Pest Alert

Welcome to another issue of Pest Alert. Categories for topics are as follows, H - Herbaceous plants and flowers, W - Woody Plants, V - Vegetables, F - Fruit and L - Lawns.

L,V,W,H POWDERY MILDEWS are severe on lilac, phlox, roses, Monarda and Zinnia. They also occur on many other hosts, including vegetables, especially pumpkins, squash and other cucurbits. Powdery mildews are easily recognized by the dusty, powdery appearance they cause on 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 85°F. 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. It is probably too late to do much to reduce the problem on vegetable crops. 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 on the label.

L RUST ON TURFGRASSES. Warm days and cool nights favor the development of rust on many hosts including turf grasses. The fungus that causes rust on turf grasses blows in from southern states each year. Once it is here it can reinfect grasses in area lawns. It is most common on newly seeded lawns where the grass may be left a bit longer during establishment. Young, tender plants also seem to be slightly more susceptible to the disease. Common bluegrass is somewhat susceptible, but the bluegrass cultivars ‘Merion’, ‘Touchdown’, and ‘Windsor’ are very susceptible. Lawns stressed by low fertility, drought stress, or compaction, may also be more likely to have a rust problem.

Control rust in turf by catching and removing your clippings. This is a form of sanitation that helps eliminate the pathogen from the site by removing infected grass blades. Improve your fertility with a light nitrogen application. At this time of year a cut rate of about 1/3 of a pound of actual nitrogen will help with growth without causing too heavy a flush of growth. Fungicides are not usually needed unless the disease is very severe and the weather favors continuous infection. Chlorothalonil, triadimefon (Bayleton, and Green Light Fung-Away) and mancozeb (Fore, and others) are all good choices for rust management.

V BEAN LEAF BEETLES and other insects have been feeding on snap beans throughout the state. Generally, these voracious eaters feed on the leaves, chewing small holes in them but these small green and yellow beetles will also chew small holes into the pods. Crickets and grasshoppers may also be feeding on your beans too. Treatment is essentially the same for all of these pests. First of all, clean harvest to remove all the edible sized fruit then treat with an insecticide like Carbaryl (Sevin), Esfenvalerate and rotenone containing products. Be sure to follow the pre-harvest interval for the product you are using.

L WHITE GRUB INFESTATIONS should be treated now. Symptoms include a general browning of the turf similar to severe drought stress. This is due to the severing and consumption of turf grass roots by the final larval stages of certain Scarab beetles, such as May/June beetles, Masked Chafers, and Black Turf grass Ataenius. With little or no roots, the turf cannot take up water and is no longer anchored in the soil. Large patches of turf can be easily lifted from the lawn. Watch for activity of foraging animals such as skunks, raccoons, moles, and birds, which may indicate the presence of grubs. Rolling back the sod should reveal a cream-colored, C-shaped grubs. If populations are less than 8 to 10 per square foot for Masked Chafers or 3 to 5 per square foot for May/June Beetles, persistent watering may allow turf survival without the use of insecticides. If chemical treatment is warranted, Dursban or Diazinon can be applied now. Be sure to follow insecticide applications with 1” of water in order to move the product into the soil where the grubs are feeding. Since grub populations in the lawn are usually concentrated in certain areas, scouting for these areas and spot treating can reduce insecticide amounts. If populations are present this year, consider using one of two new products, Merit or Mach 2, next year. These products have low mammalian toxicity, are more environmentally friendly, and have season-long residual activity when applied in Spring. Don’t apply Merit or Mach 2 this late in the season since their mode of action affects growth regulation between larval instar stages, and won’t be effective.

W Oystershell scale infestations are appearing on green ash in the southeastern portion of our state. Oystershell scale does not look like a typical insect, appearing instead as a small teardrop-shaped shell along the twigs and branches of trees. These adults do not have legs, eyes or antennae. They are attached to the plant by their mouthparts. The young, known as nymphs or crawlers, hatch out in May and walk along the branches until they locate a spot to feed and then become sessile as an adult. While the scale has been found on green ash, it has a large host range and can be found on lilacs, willows, poplars and maples. Infestations usually begin on a single branch but can quickly expand to cover the entire tree. Heavy infestations, where almost the entire branch or trunk is covered, can result in branch or tree mortality. Treatments are not effective at this time. Treatments of either ultra fine oil or insecticidal soap can be used against the crawlers next May.

