Yard & Garden Line News Volume 2 Number 7                                                              May 15, 2000

Features this issue: Pine Bark Adelgid Forest Tent Caterpillar Grape Flea Beetle Carpenter Ants Swarms What Is the Worm on the Floor? Large Mystery Insect Understanding Soil Test Reports Creeping Charlie, Revisited Heading into Drought? Gardening Under Trees It's Time to Protect Your Colorado Blue Spruce Shoot Blights of Aspen, Lilac, Apple, and Pear Be on the Look for Rust Fungi Editorial Notes

Pine Bark Adelgid
Jeffrey Hahn, Assistant Extension Entomologist

Adelgids on white pine. Photo credit: U of M Dept of Entomology

Pine bark adelgid, Pinus strobi, has recently been found laying eggs on pine. This aphid-like insect overwinters as a nymph under mats of whitish woolly material and matures into an adult in April. In late April or May it lays eggs. Pine bark adelgid goes through as many as five generations in one year.

This adelgid is found particularly on white pine but also feeds on Scots and Austrian pine. It feeds on the bark of trunks and branches inserting their needle-like mouthparts into the phloem layer. When they are abundant, they give the appearance that trees have been flocked or painted. It is believed that pine bark adelgid uses spruce as an alternate host, although it only reproduces on pine.

Pine bark adelgids do not normally injury pine, particularly well-established, vigorously growing trees. When heavy infestations occur, their feeding could stunt the growth of branches. If an insecticide is necessary, try carbaryl (Sevin), acephate (Orthene) or dimethoate (Cygon).

Forest Tent Caterpillar
Jeffrey Hahn, Assistant Extension Entomologist

This insect is active now throughout Minnesota, particularly the northeast area. Their populations are expected to continue to increase over the next two years. In response to this insect outbreak, we have written a publication on forest tent caterpillar that is currently available as a Yard and Garden Brief. County extension offices have been sent hard copies which they should receive this week. This publication is also available via the internet on the Yard and Garden Line homepage. Go to: Forest Tent Caterpillars in Minnesota.

Grape Flea Beetle
Jeffrey Hahn, Assistant Extension Entomologist

Damaged grape buds and flea beetles. Photo credit: Yard & Garden Line

Grape flea beetle has been reported attacking grapes, particularly in Washington county. This beetle is about 1/5 inch long and iridescent blue-green. You can verify it is a flea beetle by nudging one; a flea beetle will jump away.

This beetle overwinters as an adult. In early spring, it attacks buds just before they begin to open. The flea beetle chews a hole in the side or the tip of the bud and then hollows out the center, killing it. Later in the season, a brownish worm-like larva may be found skeletonizing leaves, although this has little impact on the grapes. The larva drops to the ground and pupates in the soil. By mid to late summer, adults emerge. The adult grape flea beetle feeds a little but then finds a protected place to overwinter. In addition to grapes, grape flea beetle has also been recorded feeding on apple, beech, elm, plum, and Virginia creeper.

This insect is usually not numerous enough to be considered a pest but when it is abundant on grapes it can be quite damaging. The best time to protect grapes is when grape buds are swelling. It is too late to treat grape buds any more this year. Also it is not important to treat grape flea beetles feeding on leaves later in the season. However watch your grapes closely next spring. Particularly monitor grapes where flea beetles were a problem this year. If an insecticide application is necessary, use permethrin, carbaryl (Sevin), diazinon, or malathion (be sure the particular product you wish to use has grapes listed on the label).

Carpenter Ants Swarms
Jeffrey Hahn, Assistant Extension Entomologist

Carpenter ant swarm. Photo credit: Dept. of Entomology,

Nearly all ants produce a mating swarm, i.e. winged queens and males that leave the nest together in a large number. After queens mate, they fly off to start new nests of their own. However, different ant species may swarm at different times of the year. For example, carpenter ants generally swarm in late winter and spring with most swarming activity occurring in May. People describing "big, black ants with wings" are describing carpenter ants. Carpenter ant queens can be as large as 3/4 inch in length, although they can be as small as 5/16 inch long. Carpenter ants can be black or black and brown or black and red.

Field ants (also know as thatching ants) are similar in size and color and can be confused for carpenter ants. However, field ant reproductives do not swarm during spring but rather are seen in July and August. Pavement ants can be found swarming from May into July. They are generally smaller than carpenter ants but could be confused with carpenter ants. Color and size can help in identifying winged ants but not always. If there is any doubt what ant is the problem, submit a sample for identification.

Observing a carpenter ant swarm can help determine where a carpenter ant nest is located. This is important because the most effective treatment of carpenter ants is an insecticide treatment into the nest. This is often challenging as nests are usually concealed in sites, such as wall voids and hollow doors. When a swarm is found indoors in a particular room, not only does that confirm a nest within the building but the nest is also most likely behind one of the adjacent walls.

