, kill the grass with glyphosate…carefully avoiding any spray drift to young stems, leaves and your neighbor's vegetable garden.

If mineral mulches (gravel, crushed rock, etc.) are more desirable, then use a weed fabric groundcover before the mineral mulch is applied. Try to avoid using plastic as a groundcover. Generally, though, organic mulches are preferred for plant health.

Part Four: Some Final Myths

1. Watering trees and shrubs is expensive . False. Caring for declining plants or removing dead trees and shrubs is expensive.

2. Water from soaker hoses or watering tapes only moves downward . False. Soil moisture moves both vertically and horizontally, depending on the soil texture. Keep checking your specific rhizosphere soil with a soil probe to determine the optimum spacing for these watering devices.

3. Watering trees and shrubs in the autumn stimulates new, lush growth that will be damaged by winter temperatures . False. Good grief, where did that myth start? Don't believe that autumn watering delays dormancy and encourages delayed dormancy. Autumn rains are normal and dormancy is a function of photoperiod, temperatures and genetics. Autumn droughts encourage cold temperature damage to trees and shrubs.

4. Moist soils freeze deeper and get colder than dry soils . False. Just the opposite. See notes above about droughty autumns.

5. The more money spent on high tech and fancy watering equipment, the healthier the trees and shrubs will be! No relationship. It's interesting how some property owners will willingly part with hundreds of dollars for bells and whistles, yet complain that watering trees costs too much! Invest your dollars in conservative water monitoring. Use soaker hoses or any other technique that drips water to the rhizosphere, rather than spray it to great heights and hope that a percentage of it reaches the ground. Invest your dollars in a soil probe. Who cares how much water is applied? The amount of water reaching the roots is most important.

There is no substitute for efficient, conservative watering techniques (soakers, drips and mulches), and knowing how much water is getting to the roots (soil probe). Don't avoid it, just do it for the life of the trees and shrubs.

 

 

 

Invasive plants can cause economic and environmental damage. Nonindigenous plants cost an estimated 34 billion dollars annually in losses, damages, and control costs (Pimentel et al., 2000). In agricultural and natural areas, they can displace desirable vegetation, resulting in reduced productivity, wildlife forage, and habitat.

Many invasive plants have the uncanny ability to migrate along transportation corridors such as roadways and then move into fields and natural areas where they proliferate with alarming speed. As new roads are constructed and existing roads are expanded, the disturbance created with vegetation removal and soil movement can render areas vulnerable to invasive plants. Mowing of roadsides, usually done for safety purposes, can also spread seeds. Additionally, seeds can be moved on vehicles. All of these situations together create ample opportunities for invasive plants to spread. As we travel along roadways, we see these invasive plants and may wonder how they are dealt with. Agencies such as the Minnesota Department of Transportation (Mn/DOT) utilize a variety of tools to manage weeds.

Biological control is one tool that targets specific weed species such as leafy spurge, spotted knapweed and purple loosestrife. Classical biological control is the practice of reuniting a pest with its natural controls. This control method is sustainable, long lasting, and cost effective. For example, in its native range leafy spurge is kept in check by naturally occurring insects and diseases. When leafy spurge was accidentally introduced to North America , it proliferated uncontrollably without diseases and insects to hold infestation levels down. To bring leafy spurge into balance, Aphthona species of flea beetles are released at large leafy spurge infestations. Since the beetles are native to Eurasia , they underwent rigorous testing to ensure that they are host specific so will not feed on native or other desirable vegetation. The beetle larvae feed on leafy spurge roots and will weaken or kill the plants when a large beetle population is present. Since it takes many years for the beetle population to build to a damaging level, biological control is a long-term approach that takes patience.

Mn/DOT and many counties manage weeds such as leafy spurge and spotted knapweed with biological control. Many infestations have been successfully controlled to date. See the map above for new (2004-2007) leafy spurge biocontrol releases in the metro area and watch the infestations decrease over the coming years.

Weed biological control is a cooperative program in Minnesota . This means that agencies, organizations, businesses, and individuals can partner to share biological control insects. When bioagent populations are sufficiently large at a site, they are collected and distributed to new sites. The Minnesota Department of Agriculture (MDA) coordinates programs for leafy spurge and spotted knapweed biocontrol and the Minnesota Department of Natural Resources (DNR) coordinates the purple loosestrife program. Much of the work is done at the local level by County Agricultural Inspectors, Mn/DOT, and other cooperators.

