|Yard & Garden Line News
Volume 6 Number 12 August 1, 2004
Feast or Famine? Recent Weather Affects Trees
David Hanson, Research Specialist, Urban Forestry
In the last two years Minnesota's trees have really been put to the test. A test of extremes; first the winter of 2002-2003 started with an autumn drought and ended with late winter subzero temperatures combined with no snow cover that pushed frost to extreme depths. Late spring and early summer of 2003 started out extremely wet followed by extreme soil moisture deficits June through November. So, we entered the winter of 2003-2004 under drought conditions with many trees already "stressed out."
This American elm has lost the battle to Dutch Elm Disease (DED).
Photo credit: Davis Hanson|
(See excellent article in Minnesota DNR: Forest Insect and Disease Newsletter on drought
Any one of the events mentioned above can be serious, but typically not fatal for a healthy tree. These events are referred to as contributing factors to tree decline. Much like insects defoliating a tree, cold and drought events cause stress and reduce the trees ability to create and store nutrients. So, these don't explain all current tree problems but might have a relationship to some of the problems.
The extreme events such as drought and deep frosts over the last two years have affected the root systems of many trees. During periods of drought soil moisture levels drop. Tree roots require adequate moisture and without it the roots will begin to die. The cold soil temperatures that occurred during the winter of 2002-2003 also had negative affects on the fine roots of trees. These fine roots can be destroyed by dry soils and cold soils. When fine roots are lost the tree loses the ability to take up moisture and nutrients from the surrounding soil. Big deal?
Very big deal! - Reports are coming in regarding trees exhibiting browning of leaf edges, yellowing of leaves, early fall color, or leaves dropping after what appeared to be normal leaf set this spring. Why might this be happening?
First, energy reserves in some of these trees are down due to the root system damage. The damage affects the trees ability to take up nutrients and moisture; thus, photosynthesis is affected leading to a decrease in the creation and storage of nutrients. Bottom line, the stored nutrients become depleted. In some cases this can explain the foliar problems described above.
Secondly, symptoms like browning of leaf edges or early fall color can be symptoms of drought like conditions. With our cool, wet spring a person might assume that the drought is over and the trees should be fine. However, it takes a minute to explain that while there is now ample soil moisture , due to damaged root systems (loss of fine roots) the trees are not able to utilize the moisture. So, with root damage the tree continues to appear as though it is in a drought.
Not only are we seeing direct relationships to drought, but now the secondary invaders are taking advantage of the trees under stress. During the summer of 2004 Dutch elm disease (DED) is hitting the elm population extremely hard. On another front insect groups are taking advantage of the stressed trees: two-lined chestnut borer on oaks, pine bark beetles attacking various pines, bronze birch borer on birch, ash-lilac borers hitting lilacs and ash trees and this list continues to grow.
Green ash exhibiting crown dieback after ash-lilac borer attack.
Photo credit: Davis Hanson|
So, when looking at foliar symptoms in the present, keep in mind the not so distant past and the weather extremes that these trees have had to endure. Quite simply a number of them won't endure another round of drought stress or insect infestation without some help from us. Some good advice: http://www.cnr.umn.edu/FR/extension/watering.html
The following site from Colorado lays out a lot of information regarding drought stress.
We are not the only state dealing with "stressed out" trees. "The Colorado Springs Gazette reported on July 13th that the city's forester Jim Mc-Gannon was looking at the removal of up to 200 prominent city trees related to Colorado's extended drought. Yet, Colorado Springs was feeling "Ok" with this considering the conditions in neighboring counties where up to 90 percent of the spruce and pine populations were being lost to drought and drought related insect infestations.
Ed Sealover, "City Must Cut About 200 Downtown Trees." The Colorado Springs Gazette, Online. http://msnbc.msn.com/id/5430072, July 13, 2004.
Think About Lawn Weed Control
Deborah Brown, Extension Horticulturist
It's not too soon to think about weed control strategies for your lawn, though it's probably too hot – and a little too early – to actually do anything.