What Is the Worm on the Floor?
Jeffrey Hahn, Assistant Extension Entomologist

Blow fly larvae. Photo credit: M. Lee. Goff, Univ. of Hawaii

A blow fly is metallic green or blue colored fly that lays its eggs on dead animals. The larva is a smooth, cream-colored, legless worm. This maggot is narrow at the head end and becomes broader at the tail end. When full grown, it is about 3/4 inch long. Mature maggots often wander away from their food source to a less crowded site to pupate.

When a dead animal is inside a ceiling or wall void, it is not uncommon for maggots to inadvertently end up in the living quarters of homes, moving through light fixtures or other spaces. Because they are found on floors, they are sometimes thought to be carpet beetles. Carpet beetle larvae, however, are hairy and have legs. Blow fly maggots are harmless to people and their property. In fact they are doing a service by removing and recycling organic material.

A blow fly maggot infestation will only persist until the carcass is consumed. The most effective method to control blow flies is to remove the food source, i.e. the dead animal. Unfortunately, this is often impractical as the animal is trapped in an inaccessible place. Then people need to be patient and wait for the carcass to be removed naturally by the maggots. Blow flies will go away on their own once the food source is consumed. This generally takes about one to two weeks to happen. If blow fly infestations become an ongoing problem, then it is important to discover how animals are getting inside. Make any necessary repairs so animals do not have easy access into the building. If they can't get inside, then they do not have an opportunity to become stuck and die and attract insects.

Large Mystery Insect
Jeffrey Hahn, Assistant Extension Entomologist

Chris Hahn with giant water bug. Photo: Jeff Hahn

Giant water bug. Photo credit: Y & GL

People from around Minnesota have been reporting a 2 to 2 ½ inch long, brownish insect with claw-like front legs. This insect is a giant water bug, Lethocerus americanus. If you examine it closely, you will notice a short, stout peak and fairly conspicuous eyes. A giant water bug is predaceous, feeding on other insects, tadpoles, and even small fish. Its front legs are raptorial, i.e. designed for grabbing and holding on to prey. A giant water bug is not aggressive towards people and is not considered a biting insect. However, if one is mishandled, it can administer a painful jab in self-defense.

A giant water bug is aquatic. It overwinters as an adult in shallow, muckish areas of ponds and lakes. The warm, dry spring has served to make giant water bugs quite active. Its overwintering sites have also been drying out encouraging this insect to take wing and look for a new habitat. This helps explain why they have been reported so commonly this spring. They are attracted to lights and it is common to find giant water bugs flying to yards, parking lots, ball fields, and other places lit by outdoor lighting.

This is strictly an outdoor phenomenon. However, there was one report recently of a giant water bug that had gotten inside and was found ‘wrestling with the cat‘. No control is necessary (just remove any that get inside by hand), this insect is just a curiosity.


Understanding Soil Test Reports
Carl Rosen, Department of Soil, Water, and Climate

Taking a soil sample. Photo credits: Beth Jarvis

For many home gardeners soil test reports can be very confusing. The reasons for the confusion are usually related to the fact that fertilizers are available in many different formulations and that recommendations based on a soil test are actually given for the amount of nutrient that is needed rather than for a particular fertilizer. In addition, many gardeners want to use compost or other organic type fertilizers that often have unknown nutrient contents and this leads to more confusion. To understand how to interpret a soil test, it is important to understand fertilizers. The purpose of this discussion is to help you understand what a fertilizer label means and then how to use this information for determining what type and amount of fertilizer is needed based on the soil test.

What is fertilizer?

Some healthy, well-fed zinnias. Photo credit: Beth Jarvis

Any substance that contains one or more essential plant nutrient elements has the potential to be used as a fertilizer. Fertilizers are broadly classified as either organic or inorganic, although the distinction between the two types is not always clear cut. Inorganic fertilizers are usually chemically synthesized using an energy source or mined materials that are chemically altered to make the nutrients quickly available for plant use. Urea, for example, is a naturally occurring organic compound, but chemically synthesized urea is generally grouped with inorganic fertilizers. A natural organic fertilizer is one that is derived from either plant or animal materials containing one or more elements (other than carbon, hydrogen, and oxygen) that are essential for plant growth.

Organic fertilizers are more complex chemical substances that take time to be broken down into forms usable by plants. They are slow-release type fertilizers, compared to the quick-release characteristics of most inorganic fertilizers. It is important to apply organic fertilizers well before periods of rapid plant growth. Organic fertilizers usually have a low salt index, so larger amounts can be applied at one time without causing injury to plant roots. Manure, compost, and many other materials used as organic fertilizers add considerable quantities of organic matter to the soil. Organic matter can increase soil drainage, aeration, water holding capacity, and the ability of the soil to hold nutrients. The beneficial effects of organic matter on soil structure can have a greater effect on plant growth than the fertilizer value of some of these organic materials.