Individuals can help control invasive plants by notifying their County Agricultural Inspector (CAI) of infestations. The CAI can then work with the appropriate land manager to implement control methods. If individuals are concerned that they have leafy spurge, spotted knapweed, or purple loosestrife on their land and would like to try biological control, they can work with their CAI to receive bioagents. A listing of CAIs can be found at
www.mda.state.mn.us/plants/weedcontrol/cailist.htm

Future projects include researching garlic mustard and buckthorn biocontrol (coordinated by the DNR) and common tansy biocontrol (coordinated by the MDA). Bioagents for these plants are being tested at this time and are not available yet.

For more information on leafy spurge, spotted knapweed, or common tansy biocontrol:

Monika Chandler
Minnesota Department of Agriculture
651-201-6468
Monika.Chandler@state.mn.us
www.mda.state.mn.us/plants/weedcontrol/

For more information on purple loosestrife, garlic mustard, or buckthorn biocontrol:

Luke Skinner
Minnesota Department of Natural Resources
651-259-5140
Luke.Skinner@dnr.state.mn.us
www.dnr.state.mn.us/ecological_services/invasives/

Reference
Pimentel, David, Lori Lach, Rodolfo Zuniga, and Doug Morrison (2000) Environmental and Economic Costs of Nonindigenous Species in the United States . BioScience 50(1) pp. 53-65.

photo credits: MDA Biocontrol

 

 

 

 

Beautiful and versatile, native switchgrass (Panicum virgatum) has everyone talking about it. Even the President of the United States has mentioned switchgrass in recent press conferences! Wow, grasses have really come into their own!!

What's so cool about switchgrass?

• It's big, especially below ground.
• It's an attractive native ornamental, easy to grow, and changes through the seasons.
• It's a source of food and cover for wildlife.
• As a biomass fuel source, it has good potential as a renewable energy source for the future.

Panicum is one of the largest grass genera in the world, with about 475 species widely distributed in warmer climates. Approximately 170 species exist in the U.S. Panicum virgatum , or switchgrass, is one of these 170 species and is a tall, robust bunchgrass adapted to low prairies, riverbanks, and swale areas. It is native to all states in the U.S. except Washington , Oregon , and California . Panicum derives its name from its type of inflorescence, a panicle, which is a large, many-branched flowering structure with individual flowers on the ends of branches.

For years switchgrass has been used as a forage grass for pastures, providing hay and cover for erosion control in the Midwest . The Natural Resources Conservation Service, NRCS, part of the USDA and formerly known as the Soil Conservation Service, has researched and released plants for conservation purposes. Since 1940, NRCS has released 20 different selections of switchgrass, all from native collections originating in the Midwest . Perennial plant growers, especially in Germany , recognized grasses as beautiful ornamentals for the garden and new selections of switchgrass started to come into the market in the 1970s.

Switchgrass is a robust, long-lived grass, ranging in height from 2 feet in dry upland sites to 10 feet in wet areas in the southern Midwestern states. Of all the native prairie grasses, switchgrass roots are the most extensive, growing 3 to 4 mm in diameter and penetrating to depths of 9 to 11 feet (Weaver, 1968). Switchgrass is aggressive, forming dense stands that can exclude other species. Heights of 6 to 10 feet are common in the south, but more often plants reach 4 to 5 feet in Minnesota . Switchgrass grows primarily in clumps, but may form sod with rhizomes as well as self-seeding to form sizable colonies.

Switchgrass is one of the co-dominant grass species of the original tallgrass prairie and is a common roadside plant throughout Minnesota. In the garden, a single plant will be very well behaved. Switchgrass generally requires cross pollination so one plant is very unlikely to set seed. However, if you grow several different switchgrass cultivars, you will likely see seedlings.

The topic of biofuels is usually mentioned in the same sentence with switchgrass because this amazingly long-lived perennial grass actually has more biomass BELOW ground than above, due to its extensive roots. In Weaver's book, Plants in Prairie Communities , you can see pictures of men down in deep trenches, investigating the depth of plant roots. Also, switchgrass is a C 4 plant which means it is very efficient at using CO 2 (carbon dioxide) and water to make carbohydrates for plant growth during periods of heat and drought. The chromosomes of switchgrass are diverse, from normal diploids with 2 sets of chromosomes to tetrapoids (4 sets) and octaploids (8 sets). This variability of DNA is one of the reasons we see such great diversity in plant size and form in switchgrass.

While you may be passing switchgrass everyday on the roadside, gardeners are interested in the ornamental forms that are especially showy for their form and flowers. Because switchgrass has such a wide native range across the U.S. there are literally millions of different forms of switchgrass. It's no wonder we have many ornamental forms available to buy at garden centers. From the swamps in Florida to the hilltops of Maine , you can find switchgrass. In Minnesota , we usually find it in wetter sites. It thrives in roadside ditches, low spots near lakes, and wetlands, or, as the British call them, “water meadows”.