If you've started using corn gluten meal (CGM) to prevent weed seeds from sprouting – or you'd like to begin an "organic" lawn care routine, plan to apply CGM around mid-August. Then follow through with another application next spring – in late April or early May. Best weed control is achieved when the product is used both spring and late summer for three or four consecutive years.
Mid-August application timing is not cast in stone. Because corn gluten meal is 10 % nitrogen, it also serves as a fertilizer. If weather conditions are hot and dry, and your ability to water the lawn regularly is questionable, hold off applying it until temperatures drop and moisture is no longer a problem. Fertilizing grass that's moisture-stressed is counter-productive.
Corn gluten meal is effective against a wide spectrum of weed seeds, not just crabgrass and other annual weeds. Keep in mind, though, that it does not discriminate between seeds you like and seeds you dislike. If you apply it in August or September, you will not be able to plant new grass seed until the following spring – and then, only if you don't use more CGM at that time.
If your lawn has lots of broad-leaf perennial weeds such as dandelions, plantain, or creeping charlie (ground ivy), corn gluten meal won't be of much help. It only works to stop their seeds from sprouting. Plan to dig those broad-leaf weeds after a heavy rain when the ground is soft, or spray them with a broad-leaf weed-killer in mid-to late September, then a second time 10 to 14 days later. Next spring, when everybody's lawn is plagued with dandelions, you'll be glad you got rid of yours this fall.
Septoria Leaf Spot
Janna Beckerman, Extension Plant Pathologist
Septoria leaf spot, caused by the fungus Septoria lycopersici, is one of the most devastating tomato diseases of the upper Midwest. This disease primarily infects leaves, although stem, petiole and fruit lesions may occur. Septoria leaf spot can occur at any stage of plant development, but usually appear after fruit set.
Septoria leaf spot on cultivar 'Red Currant.'
Photo Credit: Janna Beckerman
Symptoms usually first appear on the lower leaves after fruit set. Initially round, yellow spots develop. Later, these spots enlarge and turn brown to gray. Tiny black fruiting bodies (pycnidia) eventually form in the center of the leaf spots. These pycnidia produce spores which cause secondary infections, usually in an upward direction, throughout the plant. Heavily infected leaves turn yellow, then brown and fall from the plant. Symptoms occasionally appear on petioles, stems and fruit. Defoliation can expose fruit to the sun, which results in sunscald damaged.
Careful examination of lesions will reveal tiny, black fruiting bodies (pycnidia) in the center of the leaf spots. These pycnidia produce spores which cause secondary infections, usually in an upward direction, throughout the plant.
Under warm temperatures and wet conditions, spores (conidia) are produced and spread by splashing rain, insects, and even hands and clothing of careless gardeners. Infection occurs through stomates and requires free moisture. Leaf spots appear within five days, soon followed by pycnidia (within 7-10 days). Spore production and repetition of the lifecycle can occur within 10-13 days.
Septoria overwinters in the debris of diseased plants incorporated in the soil and on solanaceous weeds. In Minnesota, black nightshade (Solanum nigrum) is the most common, susceptible weed. Although rare, potato and eggplant can serve as hosts of this disease, as well.
As with many diseases, no single management strategy will cure this problem. Rather, a combination of methods should be used to decrease its effects. Reducing the number of spores that cause primary infections can be accomplished through cultural practices such as sanitation and crop rotation. Sanitation involves the removal of all plant material and weeds throughout the season, as well as after harvest. Planting disease-free seeds and plants can help control Septoria leaf spot. To reduce secondary infections, water plants at the base in the morning and stake plants to improve air circulation. Apply mulch around the base of plants to minimize water splash. Unfortunately, the only cultivar that was reported to be resistant to this disease. 'Sweet Million,' developed Septoria during the 2004 PREP trial.
Conidia of S. lycopersici.
Photo Credit: Plant Disease Clinic
Chemical control: Fungicide applications may be necessary during rainy seasons. Read the label carefully and apply only as directed. Follow a regular fungicide application program. Start 2-3 weeks after transplanting or after emergence of seedlings. In plants that are already badly infected, it may be unrealistic to expect good control at this point. However, removing the most severely infected foliage, and applying a fungicide to foliage that does not yet show symptoms will reduce the spread and impact of this disease. The following fungicides are labeled for control of Septoria leaf spot. Apply one of the following at 7-10 day intervals at the first sign of disease or immediately after bloom.
