Pest Alert

May 1, 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,F APPLE SCAB attacks apples and crabapples. Abundant spring rains may have created ideal conditions for this disease to become sever this year. Now is the time to begin your apple scab spray program. (Photo of apple scab on leaves of apple.)  The first recommended spray for apple scab is when the buds have opened and the leaves are about 1/2 inch in length (referred to as "1/2 inch green tip"). Additional sprays should follow to maintain control during bloom and flower petal fall, as well as throughout the summer. Fungicides such as Captan and Benlate should be effective (read label for directions).

W ASH ANTHRACNOSE is a foliage disease of green ash. The symptoms include blotchy spots on the leaves which may cause leaflets to drop.Treatment is rarely necessary. However, the best treatment is to apply Captan, beginning just after bud-break and continue at 10-day intervals as long as cool (below 55F), moist conditions persist. Again, plentiful spring rains may make this disease more severe this spring and summer.

W,F BLACK KNOT on cherry is a perennial problem in the Northern Plains. The disease occurs on wild plums and cherries but is most common on the Canada Red or Shubert chokecherry. It appears as a black, elongated gall on the twigs and branches. Generally the twig growth beyond the infection is killed. Control of the fungus is not easy. The "galls" should be pruned out of the tree and burned in early spring before spores are released.  (Photo of new developing gall.)   Lime sulfur sprays can be applied every 10 days from now until the terminal growth stops, typically June, however these applications are rarely effective.

F,W CEDAR-APPLE (HAWTHORN) RUST has already shown up West River on eastern redcedar and Rocky Mountain juniper with recent rains. Expect it to show up state-wide with this week’s rains. Affected plants are sometimes completely covered with orange, gelatinous round masses on the tips of branches. Some young plants have had branches break under the heavy load of these fruiting bodies. These fruiting bodies are releasing spores that will infect susceptible apples, crabapples, hawthorns and juneberries. Symptoms of the rust on these trees include bright yellow to orange spots on the leaves. This summer these infected deciduous hosts will produce fruiting bodies that will release spores that infect the junipers. These evergreens can be protected with an application of chlorothalonil when spores are released later this summer. Do not spray the junipers now. It will not eliminate the fruiting bodies.

Cedar Hawthorn rust, a related disease, can infect apple fruit causing it to become malformed. Preventive fungicides include Ferbam, Thiram and Maneb which will also control apple scab. While apple trees may be sprayed to protect them from cedar-apple rust, it is often not necessary since the leaf spotting typically does not significantly harm the tree or reduce fruit yield.

W,F FIRE BLIGHT may be severe this year with the frequent rains we have been receiving. Rainy weather during apple and pear flowering could lead to lots of blossom infection. This bacterial disease attacks apples, crabapples, cotoneaster and mountain ash. This disease is carried from tree to tree by insects. The cankers on infected trees will soon begin oozing a milky to amber-colored exudate that contains the bacteria. This sticky material attracts insects that carry the bacteria to other trees. The bacteria enter the host through the blossoms, leaves or wounds. This disease is managed by utilizing a number of strategies including chemical, pruning and fertility. Trees should be checked several weeks after bloom for the presences of new infections; wilted and blackish leaves and new growth; and these infected parts pruned out. Pruning equipment should be dipped in a solution of 1 part household bleach and 9 parts water between cuts. Avoid heavy applications of nitrogen to infected trees.

F PLUM POCKETS is a fungal disease infecting plums. Best treatment is to apply lime-sulfur at bud swell.

L DEAD SPOTS IN YOUR LAWN? Gray Snow Mold, Pink Snow Mold, or Dollar Spot may have left circular patches of dead turf in your lawn. If the patches are not too large, spreading turfgrasses, such as Kentucky bluegrass, may fill in the dead area without reseeding. Larger areas of dead turf will require a good raking to loosen up dead plant debris, thatch, and soil prior to reseeding. Good seed-to-soil contact is important, as well as keeping the seedbed constantly moist until seed has germinated. Avoid application of preemergence herbicides to areas you wish to reseed, as these herbicides will kill germinating turfgrass seed as well as weed seed.