Slow release fertilizers are inorganic fertilizers made up of either larger molecules that require microbial action for degradation or regular fertilizer such as urea that is coated in some way to reduce solubility. Like organic fertilizers they have a low burn potential. They also release fertilizer over a longer period of time. Many formulations are now available that have release rates of 50 days to more than one year.

The Fertilizer Label and Grades

Fertilizer bag label. Photo credit: U of M Extension Service

The grade or analysis of a fertilizer represents its percent composition of the three primary plant nutrients - nitrogen, phosphorus, and potassium. Fertilizer grade is important because it provides the basis for deciding which fertilizer is best for your garden or lawn. By convention, nitrogen is expressed on an elemental basis as % N, whereas phosphorus and potassium are expressed on an oxide basis as % P₂O₅ (phosphate) and % K₂O (potash), respectively. Minnesota state law requires that any material sold as fertilizer be clearly labeled with its fertilizer grade (e.g., 19-6-13, 10-10-10) and this analysis is guaranteed by the manufacturer. The first number in the series is the % N, the second number is the % P₂O₅, and the third number is the % K₂O and will always be in this order on the fertilizer bag. Fertilizers containing all three nutrients are referred to as complete fertilizers. Other fertilizers may contain only one nutrient - (eg. 46-0-0, 34-0-0, 0-0-60) and are termed single nutrient fertilizers.

It should be noted that N, P₂O₅, and K₂O do not exist in fertilizer in these forms. Rather, these forms are calculated based on the elemental analysis and then simply used to allow a convenient way of comparing the nutrient value of one fertilizer with another. For example a 10-20-10 fertilizer has the same amount of nitrogen and potash, but twice as much phosphate as a 10-10-10 fertilizer. A 25-3-12 fertilizer has 2.5 times as much nitrogen, about a third of the phosphate and about the same amount of potash as a 10-10-10 fertilizer. Also note that the percentages do not add up to 100. This is because the fertilizer is made up of other elements not included in the analysis and in some cases may also contain a filler or carrier.

When you visit a garden center there are many different kinds of fertilizer grades available. In many cases the fertilizers are marked as lawn fertilizer (eg. 27-3-3), vegetable fertilizer (15-30-15) general purpose fertilizer (20-20-20, 10-10-10). The problem with these general categories is that they are not specific for you soil. Continuous use of a 10-10-10 or 20-20-20 fertilizer will eventually build up very high levels of phosphorus in your soil, which may not be a problem for growing plants but could potentially result in environmental problems due to high levels of phosphorus in run off. The best fertilizer grade to use will depend on your soil test results. If your soil is high in phosphorus (based on a soil test report) then a fertilizer with a low or zero middle number should be used. Almost all plants will require some additional nitrogen so most fertilizer should be applied based on its nitrogen content.

How to Determine What Fertilizer and Amount of Fertilizer to Apply Based on a Soil Test

Soil test report Click for full screen size image

The soil test report will tell you what the level of phosphorus and potassium is and how much of each nutrient is needed for your garden. Because of the mobility of nitrate in soils and the complex transformations of nitrogen from soil organic matter, soil tests for nitrogen are not reliable for predicting nitrogen fertilizer needs in many garden situations. Nitrogen fertilizer recommendations are based on the kinds of plants being grown, management, and the organic matter content of the soil. Ironically, it is nitrogen that is usually most limiting for plant growth.

The following soil test report for a vegetable garden will be used as an example to select a proper fertilizer:

Based on the soil test results, soil phosphorus was 50 ppm - considered very high, and soil potassium was 80 ppm - considered medium. Soil organic matter was 3.5% and considered to be in the medium range. Based on these soil test values, the recommended nutrients to apply are: 0.15 lb N/100 sq ft.; 0 lb P₂O₅/100 sq ft, and 0.3 lb K₂O/100 sq. ft. or a fertilizer ratio of 15-0-30. This information tells you what nutrients are needed but it may be difficult to find a fertilizer in your garden center that has a grade of 15-0-30. The next step is to find a fertilizer that comes as close as possible to the ratio of 15-0-30. Let's assume that your garden center has the following fertilizers available: 27-3-3, 10-10-10, 10-20-10, and 13-3-9. None of these fertilizers are correct, but the 13-3-9 is closest to the ratio of 15-0-30. 10-10-10 and 10-20-10 would supply too much phosphorus and the 27-3-3 fertilizer would not supply enough potassium. Even the 13-3-9 will not supply enough potassium and will supply a small amount of phosphorus, but it is the closest ratio to the one recommended. Now that we have decided on the 13-3-9 fertilizer, how much of this fertilizer is needed for a 100 square foot garden? To determine the amount to apply, it is best to match the nitrogen requirement and compromise somewhat for the phosphorus and potassium.

