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 ASH DECLINE is occurring in a number of areas of the state. The symptoms are either the entire tree or a side of the tree producing extremely stunted leaves and much reduced twig growth. These same trees are described by the homeowners as being healthy the year before. The symptoms seem to describe ash yellows, caused by a mycoplasmalike organism (MLOs). This is a systemic disease responsible for the decline and death of ash in parts of the north-central and northeastern United States. However, we have not yet conducted a laboratory diagnosis on these trees so ash yellows remains only a possibility. We will continue to investigate this problem.
W DUTCH ELM DISEASE (DED) calls have been coming in at an increased rate though not unusually high for this time of year. People have noticed the ground beneath their elm covered with yellowing and browning leaves. In some instances these fallen leaves are due to aphids feeding in the upper canopy. If the leaves are yellowing only in patches throughout the crown and the fallen leaves are sticky, the problem may be aphids rather than DED. If the fallen leaves are still moist and covered with black spots, the problem may be black spot, a common fungal leaf disease. If the leaves are yellow-brown and wilted, the problem is most likely DED, though the affected branches should be checked for the characteristic brown streaking in the wood. It is not uncommon for an elm to have DED and aphids or black spot.
DED management may be changing in the future. A new biological control agent called Dutch Trig is undergoing trials now as a preventative control measure. The agent, which consists of live spores of the fungus Verticillium dahliae, is injected into the trunk of healthy elms. The fungus triggers a reaction that increases the ability of the tree to resist DED infection. In one study only one of the 19 trees injected with Dutch Trig and then infected with DED developed symptoms, whereas the 15 trees infected but not injected all developed symptoms of DED. While these and other results look promising, the product must undergo further testing. Dutch Trig can be injected into a tree in less than 10 minutes and is expected to cost substantially less than the current chemical products on the market.
L,W,H POWDERY MILDEW: The humid weather that has occurred over much of the state this summer is showing how favorable it can be for powdery mildew development. Powdery mildews are severe on lilac, phlox, roses, and Monarda. They also occur on many other hosts. Powdery mildews are easily recognized by the dusty, powdery appearance they cause on leaves of their hosts. When severe, powdery mildews can cause deformation of the leaves. Roses and other plants that have green stems may also be infected on that plant part. Powdery mildews will also colonize flowers and buds on rose, causing color breaks on flowers and bud abortion. During cool weather, most hosts can be treated with sulfur for powdery mildew control, but do not apply sulfur if the temperatures exceed 85oF. If temperatures are hot during application sulfur may burn the plants. Never use sulfur on sensitive crops such as apricot. They will always respond with a phytotoxic reaction. Most ornamental plants can also be treated with the fungicide Funginex for control. Be sure to check the label to see if the plant is listed on the label.
L RUST ON TURFGRASSES: Warm days and cool nights also favor the development of rust on many hosts including turfgrasses. The fungus that causes rust on turfgrasses blows in from southern states each year. Once it is here it can reinfect grasses in area lawns. It is most common on newly seeded lawns where the grass may be left a bit longer during establishment. Young, tender plants also seem to be slightly more susceptible to the disease. Common bluegrass is somewhat susceptible, but the bluegrass cultivars Merion, Touchdown, and Windsor are very susceptible. A number of Perennial Ryegrass cultivars are also quite susceptible. Lawns stressed by low fertility, drought stress, or compaction, may also be more likely to have a rust problem. (Photo of rusty brown spores on shoes.)
Control rust in turf by catching and removing your clippings. This is a form of sanitation that helps eliminate the pathogen from the site. Improve your fertility with a light nitrogen application. At this time of year a cut rate of about 1/3 of a pound of actual nitrogen will help with growth without causing too heavy a flush of growth. Fungicides are not usually needed unless disease is very severe and the weather favors continuous infection. If you choose to use a fungicide, most of the products labeled for turf application will help. Chlorothalonil, triadimefon (Bayleton, and Green Light Fung-Away) and mancozeb (Fore, and others) are all good choices for rust management.
