Pest Alert

October 7, 1999

Welcome to Pest Alert.

Categories for topics are as follows, H - Herbaceous plants and flowers, W - Woody Plants, V - Vegetables, F - Fruit and L - Lawns.

DISEASES

W POWDERY MILDEW is continuing to show up on lilacs and snowberries (including coralberries). The symptoms include white to gray, dusty patches with small pinpoint-size black dots in the patches. Many of the infected leaves were infected this summer and only now, as the patches have enlarged to cover the leaves, are people noticing the problem. The disease is not a serious health threat to the plant but it can be unsightly. The recommended control is to remove the infected leaves in the fall. It might also be a good time to prune out the plant to allow for better air circulation next summer.

V,H SANITATION IS IMPORTANT. Now is a great time to clean up that vegetable and flower garden to get it ready for winter and next year's plants. Many of the most common diseases overwinter on diseased plant debris from the previous year. Careful removal of old plant stems and leaves, after they have frosted, can reduce future problems. Clean-up in the fall is preferable to spring since the plant debris will be more intact making it easier to do a thorough clean-up. If you don’t physically remove the material, plowing or spading it under will work well too. However, rototilling the garden will only bury some of the debris and leave much of it at or near the soil surface where it can start disease problems for next season. Organic waste from the garden makes excellent material to add to the compost pile. And, as long as the pile is active, the material will be safe to incorporate back into the garden next season as compost. For additional information on composting see ExEx 6004 - Composting Yard Waste and ExEx 6005 - Recycling Lawn and Yard Waste.

W SEPTORIA LEAF SPOT is showing up on cottonwood trees across the state. Infected trees are easily identified at this time by cottonwood shelterbelts with only foliage near the very top of the trees. The disease overwinters in dead leaves and twigs. In the spring, during wet weather, the leaves on the lower branches become infected. Later, secondary infections continue to infect higher foliage. Usually by late summer, most of the leaves, except for those at the very top, have turned yellow and fallen. As with most fungal diseases, now is not the time for control. The only recommended control at this time is to remove and destroy infected leaves.

 INSECTS

H HAVE YOU CHECKED YOUR HOUSEPLANTS? Many home gardeners routinely move some of their houseplants outside for the summer. While this can be a great way to revive plants that have been suffering from low light levels inside the home, it can also lead to some real insect and mite problems in the home this fall and winter. Houseplants are exposed to a much larger variety of insects, mites and other animals while outside. When plants are brought back into the home, some of these unwelcome pests may be coming along for the ride. Be sure to check your plants carefully for pests like aphids, scale, spider mites, slugs and other pests. Examine the undersides of leaves, new shoots and even knock plants out of their pots to look for pests. Consider isolating incoming plants for a while to see if anything shows up. Some pest may we washed from the plants with forceful jets of water or a houseplant insecticide may be used.

WEED CONTROL

V ASPARAGUS can be treated with Roundup to control perennial grass that encroaches into the bed, but do it very late in the fall after all asparagus stems have been killed. Treat the border area to prevent grass from moving into the patch.

L,V,H LATE FALL WEED IDEAS. 1) Perennials like quackgrass and field bindweed in the garden area can be treated with Roundup. Wait at least a week before tilling. 2) Dandelion can be treated very late. It doesn’t freeze easily. Recent rain will trigger more seedlings if it warms. 3) Use Roundup to treat grass and weeds if you are starting a new garden area for next year. 4) Burning weeds that have been raked into a pile in the garden likely has only limited weed control value. Most seeds have shattered and spread before they were moved into the pile and are not affected by the fire. 5) Check chemical storage. Glass bottles break if they freeze. Clean hand sprayers with ammonia and soap. Don’t store them in a manner that hoses are bent or kinked. 6) Perennial grass is not damaged by early freezes. Roundup can be applied as a "border" barrier to keep grasses from encroaching into gardens, asparagus patches, in gravel drives, around posts or trees, or in rock borders. This can often be doe in late October. 7) Don’t try to use Roundup to take out invading grass in raspberries. The new shoots will translocate the chemical into other plants in the patch. 8) Retreat groundivy with broadleaf spray herbicides (such as 2,4-D, MCPP, diacamba, mixes). Two applications in fall are usually required. The weed grows after temperatures drop into the 20's.

L LAWN WEED CONTROL Ground ivy or creeping Charlie requires a second application of broadleaf herbicide spray (such as Trimec) this fall. Tests show 75 to 85% control with this program; spring treatment is much less effective. Dandelion, white clover and ground ivy can usually be treated after a freeze. Temperatures into mid_20's usually do not cause excessive damage to the leaves. Pick a warm ~60° F, sunny day to treat. Leaves will brown and curl after freeze damage. Canada thistle shoots continue to emerge in lawns this fall. Use a small hand sprayer or "trigger spray bottle" to apply a broadleaf herbicide to the shoots. This reduces the chemical used if the other areas do not receive treating. Wild violets are not easily controlled with 2,4_D. A spray product containing triclopyr (such as Ortho Brush BGon) win be more effective. Treat individual plants. Fall is a good time to treat.

OTHER NOTES

W COLD IS NOT THE ONLY PROBLEM that plants need winter protection from. Heavy snow and ice can break or bend branches. Most of our snow and ice problems are with upright junipers and arborviates. These plants usually have multiple stems and heavy loading causes these stems to bend outward. The best protection is to simply wrap natural twine around the stems are two or three locations to hold them together. The twine should be removed in the spring or it may damage the stems as they begin their spring growth.