Two approaches can be taken at this point. The first is to actually do the calculation required to the amount of fertilizer needed for 100 sq ft. The formula to use is:

lb nitrogen recommended per 100 sq. ft) divided by % nitrogen in the fertilizer =lb. of fertilizer to apply per 100 sq ft.

For the 13-3-9 example, the calculation is:

0.15 lb nitrogen recommended per 100 sq. ft. divided by 0.13 nitrogen in the fertilizer= 1.16 lb of 13-3-9 to apply per 100 sq ft.

The second approach is to use the following table that simplifies the calculation by providing the total amount needed of commonly available fertilizers based on their nitrogen content. From this table, find where the fertilizer grade 13-3-9 is located (see bold) then look under the nitrogen recommendation column labeled 0.15 lb. The total amount of 13-3-9 to supply the required amount of nitrogen is 1.16 lb per 100 sq ft. Total amounts of various grades of fertilizer to apply based on recommended amounts of actual nitrogen.

Fertilizer Grade
	per 100 sq. ft.			per 1000 sq. ft.
	0.1	0.15	0.20	1.0
	Total amount of fertilizer to apply (lbs)
46-0-0 (urea)	0.22	0.33	0.44	2.2
37-3-3	0.27	0.41	0.54	2.7
36-6-6	0.28	0.42	0.56	2.8
33-0-0 (ammonium nitrate)	0.30	0.45	0.60	3.0
32-4-4, 32-3-10	0.31	0.47	0.62	3.1
30-4-4, 30-0-10	0.33	0.50	0.66	3.3
28-3-3, 28-4-6	0.36	0.54	0.72	3.6
27-7-7, 27-3-3	0.37	0.56	0.74	3.7
25-5-5, 25-3-12	0.40	0.60	0.80	4.0
24-8-16, 24-0-15	0.42	0.63	0.84	4.2
22-4-4, 22-6-3	0.45	0.68	0.90	4.5
21-0-0 (ammonium sulfate)	0.48	0.72	0.96	4.8
20-20-20, 20-4-8, 20-10-10	0.50	0.75	1.00	5.0
19-19-19	0.53	0.80	1.06	5.3
18-6-12, 18-3-6	0.56	0.84	1.12	5.6
16-8-8, 16-4-8	0.63	0.95	1.26	6.3
15-15-15, 15-5-5	0.67	1.00	1.34	6.7
13-3-9, 13-25-12	0.77	1.16	1.54	7.7
12-12-12, 12-4-4	0.83	1.25	1.66	8.3
10-10-10, 10-20-10, 10-5-5, 10-10-20	1.00	1.50	2.00	10.0
6-12-12, 6-2-0	1.67	2.51	3.34	16.7
5-10-10, 5-10-5	2.00	3.00	4.00	20.0

If you have a 300 square foot garden, then you would need three times the amount of fertilizer for that area. A 400 square foot garden would require four times as much, etc.

Another problem home gardeners often encounter is that they do not have a scale to weigh the fertilizer. In that case, use the following conversion: two cups of fertilizer weigh approximately one pound. In the above example for 13-3-9, about two and one third cups of fertilizer are needed for 100 sq. ft.

What About Using Organic Amendments as a Fertilizer?

Compost happening. Photo credit: Beth Jarvis

Calculating fertilizer rates using organic fertilizer sources can be difficult. Their exact nutrient content is frequently unknown, so fertilizer rates can only be approximated using general values for particular materials. Even though a total nitrogen content of the material is often reported, only a portion of that nitrogen may be available to plants the year of application. Nitrogen availability in organic materials depends on many factors including soil temperature, moisture, and carbon to nitrogen ratio of the material. The weight of the applied organic material must also be corrected for its moisture content. Bulky organic materials are usually low in nitrogen and must be supplemented with inorganic nitrogen fertilizers or an organic source that is high in nitrogen. If the grade for the organic fertilizer is known, then the amount of fertilizer to apply can be calculated in the same manner as for inorganic fertilizers.

Application of composted yard waste for general gardening is usually done to improve soil physical properties as well as to provide nutrients. An application of 100 lbs of moist compost per 100 square feet (about 4 to 6, five gallon buckets) is sufficient for most gardens. Incorporate the compost to a depth of 6-8 inches. With this application of compost, the amount of fertilizer recommended can be cut in half.

For further information on soil test interpretations refer to the following bulletin:

Soil test interpretations and fertilizer management for lawns, turf, gardens, and landscape plants - BU-1731-F (1998).