Skipper butterflies feed on switchgrass as larvae: Leonard's skipper and tawny-edge skipper prefer this plant. Because it stands up well in winter, it provides good wildlife cover and its seeds provide food for many birds and small mammals.

Listed below are some of the very distinctive cultivars of switchgrass. All of these, except ‘Prairie Fire', have been grown at the Minnesota Landscape Arboretum in the ornamental grass collection. Results and information are based on trials conducted since 1987 at the U of Minnesota Landscape Arboretum and at Research and Outreach centers at Morris and Crookston. The grasses are fun to see at any time of year, but to see switchgrass in full flower, visit the Arboretum after late August.

Switchgrass cultivars for gardeners:

‘Cloud 9' - Discovered near Philadelphia , PA by nurseryman Dick Simon, this is a huge grass. One plant makes a giant cloud over the top of other perennials, extending to about 8 feet across and close to 8 feet tall. The medium- to coarse-textured blue-grey foliage is upright, but the size of the immense panicles or seedheads can cause the top half of the plant to lodge (fall over) if not supported by other perennials or staking.

‘Dallas Blues' - Another giant plant, this cultivar has wide blue foliage and grows to about 6 feet tall and 6 feet wide in Minnesota. The flowers have a soft purple hue and are giant whorls of cloud-like seedheads. Winter hardiness can be an issue over the years in our region. Only one plant now survives at the Arboretum, and the overall height for us is smaller than when the plants are grown in Zone 5 or in even warmer Texas where ‘Dallas Blues' originated. This was one of the first patented grasses. This cultivar can lodge, especially when planted in rich, fertile soils and overwatered.

‘Heavy Metal' - Selected by Kurt Bluemel, veteran grass grower in Maryland , this form has stiffly erect leaves that are metallic blue in summer and yellow in fall. An erect plant, growing 4 to 5 feet, rarely lodges, and is wide and full.

‘Northwind' - Growing 5 to 6 feet tall and only about 2 feet wide, this is the straight-as-an-arrow cultivar that will not lodge at all. Actually, it's almost impossible to bend the plant stems without breaking them! Medium to coarse green foliage; the typical airy panicles form inside the foliage and gradually push out above. Selected from Wisconsin .

‘Prairie Sky' - This beautiful blue-foliaged cultivar lodges a lot - in fact, it's pretty much a ground cover by September - so if that is not the look you want, select another form. Beautiful foliage color, typical panicle flowers. 3 feet tall and equally wide by late summer.

‘Rotstrahlbusch', ‘Rubrum', ‘Rotbraun', and ‘Hanse Herms' - These red forms of switchgrass originated in Germany. They are all similar, with foliage, flowers, and seedheads tinted red and purple. They can form a soft, red cloud in the garden in late summer. Some of these red forms are weaker plants and green seedlings can easily grow among the original plants and overtake the original red forms, so gardeners should remove green forms that develop. 3 to 5 feet tall, not much lodging.

‘Shenandoah' - Has outstanding burgundy foliage - the leaves start showing dark red tones by midsummer and are fully colored by early fall. Shorter, growing 3 to 4 feet tall, this red form was selected by Hans Simon, a German nurseryman who gave it the American name to show its origins from the Midwest U.S.

‘Trailblazer ' is the only form released by the NRCS that is also sold as an ornamental in the nursery trade. It originated from Nebraska and Kansas and was introduced by the USDA-ARS in 1984. It grows 4 to 5 feet tall with blue-grey foliage and at the Arboretum it becomes very wide, since the plants lodge easily.

Other cultivars:

‘Strictum' is an older form, with few defining characteristics; newer forms are superior. ‘Squaw' and ‘Warrior' are hardy in Minnesota , growing to 5 feet with typical switchgrass characteristics.

New forms at the Arboretum are ‘Huron Solstice' and ‘Thundercloud' , planted for evaluation in 2007.

‘Prairie Fire' is a Walters Gardens introduction that's very new on the market. It has red foliage and originated in Michigan .

General Culture:
Switchgrass is easy to grow in full sun and in average, medium wet, or wet soils. It tolerates almost any soil, although it likes wet or heavy soils best. Switchgrass does not grow well in the shade. Lodging or falling over is a genetic trait of grasses: some have it, some don't. You may be able to minimize lodging by growing switchgrass in full sun in light, nutrient-poor soil. Moist, rich soils encourage growth and lodging. But the bottom line of what controls lodging is the genes in a given plant and this can override any site conditions.

Cut back clumps to the ground in late winter to early spring. Switchgrass is easily grown from seed, but each plant will be a unique individual, with different foliage and flower characteristics. Propagate cultivars by division in early spring. Watch for seedlings in the garden and remove them. Switchgrass needs no supplemental water after establishment and needs no fertilizer. There are no pests or disease problems with switchgrass and although it is native, deer do not eat switchgrass.