INSECT CONTROL

W EUROPEAN PINE SAWFLY LARVAE will soon be hatching. Their hatch generally occurs when Norway maples are in bloom – an event that is presently occurring through southeastern South Dakota. The full-grown larvae have a black head and a gray-green body with light and dark green stripes. The larvae feed in colonies on the needles of mugo pines though other pines such as Scots, Austrian and ponderosa may also become infested. European pine sawfly will not kill the pine as they feed only on the old needles but the defoliation is unattractive and the stress may make the plant susceptible to other pests. The sawfly can be treated with chlorpyrifos (Dursdan) or carbaryl (Sevin).

W MAPLE BLADDER GALL MITES will soon begin feeding on the newly emerged and expanding maple leaves, particularly on Silver Maple. The tiny mites feed on the developing leaves which induces the leaf to produce the characteristic yellow to orange-red nodule or gall on the leaf. These galls do not damage the tree and no treatment is needed. However, many people find the galls unsightly and want to get rid of them. If a tree has been infested in the past, chances are good that the tree will be reinfested again this year. Once the galls appear, it is too late to treat. Treatment must be applied as the new leaves are emerging and are less than ½ their full size. Kelthane is the best miticide to use but Dursban and Sevin are also labeled for this pest.

W MOUNTAIN PINE BEETLE is much in the news throughout the Black Hills. This insect is native to the Black Hills and periodically, about every ten years or so, undergoes outbreaks that can result in the loss of thousands of trees. The most famous outbreak occurred about 100 years ago and resulted in the loss of an estimated 10 million trees. An outbreak in the early 1970s killed about 500,000 trees during a five year time period. A new outbreak appears to be starting in the Hills at this time and is expected to last for several years. The mountain pine beetle primary host in the Black Hills is ponderosa pine. The adult beetles emerge from infested trees in late June or July and fly to likely hosts – often trees that have been struck by lightning or had the tops blown out by a wind storm. However, under outbreak conditions all crowded stands of ponderosa pine trees in the general area of an infestation are susceptible. Trees are typically mass attacked and the larvae that soon hatch quickly girdle the tree. Evidence of an attack are numerous pitch tubes, 1- or 2-inch pitch masses, along the lower trunk. Red boring dust can be found at the base of the infested tree. (Photo of feeding galleries under bark.) Infested trees remain green the remained of the year but quickly turn a bright red the next spring. Trees that have turned red should be removed before June 15 and burned to prevent the emergence of new beetles. Individual trees in the vicinity of an infestation can be protected with an application of carbaryl (Sevin). This treatment must be applied before June 15 and the coverage should extend from the base of the tree to within the upper ¼ of the canopy. More information regarding mountain pine beetle management will appear in future Pest Alerts.

W SCALE CRAWLERS will be emerging soon. The crawlers are the newly hatched nymphs of the adult scale insects. Crawlers are quite easy to control since they have not yet developed the tough waxy body covering characteristic of the adults. Pine needle scale and oyster shell scale are the two most common scale insects found in South Dakota. Check for crawler emergence by doing a tap test as is done with spider mites. Once the crawlers emerge use an insecticide to control them. While a dormant oil spray can do a pretty good job of controlling scale, it is probably too late to apply now since most shrubs and trees have already leafed out. Superior oils (Sun Spray) can be used after leaves emerge and is highly effective on the crawlers yet does not harm predatory and other beneficial insects. Malathion, diazinon or orthene may also be used. In severe infestation on deciduous shrubs, heavily infested branches may need to be pruned out to help the plant recover. Also, check the plants for other types of site-related stresses like as water, temperature, light or nutrient extremes which may be contributing to poor plant health. Remember, heavy scale infestations are often a symptom of other problems.

W SPRUCE NEEDLEMINER populations still appear to be increasing, particularly in the northeastern part of the state. Many blue spruce trees have their lower branches completed infested with this small insect. The typical signs of an infestation are needles along the lower branches, particularly the tips, are absent and instead, clusters or clumps of needles bunched together. If these clumps are closely inspected, the small hole at the base of the detached needles can be seen. Also within the clump can be found frass and a small dirty white to reddish larva. Control is difficult at time as the larvae are protected by the clump of needles. Treatment should be delayed until the adults flight period, around the 4^th of July.

W TENT CATERPILLARS should soon be appearing as their hatch coincides with the bud-break of crabapples and plums. The presence of tent caterpillars can already be predicted by inspecting the twigs of susceptible host – crabapples, plums, ash and others – for egg masses. The eggs were laid last year and now appear as a shiny gobbles the encircle the twig. If egg masses are found on a tree, they should be pruned out and the masses burned or otherwise disposed of. Do not merely throw the egg masses on the ground beneath the tree!