Creeping Charlie, Revisited
Deborah Brown, Extension Horticulturist

Creeping Charlie Photo credit: Deb Brown

Based on many years of answering homeowners' questions about lawn care, I'd say the number one weed people worry about is creeping charlie, Glechoma hederacea. Known in various parts of the country as "ground ivy" or "creeping jenny," this invasive member of the mint family was introduced to our continent by early settlers who thought it was a good groundcover for shade. Boy, were they ever right!

The problem, as everyone knows, is that it takes over in shade, then happily expands into sunnier areas. And it's difficult to eliminate. While you can pull it out of a garden quite easily (it comes up in great long ropes), pulling it out of the lawn is next to impossible because it roots down wherever leaves sprout from its viny stems. Any little bit that's left behind in the soil after pulling will continue to grow.

The best way to attack creeping charlie is to spray it with a broadleaf herbicide once or twice in autumn, after summer temperatures have cooled. You can spray now, but results may only be so-so, and there's more potential for injuring tender new growth on other plants in the vicinity.

Many people have been intrigued with the idea of fighting creeping charlie with borax, though reports of its efficacy have not been all that positive. To try it, buy Twenty Mule Team Borax, then apply it according to the following directions. Assess your results next autumn.

A solid stand of creeping Charlie. Photo credit: Deb Brown

Boron, the natural herbicide in borax, will not break down or dissipate in the soil, so you should only use it once or twice in the same area. If too much is applied, not only will creeping charlie die, but desirable grasses will die too. To sod or re-seed you'd have to scrape up and replace the "contaminated" soil.

DIRECTIONS: Dissolve 10 oz. of Twenty Mule Team Borax in 1/2 cup of warm water (or enough water so it actually dissolves).

Dilute this solution into enough water to total 2 1/2 gallons.

Spray the mixture evenly over 1,000 square feet of lawn.

A day or two before applying the borax mix it's a good idea to walk around the 1,000 square foot area and spray it with 2 1/2 gallons of water, just to get a feel for how rapidly you must move to spread the solution evenly. If the area you wish to treat is less than 1,000 square feet, reduce the amount of water (and borax) accordingly.

Remember, if you kill the creeping charlie, but you can't get anything to grow vigorously enough to replace it, the weed will reappear, regardless of how you got rid of it originally.

Heading into Drought?
Deborah Brown, Extension Horticulturist


Photo credits: AAS

Moss roses thrive in heat.

Marigolds. Photo credits: Deb Brown

'Crystal White' Zinnias Photo credit: AAS

Gazanias. Photo credit: Deb Brown

With the drought years of '87 and '88 still fresh in many people's memories, there's been a lot of talk recently about overcoming the effects of our current dry weather conditions. Much of the state failed to receive normal amounts of rain last autumn, snowfall has been below average this winter, and until early May we've been in the midst of a dry and at times, very warm spring.

In the Twin Cities, last weekend's 1/2 inch rainfall finally resulted in lawns turning lush green. The question is, how long will it last? Meteorologists are predicting a hotter and much dryer than average summer. If that's the case, we probably should be looking at some strategies for dealing with drought.

Based on the forecast, this may not be a good time to seed or renovate large areas of lawn. Why not wait until fall, or even next year if necessary, to see what the moisture situation is like. If we do get enough rain over the summer, or you're able to sprinkle freely in September, these projects can still be done successfully. Smaller, more manageable seeding projects can probably be undertaken this spring, regardless.

Do not fertilize or use weed-killers on moisture-stressed lawns. Wait until mother nature provides enough rain to get grasses growing well, or you are able to water regularly -- which just might not be a viable alternative if warm, dry weather persists.

In fact, early autumn is actually the best time of year to plant, renovate, power rake, or de-thatch a lawn. It's also the best time to fertilize (once late August or early September, followed by a second application mid-October).

Dry growing conditions also necessitate watering young landscape plants on a regular schedule, based loosely on temperatures, soil type, and how windy it's been. Besides young trees and shrubs, all evergreens and birch trees should be watered regularly and thoroughly when rainfall is inadequate.

Mulching these woody plants with four to six inches of wood chips, shredded bark, or even chipped leaves or grass clippings will help conserve moisture and insulate the soil, helping to keep roots cooler. Mulch gardens as well. Flowering perennials, annuals, and vegetables will all benefit from two to four inches of mulch.

When you water gardens, use a soaker or oozing hose, or even drip irrigation, if at all possible. Overhead sprinklers are far more inefficient, shooting water into the air where much of it is able to evaporate. If you do water overhead, aim for early morning hours when temps are coolest and there's less breeze.

Avoid watering overhead in the evening as plants are slower to dry, and will be more vulnerable to disease development. However, if evenings are the only time you can water, by all means, do water plants that need it.