· Copper containing products (Bordeaux 8-8-100 ,Kocide, TopCop). These products are considered acceptable for organic production
· Chlorothalonil containing products (Daconil 2787, Fungonil)
· Maneb containing products (Bonide Manzate). Do not apply within 5 days of harvest.
· Mancozeb containing products (Acme Maneb Tomato & Vegetable Fungicide, Greenlight Maneb Plus, Dragon Mancozeb Disease Control)
Chiggers in Minnesota
Jeffrey Hahn, Assist. Extension Entomologist
One of the banes of summer is attacks from chiggers. Although they are generally not very common in Minnesota, chigger bites can be very annoying. Chiggers refers to the immature larvae of trombiculid mites. They are reddish, yellowish, or orange but are nearly invisible to the naked eye. While these six-legged larvae attack humans and animals, the nymphs and adults are predators, feeding on the eggs of springtails, mosquitoes, and sowbugs.
University of Kentucky College of Agriculture
Chiggers are found in grassy, weedy, shrubby, and other overgrown areas, especially near swampy or otherwise moist locations. They typically have a patchy distribution at a given site instead of being generally distributed. When chiggers hatch from eggs, they climb up on foliage and wait for hosts to come by. They grab onto people or animals that pass close enough and proceed to feed.
When they latch onto a person, these tiny mites attach themselves to skin. They will feed particularly where the skin is thin to accommodate their small mouthparts. This is often at the openings of hair follicles. Despite poplar belief, chiggers do not burrow into skin or feed on blood. They feed externally on partially digested cells that have been broken down from their salvia. The sites of these bites become itchy and are accompanied by rash. Bites are particularly common in areas where clothing is tight, e.g. under waistbands, socks and bras and where skin is thin, including behind knees, ankles, and groins. The majority of chigger bites occur below the waist. While their bites are irritating, they are not know to transmit disease to people.
To protect yourself from chiggers, stay out of areas where chiggers are likely to be found, i.e. grassy, overgrown areas. If it is necessary to enter sites where chiggers occur, you can also protect yourself with an application of a repellent, such as DEET. Particularly treat pant legs, the tops of socks, and exposed skin. If you have been outside and think you may have encountered chiggers, take a bath or shower and liberally clean yourself with soap. Also wash your clothes in hot, soapy water. If clothes are washed in cool water, the chiggers will survive and be present to bite the next time those clothes are worn.
You can minimize chiggers in your yard by cutting down overgrown areas. Insecticides, such as carbaryl (Sevin) can be sprayed in areas where chiggers are found to help reduce their numbers. You can test an area to determine if chiggers are present by holding up a piece of dark-colored cardboard with the edge along the ground. Any chiggers that are present will quickly climb up to the top of the cardboard. Their light color will show up against the dark background of the cardboard. Test at least 10 -12 spots. Knowing where chiggers are located makes it easier and less expensive to treat them with an insecticide.
If you have areas on your body that become bitten by chiggers, you can relieve the irritations by treating them with a type of anti-itch medication, such as hydrocortisone, calamine, or benzocaine.
Black Swallowtail Caterpillars
Jeffrey Hahn, Assist. Extension Entomologist
An attractive caterpillar you might find in your garden at this time of year is the black swallowtail, Papilio polyxenes. Also known as the parsleyworm, this common butterfly is found throughout Minnesota. This caterpillar turns into an pretty butterfly with black, blue, and yellow wings each with a ‘tail'. The black swallowtail butterfly is moderate-sized with a wingspan as large as 3 1/2 inches.
Photos: Jeff Hahn
As caterpillars, black swallowtails feed on many plants in the Umbelliferae including parsley, carrots, dill, fennel, celery, and Queen Anne's lace. They prefer eating the flowers or small seeds. When the caterpillars first hatch they are black with a white band around the middle of its body. As they grow, they gradually turn light green with black, yellow, and white markings and are about 1 1/2 inches long when fully grown.
