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 lesions should now be visible on infected leaves. Lesions will appear as small, irregularly shaped olive green spots, often located along veins in the leaves. Infected leaves often will turn yellow and drop from the tree later in the season. Recent rains and humid weather conditions have helped to foster scab development. Continue applications of fungicides for control of this fungal disease. Fungicides such as Captan and Benlate should be effective (read label for directions).
W ASH RUST AND ASH ANTHRACNOSE is showing up throughout northeastern South Dakota. This area of the state has received above normal precipitation and these wet conditions favor disease development. Trees infected with ash rust have bright orange spots on their leaves and petioles. The petioles may also have "gall-like" fruiting bodies forming on them. The disease will typically result in premature defoliation. Ash anthracnose symptoms include large, irregular, tan to dark brown lesions along the margin of the leaves. The disease will also result in distorted leaves and premature defoliation. These two diseases often result in more cosmetic damage than injury to the tree, however, repeated defoliation can weaken the tree and make it more susceptible to other pests. Currently the recommendation for ash rust is three applications of sulfur spaced about 10 days apart beginning when the leaves first expand. Ash anthracnose recommendations call for three chlorothalonil applications, again spaced 10 days apart, beginning when the leaves first begin to expand.
W DIPLODIA TIP BLIGHT treatment window is rapidly approaching. This is a common disease of Austrian and ponderosa pine, but can also occur on Scots and mugo pine. Symptoms begin in late spring with the newly expanding shoots and needles becoming brown and stunted. The symptoms usually begin on the lower branches. The only effective treatment for this disease is Thiophanate-methyl applied just before bud-break with two more treatments spaced about 10 days apart.
W DUTCH ELM DISEASE is already showing up in the central part of the state. The typical symptoms are leaves on individual branches wilting and turning yellow then brown. The browning leaves often remain attached for a short time before falling. Affected branches usually have greenish streaks in the outer sapwood. The disease is easily transmitted by root grafts between an infected and a healthy tree, thus early detection and prompt removal of infected individuals in a grove or boulevard planting of elms is necessary. There are treatments available for Dutch elm disease. Arbortect 20S and Alamo are both used for preventative and therapeutic treatments. Therapeutic treatments are most effective if the disease is limited to a single branch rather than a systemic infection.
W,F NEW FIRE BLIGHT INFECTIONS may become evident on apples, crabapples, cotoneaster and mountain ash across the state. One of the most common ways this disease spreads is trough blossom infections. Look for small shoots or spurs that have now turned brown or black as evidence of this type of infection. This disease is managed by utilizing a number of strategies including chemical, pruning and fertility. These infected parts should be pruned out to avoid having the disease spread throughout the tree. 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.
W RHIZOSPHAERA NEEDLECAST should be appearing on spruce, particularly blue spruce in the next week or two. If you look closely at infected one-year old needles now you'll see small black fruiting bodies emerging from the stomata. These fruiting bodies will soon be releasing spores that will infect the new needles that are forming. Next year these needles will turn a yellowish-green then a purplish-brown before falling. Infected trees may have only one- or two-year old needles rather than needles up to six or seven year's old. The recommended treatment is Chlorothalonil when the new needles are half elongated and a second treatment when the new needles have fully expanded.
INSECTS
W APHIDS continue to generate concern with on a wide array of ornamental trees in shrubs. They are feeding in large numbers on the new succulent shoots and leaves causing leaf and shoot malformation. (Closeup picture of some aphids. Note, aphids can come in many different colors.)Treatment may be warranted on young or newly established trees and shrubs. Best treatment would be to use acephate since its systemic activity will be more effective at getting the aphids hiding in curled leaves. Malathion and diazinon could also be used. Forceful jets of water can also remove many of the aphids from the foliage.
W THE ASHGRAY BLISTER BEETLE is causing defoliation of peashrub and honeylocust throughout the central portion of the state. The adult beetles are about ½ inch long, elongated and gray to black. They can usually be found feeding in groups. The adults are slow movers and can be easily picked by hand, however, the body fluids of these beetles contains cantharidin, a substances that causes watery blisters to appear on the skin with contact. The recommended treatment to prevent defoliation is carbaryl.
W ASH PLANT BUGS are causing some concerns across the state. The feeding by these small, green to tan bugs results in yellowing stippling and spotting with infested leaves often turning brown. The premature defoliation of ash occurring in the northeast part of the state is primarily due to ash anthracnose and rust rather than ash plant bugs. Recommended treatments for ash plant bugs are carbaryl and acephate when the leaves are expanding. Imidacloprid as a soil or trunk injection also provides excellent control but it must be applied at least 60 days before the ash plant bug begins feeding. (Photo of ash leaves showing stippling damage and spotting from anthracnose.)