Keep drought conditions in mind when choosing which flowers to plant this spring. It makes more sense to pick plants that don't need much water; marigolds, moss roses, gazania, sweet alyssum, bachelors buttons, African daisy (Arctotis), dianthus, creeping zinnia, verbena, and vinca (Catharanthus) are just a few of the many possibilities.

With any luck, the good soaking rain we've had recently will be repeated often enough that a bad drought never materializes. If it does, we'll just have to decide which plants to concentrate our watering efforts on, and which to let fend for themselves. Fortunately, right now it's too soon for that.

Gardening Under Trees
Gary R. Johnson, Department of Forest Resources, Urban and Community Forestry

Wood chip mulch around trees.

Understory plantings in nature.

Evergreens as understory plantings.

Daffodils under trees.

Azaleas under trees. Photo credits: Gary Johnson

Not everyone wants turfgrass right up to the trunks of the trees in their landscapes. As a matter-of-fact, trees grow much faster and healthier when turf competition is eliminated and replaced with a mulch of some sort. To really benefit tree health, the mulched area should be more extensive than a 2-3-foot-wide swath around the tree trunk. For a semi-mature to mature tree, that mulched area should be at least 10-12 feet in diameter if it is to be a truly effective rooting environment. There lies problem number one: no one wants their landscape to look like a sawmill with piles of wood shavings punctuated by specimen trees.

Problem number two relates to the fact that tree roots are characteristically located in the top 2-3 feet of the soil and specifically, the fine roots - those that absorb most of the water and nutrients from the soil - are in the upper 12 inches, sometimes shallower. So, can you garden under tree canopies without damaging the roots of the trees? The answer is absolutely yes, if you practice a little "bio-logic."

Obviously, the best time to begin an understory garden (one that grows under the canopy of trees) is when the tree is planted. You will know exactly where the tree roots are because they are in the soil ball that you just planted. Then as the tree grows and your understory garden grows, the roots will intermingle and coexist just as tree and understory plants grow in forests.

If you're concerned that understory plantings will stunt the new tree growth just as the turfgrass competition for water and nutrients would, you can relax and worry about something more important. The competition that shrubs, perennials and bulbs present to tree health pales in comparison with turfgrass. As a matter-of-fact, the benefits from understory planting - cooler soils and less evaporation of soil water due to the ground shading by the plants - will outweigh any negative competition factors.

A more challenging situation occurs when the trees are already established and the understory garden will be introduced to the extensive rooting area of the tree. This is the situation where potentially a lot of harm could be done to the tree. There are two distinct methods of establishing a garden that are non-destructive and overall beneficial, and two methods that are certain to harm, maybe even kill the tree.

"Bio-logical Techniques"

The first method involves locating the branch roots, those larger, woodier roots of the tree, and planting in the more open spaces among them. To locate these roots, soak the soil thoroughly - about 2-3 hours. Then, using a stiff wire probe or tile probe, locate and mark the branch roots and their growing directions. Start at the base of the tree and probe down until you hit a branch root. Then continue probing outward to determine its growth direction. Once you have those roots marked, plant your shrubs, perennials and bulbs in the open spaces among that network. Don't worry that the initial planting may look unsymmetrical and not evenly spaced. As the understory plants mature, they will fill in the area just as they do in the forest. And don't be overly concerned when you cut fine roots during the planting process. They grow off the larger branch roots and the root system will soon regenerate. Water and then mulch the garden area. The tree will share the additional irrigation that you will be providing for the understory garden and all the plants will benefit from your attention.

The second "bio-logical" technique is used where the branch roots are literally at or just below the surface and digging planting holes without major damage to the tree roots is nearly impossible. In this situation, placing a new layer of topsoil over a tree's root system and planting in that new layer can be done without damaging the tree's long-term health and condition.

You will need to "construct" a new topsoil that is organic, stable and yet allows easy access for oxygen and moisture, both essential for healthy root growth. A 1:1:1 mixture (by volume) of composted plant material, coarse sand and a loamy soil works well. For most trees, you can safely add 10-12 inches of this mixture over existing roots with no adverse effects. DO NOT PILE THIS SOIL AGAINST THE TREES' STEMS, HOWEVER! You could create a perfect environment for stem girdling roots to develop undetected and eventually lose your tree. Plant the area, water and mulch.

Bone-headed Techniques

Roto-till the entire area. That way you'll chew up and kill all of the tree's critical roots as well as loosen every tooth in your head.

Use excavated soil or any clay soil to create that new topsoil layer. Or, figure that if 10-12 inches is okay, 24 inches would be fantastic! Either way, you will create a rooting environment with a very low oxygen diffusion rate and you can watch your tree die within 2-4 years. In the meantime, build a fireplace because you will have a lot of cordwood.

