Four main insects are bugging fields this season in North Dakota. Growers should be on the lookout for bean leaf beetles, cereal aphids, pea aphids and grasshoppers.

Specialists at North Dakota State University Extension offer this roundup on the pests:

Bean leaf beetle. This pest has been slowly increasing in North Dakota along with the number of soybean acres. Last year, the distribution of bean leaf beetle expanded from southeastern North Dakota to its east-central, central, south-central and north-central regions. Bean leaf beetles can be an insect pest problem of dry edible beans.

The beetle is about a quarter-inch long and can vary in color from yellow-green to reddish-brown. With a black triangle behind their thorax, adults may have up to four black spots, if any, and a black border on the edge of the wing covers. Adults emerge from overwintering sites and move into bean fields as the seedlings emerge.

Insecticide seed treatments frequently used on soybeans provide good protection against the overwintered adults. The beetle’s cause defoliation creates characteristic circular holes in leaves.

The white larvae develop in the soil, feeding on the roots and nodules. New adults emerging in July feed on foliage and pods. This is another key time to scout for bean leaf beetle.

The injury to pods can bring about secondary infections by viruses, fungi and bacteria, causing rotting and discoloration. If large numbers of beetles are present during the R6 growth stage, watch for pod feeding or clipping and be aggressive with an insecticide treatment.

A sweep net is used to determine if bean leaf beetles are present since they are secretive and hard to visually observe in fields.

Cereal aphids. These were first found in wheat at the beginning of June. Scouting is critical to monitor aphid populations, from stem elongation through the early dough stage of wheat and other cereal grains. Predators of aphids, such as lady beetle adults and larvae, and lacewing larvae, are good indicators that aphids may be present in fields.

Seeing large amounts of honeydew or sooty mold growth also are good indicators that aphids are present. The greatest risk of yield loss from aphid feeding is from vegetative through heading stages. However, economic loss also can occur through the early dough stage. Beyond early dough, yield loss is unlikely to occur.

Pea aphids. These small pests at about an eighth-inch long are pale to dark green with reddish eyes. Pea aphids have multiple generations per year and overwinter as eggs in alfalfa, clover or vetch. In the spring, nymphs hatch from eggs and appear similar to the wingless adult but are smaller.

Nymphs molt four times and mature into adults in 10 to 14 days. Pea aphids can reproduce rapidly when temperatures are around 65 degrees F and relative humidity is near 80%. Infestations can originate from local alfalfa fields, and often move out of recently cut alfalfa fields to pulse crop fields. Pea aphids also can migrate into North Dakota or Montana from the Southern states.

Scouting for pea aphids is done by either using a sweep net or examining the number of aphids per plant tip when 50% to 75% of the crop is flowering. Check at least five tips of 8-inch plants from four different locations in the field, and population estimates should be calculated by averaging counts from the separate areas.

Aphids suck the sap from plants and may vector viral diseases. Populations of only 10 aphids per plant can cause economic damage, especially if plants are heat-stressed. Pulse crops are especially susceptible to aphid infestations in the flowering and early pod stages. Aphid feeding on peas in the flowering and early pod stage can result in lower yields due to less seed formation and smaller seed size.

Grasshoppers. These insects were commonly observed in fields across North Dakota in June, with non-economic numbers of nymphs seen. Be vigilant in scouting for grasshoppers throughout the summer until harvest. With high numbers of grasshopper egg load last fall and hot and dry weather for grasshopper survival this spring and early summer, high populations of grasshoppers are expected, similar to 2022. Most field crop grasshoppers are still in the nymph, or immature, stage and peak egg hatch usually occurs during mid- to late June.

For more information on pest scouting and control, contact your local Extension office.

Source: North Dakota State University Extension