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 ASH RUST calls are still coming in from the northeastern portion of the state. The rust disease results in distorted leaves with fuzzy, yellow-orange dots forming on the underside of the leaves. These infected leaves will often fall prematurely. Controls are ineffective at this time as the disease is already in the leaf.
W BLACK SPOT on roses will probably be showing up soon. Watch for the first dark colored spots to appear, typically on lower leaves. The disease can quickly spread to other parts of the plant during wet weather. The first diseased leaves can be picked off to reduce the spread. Mulching around the plant helps to reduce infection by covering up old leaf debris which acts as a source of the disease. Protective sprays of Funginex are quite effective.
W CROWN RUST ON BUCKTHORN is common in many areas. It causes bright orange swollen spots on the leaves, petioles and green stems of buckthorns. Buckthorns are the alternate host for oat and rye crown rust but the rust may attack a wide range of other grasses. No treatment is recommended.
F GRAY MOLD ON STRAWBERRIES is a common problem. Clean harvesting of all ripe fruit will greatly help to reduce problems with botrytis gray mold. This very common fungal disease grows rapidly on over-ripe or damaged fruit and can quickly infest an entire fruit cluster under moist conditions.
H HOLLYHOCK RUST has been common again this year. Symptoms are numerous, small, raised, rust-colored spots on the leaves. Thorough cleanup of old plant debris in the fall helps to reduce the disease next season. Fungicide treatment now would be of little value.
W MAPLE ANTHRACNOSE has been seen on some trees in the state. Like ash anthracnose, it causes fairly large, irregularly shaped brownish spots, typically along the margin of the leaf. However, these infected maple trees will generally not drop as many leaves as ash trees do when they are infected. Control strategies are similar to that of ash so treatment now is probably not going to be very effective. Maple anthracnose is usually not as much of a problem so treatment is generally not needed. Young trees can be sprayed with a protective fungicide like chlorothalonil in the spring when new leaves are developing.
INSECTS
W BLACKHEADED ASH SAWFLY larvae are occasionally found in the central part of the state. This white or light yellow larvae have a black head (hence the name) and are about 3/4 of a inch long. You can find them feeding in colonies along the margin of the leaflets. The larvae will soon be pupating so no control is recommended at this time. There is only one generation per year.
V COLORADO POTATO BEETLES are actively feeding on potatoes and related plants in many areas of the state. Heavy feeding can reduce the leaf surface of the plant to the point where yield will be reduced. Hand picking of the orange, spotted larvae is a safe, non-chemical approach to control however, this may not be practical on a large scale. Insecticidal dusts or sprays containing sevin (carbaryl) will be quite effective. Bacillus thuringiensis var. tenebrionis (M-Trak) is another option. (Short Windows video segment of a Colorado Potato Beetle feeding on a potato leaf.)
W HONEYLOCUST POD MIDGE injury is showing up across the state. The oblong, pod-like galls form on the new leaflets of honeylocust. Within each of these pods you can usually find several small, yellowish larvae. The larvae pupate within the pod after about 3 weeks and then emerge as small, mosquito-like flies. There are several generations per year. While the injury looks unsightly, it rarely results in any serious decline for the tree. Sometimes a few interior branches will decline and occasionally a young, stressed tree will die. Recommended control is carbaryl when the new foliage begins to expand and repeat every two weeks through June.
M MAPLE BLADDER GALL MITE calls are coming in across the state. Every year people become alarmed at finding these small, multicolored bumps on the upper leaf surface of their silver maple trees. These bumps are due to feeding by the mite and it's many offspring. Control is not effective at this time as the galls have already formed and will not go away. Control is rarely warranted at any time as even trees with every leaf infested with the galls show no injury due to the feeding or gall formation.
F PLUM WEB-SPINNING SAWFLY feeding has been reported in some areas. The small tan larvae feed in small groups in webbed twigs of plums and a few other plants. The larvae have yellow to orange heads with short, prominent, black antennae. Chemical control is difficult due to the webbing. Often control is not necessary but if a tree is heavily infested it could be defoliated. In this case, prune out infested twigs and destroy them.
W,F PEAR- & ROSE-SLUGS should be showing up soon. The pear slugs can be found feeding on a wide range of plants but seem to prefer cotoneaster. The slimy looking pests are actually the larvae of an insect and not true slugs. They are usually light green to dark green and often have a dark colored dab of fecal material on their back. They feed on the underside of the leaves and cause a skelotonization type damage. They may defoliate plants in a few days when they are feeding in high numbers. Sevin, Malathion and Orthene are quite effective in controlling these pests but best results will be seen if the spray is directed on the undersides of the leaves.
W SPRUCE NEEDLEMINER late instar larvae are still present though most have pupated by now. The pupae are brown, about ½ inch long and can be found in the needle "nests" along the branches. Do not treat at this time. The few larvae that are still out have completed most of their feeding and control now will be ineffective. Treatment should be delayed until the adult flight period begins which is probably a couple a weeks away. More information will be given in the next issue of pest alert.
WEEDS
V,H CREEPING JENNY roots can be 20 feet deep. Control by pulling or hoeing in flower beds or gardens. It grows through loose mulch; here are no herbicides for use these gardens.
V DRIFT FROM 2,4-D type herbicides cause leaf distortion in new growth. Harvesting vegetables that are obviously affected is not recommended. Drift symptoms can usually be noted o more than one species.
H,V,W PREEN is a granular product containing trifluralin. It is used on several vegetables and around ornamental trees and shrubs. Do not use in lawns. It controls annual grass before emergence.
V DON'T TRY TO USE ROUNDUP IN ASPARAGUS now during the growing season. Roundup can be used in late fall after killing frost has stopped asparagus growth.
OTHER NOTES
V ASPARAGUS HARVEST SEASON is about to a close. Remember, the longer asparagus shoots are harvested, the greater the drain on the stored carbohydrates needed for the production of big thick spears. Therefore, it is important to allow lots of the shoots to grow up, mature and be allowed to remain on the plant until a killing frost. These ferny shoots manufacture the carbohydrates that are stored for next year's spring shoots.
W DECLINING ASH TREES are becoming a problem in several areas of the state, most notably Watertown, Sioux Falls and Rapid City with Watertown experiencing most of the problem. Affected trees either failed to leaf out this spring or only have partially leafed out. Oftentimes these leaves have unusually narrow leaflets. These trees have been described as "healthy" last year and an inspection of the growth rings bears this out. Several of the trees that died this spring show excellent growth up till the last year or two. The reason for this decline is not known and is probably a complex rather than due to a single agent. Calls are going out to extension specialists in the surrounding states to see if they are experiencing the same problem.
V FROST AND LOW TEMPERATURE INJURY occurred on many vegetables last week. Many of these plants have multiple buds on the lower stems that probably survived and are now growing out despite what may have appeared to be major damage to these plants. Some vegetables however, like cucumbers, squash and melons, may not have survived since they are very sensitive to cold and do not have buds at the base of the stem.
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Most recent revision Thursday, June 16, 1998 by David F. Graper.