|Yard and Garden Line News
Volume 1 Number 1 April 15, 1999
Spring Pruning Tips:
Deborah Brown, Extension Horticulturist
* Finish pruning fruit trees in early April. Wounds will heal
rapidly once new growth begins; no pruning paint is needed. Thin
fruit tree branches, but never "top" the trees. Topping results
in a surge of new growth....all of it thin, spindly, disease-prone and very vertical. With fruit trees, you really want
fewer, sturdier, more horizontal branches; branches that will be
able to support the weight of developing fruit.
Photo credit: Deb Brown
* If hedge plants look uneven because of winter die-back,
prune the entire hedge back hard. Work in fertilizer along the
front and back of the hedge, and water it regularly throughout
the growing season. Prune new growth so the top of the hedge is
slightly narrower than the base, to allow sunlight to reach right
down to the ground. When shrubs assume an umbrella shape, lower
branches are shaded and are unable to maintain their leaves.
* Badly damaged or overgrown evergreens probably need to be
replaced; it's just about impossible to rejuvenate them
successfully. If there are just some brown tips, those can be
pruned out once you're able to see new growth expanding. Then be
sure to leave some of that light green foliage. Evergreens
rarely, if ever, send out new growth from the base. It's always
from the youngest stems. Eventually the older, inner portions
dry and drop.
* Remember, pruning flowering shrubs early in spring usually
removes that year's flower buds. Only plants that bloom on new
stems (hydrangea, for example, or Anthony Waterer-type spireas)
can be pruned early and still go on to bloom nicely. When in
doubt, and you want to enjoy the flowers, wait to prune until
just after your shrub finishes blooming.
Early Spring Lawn Care
Deborah Brown, Extension Horticulturist
* Rake the lawn to remove leaves, dead grass and weeds, dog
bones, twigs and other debris that may have accumulated over the
winter. Left on the lawn, hard object can become hazardous when
kicked up by a power mower. Compost the organic matter, if
possible, rather than filling plastic yard bags to be hauled to a
* If you fertilized twice last fall, you probably won't need
to fertilize at all this spring. But if you plan to fertilize,
wait until grass greens up and is ready to mow before applying
it. Then be sure to water the fertilizer lightly so it reaches
the soil and is less apt to "wash off" in the first rainstorm.
*If you are going to use a pre-emergent herbicide (crabgrass
preventer), be aware that they are most commonly available in
combination with fertilizer.....and that one application will
certainly provide enough fertilizer for spring. Even corn gluten
meal, the new all-natural crabgrass preventer, is 10% nitrogen,
making additional spring fertilization unnecessary.
* If April weather continues to warm rapidly, you may decide
to apply crabgrass preventer towards the end of April (in the
southern half of the state, anyway). Otherwise, wait until the
first or second week in May. It's also a good idea to apply pre-emergence herbicides a week or two early in "hot" areas, adjacent
to a sidewalks or asphalt driveways, or on sunny, south-facing
slopes, particularly if soil is sandy.
* You can reseed sparse areas of the lawn as soon as the soil
is dry and firm enough to walk on without feeling soft and moist
underfoot. Be sure to use a heavy garden rake to loosen the soil
before seeding. Don't use herbicides in reseeded areas. (You
can use crabgrass preventer only if it's labeled specifically for
use with newly seeded grass.)
Seed Early Flowers and Veggies Directly into the Garden
Deborah Brown, Extension Horticulturist
Everyone is anxious to get outdoors to plant their gardens. A
word of advice, though: wait until soil thaws and dries enough so
you can work in it without it packing into clods of mud. Gardens
in sandier soils and on south-facing slopes will be ready before
Photo credit: Deb Brown
Once soil temperatures reach 35 degrees at seed depth you can
direct-seed onion (seeds, not sets), peas, leaf lettuce, radish
and spinach. This is usually the third or fourth week of April
in the Twin Cities area; about a week earlier or later for every
100 miles you are located south or north of the Cities.
