Pest Alert

May 30, 1999

Welcome to the second issue of the 1999 growing season. Spring is an active time of growth for plants and pests. Weather is playing a big role in that it has been unusually wet and cool for this time of year. While the cool conditions slow down pest development, the wet conditions foster a number of foliage diseases.

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 ANTHRACNOSE is appearing east of a line from Aberdeen-Miller-Yankton. The symptoms of the disease are large, irregular, tan to brown lesions on the leaves, especially along the margins. The leaves may also become distorted. The infected leaves drop very premature - most have fallen in the last two weeks. Sometimes the entire tree is affected, other times only the lower 2/3's of the canopy. This disease "pops up" every time we experience a cool, wet spring, precisely the conditions that have been with us since April. It is too late for control. The recommended treatment is Bravo (chlorothalonil) applied when the leaves begin to expand and then two more treatments spaced 10 days apart. Raking the fallen leaves and burning them rarely provides sufficient control to recommend this practice. Defoliation, while alarming in appearance, will not harm otherwise healthy trees.

W ASH RUST is also appearing in the same region as ash anthracnose. The symptoms of this disease are bright orange spots on the petiole (leaf stalk) and underside of the leaves. These gradually enlarge and the infected leaf turns brown and falls by early summer. Several samples have come in with these orange spots mis-diagnosed as aphid eggs. No control is recommended at this time. The treatment, a wettable sulfur product, which should have been applied when the leaves first started to expand.

W BACTERIAL BLIGHT of lilac has shown up in several areas of the state. This disease, which has symptoms similar to fire blight, attacks the young shoots during wet spring weather. Typical symptoms include the browning or blackening of new growth, often resulting in the shoot tip curling over and dying. There is no treatment other than to perhaps prune out the infected shoots, cutting well below any signs of the disease.

W,F FIRE BLIGHT has been quite severe the last few years on apples, crabapples, cotoneaster and mountain ash across the state. This bacterial 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. Growers should be on the watch for signs of dying spurs and small twigs over the next month. 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 PEACH LEAF CURL is now active. While this is probably a rarely seen disease, with the scarcity of peaches in SD, some home gardeners may be seeing this leaf distorting disease. It is caused by a fungus that overwinters in bark crevices on the tree. Typical symptoms include the curling and reddening of leaves and petioles with the underside of affected leaves having a whitish appearance. No treatment is possible now, mark your calendars for next spring to apply lime-sulfur just prior to bud break. Control is often very good with this treatment.

W POPLAR SHOOT BLIGHT has been observed in several locations around the state this year. The symptoms of the disease have become most obvious over recent days. Poplar shoot blight occurs during cool and wet weather, causing the newest growth of the poplar branches to turn black and die back. Often it is first observed when the leaves are about one half their full size. The dead branch tips may fall from the tree in high winds.

Poplar shoot blight is quite common around the Dakotas and Minnesota and is not a problem on mature trees. Young trees may benefit from an early season application of a fungicide containing chlorothalonil. Application at bud break and 10-14 days later should minimize the effects of the disease. However, by the time the disease is observed it is too late for treatment.

W,H POWDERY MILDEW: The humid, wet weather that has occurred over much of the state this spring has been very favorable for powdery mildew development. Powdery mildews can be severe on lilac, phlox, roses, current and Monarda. They also occur on many other hosts. Powdery mildews are easily recognized by the dusty, powdery appearance they cause on the 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.

W,F RHIZOSPHAERA NEEDLECAST OF SPRUCE is a major problem with blue spruce across most of eastern South Dakota. Symptoms begin in midsummer with the infected needles (usually the one-year old needles) turning yellowish-green then purplish-brown by late winter. These infected needles will have rows of small black fruiting bodies along the stomates at this time. Control is two applications of Bravo (chlorothalonil). The first application should have been made when the new needles were partially elongated. Make the second application about 2-3 weeks later when the new needles have fully expanded. Remember that this control can only prevent or reduce new needle infection. Needles that were infected last June will still turn purplish-brown and fall prematurely.

 INSECTS

W THE ASHGRAY BLISTER BEETLE may be showing up on peashrub and honeylocust. The adult beetles are about 1/2 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 will soon be showing up 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 eastern 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.

V BEAN LEAF BEETLES are actively feeding on many small bean plants in the garden. Typical damage symptoms include many small 1/4-3/8" holes in the leaves. The beetles are small, aout 1/4" in diameter, yellow with black spots. They may be rather difficult to spot on the plants. Treat by applying a garden dust that contains Carbaryl.

W BRONZE BIRCH BORER adults are beginning to fly in most of the areas of the state. The adults are dark bronze and torpedo-shaped. They can be found crawling along the lower trunks of acceptable hosts. Infested trees can readily be identified by small bumps along dying branches and D-shaped adult emergent holes. Susceptible birch trees can be protected with a bark application of Turcam (bendiocarb) or Dursban (chlorpyrifos) made now and repeated two more times with each application about 2-3 weeks apart. The most common host in our area are the European white birches, particularly the cutleaf cultivar. Paper birch and gary birch, including the cultivar 'Whitespire' - now known to be a gray birch, not Japanese, are also susceptible. River birch is not attacked by the bronze birch borer.