Sometimes when disturbed, black swallowtail caterpillars, like other swallowtail larvae, will displayed a forked appendage on the top of their head known as an osmeterium. This fleshy Y-shaped organ emits a foul smell and is used to help protect the caterpillars from natural enemies. It may look frightening but it is harmless to people.
If you encounter black swallowtail caterpillars in your garden, tolerate them whenever possible. Their feeding in many cases is not serious. If he do find that they are causing significant damage, the easiest solution it to handpick the caterpillars and destroy them.
The Black Witch Project
Jeffrey Hahn, Assist. Extension Entomologist
One of the most spectacular moths in North America is the black witch, Ascalapha odorata. With a body length of 1.5 inches and a wingspread of about 6 inches, it is easily one of the largest insects found in United States. The wings are mostly brown with a small eyespot on the forewings near the front margin. The female is somewhat more ornate as it is has a whitish band running down both wings. Because of its large size, this moth can easily be mistaken for a bat.
There is much folklore and myth surrounding the black witch. It has been called the ‘butterfly of death' and has been reputed to be an omen that someone is going to die when this moth enters a home. There are several variations of this theme depending on what part of the world you in. Another myth has it that when a loved one dies, the moth becomes the embodiment of the soul of the dearly departed come back to say goodbye. Yet another myth says that when a black witch flies over your head, you are going to lose you hair (cover up just to be on the safe side).
The normal geographic range of the black witch is from Brazil north to Mexico. They are also common on some Carribean islands. However air currents can bring them over much greater distances throughout the United States, even as far north as southern Canada. Most sightings in the United States are in June and July. Recently (July 15th and July 19th), there have been two sightings of black witches in Minnesota. The first specimen was found in Burnsville in Dakota County while the second one was discovered in St. Louis Park in Hennepin County. Visits by black witches do happen in Minnesota now and again but should be considered as rare events. They are spectacular moths if you are lucky enough to see one.
For more information on black witch moths visit Mike Quinn's web site, http://home.satx.rr.com/txento/witch.htm. You can also contact Dr. Quinn if you would like to report sighting a black witch.
Get the low down on this month's insect pests at
August Garden Tips
Beth Jarvis, Yard & Garden Line
Compiled from conversations with Dave Hanson, Urban Forestry, Bob Mugaas and Bob Olson, Regional Extension Educators and Deb Brown.
(These recommendation are based on Twin Cities temperatures. Adjust for northern Minnesota..)
Tis the time to be re-seeding! If you've been staring at bare spots in your lawn this summer, from August through September is a fine time to put down new seed.
Seeding and Sodding Home Lawns will provide a lot of basic infomation.
Then everything you ever wanted to know about lawn care and repair can be found at the Sustainable Urban Landscape Information Series website at: http://www.sustland.umn.edu/maint/index.html.
Click on lawn maintenance and scroll down to the lawn care calendar for timing.
Treating for warm season grasses, such as crabgrass is not advised as the plants are getting so large that more herbicide is required, preferred grasses may be damaged and some of the weed grasses have started to set seed. Crabgrass is an annual so next year's plants come from this year's seed.
If you've been diligent about watering and you're still seeing small, drought-stressed patches on your lawn, consider sod web worm activity. For details, see: Managing Lawn and Turf Insects
Tomato harvest is just kicking into high gear. Some growers are disappointed by the quality of their earliest fruit, however. Most problems can be attributed to non-living (abiotic) conditions that lead to:
Blossom end rot
This common malady manifests itself as sunken/rotted areas on the blossom end of the fruit. This condition is caused by a lack of calcium delivery to the fruit, generally during drought stressed conditions. Proper, even watering and mulching to conserve moisture greatly reduce this condition. Growers with multiple varieties will notice significant differences in how various tomatoes express this condition.
Remember how cold it was early in the growing season; right about the time your first tomatoes were flowering? Those cold temperatures can result in poor/incomplete pollination, which results in those puckered (cat-faced) fruit. The damage is purely cosmetic, so go ahead and enjoy those first-red prizes. The larger beefsteak varieties commonly exhibit this unusual growth.