Don't plant seeds that prefer warmer temps; there's a good chance
they'll just rot, waiting for soil to warm.
Some flowers can go in early, too. Direct seed annual phlox,
bachelors buttons, wallflowers, California poppies, calendulas,
linaria and sweet peas at the same time you plant those first
Buy Seedling Pansies and Violas Soon
Deborah Brown, Extension Horticulturist
Keep an eye open for pansies, johnny jump-ups, and other violas
at your favorite garden center and buy them as soon as they're
available. Though they grow best in cool weather, many people
don't buy or plant them until late May. By then the weather
usually heats up rapidly. Pansies and violas planted in exposed,
sunny locations may begin to deteriorate within a few weeks if
not watered frequently.
Photo credit: Deb Brown
You can transplant pansies and violas into the garden before
frost danger has passed; light frost won't hurt them. Or put
them in a large container or two to set by your front doorstep.
Their bright colors will provide a cheery sign of spring, and if
we get a really bad cold snap, you can drag them indoors for a
day or two, then set them out again.
Pansies are available in almost any color you can imagine,
including black. When planting them, remember that black and
other dark colors tend to recede or fade into the background,
while gold, yellow, and other bright colors come forward. For
edging, try the 'Sherbet' mix of violas in soft pastel colors.
Individual plants make mounds of flowers, each about the size of
a nickel or a little larger.
Managing Springtime Diseases of Trees and Shrubs
Chad Behrendt, Extension Plant Pathologist
As the weather begins to warm and the rain begins to fall, trees and shrubs begin to grow. This is also the time when many springtime diseases become active. The onset of warmer temperatures and frequent rains stimulates disease-causing organisms, such as fungi and bacteria. The amount of rainfall also regulates the severity of disease. Frequent rains or prolonged periods of damp weather increase disease severity while infrequent rains or dry springtime conditions decrease disease severity. As a result, disease management should begin with the monitoring of environmental conditions, such as rainfall.
Apple scab on leaf|
Powdery mildew on lilac. |
Cedar apple rust on cedar (top), cedar apple rust on apple (bottom)|
Photo credits: U of M Plant Disease Clinic
A variety of diseases including anthracnose of shade trees, apple scab, fireblight, powdery mildew, and cedar apple rust occur yearly. These diseases tend to be most severe when environmental conditions are cool to warm and wet, and less severe when conditions are hot and dry. Most of these diseases survive the winter on infected plant tissue that has fallen to the ground. Infected tissue remaining on the plant may also harbor disease-causing organisms. Spores produced during wet periods in the spring are rain-splashed and windblown from infected tissues to susceptible plants nearby, where infection begins.
In addition to monitoring rainfall, springtime diseases can be managed with cultural practices. Chemical control, although necessary in certain cases, is usually not warranted. Cultural practices, including proper watering, fertilizing, and mulching increase plant vigor, while sanitation and pruning reduce the amount of infected plant material available the following spring.
Water plants at ground level to reduce splashing that spreads disease spores from infected tissue to healthy tissue. Water early in the day to allow plant tissues to dry. Fertilize plants according to their needs and available nutrient levels in the soil. Mulch around plants to maintain soil moisture and nutrient availability. Make sure to keep mulch pulled away from the base (trunk) of the plant.
Sanitation includes the removal of all infected plant material such as fallen leaves and fruit, infected fruit remaining on the tree, and infected branches. Pruning of dead or dying branches is a good cultural practice that also helps remove fungal spores or bacteria surviving on dead branches. Pruning to increase airflow or improve light penetration may also help reduce disease severity by reducing available moisture and allowing plants to dry more rapidly.
In addition to the general practices listed above, here are a few tips for managing springtime diseases.
