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,F APPLE SCAB symptoms have now shown up in apple and crabapple trees over most areas of the state. Apple scab causes small olive to black spots on leaves, later causing the leaves to turn yellow and fall off. These spots may be more reddish colored on some crabapples. Captan is the most commonly used chemical for control. Treat now and repeat applications at regular intervals (7 to 10 days) during wet weather.
V EARLY BLIGHT has been seen developing on tomato and potato plants in many home gardens, often on the same leaves where late blight lesions are present. This disease causes small spots that start out at about 3/8" in diameter on the leaves. They are also characterized by a target pattern of lines within the spots. Many spots may merge together to cause larger areas of the leaves to die. Like Septoria leaf spot, this disease overwinters on diseased plant debris from last year and is then spread to the lower leaves by splashing rain or irrigation water. Control is similar to that for Septoria leaf spot with Chlorothalonil (Daconil 2787) treatments beginning at the first sign of the spotting for best control.
H HOLLYHOCK RUST has been common again this year. Symptoms are numerous, small, raised, rust-colored spots on the undersides of 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.
V LATE BLIGHT, caused by Phytophthora infestans, has been confirmed on tomato plants from Brown, Clay and Beadle Counties. This is a disease that can kill entire potato and tomato plants in a few days under cool, wet weather. This is the disease that was at the heart of the Irish potato famine, 150 years ago. While late blight has occurred in the United States since 1992, the pathogen has become more important in the past 5 years. About that time a new variant of the fungus developed and spread across North America. This new form is more aggressive and is resistant to the fungicide that had been used most commonly to combat late blight.
Large blotches of dead leaf tissue are characteristic of late blight. The dead spots cross leaf veins, unlike any other disease of potatoes and tomatoes. Often the dead areas will be bordered by a yellow halo. On the underside of the leaf, a white, cobwebby growth may be present during wet weather. Dark, streaky lesions may also be present on the stems of either tomato or potato.
The disease can be controlled in the home garden by picking off diseased leaves and using fungicides such as chlorothalonil or mancozeb that are approved for use on garden vegetables. Severely infected plants should be removed from the garden. Many brands of fungicide with these active ingredients are available from garden centers and discount stores. Applications as often as every 7-10 days may be needed during periods of cool, wet weather.
V POWDERY MILDEW has shown up on cucumbers as well as a number of other types of plants. Powdery mildews are often severe on lilac, phlox, roses, and Monarda. They also occur on many other hosts. 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 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 on the label.
L RED THREAD. Recent cool, humid conditions in eastern South Dakota have provided an ideal environment for certain diseases of cool-season turfgrasses. Red thread (Laetisaria fuciformis) is a patch disease that thrives under these conditions during mid-spring to early summer, particularly under nitrogen deficiency and/or drought stress. (Drought stress can occur with prolonged saturated soils in which oxygen is depleted.) Kentucky bluegrass, perennial ryegrass, and fescues are susceptible species in lawns. Temperatures between 65 and 75F with prolonged light rain or drizzle favor the development of red thread. Symptoms include small, round, 1 to 2 inch diameter patches of tan to straw-colored turf, plus reddish sclerotia strand(s) that may extend up to 10 mm (3/8") from the surface of leaf blades. Often the strands initiate at the cut ends of mowed leaves. Maintaining proper nitrogen fertility, raising mowing heights, watering deeply but infrequently, and collecting clippings during severe infections can help control the disease. If no fertilizer was applied in spring, apply 0.5 to 1.0 lb. nitrogen per 1000 square feet now. Use mostly a slow release form of nitrogen such as urea formaldehyde, methylene urea, isobutylidine diurea, sulfur-coated urea, polymer-coated urea, or natural organic nitrogen. Red thread is a disease of leaves and stem, not roots. Fungicide treatment is rarely necessary in lawns, since recovery can usually be accomplished with more favorable environmental conditions and proper cultural practices. If red thread is a yearly problem, reestablishment with resistant cultivars may be necessary.
W,H RUST has shown up on a great variety of herbaceous and woody ornamental plants this year. The main reason for this is the favorable weather conditions that many areas of the state has had this spring. In most cases, rust will appear as raised bumps on leaves, petioles or stems that are emitting bright orange to brown spores that are evident if one rubs across the bumps. At this point in the season, chemical control will be ineffective and is not recommended. Thorough cleanup of plant debris this fall will often help reduce chances of having the disease next year. However, if a plant has been prone to the disease, chemical protectant fungicides will be useful early next season.
INSECTS
W ASH PLANT BUGS are on the increase again as the second generation emerges. Many trees are showing significant damage from these small insects. Some trees were heavily damaged earlier this year and now are having the new growth damaged again. If young, stressed or newly transplanted trees have significant numbers of insects present, a treatment of malathion, diazinon or orthene can be used to reduce further damage and stress on these trees. Photo of young ash plant bug. Photo of stippling damage. Photo of young plant bugs and fecal spotting on underside of leaf.
V CUCUMBER BEETLES are actively feeding in many gardens. 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. Good control of cucumber beetles now will reduce the chances of having bacterial wilt problems a little later in the season.