WEED CONTROL

L APPLY PREEMERGENCE TURF HERBICIDES NOW. Yearly infestations of annual grasses such as crabgrass, goosegrass, and foxtail in established turf are best controlled preemergence before weed seeds germinate. Crabgrass seed germinates when soil temperatures of 50 to 55F are sustained for several days. Germination of goosegrass and foxtail generally follows crabgrass by about 2 weeks. Products using pendimethalin, dithiopyr, prodiamine, oxadiazon, or trifluralin + benefin are effective. Be sure to follow preemergence applications with about 1 inch of irrigation (or rainfall) in order to move the herbicide into the top 1/2 inch of soil where weed seeds germinate.

L ALTHOUGH AUTUMN IS THE OPTIMUM TIME to control perennial broadleaf weeds in turf, early May is probably second best. Dandelions, ground ivy, white clover, curly dock, mouseear chickweed, plantain, common yarrow, red sorrel, and wild violet may be treated with a broad spectrum postemergence product containing 2 or more of the following growth regulator herbicides: 2,4-D, 2,4-DP, MCPA, MCPP, dicamba, triclopyr, and clopyralid. Avoid mowing several days before and after application. Some weed species may require 2 applications 10 to 14 days apart. Don’t apply these herbicides if rain appears imminent within 24 hours.

OTHER NOTES

L HOLD OFF ON THAT TURF FERTILIZER until mid-to-late May! Cool-season turfgrass naturally responds to warming soil temperatures in Spring with "green-up" and a flush of new growth. Applications of nitrogen too early may cause excessive shoot growth at the expense of root growth, and you may find that you’re time spent mowing has doubled. Application of a complete fertilizer at the rate of 1 lb. nitrogen per 1000 sq.ft., will prepare your turf for summer’s stress. Use a product that has at least 10% of the fertilizer in a slow release form.

H SPRING FLOWERING BULBS - You can help your bulbs to come back year after year by fertilizing the bulbs after flowering. Use a nitrogen fertilizer while their foliage is still green and be sure to keep that foliage alive and actively growing as long as possible this spring. DO NOT cut the foliage off after flowering, wait until it turns yellow and dies down naturally. Otherwise, dig up the bulbs and plant large new ones next fall to make it more likely that you'll have a nice display in 1999.

V RHUBARB & ASPARAGUS should be transplanted now. Each season we get lots of calls about transplanting these spring vegetables, typically right after gardeners have enjoyed that year’s crop. Unfortunately, that is not a good time to transplant or establish these plants. It is best to try to get them transplanted as early as possible, before the plants have much new growth on them. Remember if you are starting a new bed, it is best to start with new plants from a local nursery, garden center or catalog to reduce the chances of bringing a plant into your garden that has a virus or other disease.  (Photo or bare-root asparagus crown, 1 yr. old.)  (Photo of bare-root rhubarb plant.) See ExEx 6009 - Growing Asparagus for additional information.

W PRUNING - Remember most of the major pruning on trees should be completed in the next week or so. Bud-break and leaf formation require much stored energy from the tree. Pruning wounds created at this time do not compartmentalize properly due to a lack of available energy. Poor compartmentalization could result in increased decay. Also, delay livewood pruning of elms until later this summer to reduce attraction to the elm bark beetles which can spread Dutch Elm Disease.

Some trees may have experienced branch and limb breakage from the weight of the snow and ice this winter. Some trees may have only suffered minor damage and lost a few branches while others may have been nearly demolished from the excess weight and wind. The first step in dealing with this damage is to assess how much damage was done and clean up the loose debris. Carefully prune out broken and damaged branches at their base, removing them at the branch collar without damaging the trunk. If bark was stripped down the side of the tree with branches, cut off the loose bark but do not trace the wound. Branches that are only partially broken should be removed. If major damage has occurred to large trees, we recommend you contact a professional arborist for additional treatment. Do not use pruning paints or sealers on the broken or cut surfaces. Research has shown that these do not help the tree recover from the injury and may actually reduce the tree’s ability to wall-off the wounded areas.

W,F PLANTING TREES & SHRUBS - The number one killer of transplanted trees is planting too deep. When planting be sure to keep the bud union (graft) about 2-3 inches above the soil surface.