Green Beans - Insect Pests
 Bean Leaf Beetle - The bean leaf beetle is reddish to yellowish brown and about ¼ inch long. They
may or may not have black spots on their wing cover. The wings are usually
rimmed in black and the distinguishing characteristic is a black triangle just
behind the head. They overwinter as adults in wooded areas, litter, weeds and
pastures. In the spring as the temperature rises these beetles become active and
move into bean fields. The beetles feed on the foliage, chewing small round
holes into the leaves. Adult feeding reduces plant vigor, plant size and yield.
Later in the season, the second generation beetles will feed directly on the
bean pod. Damage to the pods can be severe if European corn borer or corn
earworm programs are stopped earlier than 12 days before harvest during the
second generation emergence.
 Potato Leafhopper - The potato leafhopper overwinters in the south and is blown north each spring.
The adult is spindle-shaped, about 1/8 inch long and yellowish green in color
with six light spots immediately behind the head. Potato leafhoppers will
usually jump instead of fly when disturbed. The nymphs are smaller versions of
the adults except they do not have wings so they cannot fly. Both the adults and
nymphs can cause damage to the bean plant. They extract sap from the undersides
of leaves causing them to crinkle and curl downward. Extensive feeding can cause
a characteristic triangular yellowing or bronzing of the leaf tip known as "hopperburn."
These plants are usually stunted, have small root systems and have reduced
yields and quality.
 European Corn Borer - The European corn borer overwinters as a mature larvae in the stem of the plant
on which if fed in the fall, usually field corn. The larvae ¾ to 1 inch long and
grayish pink in color with a dark head and rows of small brown spots on their
backs. The larvae pupate in late spring and the adults emerge to begin mating
and laying eggs. The eggs are laid in groups of 5 to 50 resembling overlapping
fish scales. They will hatch in approximately 5 days. The young larvae do the
most damage to green bean. They feed on leaves, buds, or flowers for 4-6 days
before boring into stem or the beans when the temperature reaches 70˚F. If the
temperature is higher the larvae will enter the stems and beans more quickly.
There are usually 2-3 generations of European corn borers in Ohio.
 Corn Earworm - The corn earworm generally overwinters in areas from the southern part of the
state and southward. Normal prevailing winds will move the adults northward. The
first generation of corn earworms appears early in the growing season so they
provide little damage to green beans. The second generation that begins with
moth flights in late July, is usually larger and more serious doing most of its
damage in late August through September. The larvae vary in color from light
green to tan, brown, pink maroon or nearly black and have light and dark stripes
running the length of the body. Their body is covered by short dense microspines.
The small larvae will feed bore into a pod to eat the seed. The larvae then back
out and look for other feeding sites.
Occassional Insect Pests
Wireworms and Seedcorn Maggots:
Beans that are planted following sod, alfalfa or set-aside could be at risk for
damage from wireworms and seedcorn maggots. Wireworms are cylindrical,
hard-bodied larvae of the click beetle. They are brownish-yellow, shiny and ½ to
1½ inches long. Seedcorn maggots are white to yellow-white beetle larvae. They
have no legs and have a pointed head. Both insects feed on the bean seed causing
poor germination and tall spindly seedlings. Planting under cool, moist soil
conditions favor the development of both of these pests. |