In conclusion, it can be done. Protect as many of the fine roots as possible, and the entire branch roots from cutting or smothering. Plant your understory garden, water thoroughly and mulch with 2-4 inches of (preferably) organic mulch. Your garden and your trees will both thrive. One final note. Keep the preemergent herbicides out of the garden. Many preemergent herbicides also reduce or inhibit tree root growth and this could undo all of the "bio-logical" preparation that you did.

It's Time to Protect Your Colorado Blue Spruce
Chad Behrendt, Extension Plant Pathologist

Infected needles. Photo credit Chad Behrendt.

The disease Rhizosphaera needle cast frequently infects Colorado blue spruce, probably the most popular and beloved landscape tree. Rhizosphaera needle cast is a fungal disease that infects the current year's needles. These needles later turn purple to brown and fall from the tree prematurely, leaving the inner portion of the branch bare. As the disease progresses, severely infected branches die, leaving the tree with a hollow or thin appearance. The disease starts near the base of the tree where humidity levels are the highest, but continues to spread upward. As the disease continues, trees become unsightly and lose their value as a visual screen or privacy fence.

Since Colorado blue spruce is not native to Minnesota, it often suffers from environmental stresses such as drought, excessive heat, and compacted soils. As a result, Colorado blue spruce is more vulnerable to infection and more severely infected than native white and Norway spruce.

To protect your Colorado blue spruce from infection, apply chlorothalonil (Daconil 2787) as soon as possible. The fungicide should be applied when the new growth is 1" to 1 ½" in length, and again one month later.

Shoot Blights of Aspen, Lilac, Apple, and Pear
Chad Behrendt, Extension Plant Pathologist

Apple fire blight. Photo credit: Chad Behrendt

Bacterial blight on lilac. Photo credit: U of M Extension Service

This spring the clinic has received several different types of shoot blight with some caused by fungi and others by bacteria. Regardless of the organism, all of these diseases produce similar symptoms.

Shoot blights, as the name suggests, infect the new growth or the new shoot as it is emerging. Usually, the disease will subside and not spread into the previous year's growth. However, some of these diseases can become severe, causing stem cankers and death of the plant.

Symptoms usually appear as a browning or blackening of the new leaves and shoot. Infections often start at the margin of the leaf and progress inward. Infection may also initiate on flowers and fruit spurs. Once the fungus or bacteria has entered the leaf it will continue to progress through the petiole and into the stem, causing death of the leaf and stem from that point outward. Dead, blackened shoots often curl at the end, resembling a shepherd's cane. Thus, curled shoots are referred to as a shepherd's crook.

These diseases can be quite severe, causing extensive death and dieback, but typically remain random or non-uniform. In other words, these diseases do not usually affect every new shoot on the plant or one side of the plant as frost damage would. To differentiate between frost damage and shoot blights, examine the plant for uniform versus random symptoms, and for evidence that the problem is progressing. If the problem is progressing, it is probably a fungal or bacterial disease.

Aspen venturia. Photo credit: Chad Behrendt

The disease affecting aspen is known as Venturia shoot blight and is caused by the fungal organism Venturia tremulae. Lilac is affected by a disease called bacterial shoot blight, caused by the bacterium Pseudomonas syringae. The disease affecting apple and pear is known as fireblight and is caused by the bacterium Erwinia amylovora.

CAUTION! Although we have identified fireblight in pear and apple this spring, it is very early for symptom development. Symptoms usually first become prominent and visible in late spring to early summer. In addition, both of the trees showing symptoms were most likely infected last year. Thus, the bacterium overwintered within the plant and became active with the abnormally warm temperatures the first week of May. In contrast, shoot blight of lilac and aspen often produces symptoms in spring.

Be on the Look for Rust Fungi
Chad Behrendt, Extension Plant Pathologist

Pine gall rust.

Cedar apple rust on junipers. Photo credits: Chad Behrendt

White pine blister rust blisters. Photo credit: Bob Blanchette

As of May 11, 2000 we have received samples of cedar-hawthorn rust, pine-oak gall rust, and white pine blister rust. Orange to yellow (rust) colored spores were observed on each host including eastern red cedar, jack pine, and white pine. These spores are then windblown to the alternate host where they cause new infections. The alternate hosts for cedar-hawthorn rust, pine-oak gall rust, and white pine blister rust include hawthorn, oak, and currant or gooseberry.

Although rust-colored spores were visible on each host, the type of spore varied among diseases. Pine-oak gall rust and white pine blister rust both produced aeciospores, while cedar-hawthorn rust produced teliospores and basidiospores. In addition, the texture of the spores varied among diseases with pine-oak gall rust and white pine blister rust producing dry powdery spores, and cedar-hawthorn rust producing wet, slimy, mucilaginous spores.