W SIROCOCCUS SHOOT BLIGHT still is generating a number of calls. See the last issue of Pest Alert for identification and management information.
INSECTS
W ASIAN LONGHORNED BEETLE, no it's not in South Dakota. However, some of you may have read the discovery of this exotic pest in Chicago. The detection of this boring beetle is resulting in the elimination of trees in a several square block area of the city. Most longhorned beetles only infest dying or dead trees. This one kills trees and there is great concern about the possibility of spread if swift action does not occur.
W FALL WEBWORM has become a concern in many areas of South Dakota. The larvae should be approaching about an inch in length and their feeding damage and webbed nests will be highly visible. The larvae, which are either pale yellow with red heads and reddish-brown spots or yellow-green with black heads and a dark stripe, feed in groups in webbed nests constructed around leaves at the tips of branches. They are sometimes confused with tent caterpillars which occur earlier in the year and construct webbed nests in branch crotches. Fall webworm can be control with applications of Bacillus thuringiensis (B.t.) if the applications are made while the larvae are still small. Carbaryl and acephate may also be used but these will also kill the natural enemies of the fall webworm. In most cases the insects are not a real threat to the tree's health, but cause mostly cosmetic damage.
W MOURNINGCLOAK BUTTERFLY LARVAE are appearing in the central part of our state. The large, 2-3 inch long, velvety black larvae can be found feeding on elms and hackberries. The insect is also known as the spiny-elm caterpillar because of the many large branched spines that run the length of the body. The larvae should be molt to the pupal stage soon so control is probably ineffective. However, if they are still less than 2 inches long, treating the infested tree with carbaryl or malathion may reduce feeding damage.
V,F PICNIC BEETLES OR SAP BEETLES are a problem in the garden and orchard as well as at backyard picnics and parties. The name comes from the fact that this insect is very prevalent at picnics and is attracted to various foods and beverages found there. There are several kinds of picnic beetles but the most common one is a small black beetle about 1/8 of an inch long with four small orange spots on the back. These beetles also burrow into vegetables and fruit such as sweetcorn, berries, and tomatoes. They are particularly attracted to fruit that is overripe or damaged in some way. Therefore the first management strategy against picnic beetles should be to keep berry and tomato patches picked on a regular schedule, removing any overripe or damaged fruit. Insecticide applications are also available, the most effective is diazinon. However, be sure to read the label carefully to determine that the crop being treated is listed on the label, and be extremely careful to observe the harvest interval between application and harvest, as treatments for picnic beetles commonly occur during the period of fruit and vegetable harvest.
OTHER NOTES
W IMPROPER PLANTING depth is still a common killer of trees in South Dakota. Inspection last week of declining spruce and pines in shelterbelts revealed that many of the 2 to 3-ft. tall trees had been planted 6 inches too deep. These trees had struggled along for a couple of years and now are showing symptoms of browning needles. As we have stated numerous times, always plant at the root collar or several inches below the bud union to ensure you are not planting too deep.
L LAWN RENOVATION time is here. Aug. 15 to Sept. 15 is considered the best time of year to start a new lawn or renovate an old one by either seeding or sodding. The first step is to kill existing vegetation. One of the easiest ways to do this is to use a non-selective herbicide like glyphosate, sold as Round-Up, Kleen-Up, and a number of other trade names. Follow label instructions for treatment recommendations. The old grass and weeds should be actively growing and have several inches of growth for best results. Water the area a few days in advance to promote growth during dry weather. Do not mow for a couple weeks to encourage more growth. If a soil test has not been done in the area for several years, now is also a great time to gain some important information that could allow you to correct a problem that could cause reduced grass establishment or stand in the future.
Once the old vegetation has been killed, (it takes about a week butr the weeds may still be fairly green) you are ready to begin reworking the soil and adding any amendments that may have been recommended from the soil analysis. Be sure to select an appropriate lawn grass or mixture for your yard. Make sure to get good seed to soil contact when seeding. Be prepared to supply supplemental irrigation during establishment, keeping the seedbed moist for at least 3 weeks.
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Most recent revision Monday, Aug. 17, 1998 by David F. Graper.