W PINE SAWFLY LARVAE are feeding on pines from Rapid City to Spearfish. The sawfly is not uniformly found throughout this area but instead occurs in scattered pockets. The preferred location is in small (10-20 foot tall trees) that are along the edge of the forest or occur as isolated individuals. The small, greenish larvae have dark heads and can be found feeding on last year's needles in colonies. If the colony is disturbed the larvae will all move in unison to startle the predator. Now is the time to treat this pest as feeding as just begun. If treatment is delayed until the larvae are large, most of the feeding damage will have already occurred. Recommended treatments include carbaryl, malathion and insecticidal soap.
W,F,V SPITTLEBUGS have been reported on a variety of ornamental, fruit and vegetable plants. These small insects surround themselves in a gob of froth or foam, resembling spittle. They feed by sucking plant sap. While they may feed in fairly large numbers the only control necessary is physical removal. A forceful jet of water usually works quite well.
W,F TENT CATERPILLARS can be found in many shelterbelt plum plantings across the state. The pale colored larva have white markings and form nests at the crotches of branches. The larvae can be seen moving from the nests during the day to feed on leaves. The best treatment is an application of Bacillus thuringiensis while the larvae are still small. This bacteria acts as a stomach poison so the larvae have to ingest it for the treatment to be effective. It usually will take several days to kill the larvae, however, infected larvae stop feeding almost immediately. Carbaryl and acephate can be used on larger larvae.
WEEDS
L,W,F POAST HERBICIDE, containing sethoxydim controls emerged annual grass like foxtail and crabgrass. It is now available in small containers for the home retail market as Fertiloam Hi-Yield Poast. It is labeled and safe for use in several garden crops including raspberry, strawberry, tomato, watermelon, muskmelon, squash, grapes, potatoes, cabbage, and several others. Labeling includes over 80 ornamental and bedding plant species, 103 species of shrubs and 106 tree species.
Check the label for approved species. It is labeled for iris and daylily; tulip or peony is not included. The application to harvest interval for garden crops vary from 14 to 45 days. Do not use in lawn areas or expose desirable grasses to the spray.
H,V,F USE CARE IF SPOT TREATING weeds with Roundup. Hand-held trigger applicators of mixed or ready to use product should be set to make a very coarse spray. Adjacent plants are often injured because fine droplets affect vegetation beyond the target spot.
OTHER NOTES
W AMERICAN ELM AND SIBERIAN ELM SEED CROP was abundant this spring. The small, disk-shaped samaras have been ripening and dispersing over the last couple of weeks. This large crop of seeds has generated calls from homeowners concerned about the "many small browning leaves in their elms." Again, these are not small leaves, but seeds and there is no need for concern. As a side note: the American elm and the Siberian elm produce their seeds in the spring, the true Chinese elm (Ulmus parvifolia), which is not found in South Dakota, produces its seeds in the fall.
W POLLEN IS BEING PRODUCED BY PINES at this time and it is especially noticeable on mugo pines. If you shake the branch, a cloud of yellowish pollen will be produced. Several homeowners have called about "the dust coming off their pines." This pollen production is of no concern even to "hayfever" sufferers. The pollen of pines and other gymnosperms is not an important factor in inducing hayfever. (Photo of pollen producing structures on pine.)
W SILVER MAPLE IS ALSO PRODUCING AN ABUNDANT SEED CROP THIS SPRING. While this seed crop is not being confused with leaves, large silver maple seed crops do usually generate calls in June after the seeds have fallen. Seeds are produced at the base of the new growth below the new leaves. Once the seeds fall, the tips of the tree appear "tufted" as the new foliage is concentrated at the tips and the base of the new growth is devoid of leaves.
W THE CANDLES ON PINES ARE BEGINNING TO EXPAND NOW. The best time to shear mugo pines and other pines is when the new needles in the candle are about one-half the size of the older needles. Shearing the candle in half at that time will reduce this year's growth by half as well as result in more buds produced for next year's growth. Pines should only be sheared during the candle phase as they only set terminal buds. Shearing at other times of the year will prevent normal bud set and result in a tree with many dead tips. (Photo showing new "candles" on pine with cones also present.)
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Most recent revision Thursday, July 16, 1998 by David F. Graper