Horticulture Pest Update - Late Summer & Fall (August, September)
submitted by Mary Jane Frogge, Extension Associate
Bagworms (Late August):
Bagworms can cause a great deal of damage during the last few weeks of feeding, and gardeners may be tempted to spray for them now. But late August sprays are totally ineffective. Understanding the life cycle of this moth will explain why and can help tremendously in planning effective control measures. Bagworms normally finish feeding and close up their bags in late summer. After that, insecticides are ineffective because they cannot reach the pest. Egg hatch does not occur until the next spring, usually during the latter half of May.
Insecticide sprays are more likely to be effective if applied when the bagworms are small. Even Bacillus thuringiensis or Bt (Dipel, Thuricide) can be effective on young bagworms. Other commonly used pesticides include Orthene, cyfluthrin, permethrin, malathion and Sevin. During most years, a spray about June 15 will give good control. Do not forget that insecticides are not the only means of control. Hand picking and destroying the bags is effective any time of year the bags are large enough to be picked.
Bluegrass Billbug (September):
Is your Bluegrass lawn dying? Check for billbug damage.
Billbug larvae are legless, cream colored with reddish brown heads, and about a half inch in size. Their appearance is similar to a puffed grain of rice. Adult is a black weevil. Newly-hatched larvae tunnel in grass stems, hollowing out stems which break away near the crown. Older larvae feed on roots, causing turf to appear drought stressed.
Under heavy billbug pressure, the lawn can brown and die. Billbug damage rarely occurs in turf stands less than three years old. Insecticides need to be applied in May to control the adult prior to egg laying. It is to late to control now. Reseed turf areas September 1 through 30.
Fall Webworms (August):
Adults are a satiny, white moth often marked with brown spots and a wingspan of 1 to 2 inches. The larvae have long, silky, gray hairs and are either pale yellow with red heads and reddish-brown spots or yellow-green with black heads, a broad black stripe and black spots. Fully grown caterpillars are about one inch long.
Adults emerge in spring and begin egg laying. After about 10 to 14 days the larvae hatch out and begin feeding. Larvae have chewing mouthparts, allowing them to eat entire leaves, skeletonize them, or leave holes in them. Leaves are completely consumed except for the midrib. The caterpillars feed in large groups, usually creating a protective tent that encloses branches and foliage on which they feed. The webs become filled with partially eaten leaves, cast skins and excrement, and are very unsightly. Significant defoliation of the tree can also occur. There is one or two generations per year.
Use a rake or broom handle to pull the webs out of small trees. Limited pruning could also be effective. When necessary, control the larvae with an application of Bacillus thurengiensis (Bt) or Dipel when damage is first noticed. MORE: Fall Webworm update from UNL-Extension Entomology Department
Squash Bugs (June):
Squash bugs are gray, half inch long, shield-shaped bugs and are major pests of squashes, pumpkins and gourds. They suck the sap from plants and this causes wilting and blackening of leaves and death of small fruits. Adult bugs overwinter in the yard and emerge over an extended period to lay eggs on undersides of squash leaves. Eggs are orangish, or tan to brown and laid in triangular or V-shaped groupings between the angle of the leaf veins. Eggs hatch in 10 days into small red-headed, greenish colored nymphs. The life cycle takes up to 6 weeks, with 2 generations produced each year. Because there are 2 generations, with overlapping stages, several treatments may be necessary.
Options for treatments include: permethrin, carbaryl or insecticidal soap.
Pokeweed is a tall (3 to10 feet), smooth-stemmed, perennial with a large, fleshy taproot. Stems are succulent, purplish, and bear alternate, lance-shaped, shiny leaves with smooth, curled margins. The small, white to greenish flowers hang in long, drooping clusters. Each round, green berry turns dark-purple or ink-black and usually contains 10 seeds. The berries are messy and stain. Pokeweed commonly grows on recently cleared land, in open woods, barnyards, pastures, fence rows, back yards and roadsides. Pokeweed is poisonous.
Immature Pokeweed Berries
Mature Pokeweed Berries
Fall needle drop of older needles on Pine and Spruce
Narrow-leaved evergreens (pines, spruce, etc.) often turn yellowish in early autumn. This is usually the normal shedding of the oldest needles.
A rather sudden yellowing affects the oldest set of needles on all the branches. The yellowing is uniform from the top to the bottom of the tree. The needles at the tips of the branches stay green. On a windy day, the yellowed needles blow off the tree and litter the ground. This is a normal process, so nothing needs to be done.
Aster Yellows on Purple Coneflower:
Purple coneflower can suffer from a common disease called aster yellows. Aster yellows causes chlorosis or yellowing of the plant, stunting, irregular growth and distortion of the flower head. This unusual growth is often misdiagnosed as herbicide damage. Aster yellows is a disease that is carried from plant to plant by insects and survives winter in infected plant material.
To manage aster yellows all infected plants should be removed from the garden and destroyed. There are no chemical treatments available for aster yellows. Since the disease can also survive in neighboring weeds, it is important to maintain good weed control in and around your garden.
University of Nebraska-Lincoln Extension in Lancaster County is your on-line yard and garden educational resource. The information on this Web site is valid for residents of southeastern Nebraska. It may or may not apply in your area. If you live outside southeastern Nebraska, visit your local Extension office