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Common Pests and Problems for
September
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Now is the time to reseed dead areas in your cool-season lawn, such as fescue and bluegrass. These areas should be reseeded between September 1 and mid-October. If this also involves killing any existing grass, kill these areas with an herbicide at least 2 weeks before planting seed. Fertilizing, dethatching, and core aerifying of warm-season grasses, such as zoysia, should stopped now for the year. They can resume again after green-up in late spring next year.
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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 when grass is actively growing or 6-10 when inactive. If this threshold is met, treat with fast acting 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
Feeding by grubs (Coleoptera) causes dead spots in lawn in late summer.
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Grubs in Lawns
Grubs (Coleoptera) can be found when the dead grass is pulled back.
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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 threat 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. In mid- to late summer fall webworms may also be seen.
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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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Fall Webworm
Fall webworm (Lepidoptera) on crabapple (Malus)
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To force poinsettias into bloom for Christmas they should be moved indoors by the 3rd week in September to a sunny windowsill. Each night, they must be kept in a cool, dark place where there is no light for 14 hours. Continue until proper color is achieved. This may take 6-10 weeks or longer. Water and fertilize on a regular schedule. More information
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Check your lawn for sod webworms now.
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Mushrooms and puffballs are commonly found in lawns at this time of year. Most are the fruiting bodies of useful fungi that decompose organic matter in the soil or exist in a beneficial relationship with the living roots of nearby trees. They cause minimal harm to grass. No chemicals are currently registered for control. Physically remove them and treat as yard waste.
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White pines normally shed old needles in the fall, usually beginning mid to late September. The yellowing and dropping of these interior needles is normal and should not cause concern.
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Powdery mildew may appear as a white coating on the leaves of lilacs, dogwoods, and other plants as temperatures cool in autumn. Damage to leaves this late in the season is purely aesthetic and is not harmful. No treatment is required.
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Moles may cause damage to lawns as they feed on earthworms, grubs and other soil inhabitants. Control options are discussed in our IPM sheet on moles below.
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Moles
Mole tunnels in lawn
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Moles
Mole, common lawn pest
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Keep your eyes open for magnolia scale. Unlike most other species of scale, crawlers of the magnolia scale are present and active now. This is the ideal time for controlling the most vulnerable stage of this troublesome pest.
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Magnolia and Tuliptree Scale
Magnolia scale (Hemiptera) on a star magnolia (Magnolia stellata) with sooty mold growing on the honeydew that has dropped on the leaves
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Unlike many spider mites that are most active in hot, dry weather the spruce spider mite proliferates in the cool temperatures of spring and fall. They can cause substantial damage to spruce, hemlocks, and junipers. Examine yellowing needles on spruce now for these mites. Treat if necessary. Controls are the same as for other spider mites. Also check of whitefly, which can become numberous at this time of year.
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Whitefly - Outdoors
Close-up of whitefly (Hemiptera) adult and pupae on sweet potato vine (Ipomoea batatas)
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Rose rosette can appear at any time of year but frequently shows up on new fall growth. If witches’-brooms are found on rose bushes at this time of year, suspect rose rosette.
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Rose Rosette
Symptomatic thorns on rose (Rosa) caused by rose rosette
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Purplish-brown needles on blue and other spruces at this time of year is often caused by Rhizosphaera needlecast disease. Infection occurs in May and June long before symptoms appear. Fungicides are available for control but must be applied in spring before infection occurs.
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Rhizosphaera Needlecast
Purplish cast of needles on Colorado blue spruce (Picea pungens) caused by rhizosphaera needlecast
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Rhizosphaera Needlecast
Needles of Colorado blue spruce (Picea pungens) dropping due to rhizosphaera needlecast disease
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Both box elder and red-shouldered bugs are commonly seen in large masses on tree trunks and the siding of buildings at this time of year. They do little damage to trees but will feed on the seeds. Homeowners may find them objectionable especially when they migrate indoors. (They look very similar to the milkweed bugs below.)
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Asian multicolored lady beetles may also be found at this time of year. For home gardeners they are beneficial but a nuisance. Control out of doors is not recommended, but insects found indoors can be vacuumed and disposed of.
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Be alert to the flight of peachtree borer adults that are active from July - September. See August and May for control measures.
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© Missouri Botanical
Garden, 2001-2009
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