Anthracnose of shade trees. Anthracnose is a fungal leaf disease of many shade trees including ash, oak and maple. Symptoms usually appear in the lower canopy of the tree causing a browning, curling and spotting of the leaf tissue. Management practices should begin with proper watering, fertilizing, and mulching to help reduce stress and increase tree vigor. In the fall, remove fallen leaves and prune dead or dying branches to reduce the amount of available fungal material. Fungicide application should only be applied to trees under severe stress, of young age, or to trees severely defoliated 3 out of 5 years.
Apple Scab. Apple scab, a fungal disease of edible apple and ornamental crabapple trees, causes a spotting on the leaves and fruit. These spots are typically black to olive-green in color and round, and may appear velvety when young. Management practices should begin in the fall with thorough removal of all infected leaves and fruit from the ground, as well as from the tree. Properly prune out dead or dying branches. Increase tree vigor through proper watering, fertilizing, and mulching. Chemical control may be required when raising edible fruit but is not usually needed for ornamental crabapples. Chemicals available to homeowners for edible fruit include Captan or all-purpose home fruit sprays. Apply fungicides according to the label. During prolonged damp weather, you may need to follow a strict spray program, whereas dry conditions may allow you to delete one or more spray applications. Finally, consider planting resistant varieties when planting new trees.
Fireblight Fireblight is a bacterial shoot blight that typically infects apples, pears, mountain ash, and cotoneaster. Infected shoots appear brown or blackened as if scorched by fire. Shoots typically curl near the end forming a shepherd’s crook. Management should begin with pruning and removal of infected shoots. Prune shoots 6” below the margin of the canker during dormancy and 6 to 12” below the margin of the canker during the growing season. Sterilize pruning shears between cuts with a 10% bleach solution (1 part bleach to 9 parts water) or alcohol. If possible, prune when trees are dormant. Avoid promoting excessive growth with over fertilization, since the bacteria aggressively colonize young succulent growth. In severe cases, chemical control is available. Chemicals containing copper or streptomycin-sulfate should be effective.
Powdery Mildew Powdery mildew, a common leaf disease of trees and shrubs, usually occurs during cool, moist periods. Symptoms usually appear as a white to grey powdery appearance on the upper leaf tissue. Powdery mildew does not usually warrant chemical control and can be managed through proper sanitation, watering, fertilizing, and mulching. Increasing airflow may also help reduce disease, by reducing the amount of moisture available.
Cedar Apple Rust Cedar apple rust is a fungus with a life cycle that alternates between junipers and apple trees. Brown woody galls on the branches of junipers produce large orange mucilaginous finger-like projections in the spring. These projections produce spores that infect the leaves of apple trees. Manage cedar apple rust with proper sanitation and pruning. Remove brown woody galls from junipers to disrupt the life cycle and stop the disease. Since spores are spread by the wind, your junipers may be re-infected by neighboring trees. Only when disease is extremely severe, should fungicides be applied. Fungicides are available for both juniper and apple trees.
Jeff Hahn, Assistant Extension entomologist
Will the mild winter influence insect populations in the urban environment this summer?
That has been a popular question but one that isn't easily answered. Insects in general are more likely to survive a mild winter than a severe one. And some insects will probably be noticeably more abundant this summer as a result, although it is not possible to guess which ones. However, spring weather has a greater influence on insect numbers than the relative severity of winter. For example, a wet spring will lead to high early number of mosquitoes; an early, warm spring will lead to above average numbers of yellowjackets. The mild winter will have some effect on urban insects but it won't have as much impact as the spring weather will have on insect populations.
Multicolored Asian ladybeetles|
U of M
Multicolored Asian lady beetles (MALB) have been commonly annoying home dwellers during late March and early April as sunny, warmer weather arrived. This is an insect that has only been in Minnesota since 1994. These lady beetles are about 1/3 inch long (a little larger than most lady beetles) and have 19 black spots on their back, although the size of the spots are quite variable. MALB also have a black ‘M' on their prothorax (behind their head). These lady beetles are very beneficial by eating aphids that can be harmful to crops and other plants.