W Mountain pine beetle is still flying in the Black Hills. The Forest Service will be conducting their annual aerial survey of the Hills to evaluate the threat and we will provide their predictions for next year in a later Pest Alert. The preliminary results from our pesticide trials, performed in cooperation with the Forest Service, indicate that Sevin XLR and Astro are equally, and highly, effective at preventing successful colonization by the mountain pine beetles. More results will be forthcoming at the end of next year.

V,F PICNIC BEETLES OR SAP BEETLES are a problem in the garden and orchard as well as at backyard picnics and parties. The name comes from the fact that this insect is very prevalent at picnics and is attracted to various foods and beverages found there. There are several kinds of picnic beetles but the most common one is a small black beetle about 1/8 of an inch long with four small orange spots on the back. These beetles also burrow into vegetables and fruit such as sweet corn, berries, and tomatoes. They are particularly attracted to fruit that is overripe or damaged in some way. Therefore the first management strategy against picnic beetles should be to keep berry and tomato patches picked on a regular schedule, removing any overripe or damaged fruit. Applications of diazinon are also effective. However, be sure to read the label carefully to determine that the crop being treated is listed on the label, and be extremely careful to observe the harvest interval between application and harvest, as treatments for picnic beetles commonly occur during the period of fruit and vegetable harvest.

OTHER NOTES

W COMMON BUCKTHORN. We typically receive lots of samples of this commonly found shrub at this time of year. Common buckthorn, Rhamnus cathartica is identified as a shrub or small tree with small, dark green, elliptical leaves, and with clusters of small black fruit. Many homeowners confuse the form with a crab apple. The twigs also end in a small thorn. Lots of would-be jam and jelly makers often wonder if the fruit is safe to eat and use. While the fruit is not considered poisonous, it does have laxative properties, (cathartic - evacuating the bowels) therefore, eating the fruit is not recommended. Birds will often eat the fruit and then deposit the seeds all over the yard. Consequently, buckthorn seedlings are frequent weeds in many yards.

W Hail damage on ponderosa pine in the Rapid City area occurred earlier this year. The trees along the western end of the city - where the hail was most extensive – exhibit typical symptoms of needle loss and browning along with twig and branch breakage, though in many instances the entire top of the canopy is brown. Many people have a difficult time understanding how hail can be responsible for this damage. But, it does occur on a periodic basis in the Black Hills though usually in more isolated areas. There is little that can be done at this time other than remove the broken branches. However, there are several treatments that may be useful next year. These trees are highly stressed and will be susceptible to colonization by the pine engraver beetle or Ips. Highly valued trees should be sprayed as a preventative measure. Since the pine engraver beetle is active until October it may be a useful measure to treat the trees yet this fall with Sevin XLR. The other possibility is Diplodia tip blight. Due to the mechanical damage on the twigs there are numerous potential infection sites. Generally a year or two after a hailstorm we see diplodia in the trees. Treatments should not be applied until next year, however.

W Storm damage is extensive in the Northern Hills. A large number of mature trees have suffered damage to their canopies, primarily branch and trunk breakage. There have also been many large trees, generally spruce, that now are leaning due to the strong winds. If the trees have developed more than a 15° lean, generally the recommendation is to remove the tree. If the lean is less than 15 trees, the tree can often be pulled back to its original position and guyed. The guys need to be left in place for several years but eventually the tree will regain its stability. Trees that have broken branches should be properly pruned at this time to reduce the possibility of decay. These pruning wounds do not need to be painted. If in doubt about the damage to a tree, call a professional arborist to evaluate the tree for structural defects before performing any pruning.

V WATERMELON HARVEST is in full swing in Sanborn County but how do you tell if the melons in your garden are ready to harvest. There are several signs to use to tell if a melon is ready to harvest. First of all, ripe watermelons develop several characteristics: the tendril attached to the stem by the melon will turn dry; the melon will often develop a yellow-orange ground spot under the fruit, color will be duller and of course that hollow sound when thumped. Muskmelon will develop a strong muskmelon odor; fruit will soften somewhat, especially at the blossom end of the fruit and the stem will easily pull from the fruit. Some melons will have a definite rind color change, perhaps from green to yellow or there may be other changes to look for. Generally with some careful observation skills, some practice and a bit of luck you will pick the melons at their peak of flavor.

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Most recent revision Monday, August 28, 2000 by David F. Graper.