F,W FRUIT TREE LEAFROLLERS have been identified on a number of different trees but are most commonly found on apples. They may also attack ash, elm, oak, maple, cherry and caragana. These small light green caterpillars feed by webbing the edge of the leaf together and then eating the leaf protected on the inside. They usually do little damage to the tree so treatment is usually not needed. Once in the leaf they are more difficult to control but may be treated with carbaryl, Malathion or Bacillus thuringiensis (B. t.). Orthene can also be used on non-fruiting trees like maple and oak.

V,H,F GRASSHOPPERS have begun hatching in most areas of the state. The tiny hatchlings will soon begin feeding on tender shoots and grasses. Hatch is expected to continue into early August. Now is the time to start thinking about management strategies. Vegetable gardens should be monitored for feeding activity on a regular basis. Border areas around the garden should be kept mowed or even tilled to provide a low-food zone around the garden to discourage foraging grasshoppers from moving into the garden. Border areas can also be treated with insecticides like Tempo, Orthene or carbaryl. Vegetable gardens may be treated with various types of insecticides containing carbaryl. A wheat-bran bate, impregnated with carbaryl, has been quite effective in controlling young grasshoppers. Turkeys, chickens and geese offer a non-chemical means of control.

W JUNE BUGS (Phyllophaga spp.) are also known as May bugs but are actually a type of beetle. They are causing extensive defoliation of ash trees from Platte to Winner. There have been several reports of ash trees in shelterbelts being stripped of almost every leaf. The ground beneath these trees is described as "swiss-cheese" due to the numerous holes created by the emerging adults. The adult are chestnut brown and about 3/4-inch long. They are typically night fliers so they may never be seen on the trees they are defoliating. The adult beetles feed on the foliage of ash, elm, lindens (basswood) and willow during the months of May and June. While they are rarely a problem, the feeding can result in localized, but complete defoliation, of shelterbelts. The larvae can be found in the soil feeding on roots. They are 1-inch long, milky white, with a brown head and are C-shaped. The larvae have 3 pairs of legs. There is a 2-3 year life cycle to this particular insect so it is possible to find both adults and larvae at this time. At this time controlling the adults is probably ineffective as they have just about completed their feeding, but the larvae can be controlled with a soil application of either Dursban (chlorpyrifos) or Diazinon (diazinon).

W LACE BUGS have been seen feeding on hackberry in the North-eastern part of South Dakota, but these tiny insects can probably be found on other plants as well. These sucking insects generally do not do much damage to plants unless they are feeding in large numbers on young or newly established

trees. The insects are gray to brown, about 1/8" in size, and have rather lacy-looking wings and bodies. Look for the dark fecal spots on the undersides of the leaves and the whitish-yellow stippling spots on the leaves. Horticultural oils, carbaryl or Malathion should be effective in controlling them in severe infestations.

W MOUNTAIN PINE BEETLES are beginning to pupate in the Black Hills. At this time debarking or chipping is no longer an effective means of controlling the insect. The adults will still be able to emerge. Solar treatments, where infested trees are cut into logs, sprayed with a pesticide and covered with plastic, are also not recommended. Infested trees felled at this time will still not have time for the wood and bark to degrade, pesticides applied to the bark will not kill emerging adults and the adults can easily chew through plastic. Any infested trees should be felled and immediately burned (be sure to obtain a burning permit from the nearest office of the South Dakota Division of Conservation and Forestry). Infested trees can be identified by their yellow to bright red canopies, pitch tubes (masses of pitch about 1/2- to 1-inch long) along the lower 15 feet of the trunk and red boring dust around the base of the trees.

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 to control them or an application of insecticidal soap is quite effective.

F,W SPRING CANKORWORMS have been seen in fairly large numbers in the Brookings area, feeding on apple trees. These slender loopers are now about 1" in length, have a medium brown head and a striped body. They move with a typical "inch-worm" movement and feed on apples, elms and a number of other trees species. Their damage is generally minor but they can cause significant damage if feeding in large numbers. Typical damage is skelotonization of foliage. Cankorworms can be controlled by using typical orchard sprays on apples or with B.t. products, carbaryl or malathion.

W TENT CATERPILLARS continue to generate lots of calls. These dark colored caterpillars have a blue strip down the side of the body. Caterpillars are probably approaching full size by now at about 2" in length. Nests can be physically destroyed with a stick or one?s hand and the larvae killed. Chemical treatments at this point are not as beneficial as they could have been a few weeks ago, since most of the damage is already done. Carbaryl would be the best choice at this late date.

OTHER NOTES

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.

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.

W SPRUCE "CAPS" have been created a few calls to the office. At this time of year the covering on the terminal buds of spruce dislodges as the candle begins to expand. This greenish-brown covering or cap can often be found in small piles beneath a large spruce. Sometimes the wind can sweep them into piles along side of garages or other structures. The caps are certainly not a problem but just part of the normal seasonal growth process.