Unfortunately, MALB commonly cluster around homes and other buildings during fall. Last year was the first fall there has been significant problems with this insect hibernating in wall voids and attics. When people see these lady beetles during spring, they have few options except to vacuum them, sweep them into a dust pan, or in some other way physically remove them. Because they are beneficial, try to release MALB outside when possible. Eventually they will escape to the outside or die inside. Although last year's mild late autumn probably contributed to a worse than normal problem, we can expect to hear from multicolored Asian lady beetles every year.
Ant questions are very common, especially in spring. The first step in dealing with a pest ant is to know what species it is. In Minnesota, there are about 10 species that might reasonably be seen indoors. The most common of these are carpenter ants. Also common are Pharaoh, cornfield, pavement, and yellow ants. Although color and size can help narrow down what species may be present, it may be necessary to closely examine specimens for a correct identification. Knowing which species of ant you have is important because different species are treated differently. For example, carpenter ants would require an insecticide treatment into the nest, usually located in a wall void. On the other hand, cornfield ants only nest outside in the soil; treating nests in the soil or treating the outside foundation would be sufficient. A useful resource for ant problems in Minnesota is What To Do About Household Ants, FO-1066 (http://www.extension.umn.edu/distribution/horticulture/DG1006.html). Ant samples may also be submitted to the Yard and Garden Clinic for identification.
Check iris now. Iris borers are one of the most injurious pests of iris. They overwinter as eggs on old foliage which hatch early in spring. Iris borers often are difficult to manage and an insecticide application of dimethoate (Cygon) is important to protect iris. However, the timing is critical. Because eggs hatch early in the season aim your application when new growth is about 4 - 6 inches high. Some iris in southern Minnesota may already be higher than that, but most new growth in the state should be approaching 4 - 6 inches or less. A second application of dimethoate can be made 10 - 14 days after the first treatment.
Other common insect questions: Indianmeal moths and other stored product insects
Trees and Shrubs for the Drainage-Challenged Landscape
Gary R. Johnson, Urban and Community Forestry
Department of Forest Resources
How do poorly-drained or water-logged soils harm trees and shrubs?
All living plant cells must respire (release energy) in order to function normally and grow, including root cells. When oxygen is reduced to sub-minimal levels in the soil (less than 10%), roots cease to respire normally, decline and/or die. And when the roots go, the rest of the plant suffers sooner or later.
Soils, no matter what texture (clayey vs. sandy) become deficient in soil oxygen when water displaces it in the pore spaces. However, there are different degrees of poor drainage and species tolerance to low soil oxygen.
Well-drained, poorly-drained and flooded soils. A well-drained soil (for trees and shrubs) is generally defined as a soil that characteristically allows water to drain through (percolates) at a rate of one inch per hour. To apply this to the landscape situation with trees and shrubs, dig a hole 24 inches deep, fill with water, let it drain completely and then fill once again. The 24 inch deep hole should drain within 24 hours, which is considered close to optimum for most landscape trees and shrubs.
A poorly-drained soil will take more than 24 hours to drain a 24 inch deep hole, but there are obvious degrees of poor drainage. It's not great if it takes 36-48 hours to drain, but it's not nearly as bad as a soil that percolates at a rate of 24 inches in seven to ten days.
Flooded soils are usually the result of some type of periodic loading of either rain or melted snow. Depending on the time of year, flooding may or not be a problem. If it floods in late winter or early spring when the trees and shrubs are not actively growing, and the water recedes before growth begins, flooding usually is not a problem. When flooding occurs during the growth season, especially during warmer weather, one to two weeks of flooding can cause major, long-term damage to sensitive trees and shrubs…even death with some species. Other species can survive as long as three to five months in flooded situations.
Are there trees and shrubs other than willows that survive in poorly-drained soils?
Absolutely! Since there are different degrees of poor drainage, there are few plants that can be labeled as totally tolerant of all poorly-drained landscape situations, but there are several trees and shrubs that grow in Minnesota that have some degree of tolerance. This list of trees and shrubs includes those that grow reliably in southeast Minnesota. They may not be completely hardy in all regions of the state, so check with your local extension office for more detailed information on questionable species.
