At this time of year, several pests will feed on annual and perennial flowers--both leaves and blossoms. Slugs were addressed in detail in issue No. 9 and are probably the main culprits in flower destruction this year. Remember that their damage normally occurs as holes in the leaves. Other pests primarily eat the leaf margins of leaves and petals.
Earwigs have emerged in large numbers this year in Illinois. We are receiving reports of many in both northern and central Illinois. This insect is particularly numerous in northeastern Illinois southwest to Morris and west to Rockford. There also are many earwigs in the Champaign area. The European earwig is about 5/8 inch long, slender, reddish brown, with pincers on the back end of the body. Males have larger, curved pincers shaped like ice tongs; females' pincers are smaller, straight, and fit close together.
Earwigs prefer moist situations and hide in cracks and crevices during the daytime. They emerge at night to feed on mulches and other decaying organic matter, fleas and other insects, and the leaves and blooms of some plants. They are particularly damaging to marigold, aegeratum, zinnia, and the flower petals of rose and daylily. Earwigs are more numerous where there is damp organic matter such as mulch. They become obvious in late June when they approach adulthood, and continue to be a problem until mid to late August. Eggs are laid in the soil and hatching occurs in late winter to early spring. Earwigs do not lay eggs indoors, even in flowerpots, although they can be a year-round problem in greenhouses.
Sowbugs and pillbugs are also very numerous in flower beds this summer. They thrive in consistently moist situations and feed primarily on decaying organic matter such as mulches. Both of these crustaceans look like tiny armadillos, having a series of plates across the back and ranging from gray to blackish. Pillbugs can roll up into a ball when disturbed and are more dome-shaped than the sowbugs, which cannot roll up. We usually don't consider these relatives of crayfish and shrimp to be damaging, but in very high populations they can eat the edges of the thin leaves and flower petals of hosta, violets, impatiens, and other plants.
Grasshoppers also feed on the leaves of flowers, eating the margins until there is little or no leaf left. They can also eat large holes in the leaves. Several of the grasshopper species that are very obvious and numerous in late summer as adults have recently hatched into young grasshopper nymphs that are about 1/4 inch long. These nymphs are very numerous, but most will die from fungal diseases if rainfall is moderate or heavy. Also present, in smaller numbers, are some other species' older nymphs and adults that eat more per hopper than the young ones. Grasshoppers severely attack iris, daylily, and sunflower, but also can be devastating to many other flower species.
Black vine weevil, strawberry root weevil, and imported longhorned weevil adults also feed on flowers, preferring those with large leaves and petals such as daisy and coreopsis. Look for half-moon shapes eaten into the edges of petals and leaves. All three weevils have rounded, hard-shelled bodies with the heads elongated into short snouts. Black vine weevil is about 3/8 inch long and blackish with indistinct yellowish spots. The other two weevils are about 3/16 inch long. Strawberry root weevil is black or brown; imported longhorned weevil is tan with irregular brown spots. These two smaller weevils are commonly found hiding in blossoms. Much of their feeding is done at night. Although the black vine weevil is larger, there is no lesser of any two of these weevils. (I'm not sorry for the pun, I just had to put it in!)
Flower petals are eaten by various leaf beetle adults. The most common ones in Illinois are northern corn rootworm, western corn rootworm, and southern corn rootworm, also known as the spotted cucumber beetle. These and other leaf beetles are about 1/4 inch long. The northern is green, the western is yellow and black striped, and the southern is greenish yellow with black spots.
Two milkweed beetles eat the leaves of milkweeds such as butterfly weed, bloodflower, and swamp milkweed. The milkweed leaf beetle is about 3/8 inch long, roundish, with a black and orange color pattern. The other milkweed beetle is 1/2 to 3/4 inch long and red with black spots and long black antennae. These two beetles usually do not cause enough damage to require control.
To chemically control these chewing insects on flowers, apply carbaryl (Sevin). Many other insecticides are also effective. Keep the insecticide off the blossoms, to avoid killing beneficial bees and other pollinating insects. Insects that feed on the flowers also feed on the leaves and will be controlled with insecticide applied there.
(David Robson, Sprigfield Center Educator, also contributed to this article)