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Common Pests and Problems for
August
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By late summer cool-season fescue lawns are often in tough shape. Dead spots resulting from disease, grubs, and/or summer heat often need to be reseeded. These areas should be reseeded between September 1 and mid-October. If this also involves killing any existing grass, start killing these areas in mid-August. Read the product label information for waiting time required before seed can be planted.
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Dollar Spot
Small, straw-colored dead spots in a lawn killed by dollar spot
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In late summer we often see a variety of problems with tomatoes. Blossom-end rot is common, as is septoria leaf spot and fusarium wilt.
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Other tomato problems include late blight, stink bug, and spider mite damage (see general information on spider mites below.)
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Stink Bugs
Stink bug (Hemiptera ) damage to tomato (Lycopersicon) fruit
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Spider Mites - Outdoors
A heavy spider mite infestation (Acari) caused the curling, distortion, yellow patches and bronzed patches on the leaves of this tomato plant (Lycopersicon)
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Cracking fruit, which is caused by water fluctuations and is more common in some varieties than others, may also be observed. You may also encounter sunscald on fruit of tomatoes and peppers or poorly formed fruit on cucumbers and other vine crops due to pollination problems.
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Environmental
Close-up of radial growth crack on tomato (Lycopersicon), caused by overfertilization and extreme fluctuations in temperature and/or moisture
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The yellow jackets is a wasp that makes its home in the ground and is aggressively attracted to sweet items at your picnic. They can deliver a painful sting so use caution. Locate the nest during daylight hours but treat it after dark when the insects are not flying. Apply Sevin dust or an insecticide containing permethrin to the hole entrance and seal the entrance with soil or a flat metal or plastic sheet held down with a heavy weight.
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Yellow Jackets
Yellow jackets (Hymenoptera), often mistaken for bees, are actually wasps
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July or August is a good time to replant iris and remove any rhizomes that are infested with iris borers. Iris is best dug and divided every 3-4 years. Watch for the tomato hornworm feeding on tomatoes.
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Iris Borer
Larva of iris borer (Lepidoptera) tunneling in iris rhizome (Iris)
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Hornworms
Tobacco hornworm (Lepidoptera) on tomato (Lycopersicon); note reddish colored spike or "horn" at tailend that gives the hornworm its name
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Small branches scattered around the yard may be the result of twig girdlers, insects that feed on small branches and result in them breaking off. Damage is usually slight, but collecting the fallen branches and disposing of them through municipal composting may help control the pests by not allowing the insect to complete its lifecycle in your yard.
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By the end of July Japanese beetle damage should be all but over for the season as around this time the adults have laid eggs in the ground and died. Japanese beetles have a one-year lifecycle.
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Japanese Beetle
Japanese beetles (Coleoptera) feed on over 300 species of plants
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Monitor and treat for grubs in lawns if required. Treating is only necessary if 10-12 grubs are found in a one square foot area. If this threshold is met, treat with trichlorfon (Dylox) now. Treatment with imidacloprid (Merit) or halofenozide (Mach 2) should have been made in July as they take longer to act.
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Grubs in Lawns
Grubs (Coleoptera) can be found when the dead grass is pulled back.
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Damage from spider mites may be observed on many plants. It may be too late to affect much control this year, but note their symptoms so you can use safe and effective controls, such as removal with a strong stream of water, in subsequent years.
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Spider Mites - Outdoors
Spider mites (Acari) caused the bleaching and stippling of some leaves on this burning bush (Euonymus alatus)
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Feed zoysia lawns for the last time in late July or early August.
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Don't apply nitrogen fertilizer to roses after mid-August or fertilize trees and shrubs in late summer or early fall. Late fertilizing can result in tender growth that may be damaged by cold weather.
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Scorch is a common problem in hot, dry weather. Be sure and keep plants well watered during periods of drought. Stressed plants are more susceptible to attack by insects and disease. Many plants may also exhibit wilting leaves or yellowing foliage due to lack of adequate water. Water during dry spells.
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Galls are common on many plants throughout the season. Generally galls on leaves are just cosmetic and do little damage. Horned and gouty oak gall affects twigs and although usually not a serious treat to the health of the tree can be unsightly. Unfortunately, little can be done to control them. An arborist can remove them, but there is no guarantee that they will not recur again.
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Galls on Trees
This gall on an oak leaf (Quercus) looks like an oak flake gall caused by a wasp (Hymenoptera) but dissecting the gall is the only sure way to tell what caused the gall
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Apply a preventative insecticide spray to the trunks of peach trees and other stone fruits in the first half of the month to control peachtree borers. Apply again in August.
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© Missouri Botanical
Garden, 2001-2009
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