References:

NRCS. 2007. Plant Releases by Scientific Name. http://plant-materials.nrcs.usda.gov/releases/releasesallbysci.html

USDA. 2007. Plants Database. http://plants.usda.gov/java/profile?symbol=PAVI2 .

Weaver, J. E. 1968. Prairie Plants and Their Environment . University of Nebraska , Lincoln , NE.

 

 

 

 

As the growing season progresses, several new arrivals are sprouting in Minnesota 's gardens. These new arrivals did not come from a seed catalog or the local garden center. They arrived on the wind or with the help of some neighborhood insects.

Stinkhorns and slime molds are common in Minnesota throughout the growing season. Although not typically considered as appealing as many garden flowers, stinkhorns and slime molds are an interesting part of Minnesota 's natural world.

Stinkhorns

If you have stinkhorns in your garden this year, you will probably smell them before you see them. Stinkhorns earn their name by producing a foul or putrid smell designed to attract flies. The stinkhorn itself is the reproductive structure of a fungus that spends most of its life feeding off of organic matter like leaf debris and decaying wood. Since this activity occurs in the soil or just on top of it, most gardeners never know the stinkhorn fungus is present until the reproductive “horns” emerge.

Stinkhorns start as small oval egg-like structures at about soil level. Much like a chicken in an egg, the fungus remains in its “egg” stage for several days while the stinkhorn develops inside. When fully developed, the stinkhorn ruptures the outer layer of its “egg” (known as a peridium) and emerges in a matter of hours. The stinkhorn includes a stalk made of spongy fungal tissue that is typically hollow inside. Stinkhorns in the genus Phallus have a pointed cap on top of the stalk. Those in the genus Mutinus taper off at the tip but have no distinct cap. Both types of stinkhorns will have a coating of greenish gelatinous slime at the tip. This slime is full of fungal spores and is responsible for the foul odor. As flies carry away bits of slime and spores, the gelatinous coating at the tip of the stinkhorn will be reduced, as will the smell.

Since Stinkhorns feed off dead organic matter, they will not injure garden plants, trees, or shrubs in any way. Nothing needs to be done about stinkhorn fungi in the garden. Since much of the fungus lives in the soil, removal of the entire fungus is not possible. If the stinkhorns themselves are too smelly to bear, they can be cut off and thrown out. Typically they will fade on their own as the spores are released and their lifecycle continues.

Slime Molds

Slime molds are unusual, interesting creatures that scientists once thought were fungi, but now realize are more closely related to bacteria. Slime molds can exist as individual amoeba-like cells or individual cells with a string-like tail called a flagella used for moving around. Each cell can switch back and forth between these two forms. Both of these cell types feed on bacteria, fungal spores, yeast and possibly organic matter, but only the amoeba-like cells can reproduce. These types of slime mold cells along with slime mold spores can easily be found in bark, soil, and earthworm castings, but most gardeners would never know they are there.

When the population gets big enough, however, two cells fuse together to form one cell with twice the DNA. This cell creates more nuclei but never divides. The result is a large gelatinous blob with a slime layer, a cell membrane, and many nuclei called a plasmodium. This plasmodium continues to feed on bacteria and other microscopic organisms, stalking its prey at the speed of 1 mm per hour. If a plasmodium meets another plasmodium of the same species, they will fuse together. Plasmodia several feet across have been recorded.

It is these large blobs that catch a gardener's eye. Slime molds like moist areas near decaying matter where bacteria and other food can be easily found. They are commonly seen on lawns or in garden mulch. Their colorful common names like the scrambled egg slime, the tapioca slime, and the dog vomit fungus clearly describe what a slime mold looks like.

Unknown to most gardeners, slime molds have yet another life stage that looks completely different from the plasmodial blob. In response to changes in temperature, moisture, light or food availability, the entire plasmodium will change into tiny stalked spore-producing structures no more than a few millimeters tall. These can often be seen on decaying wood or other substrates, and can be a wide variety of colors and shapes. The spores these structures produce are small, round, and easily carried to a new location on air currents. Under dry conditions these spores have been known to survive up to 75 years before germinating to start the cycle all over again.

Nothing needs to be done about slime molds in the yard and garden. Although slime molds may be found directly on top of garden plants, they are there to feed on bacteria and do not hurt the plant. A rake or a blast of water from the garden hose can be used to break up the plasmodium if desired, but typically the plasmodium will become less noticeable and eventually disappear altogether as it completes its lifecycle. Since spores and single cells are present in soil and organic matter, there is no way to prevent slime molds. Instead, just enjoy this unusual life form that has intrigued scientists and gardeners for years.