W,F DEER CAN ALSO BE A WINTER PROBLEM. There are several methods of protecting trees from deer. A Pennsylvania study list the following repellents by their percent effectiveness:

Repellant                                 % effectiveness at repelling deer

Ground chicken feathers                                  98%

Deer Always (putrescent egg solids)                  97%

Chaperone (Thiram)                                        89%

Hinder (ammonium soaps of fatty acids)          87%

Hot sauce (capsaicin)                                     85%

Blood meal                                                     70%

Human hair                                                    58%

W FALL NEEDLE DROP IS OCCURRING NOW. The fall coloring and loss of inner foliage is a natural occurrence of evergreen trees, including juniper (cedar) and arborvitae. The normal shedding of needles is most apparent on pines and spruce and results in numerous calls from alarmed tree owners. The critical factor is the age of the affected needle. Healthy pines retain their one- and two-year old needle while shedding their third. Healthy spruces retain their one- to six-year old needles while shedding their older ones. However, we have been receiving calls from people concerned about excessive needle loss on spruce. Generally this is due to a combination of normal interior needle drop and the loss of current and one-year old needles from rhizosphaera needlecast disease. Usually the interior needles merely turn yellow before falling, the needles infected with needlecast turn a purplish-red before falling. There is no recommended control of needlecast at this time of year. Control is initiated in the spring just as the new growth begins.

W PROTECTING TREES FROM THE WINTER. At this time we start getting questions on the use of anti-transpirants. Do they work and when should they be applied? Anti-transpirants are chemicals designed to reduce transpiration. They are primarily used in the winter months to protect conifers from winter-burn. Evergreen exposed to windy, sunny winter conditions can lose water from the foliage. This water can not be replaced as the stem and soil are frozen or very cold. (water movement is extremely slow in soils or stem at temperatures below 40F). Once the water is lost, the needles turn a yellow to reddish-brown. The idea is by coating the needles with a waxy film, the anti-transpirant, the needles will give up less water. Tests have shown that anti-transpirants do not reduce winter-burn when the air temperatures are below freezing, but are useful when the air temperatures are above freezing but the soils are still cold or frozen. Thus anti-transpirants are most valuable for protecting conifers from late season winter-burn. This time period, late February to April, is when most winter-burn occurs so a midwinter application of an anti-transpirant can be helpful. The best time to applies in during one of our January thaws and repeat later in March. Once last point. Anti-transpirants are very useful as a means of prolonging the freshness of cut Christmas trees.

W,H OVERWINTERING ROSES & OTHER TENDER PERENNIALS. Hybrid tea roses are very susceptible to winter injury here in South Dakota. The best protection is often provided by the following process. First, mound soil over the bottom 8 to 12" of base of the plant in the fall, before the ground has frozen. Next, insert and anchor some caging, chicken wire, hardware cloth or other material around the roses, extending up at least 18 to 24" high. After the ground has frozen, fill the caging with a good organic insulating material. Clean, weed-free straw or hay works the best but other materials like dry leaves may also be used. Mound this around and over the canes as much as possible. Finally, cover the plants with more chicken wire or other material to keep the mulch from blowing away. Next spring, when new growth begins to form on the plants, carefully remove the chicken wire and gradually remove mulching material over the course of a week or two. Prune off any blackened or dead canes back to healthy tissue.

Tender perennials and other perennials can be protected in a similar fashion to that described above but will probably not need as much mulching as roses. Generally a layer of mulch 8 to 10" deep will be plenty. Try to apply the mulch after the ground has frozen to help to insulate the

L TIRED OF RAKING LEAVES? Fallen tree leaves can be recycled into your lawn with several passes using a mulching mower or regular rotary mower with the side discharge unit blocked. Recent studies have shown that mulching of leaves is not detrimental to the turf, and may provide a number of benefits, including increased microbial activity, water infiltration, and improved soil structure. Additionally, nutrients are recycled back into the turf profile. Application of 1 lb. of nitrogen per 1000 ft2 in late fall will help to adjust the temporary change in the carbon:nitrogen ratio due to the introduction of leaf residue.

W WATERING IS STILL A GOOD IDEA for trees and shrubs. In many parts of the state we have had limited precipitation during August and September. Some people are concerned that watering during early fall will delay hardiness and increase winter injury. While this can occur if marginally hardy trees are provided with luxurious amounts of water during this time, this is the exception rather than the rule. Instead, providing trees and shrubs with water will usually not delay dormancy and can increase winter hardiness.

W WE ARE AT THE BEST TIME TO FERTILIZE TREES AND SHRUBS. Fertilizing after the first hard frost will allow time for the tree to absorb and utilize the nutrients this fall. Fall fertilizing will not result in an expansion of shoot growth, or a reduction in winter hardiness. Fall fertilizing will improve spring growth, however, as 70 percent of the nutrients used in the construction of spring growth are absorbed during the previous fall. The best tree and shrub fertilizer is primarily nitrogen with low amounts of phosphorous and potassium, a 30-5-5 for example. High phosphorous fertilizers do not improve winter hardiness of woody plants nor do they promote better root growth or flowering next year.

W WHY ARE MY TREES DROPPING THEIR LEAVES NOW? We sometimes get this question from tree owners concerned that their tree is dropping leaves before the others in the neighborhood. There are several reasons to explain this and not all of them indicate a problem.  It might be due to drought. Trees in most of New England were dropping their leaves in late August due to the extended drought occurring in the region. If the tree is not able to provide water to the foliage it will begin to shed the leaves prematurely. While most of the state has been receiving adequate moisture, there are a few areas that still have not received much precipitation since July and in some of these areas (such as parts of southcentral South Dakota) many trees have having the leaves turn yellow and drop.  It may be due to a fungus. A number of trees, most notably ash, walnut and oak, have anthracnose. This is a fungus disease that results in botches forming on the leaves and often causes the leaves to drop prematurely. There is no recommended control at this time other than removal of the infected, fallen leaves. While it may not be a great help in controlling the disease, it can provide some reduction of spores the following spring.