Trees and Shrubs Tolerant of Poorly-Drained or Flooded Landscapes
Boxelder (Acer negundo)
Red maple (A. rubrum)
Red Sunset maple (A.r. 'Franksred')
Silver maple (A. saccharinum)
Ohio buckeye (Aesculus glabra)
Black alder (Alnus glutinosa)
White alder (Alnus incana)
Speckled alder (Alnus rugosa)
River birch (Betula nigra)
Paper birch (B. papyrifera)
Northern catalpa (Catalpa speciosa)
Common hackberry (Celtis occidentalis)
Pagoda dogwood (Cornus alternifolia)
White ash (Fraxinus americana)
Black ash (F. nigra)
Green ash (F. pennsylvanica)
Tamarack (Larix laricina)
European larch (L. decidua)
Sycamore (Platanus occidentalis)
Eastern cottonwood (Populus deltoides)
Bigtooth aspen (P. grandidentata)
Waferash (Ptelea trifoliata)
Bicolor oak (Quercus bicolor)
Bur oak (Q. macrocarpa)
Eastern pin oak (Q. palustris)
Peachleaf willow (Salix amygdaloides)
White willow (S. alba)
Black willow (S. nigra)
Showy Mountain-ash (Sorbus decora)
Baldcypress (Taxodium distichum)
American elm (Ulmus americana)
White spruce (Picea glauca)
Black spruce (P. mariana)
Northern white-cedar (Thuja occidentalis)
Canadian hemlock (Tsuga canadensis)
False Indigo (Amorpha fruticosa)
Buttonbush (Cephalanthus occidentalis)
Gray dogwood (Cornus racemosa)
Red-osier dogwood (Cornus sericea)
Leatherwood (Dirca palustris)
Common witchhazel (Hamamelis virginiana)
Common winterberry (Ilex verticillata)
Comon ninebark (Physocarpus opulifolius)
Pussy willow (Salix discolor)
American elder (Sambucus canadensis)
Coralberry (Symphoricarpos albus)
*Northern white-cedar shrub forms (Thuja occidentalis)
American cranberry (Vaccinium macrocarpon)
Arrowwod viburnum (Viburnum dentatum)
Nannyberry (V. lentago)
American cranberry bush (V. trilobum)
Today is the Day to Stop Pruning Oak Trees!
Chad Behrendt, Extension Plant Pathologist
Preventing oak wilt is as simple as stopping pruning on or before April
Oak wilt is a fatal disease of oak trees, causing great losses in
Minnesota. This disease initially becomes established when Nitidulid
(picnic) beetles carrying spores of the fungus feed on freshly wounded
trees. There they introduce spores of the fungus into the tree allowing
the fungus to become established.
Once the fungus is inside of the tree, the tree tries to defend itself by
producing inhibitory/defense compounds in the water-conducting tissue.
These compounds plug the water-conducting tissue causing the tree to
express drought-like symptoms and wilt.
Oak trees should not be pruned when the fungus and the beetles are active.
Traditionally, the time to avoid pruning has been April 15 through July 1.
New guidelines published by the University of Minnesota, in 'Oak Wilt in
Minnesota' now divide the calendar year into three periods:
* High risk period: April, May, and June. DO NOT prune oak trees during
this time. If pruning is unavoidable or a tree is wounded, paint the
wound immediately--within minutes-- with a water-based paint or shellac.
This acts as a barrier to the fungus; it does not help the tree to heal.
*Low risk period: July through October. Infection can occur on rare
occasions, given predisposing weather conditions and insect populations.
Painting wounds is optional.
*Safe period: November through March. This is the ideal time to prune
oak trees, since the fungal pathogen and insect vectors are inactive.
If your oak tree becomes infected contact your community or county
forester, since funds may be available for implementing control measures.
We hope you've enjoyed reading this first issue of Yard &Garden Line News. 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.
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