 

 

 

 

Visual Diagnosis

Visually inspecting your plants on a regular basis is a useful way to monitor the health of your home landscape. There are many causes of poor plant growth and sometimes it is difficult to pinpoint the underlying cause, but there are characteristic symptoms for a number of plant growth problems that can help the observant gardener. Nutrient disorders (deficiencies or excesses of specific nutrients) are one cause of poor plant growth. Fortunately there are distinct symptoms for many nutrient disorders, although they may resemble, interact with, or be masked by symptoms of other growth problems.

Scouting for insects and diseases is very important, because they can be controlled much more effectively when found early in their development. It is also important to see signs of nutrient disorders at early stages of their expression. Unfortunately, the visual symptoms of nutrient deficiency or toxicity often occur when the problem has reached an acute stage, rather than being early warning signals. For this reason, gardeners should not depend on visual observations alone to form the basis of their soil fertility program.

Instead, use soil testing to identify inadequate levels of the major plant nutrients at a stage where plant growth and vigor could be affected, but before visual symptoms are apparent. Soil testing also includes a pH measurement, which can help determine if availability of micronutrients such as iron may be limited. Therefore, soil testing is the foundation of nutrient management and visual diagnosis is a tool that should be used in conjunction with soil testing, not as a replacement for it.

Nutrient elements differ in their mobility within the plant after they are taken up and this characteristic helps identify the nutrient that may be responsible for a visible symptom. Mobile nutrients are readily translocated from older leaves to active growing points and young, rapidly expanding leaves with high nutrient demands. Therefore, deficiency symptoms of mobile nutrients occur first on older leaves that are lower on the plant. Mobile nutrients include nitrogen, phosphorus, potassium, and magnesium.

Conversely, deficiencies of nutrients that are not readily translocated occur first on the younger, upper leaves. Immobile nutrients include calcium and the micronutrients iron, manganese, zinc, copper, and boron. Sulfur deficiency can have characteristics of both a mobile and immobile element. Rapidly developing fruits with high nutrient demand are also prone to shortages of immobile nutrients. Calcium disorders, such as blossom end rot of tomato and bitter pit of apple, are the most common.

Identification Key for Visual Diagnosis

A simple identification key for visual diagnosis of nutrient deficiency and toxicity can be found through the University of Minnesota Extension website at: http://www.extension.umn.edu/distribution/horticulture/M1190.html . The article it appears in is called “Diagnosing Nutrient Disorders in Fruit and Vegetable Crops”, but the key and other information the article contains are also applicable to home gardening situations.

The first level of the key is to select whether the observed symptom appears on upper or lower leaves, which relates to nutrient mobility in the plant as discussed above. For each of those categories (upper vs. lower leaves), there are four choices of different visual symptoms that may appear on unhealthy looking plants. After you identify the symptom description that you see on your plants, you move to a nutrient or group of nutrients that can cause this symptom when it is deficient. Alternatively, for some of the symptoms there are nutrients (or high soluble salts) listed that can cause the problem when they are present in excessive amounts. This key can be used to quickly narrow down the list of potential plant nutrient candidates as the cause of a specific symptom.

When the key leads you to more than one choice for the cause of a visual symptom of nutrient deficiency or toxicity, additional information can be used to select between these choices. The more information you have about soil, plant, and cultural conditions the more accurate your diagnosis will be.

Additional Diagnostic Tools

More complete descriptions of visual symptoms of nutrient deficiency or excess can be found at: http://www.extension.umn.edu/distribution/cropsystems/components/5886_31-32.pdf . These descriptions can help distinguish between nutrients that cause similar symptoms. They also identify soil conditions, interactions with other nutrients, and some fruit and vegetable crops where specific deficiencies are most likely to occur. Nutrient interactions or imbalances are also discussed in the “Diagnosing Nutrient Disorders” article containing the Identification Key (see the website link in the previous section).

Because visual symptoms of nutrient disorders can be caused by more than one nutrient, or result from causes that are not nutritional, the only way to conclusively confirm a nutrient deficiency or excess is through plant tissue analysis. Tissue analysis can also detect nutrient deficiencies before visible symptoms occur, as well as identify nutrient imbalances. Unfortunately, nutrient sufficiency levels for many ornamental plants are not well defined. In addition the cost of plant tissue analysis is much higher than soil tests, so it is not a tool that is generally recommended for the home gardener.

A soil test report certainly provides information that can be used to pinpoint a nutrient disorder or an associated pH problem. If a soil test was not done before planting, you can still take one during the growing season when potential deficiency symptoms occur. When low or marginal levels of a nutrient are present, and visual symptoms are characteristic of that nutrient, you have probably found the culprit. Soil tests can also help identify nutrient imbalances. For example if potassium is very high and symptoms resemble magnesium deficiency, you have two lines of evidence pointing to the same conclusion since excess potassium can inhibit magnesium uptake.