V,H GRASSHOPPERS are feeding on many vegetables and flowers, especially in most areas of South Dakota. Grasshopper numbers are very large again this year. Chemical treatments are most effective on the smaller grasshoppers. Unfortunately, with the populations as high as they are, good, season-long control will be extremely difficult. NOW is a good time to start controlling them. Some protection and control can be gained by spraying with Malathion, Sevin, Orthene, Dursban and Tempo on ornamental plants. Vegetables and fruit trees can be treated with Sevin, Malathion or Diazinon. Re-spraying will be necessary as often as the grasshopper population continues to rebuild and move in from surrounding areas. Border areas around vegetable gardens should be treated to reduce the movement into the garden. Tempo and Dursban may prove to be most effective but these cannot be used on vegetables but work well in the border areas. De-Bug, a bran bait impregnated with Sevin may also be used and can be effective against some species of 'hoppers. Finally, protective barriers will also be helpful in dealing with the grasshoppers. Floating row-covers can work well but must be applied while few or no grasshoppers are present on the plants.
L JUNE GRUBS. Homeowners who have been told that their current turf problems are due to white grubs may want to verify the diagnosis themselves by lifting loose sod sections and inspecting for grubs in the top 2 to 3 inches of soil. If neither loose sod nor grubs are present, it is probably because it is too early in the year. Most grub damage occurs in late summer to early fall when the final larval instar is present in the upper rootzone of the turf.
W LACE BUGS have been feeding heavily on a variety of ornamental plants. These, fairly small, flattened insects often feed in large groups on the undersides of leaves. They are sometimes rather inconspicuous since the back of the insect often blends in well with the coloration of the leaf. The black fecal spots are often more noticable. These sucking insects are usually not going to damage a well-established tree. However, treatment with malathion or orthene may be needed on young or newly established plants. Lace bugs have been seen on ash, oak and cotoneaster plants.
V SQUASH VINE BORER ADULTS have been reported to be flying in Minnesota so they will probably be active here in South Dakota as well. These attractive bluish moths deposit eggs near the base of squash, pumpkin, and occasionally melon vines. Newly hatched larvae immediately burrow into the stem where they continue to feed until they reach approximately one inch in length. This feeding eventually kills the vines, although it appears to happen quickly because the vines suddenly wilt. Vines must be protected from late June through mid August from egg laying adults and newly hatched larvae with an insecticide application to the base of plants. Dust formulations are probably best for this insect, including sevin, rotenone, and methoxychlor, which is available as Ortho Vegetable Garden Insect Dust.
WEEDS
V DRIFT OF UNREGISTERED HERBICIDES into vegetable crops can result in residues as well as damage. Food use of exposed parts or from plants showing damage is not recommended.
L GROUND IVY (creeping charlie) is most effectively controlled with fall herbicide. SDSU tests indicate 90% control is possible with two fall applications of 2,4-D + MCPP + dicamba (such as Trimec). Start after the first light frost.
Borax has been reported to provide a measure of control; Iowa State reported satisfactory results. However, questions about margin of safety to grass, residual effect and related issues are unanswered. The recipe calls for 10 oz. Twenty-Mule Team Borax dissolved in 2.5 gal. water and applied to 1000 sq. ft. Some reports also add a surfactant to the mix.
L,V,H,W HOT WEATHER ITEM spraying 2.4-D type broadleaf herbicide around the yard is not recommended during summertime temperatures. If treatment is required for bindweed or Canada thistle shoots in the lawn, limit use to individual weed shoots when it is calm and cool late evening. Large area applications should be delayed until fall when non-target vegetable and ornamental plants are less likely to be damaged.
L CRABGRASS POSTEMERGENCE herbicides available for use in home lawns should be applied when crabgrass seedlings have 2 to 3 leaves; control diminishes after crabgrass tillers into a large, flattened plant. Commercial applicators may use products such as Acclaim Extra, or translocated herbicides that will be more effective on larger crabgrass or sandbur in turf.
L MOW HIGH and water to keep grass active and competitive with new crabgrass seedlings. Crabgrass will come fast during hot weather if there is moisture.
L,V,H,W ROUNDUP DOES NOT VOLATILIZE but use care when treating sidewalk cracks or gravel driveways to avoid fine droplets from moving off-target. Spray should be coarse and applied at low pressure. Droplets cam "bounce" from concrete surfaces if applied at high pressure.
OTHER NOTES
H IRIS DIVISION can be done at this time. Most cultivars are now done blooming for the season so it is OK to divide them. Large overgrown iris beds that may not be blooming as well as in the past, plants with a lot of leaf disease or plots that are heavily infested with weeds may benefit from division. Carefully dig up the old plants and divide the rhizomes into plants that have a nice fan of leaves with each division. Typically the foliage is cut baclk to about ½ its normal height to facilitate handling and reestablishment. If necessary, the divided plants may be stored in a cool place for a few weeks before replanting. This may be helpful if weed control is the main objective in dividing the iris. Replant in a well-drained location with the tops of the rhizomes close to the soil surface.
L MUSHROOMS are becoming a real problem in some areas of the state that have had continued wet conditions. There are several kinds of muchrooms that may be found growing in a lawn area. In most cases they are there because the main body of the fungus is feeding on wood or roots that is under the soil. In some cases mushrooms will be found in a lawn that are actually growing on the thatch in the soil, as in fairy ring mushrooms. Generally, there is little that can be done to get rid of the mushrooms. They will continue to appear following wet weather as long as there is more wood or thatch for the fungus to feed on. Once that has been consumed by the fungus, the mushrooms will disappear. However, that often takes several years to occur. The best solution is to ignore the mushrooms or rake them out when they appear. There is no spray that will make them go away, not with out killing everything else in the soil as well. Many of the common mushrooms in the yard can be eaten but MUST be positively identified first. The inky cap and shaggy-mane are some of the most common mushrooms found growing in yards.
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Most recent revision Thursday, July 16, 1998 by David F. Graper.