Be on bean pest alert
Last season, several new and unusual insects showed up in Nebraska soybeans, with others expected in the near future moving in mostly from the South and East. Damage from these new insects is sporadic. While some of these bugs may rise again in 2012, nothing is certain. Here is a primer on new pests to watch for:
At a glance
• New soybean insects are moving into the state from the South.
• Most insects are opportunists, hitting plants that are already stressed.
• Stinkbugs may have the most potential to be a major soybean pest in the state.
• Japanese beetles. These beetles have been a common pest in the eastern Corn Belt for years, but last year was the first time crop injury reports came in from Nebraska fields, with severe infestations reported in southeast counties. Treatment is recommended when adult beetles are present and plant defoliation is expected to exceed 20% in reproductive stage soybeans. “So far, it is still isolated, so they probably won’t be a big problem for a while,” says Keith Jarvi, University of Nebraska Extension educator. “They feed on a lot of different plants, and we have had them in urban areas around Lincoln, Omaha and even South Sioux City.”
• Soybean gall midges. Midges are new to Nebraska, with no previous reports before last season. They are opportunists, feeding on plant tissue that has been damaged from hail or disease. Appearing as small, white to bright-orange or red maggots, they are not believed to cause direct damage to plants, so treatment is not recommended. “We don’t believe they will become a pest that attacks healthy soybeans, but we’ll have to wait and see,” Jarvi says.
• Silver spotted skippers. Known for an extremely large head compared to its body, these yellow caterpillars showed up late last season in southeastern Nebraska. With two generations per year, skippers web together soybean leaflets as they feed. Jarvi calls last year’s occurrences unusual and doesn’t believe they will be a major problem in the near future.
• Brown marmorated stinkbugs. Stinkbugs aren’t new to Nebraska, with four known species. But the brown marmorated stinkbug has been abundant in the eastern United States and is moving west, most likely into Nebraska soon. Jarvi says these stinkbugs are now in Missouri and are expected to move north. “This has potential to be a bad pest because it can possibly become a pest of fruits and vegetables, as well as field crops,” he says.
• Soybean stem borers. Stem borers continue to expand their range in south-central Nebraska. These long-horned beetles overwinter as fully grown larvae at the base of the plant in which they developed. Most of the damage they cause is from larval feeding at the base of the stem, which results in lodging and harvest time losses. They are also found in sunflowers, cocklebur and ragweed. “They are slowly spreading northward,” says Jarvi. “And they are tough to control.” They are currently being studied more closely.
• Trochanter mealybugs. The last time mealybugs were reported in Nebraska was in a cornfield in Thayer County in 1909. But in recent years, they have damaged soybean fields in the southern Midwest states. While they have not been observed in Nebraska yet, it is expected that they will show up, causing injury through leaf yellowing and stunting.
Among these potential soybean insects, Jarvi says all species of stinkbugs pose the most risk of becoming major pests because their populations are rapidly increasing in the state. “Most problems with insects are compounded when plants are already under stress,” he says. “Usually this is when plants are under moisture stress, but diseases can also weaken plants and make them more susceptible to insect damage.”
For more information, contact Jarvi at 402-584-3819 or UNL Extension entomologist Tom Hunt at 402-584-3863.
This article published in the March, 2012 edition of NEBRASKA FARMER.