Roots are the plant organs that take up nutrients, so examining plant root growth is often helpful in diagnosing the cause of a nutrient disorder. If a plant root system is restricted by soil conditions or disease, nutrient deficiency can occur even when the soil contains adequate nutrient levels. Applying fertilizer will not help in this case and the solution is to identify and eliminate the cause of poor root growth.

Consideration of cultural practices used on problem plants or the landscape surrounding them can also help identify specific nutrient disorders or alternative explanations for symptoms that resemble nutritional problems. For example, the visual diagnosis key says that “browning of leaf edges” on lower leaves can be caused by potassium deficiency, salt toxicity, or boron toxicity. If plants have been adequately fertilized with potassium according to soil tests (and root growth is good), then potassium deficiency is not a likely cause of the symptoms. Salt toxicity can result from excessive fertilization or fertilizer application too close to plants, high rates of compost application or the use of compost that is high in salts, or a salt buildup in the soil caused by runoff of deicing salts used on surrounding pavement. If any of these conditions are present, then salt toxicity is a likely candidate for the problem. Boron is the plant nutrient with the smallest margin between deficiency and excess, so boron applications can cause problems for both current and future plants. It takes only a small amount of boron to correct a deficiency and it can cause toxicity instead if the rate is too high. If boron was applied the previous year to a high boron requiring vegetable crop like cauliflower or broccoli, then boron toxicity can occur on the following crop if boron is over-applied and the succeeding crop is sensitive to high boron levels. When there is a recent history of boron application, it should be seriously considered as the cause of browning of leaf edges or leaf cupping. This symptom can also be caused by non-nutritional factors like herbicides . Herbicides that are improperly applied to an area can drift and damage surrounding plants. Herbicide injury can also occur on plants that are normally resistant if the herbicide is applied when plants are too young or during very hot weather. Recent herbicide activity should always be examined as a potential cause of marginal burning of leaves.

Trouble Shooting Summary

• Visual inspection of plants on a regular basis is a useful way to monitor their health
• Nutrient disorders have characteristic symptoms that can be detected by visual observation
• A simple key to “Visual Diagnosis of Nutrient Disorders” is available
• Visual diagnosis is complicated by the fact that some symptoms can be caused by deficiencies of more than one nutrient or excessive amounts of another nutrient
• Visual symptoms may also be caused by non-nutritional factors like herbicide injury
• Visual diagnosis requires consideration of information on cultural practices and the plant environment that can help distinguish between different causes of similar symptoms
• By the time visual symptoms of nutrient disorders occur, plant growth has already been significantly affected
• Visual symptoms of nutrient disorders are a supplement to, not a replacement for, soil testing on a regular basis

 

 

 

 

Sphecid wasps are a familiar and diverse group of solitary wasps. During mid to late summer, sphecid (pronounced SFEE-sid) wasps are commonly found around their nests and flowers.

They vary from slender- to stout-bodied insects. Some are less than half an inch long but many are larger, ranging from ½ to 1 ½ inches long (they can appear considerably larger when they are alive and active!). Many are black and yellow while others are black and orange and a few are iridescent blackish purple. These wasps are solitary, living in individual nests. However you can find many in a small area as a lot of species live together gregariously. Most sphecid wasps nest in the ground, while some nest in cavities, such as in hollow plant stems or cavities in wood, while a few construct nests made of mud.

Sometimes sphecid wasps are confused with bees. You can distinguish between them as bees are hairy and the ends of their hind legs are flattened while sphecid wasps are generally smooth and have normal-looking back legs. These solitary wasps can also be confused with yellowjackets, especially when they nest in the ground. However, most of the commonly encountered sphecid wasps are generally larger than yellowjackets. If you watch them, just one individual sphecid wasp goes into a nest but there may be many nests in one area. Yellowjackets, on the other hand, will have many different individuals entering and leaving a single nest opening.

Sphecids prey on insects or spiders which they paralyze and then feed to their young. They either drag the immobilized prey to their nest or they carry them back while they are flying. A particular sphecid wasp usually attacks a specific type of insect.

A common group of sphecid wasps are the thread-waisted wasps. They are recognized by the thin, conspicuous pedicel (actually part of the thorax) connecting the thorax and the abdomen. There are a couple of common species known as mud daubers. Sceliphron caementarium is about 3/4 to 1 inch long and is black with mostly yellow legs and yellow markings on its thorax. This insect visits moist soil to make balls of mud to build its nests which can be commonly constructed on homes. Another mud dauber is Chalybion californicus. Unlike S . caementarium, this wasp is black with just a little iridescence. It constructs its nests in cavities in plant stems and in buildings. However, instead of gathering mud like S. caementarium , it carries water to a source of soil near its nest to moisten it so it can use the mud to build its nest. Both mud daubers provision their nests with spiders.

