Welcome to the second issue of the 1998 growing season. Spring is an active time of growth for plants and pests. Some new problems have crept up in certain areas of the state. Weather is also a big concern with many areas of the state concerned about very dry conditions to others that are contending with flooded conditions. 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 activity is probably on the rise in many areas of the state thanks to the recent rains and humid weather conditions. 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 attacks ash. 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.
W,F BLACK KNOT cankers continue to develop and will be releasing spores soon. Prune out new swellings on the branches to reduce the spread of this disease.
W,F CEDAR-APPLE (HAWTHORN) RUST will be showing up on eastern redcedar and Rocky Mountain juniper across the state with recent 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 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. 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 MUSHROOMS have made a rapid appearance in many home lawns following recent rains. They are actually the fruiting structures of a much larger fungus body growing beneath the soil surface. The two most common mushrooms, seen growing in lawns, are the inky caps, which grow up in large clumps in the lawn, usually close to an old stump and fairy ring mushrooms. These mushrooms are usually smaller than the shaggy cap mushrooms and they generally grow up as single mushrooms but are arranged in the shape of a ring. They are also growing on organic matter in the soil but are generally not closely associated with an old stump.
There is no easy control for either of these mushrooms short of digging up the lawn to remove the organic materials they are growing on. The best solution is to just rake them out when they appear or simply ignore them.
W,F RHIZOSPHAERA NEEDLE CAST will soon be active and spreading to the new growth on blue spruce. Best treatment is to use Chlorothalonil or Bravo, apply it now, when the new shoots are half elongated (about 1/2 to 2" long) and again when needles have fully elongated (about 3 weeks later). Repeat this treatment for two consecutive years to control this disease. This disease has been very serious the last few years and is expected to continue to be a problem as long as we continue to have wet spring conditions.
INSECTS
W APHIDS are a common sight on a wide array of ornamental trees in shrubs, especially in drier areas of the state. They are feeding in large numbers on the new succulent shoots and leaves causing leaf and shoot malformation. Treatment may be warranted on young or newly established trees and shrubs. Best treatment would be to use Orthene 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.
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,V GRASSHOPPERS are already out and looking for soft succulent plants to feed on. These very early instars are quite small and don't eat much but they are very easy to control. The mild winter and dry spring conditions have been very favorable for these insects to overwinter and get off to a good start this spring. Control now is probably not warranted but may be necessary if feeding damage begins to occur. Try to keep surrounding grassy areas mowed to reduce areas for their feeding and cover.
W HONEYSUCKLE APHIDS are actively feeding on shrubs all over the state. These are the insects responsible for the malformed "witches broom" type appearance of the new shoots. A treatment be applied once the new growth emerges in early May.
W IPS BEETLES are beginning to emerge in the Black Hills. This beetles are attracted to trees stressed by fire, drought, transplanting or other factors. Healthy trees are rarely colonized except under high population levels. Colonized trees can be identified by the beetle's gallery patterns beneath the bark. Ips gallery patterns are often Y or H shaped with the large nuptial chamber in the center. Once the tree has been colonized recovery is questionable. The best management strategy is to maintain tree health and treat susceptible trees with a bark application of Sevin XLR. This treatment is best applied before the first flight (which is occurring at this time).
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. 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. Check for crawler emergence by doing a tap test as is done with spider mites. Once the crawlers emerge use malathion, diazinon or orthene to control them. 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.
WEEDS
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.
OTHER NOTES
W FLOODING along rivers and lakes in the northeastern portion of the state is expected to impact riparian forests and landscapes. While many species can withstand flooding during the dormant season, the list of trees that tolerate growing season flooding is fairly short. Many common windbreak species, eastern redcedar, plum and apricot, are very sensitive to flooding and may decline after even experiencing one season of flooding.
L HIGH TRAFFIC LAWNS are subject to soil compaction which restricts required gas exchange in the rootzone, reduces water infiltration and percolation, and decreases water holding capacity of the soil. Maximum soil compaction occurs at field capacity, which is the water holding capacity of the soil after gravitational water has been removed. Hollow tine core aeration is recommended to alleviate the compaction problem and should be performed while there are several weeks of good growing conditions remaining before summer. Leave the pulled plugs on the turf surface until they are dry and can easily be broken up by raking or dragging a piece of chain link fence over them. The soil from the plugs will help thatch decomposition by providing an environment for plant tissue-degrading microorganisms.
W ELM PRUNING UPDATE. In past issues of Pest Alerts we have made the recommendation that elm pruning wounds made during the growing season be treated with a light application of "tree paint" to help reduce the risk of elm bark beetles transmitting Dutch elm disease to the tree. This recommendation is no longer valid. Properly made pruning cuts do not favor the transmission of Dutch elm disease. This brings the list of "why paint" down to a single situation, to reduce the possibility of beetles transmitting oak wilt, and even this is suspect.
While on the subject of pruning, there is also very little evidence of disease transmission with pruning tools. The standard recommendation to sterilize pruning tools between cuts is probably not necessary expect for pruning trees infected with fire blight.
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.
W,F NEWLY PLANTED TREES, SHRUBS, BEDDING PLANTS AND VEGETABLES will need some extra attention in areas of dry soil conditions. Be certain to provide adequate water to help these plants get established in their new site. Water thoroughly to saturate the root zone around these plants, and extend the watering out several feet from the trunk to encourage new roots to grow out from the old root ball. Do not keep the soil continuously wet however. Roots need oxygen to grow too so allow the soil to dry a few days before watering again.
L PERSISTENT, WET CONDITIONS in some areas of the state have combined with warm spring temperatures to accelerate growth of turfgrass in lawns. Saturated conditions and frequent rainfall may interrupt your normal mowing schedule. Under normal conditions, no more than 1/3 of the shoot length should be removed at any one mowing, and clippings should be returned to the lawn. If you're unable to keep up with proper mowing frequency, excessive amounts of clippings may be deposited on your lawn. Be sure to remove heavy clipping deposits from your lawn. Failure to remove these clippings may reduce the amount of sunlight available to the turfgrass, and may also initiate disease problems.
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. The active ingredient is a chemical called ethephon that breaks down into another plant growth regulator - ethylene. The presence of ethylene causes the plant to abort its flowers and therefore greatly reduce the production of fruit. Typically products containing either NAA or ethephon will be more effective than the insecticide Sevin in reducing fruit set on the tree.
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Most recent revision Thursday, July 16, 1998 by David F. Graper.