These spores were also produced on three different types of structure. Cedar hawthorn rust produces reddish-brown galls less than ½" in diameter on the stems of junipers. These galls produce short, finger-like projections, which appear mucilaginous and orange in color. The pine-oak gall rust produces round galls, usually several inches in diameter on the stem. The outer surface of the gall then ruptures to release the aeciospores formed beneath. White pine blister rust produces a swelling or canker on the stem. The bark then ruptures in many places giving the trunk a blistered appearance. Each little blister, approximately ¼" to ½" in diameter releases a mass of powdery orange spores.

The presence of these orange colored spores makes identifying rust diseases quite easy. However, one must be cautious since there are similar rust diseases that may occur on juniper and pine. For example, cedar-apple rust is a common disease occurring on juniper. To differentiate between cedar-apple rust and cedar hawthorn rust, examine the color and size of the gall. Cedar-apple galls are larger than ½" in diameter and greenish in color. The symptoms produced on pines by pine-pine gall rust are identical to those produced by pine-oak gall rust. It is impossible to differentiate between pine-oak and pine-pine gall rust without a laboratory diagnosis.

To control these rust diseases, prune and destroy the galls currently present on the tree. This will reduce the number of spores available this spring. Since some of the galls are perennial, this will also reduce the number of spores the following year. There are no chemicals treatments to control white pine blister rust, but fungicides are available for cedar-hawthorn and cedar-apple rust. Bayleton is registered for use on pine-oak gall rust although treating a large tree may be difficult and expensive. Fungicides containing the active ingredient thiophanate-methyl (Cleary's 3336) are labeled for hawthorn and apple, while chlorothalonil (Daconil 2787) is labeled for ornamental crabapple and hawthorn. Finally, removal of the unwanted alternate host will break the disease cycle, except for pine-pine gall rust, which continues to reinfect pine. Remember that spores can blow long distances in the wind. Thus, the removal of nearby alternate hosts will reduce the severity

Test your diagnostic savvy monthly with Disease Watch at: http://www.extension.umn.edu/projects/yardandgarden/PlantPathWeb/PlPa.htm
Editorial Notes

Red trillium. Photo credit: Beth Jarvis

The red trillium, a.k.a. wake robin and stinking Benjamin, are now blooming in my yard. The rain showers of last week were so welcome!

The downside of summer storms is potential wind damage. In the June 1 issue, Pat Weicherding, PhD in Forestry and Anoka Horticulture Educator, will discuss storm-damaged trees. He'll talk about selecting wind-tolerant tree species, evaluating potential problems as well as when it's time to notify next of kindling and take a hazard tree down.

In the June 15, Bob Mugaas, turf expert and Hennepin Co. Horticulture Educator, will talk about the phophorus restrictions that are popping up all over the metro. Mary Blickenderfer, wetlands vegetation specialist from the North Central Grand Rapids Research and Outreach Center, will provide information on plants for damp and wet sites. This summer, Dr. Carl Rosen, who wrote about soil tests in this issue will continue the discussion to include pH and soluble salts. Dr. George Heimpel will discuss Intergrated Pest Management as it applies ot the home garden Dr. Cindy Tong, our post harvest specialist, will talk about handling garden produce in a later issue.

I rely on your comments and questions for ideas for future articles. Please, keep the story ideas coming! We really try to be responsive to your needs.

Please feel free to cut and paste any of the articles for use in your own newsletters. All we ask is that you give our authors credit.

Back issues Yard & Garden Line News are on the Yard & Garden Line home page at www.extension.umn.edu/yardandgarden/. Our home page has clickable links to most of the components of the Yard & Garden Line, such as Bell Museum of Natural History, INFO U and the Soil Testing Lab.

Deb Brown answers gardening questions on Minnesota Public Radio's (MPR) "Midmorning" program on the first Thursday of every month at 10 a.m. Katherine Lanpher hosts the program that is broadcast on KNOW 91.1 FM, and available state-wide on the MPR news radio stations.

If you have gardening questions, please call the Yard & Garden Line at (612) 624-4771.

listserv@lists.umn.edu (note: the second E in listserve is omitted), leave the subject line blank, then in the body of the message, type: sub yglnewslist
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Happy gardening!

Beth Jarvis
Yard & Garden Line Project Coordinator

Websites
Sustainable Urban Landscape Information Series. This site contains everything from landscape design planning and lawncare to both herbaceous and woody plant selection databases. The URL is:http://www.sustland.umn.edu


For pesticide info, for both home owner and professionals, check out:

http://www.crc.agri.umn.edu/~mnhelps/

There's also some very interesting reading at Forest Products website. To get there from here, click on: http://www.cnr.umn.edu/FR/extension/

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