Sphex wasps are large-sized types of thread-waisted wasps. They build their nests in the ground and are usually gregarious although they usually establish just moderate-sized colonies. Sphex spp. prey on katydids and crickets. We have two common species in Minnesota. Sphex pensylvanicus, also know as the steel-blue cricket hunter, is 1 to 1 1/4 inch long and iridescent violet-black with smoky black wings with a violet sheen. Sphex ichneumoneus, also called the great golden digger wasp, is a little smaller, usually just short of an inch in length. This wasp is brownish and yellow with reddish orange legs, a reddish orange and black abdomen and dark-colored wings.

Another thread-waisted wasp is Amnophila spp. This group is particularly slender with a long, thin petiole. They range in size from 5/8 to 1 inch long and are generally black with red or orange markings. These thread-waisted wasps are also ground nesters but typically are not gregarious, choosing to nest by themselves. They construct their nests and then temporarily seal them just before searching for food. They prey on caterpillar and sawfly larvae.

Sand wasps are another common group of sphecids in Minnesota. Probably one of the most familiar, and largest, of all sphecid wasps is the cicada killer, Sphecius speciousus. This striking wasp is black with a black and yellow banded abdomen and grows to a size of 1 to 1 ½ inches long. They prefer to nest in the soil and are quite gregarious, sometimes establishing large aggregations of nests. As their name suggests they primarily prey on cicadas. The males are very territorial and will buzz you to discourage you from their nests but they lack a stinger and can't sting. Females can sting but they are very unaggressive and usually avoid people.

Also watch for Bembix spp. sand wasps. They are stout-bodied insects possessing a dull black body with whitish or yellowish bands on their abdomen. They commonly nest in the ground in sandy areas, such as beaches and sand boxes where they are very gregarious. These sand wasps prefer to prey on flies, including horse flies.

If you encounter sphecid wasps on flowers, the are just feeding on nectar. They are harmless to plants and should be ignored. In fact, even when sphecid wasps are found nesting in your yard they should be tolerated as much as possible. They pose very little threat to people and are very beneficial because of the insects they eat. Although sphecid wasps may potentially sting to protect themselves, they are usually quite docile and nonaggressive towards people and will mind their own business when they are left undisturbed.

 

 

 

 

Expect yellowjackets, including baldfaced hornets , to be common this summer because of the early, warm spring we experienced. Residents can generally eliminate nests that are in exposed areas with an aerosol insecticide labeled for wasps. However, nests that are hidden in wall voids, attics, and foundations should be either ignored or treated by a professional pest control service. Don't spray into these openings, (i.e where the yellowjackets are flying back and forth) or seal them. This will usually force yellowjackets into the inside of a home. See also last year's newsletter article on yellowjackets,
http://www.extension.umn.edu/yardandgarden/YGLNews/
YGLNews-Aug0106.html#yellowjackets

Finding biting mites associated with bird's nests? These are northern fowl mites . If they no longer have birds available to them, they will seek out other food sources and as a result may inadvertently bite people. Remove abandoned nests that are a mite source. However, because song birds are legally protected, nests that are occupied must be left alone. It is possible to spray a barrier to prevent these mites from entering a home as long as the birds are not at risk. Effective insecticides include bifenthrin and cyfluthrin. See also the Univ. of Minnesota publication on birds mites.
http://www.extension.umn.edu/projects/yardandgarden/ygbriefs/e600mites-bird-rodent.html

Webbing at the ends of branches of tree and shrubs is fall webworm . Their damage is primarily aesthetic as mature trees and shrubs can easily tolerate their feeding. Ignore the webs or pull them out. Insecticides are not very effective as they don't penetrate the silken webbing.

 

 

 

 

Many non-irrigated turfgrass and lawn areas around the state are completely brown as a result our continuing hot and dry summer conditions. In many instances, established lawns that are accustomed to going through these summer stresses in dry and dormant conditions will usually resume growth once more favorable growing conditions return. However, even well-established, well-conditioned lawns are not completely immune to some degree of dieback resulting from extended periods of hot (90s +) temperatures and dry conditions. As we continue through this summer, it may very well be necessary to do some overseeding or resodding of permanently damaged areas. Nonetheless, there are some practices that can ease turfgrass stress conditions and aid in the recovery of our lawns.

