Pest Alert

May 5, 2000

Welcome to another year of Pest Alert. Unlike the previous years, this one appears to be starting out dry rather than wet. Thus we anticipate that foliar diseases, anthracnose, rust and mildews, should not be as much of a problem as they have been in past years. However, the down side to this is we may experience an increase in borer problems – bronze birch borer, ash borer, etc. – as they generally find more suitable hosts during the periods of moisture stress. 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. While the relatively dry conditions this year may limit infections, it only takes a few periods of rainy weather to get the disease going. Now is the time to begin your apple scab spray program. 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). (Photo of apple scab on an apple leaf.)

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, especially in dry years like this one. However, the best treatment is to apply Captan, beginning just after bud-break and repeat at 10-day intervals during cool (below 55F), moist weather

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. Lime sulfur sprays can be applied every 10 days from now until the terminal growth stops, typically June, however these applications are rarely effective.

W,F FIRE BLIGHT may be as severe this year with the dry conditions. 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.

L DEAD SPOTS IN YOUR LAWN? Usually, we would be talking about propblems with Gray Snow Mold, Pink Snow Mold, or Dollar Spot but with the lack of snow in most areas this winter, the more likely cause is winter dessication. If the patches are small, 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, also, keep the seedbed constantly moist until seed has germinated. Avoid application of preemergence herbicides to these since these herbicides will kill germinating turfgrass seed as well as weed seed.

INSECT CONTROL

V CUCUMBER BEETLES are probably waiting for your young cucurbit seedlings to emerge. These small voracious eaters can totally consume young seedlings or they may just feed enough to inoculate the plants with bacterial wilt. In either case you will want to be on the watch for these small black and yellow striped beetles and use protective measures to reduce their damage. Floating row covers work very well to prevent the beetles from getting to the young plants. Also, treatment with Sevin or Rotonone containing products should be effective as well.

V FLEA BEETLES may already be feeding on your young vegetable seedlings. They especially like radishes and eggplant where they feed making tiny holes in the leaves. The tiny beetles are often difficult to see since they are quick moving and rather elusive. Protective treatments with Sevin, malathion or Rotonone should be effective.

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 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 TENT CATERPILLARS have already begun emerging and will be feeding on young succulent leaves of plums, cherries and apples. The tiny 1^st instar larvae are quite easy to kill by simply crushing and destroying the web they have begun. You could also use with carbaryl (Sevin), Malathion or Bacillus thuringiensis (B. t.) containing products.

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

W IF IT APPEARS TO GOOD TO BE TRUE, it probably is…. Two trees that are appearing in Sunday flyers are the Dawn Redwood (Metasequoia glyptostroboides) and the Empress Tree (Paulownia tomentosa). Both these trees are identified as "fast-growing, low maintenance, grow anywhere" trees. In fact the ad for the Empress Trees states; "you can measure the growth daily as it will soar 8 to 10 feet a year". Neither tree is recommended for South Dakota. They are hardy as far north as Omaha, beyond that the Dawn Redwood dies and the Empress Tree becomes a dieback shrub. We have one in Parker (that we know of) and it soars the same 6 to 8 feet every year since it dies back to the ground each winter.

W IMPROPER MATCHING OF PLANT SPECIES TO SITE CONDITIONS is also a continuous problem in our state. Too often people plant trees without fully considering the tree's requirements and the site conditions. Much of the state is covered with alkaline soils and there are several trees, eastern pin oak, red maple, and river birch, that become chlorotic if grown in soils with a pH that exceeds 7.0. Numerous tree species such as sycamore, Aus tree and even Norway maple are at their limits of winter hardiness and with the exception of the southeastern portion of the state and a few other favorable sites often experience winter dieback.

W LAWN IRRIGATION SYSTEMS are probably going to be operating a lot this summer. Unfortunately, they are also increasingly responsible for the decline of landscape trees and shrubs. The homeowner's desire to maintain an attractive green lawn throughout the summer can keep the soil too moist for woody plants. Many of our trees and shrubs have adapted to experience slight moisture deficiencies during the summer months. While it is difficult to monitor the amount of water added to the lawn, observing the following rule, regardless of the amount of irrigation, should help the tree – keep the water off the trunk. Keeping the lower trunk moist can increase certain fungi diseases as well as limit root growth.

W,F PLANTING TOO DEEP still appears to be a big problem in South Dakota. An informal survey of tree plantings for Arbor Day found many trees planted deeper than they should have been. Ornamental trees should be planted so the bud union is about two- to three-inches above the soil. Conservation trees should be planted so the root flare is at the soil level. If trees are planted too deep, the lower trunk - now below rather than above ground - is kept too moist and gas exchange is limited. The roots are also placed lower than they normally occur. These two conditions can result in the slow decline, over perhaps several years, and generally the death of a tree.

W PREVENTING FRUITING of crabapples and other ornamentals may be accomplished at this time of year. There are several products that can be used. They vary on effectiveness and availability. The most commonly available product is the insecticide Sevin. A 50% WP formulation can be applied at a rate of 3 T/gallon of water, two to three weeks after full bloom. DO NOT use Sevin on a tree while flowers are still present as it is very toxic to bees. Sevin will help to greatly reduce problems with messy fruit that fall from the tree and make a big mess on sidewalks, driveways etc.

Two other products are often more effective than Sevin. The first is sold under the trade names of Fruitone N and App-L-Set. These contain the plant growth regulator Napthaleneacetic Acid (NAA). NAA type products need to be applied at full bloom for best effectiveness. Another product that is effective if applied at full bloom is sold under the trade name of Florel Fruit Eliminator.