Letting that ripe tomato stay on the vine another couple of days might lead to disappointment. If we experience a sudden, dramatic change in the plant's growth (a rapid increase in temperature following days of cool weather; a good rainfall following weeks of dry conditions), the expanding fruit can rupture. This rupturing can occur as circular rings around the stem end, or can be longitudinal cracks that radiate downward. Once these fruit crack, get them off the vine before the voracious picnic beetles find them out.
Typically associated with plants that have been defoliated or infected by septoria, this condition is akin to a sunburn. As the leaves provide less protection for the developing fruit, they become more exposed to the sun, resulting in lightly-colored blushes on the sun-exposed fruit.
»Clean up all over-ripe fruit and remove from the garden. Pick up all windfalls and remove from the site.
» Remove all diseased foliage from vegetable crops to reduce the spread.
»Keep weeding those garden crops. Weeds not only compete for water and nutrients; many are hosts for nasty diseases.
» Remove those overly large cucumbers and zucchini; allowing them to remain on the vine will inhibit new fruit from developing.
»Don't de-tassel your sweet corn. Gardeners occasionally hear about de-tasseling crews working in seed production fields. The tassel is the male flower structure and provides the pollen that lands on the silks and grows down each silk tube to form a kernel. When seed companies develop hybrids they will manipulate the parental lines to get the exact crosses they want. That will include de-tasseling the (female) line so that it will not self-pollinate. In the home garden you don't have to worry about this.
Pamper your already-harvested strawberries, raspberries, and blueberries. This is the time of year they are forming buds for next year's crop. Neglect them now and cry next spring.
If your tree fruits are loaded, now is the time to brace them up. A strong wind could wipe out entire scaffold branches.
Keep up your monitoring and/or spraying program in the orchard. Insect pests of importance include: apple maggots, plum curculio, and codling moth.
Monarda or beebalm, an "improved" native.
The summer flower garden is cruising in maintenance mode right now. Be sure to water when Mother Nature doesn't and where she can't reach. There's always weeding to do, too.
Deadhead perennials when flowers fade to conserve plant energy for next year. Faded annual flowers need to be removed to ensure continued new blooms until frost.
Fertilize baskets with every couple of weeks. Purple wave petunias can even be fertilized weekly.
Aster yellows is a plant disease that becomes very apparent this time of year. Its broad host range includes vegetables and flowers. It causes abnornal flowers very noticeably in coneflowers but it also can affect other perennials and annuals.
Here's some additional reading on the subject:
Trees and Shrubs:
Reduce Dutch elm disease next year by watering your (remaining) elms this year!!
Continue to water all your trees! The TC Metro is still at a moisture deficit. Adequate soil moisture is critical now when trees and shrubs are begnning to go dormant for winter. Trees need at least one inch of rainfall each week May through July and a little less in August and September.
Do not fertilize trees right now with a high nitrogen fertilizer that will prompt growth. Slow release, low-dose nitrogen fertilizer would be ok if needed. The turf grass will probably capture most of the nitrogen.
Hold off on pruning until fall. When pruning, remove no more than 1/4th of the plant. (We used to say 1/3 but research indicates 1/4 is safer.)
It's county fair season. Monk's hood reminds me of county fairs because it bloomed in our yard during fair-time and was often featured in my 4-H arrangements. Thirty plus years later, I learn it's poisonous.
Monk's hood, Aconitum sp.
In an upcoming issue, Nancy Rose will talk about some plants for late summer color and Anne Gachuhi will write about landscaping in small spaces. There are some other ideas in the works.
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/.
Deb Brown answers gardening questions on Minnesota Public Radio's (MPR) "Midmorning" program on the first Thursday of every month at 10 a.m. The program is broadcast on KNOW 91.1 FM, and available state-wide on the MPR news radio stations.
For plant and insect questions, visit http://www.extension.umn.edu/askmg. Thousands of questions have been answered, so try the search option in the black bar at the top left of the board for the fastest answer.
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