Maintaining an actively growing green lawn throughout the summer will typically require 1 to 1.5 inches of water per week including rainfall. Reducing those weekly rates by a third or in half can help conserve water while allowing grass plants to get through these stress periods, though there may be an increased amount of brown foliage visible. Once cooler temperatures and (we hope) more frequent rainfall returns later this summer, the lawn should perk up and resume active growth.

On sandy soils that don't hold moisture very well, or heavier clay soils which often have poor water infiltration rates, it's best to apply weekly allotments of water in two or even three smaller applications rather than all at one time. In the case with lighter, sandy soils, this will help avoid water draining beyond the root zone of the grass plant too quickly and thereby being of no use to the plant. In the case of heavier clay and/or compacted soils, slow drainage can often result in water ponding on the soil surface creating its own set of problems for the grass plant and its root system.

Under hot and dry conditions, one may notice that some areas of a green or nearly-green lawn are very quick to turn a dark bluish-gray color. Those areas usually have some type of soil condition that causes the area to dry out very quickly and send the grass into water stress as evidenced by the bluish gray color. Frequently, those soil conditions include compaction, very shallow rootzones (less than an inch or two) due to underlying construction debris, rocks and/or coarse gravel, or areas with simply lighter sandy soil. While these areas can be used as indicators as to when to water a lawn, some additional investigation as to why these areas dry so quickly followed by a course of action to remedy the problem will help reduce future stress of the grasses growing there.

It is best to minimize or even avoid traffic and other forms of wear and tear, even mowing, on lawns in a brown, “crispy” condition. Grass in a very dry condition is more easily damaged or even killed compared to its normal resiliency when green and actively growing.

For lawns that are brown, not actively growing, and essentially in a summertime dormant condition delay fertilizer applications until active growth resumes later this month or into early September.

It is best to avoid the application of lawn herbicides during hot, dry conditions. Injury can occur to our desirable lawn grasses under these conditions and often with less injury (control) occurring to the weeds.

Since this is now the month of August, the threat of very hot and dry conditions will likely be with us for only another month or so. By the time we get to Labor Day, our days will be shorter, temperatures will be cooling off and both rainfall and supplemental irrigation will help promote a return to active growth of our grass plants. This will also be a good time to assess what, if any, permanent injury has occurred and do whatever reseeding or resodding may be necessary to repair those areas.

 

 

 

 

 

 

Overgrown annuals can be pruned back so they don'toverwhelm neighboring plants, or they can be replaced. Many garden centers have a fresh supply of fall plants including mums, asters, and flowering kale. Purchase plants such as mums and asters as the first flowers are opening for an extended period of color in the home landscape.

Most annuals will benefit from continued watering, fertilization, and deadheading to promote further growth and flowering.

If rainfall is deficient continue to water newly planted perennials and trees to promote continued root growth and establishment before winter.

Order spring bulbs for fall planting soon if you are ordering from an on-line or mail order nursery. This will increase the chance of having the varieties in stock you are interested in and enough time to process the order so your bulbs come at the best planting time.

As you enjoy your garden jot down notes that will help you next year. Take notes on items including which varieties performed best, striking plant combinations (or really bad ones!), and useful gardening products. This information benefits you and also your gardening friends as they are looking for ideas as well.

Divide and replant overgrown bearded iris now. Carefully inspect rhizomes and dispose of any that have soft, decayed areas from iris borer damage.

Poor or uneven fruit set on tomatoes and peppers can be caused by high heat or roller-coaster temperature changes. For specific temperature information see:
http://www.extension.umn.edu/yardandgarden/YGLNews/
YGLN-July1502.html#flowers

Remove and dispose of lower leaves on tomato plants if they start showing symptoms of early blight or septoria blight. Avoid overhead watering to reduce spore dispersal.
http://www.extension.umn.edu/projects/
yardandgarden/diagnostics/tomato-C.html

Pick up and dispose of fallen apples to reduce future populations of pests like apple maggot.

Give extra garden produce to friends and neighbors (do NOT leave bags of zucchinis on doorsteps in the middle of the night, though!). Also check with food shelves and other charitable organizations to see if they can accept your donations of fresh produce.

Sow seeds of quick-maturing (30 to 60 days) vegetables and herbs now for fall harvest. Snow peas, lettuces, spinach, other salad greens, Chinese cabbage, bok choy, Swiss chard, baby carrots, radishes, dill, and cilantro are possibilities. Keep newly seeded areas thoroughly watered. You may even want to shade the seeded area to reduce soil temperatures since most of these crops germinate best in cooler soil.

 

 

 

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Happy gardening!

Nancy Rose
Editor
Regional Extension Educator - Horticulture

The information provided in this publication is for educational purposes only. References to commercial products or trade names do not imply endorsement by the University of Minnesota Extension nor is criticism or bias implied of those products not mentioned.

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