Start Watching for 2nd Generation Bean Leaf Beetles
We have begun to receive questions about second generation bean leaf beetles, which are appearing in fields. Here is some beetle biology and management information.
Two generations of bean leaf beetles develop in Nebraska. The second generation overwinters as adults and are the beetles seen early in the year feeding on seedling soybeans. These beetles feed, mate, lay eggs and die in early-mid June. There is usually a period from mid-June to early July when few if any beetles are in the field — this is the period before the first generation emerges. However, with today’s broader range of planting dates, this period is less distinct than in the past.
Total developmental time from egg to adult can range from 25 to 40 days. Because of this range of development, it is common to see adults from the first generation and the second generation in the field at the same time. Because the generations can overlap, beetles can be present at some level from mid-July until the end of the growing season. That's why it's important to monitor beetles regularly to determine population shifts to aid in management decisions.
Bean leaf beetles will feed on soybean leaves throughout the season, but leaf feeding seldom causes yield loss. Most damage (economic yield loss) occurs when second generation beetles feed on the developing pods. This yield loss can occur in several ways. Pods may be clipped from the plants; however, this is not the primary cause of yield loss. Many flowers and pods are aborted naturally and to blame pod loss on bean leaf beetle feeding may be a costly mistake.
There are no thresholds that consider pod-drop. Beetles normally injure soybean pods by feeding on the outside layer of the pod, leaving a thin layer of tissue covering the seed. They do not usually eat into the developing seed, although this may occur on very small pods. Fungal pathogens may enter the pod from the feeding sites, causing seeds to appear shrunken, discolored, and moldy, which can result in dockage. After full pods are formed and seeds begin developing, soybeans are most susceptible to yield loss from pod feeding.
The best time to sample is before significant pod feeding occurs, but after second generation beetles have emerged. Second generation bean leaf beetles are or will be emerging and beetle numbers will build to a peak, which is usually in mid-August through early September, depending on location. Beetle numbers will slowly decline as beans continue to mature and move to overwintering sites. Economic thresholds have been developed for two sampling methods: drop cloth (beetles per foot of row) or sweep net (beetles per sweep).
Although the most accurate way to sample beetles is with a drop (or shake) cloth, almost all sampling is done in Nebraska soybean with a sweep net. In addition, a drop cloth is not well suited to narrow row or drilled beans.
When sampling with a sweep net, sweep at least five randomly selected sites. Walk through the field at an even pace, performing about 25 sweeping 180̊ arcs. The best sweeping action for bean leaf beetle is a consistent motion using as much force as needed to move the net smoothly through the foliage. Bean leaf beetle activity varies during the day. Activity patterns suggest the best times to sample are around mid-morning or in the afternoon. Try to maintain a similar sampling time in each field to eliminate variability. If bean leaf beetle populations are three or more beetles per sweep, consider an insecticide treatment.
If the beetle counts are below the economic threshold, scout the field again about five days later. Stop scouting when the beetle counts begin to decline, the soybean pods begin to yellow (R7), or the field is sprayed.
Several insecticides can be used to control bean leaf beetles. Be aware that most have preharvest intervals of 14 or more days. Information on insecticide selection and use can be found at http://entomology.unl.edu/instabls/beanlfbt.htm
Overseeding and Turfgrass Cultivars-
Overseeding to increase lawn density, fill in bare areas, or introduce improved cultivars is best done in September. When overseeding, use improved cultivars and those considered to have disease resistance.
When overseeding, it’s critical to achieve good seed to soil contact. Methods to use include using a slit seeder that plants seed through existing grass and into the soil; power raking and then removing all dead grass and debris before overseeding; and/or, core aerating (plugging) the lawn to relieve soil and provide openings for seed to soil contact. Core aerate the lawn twice, running the machine at a 90 degree angle to the first aeration. Leave the plugs on the lawn to decompose.
A list of turfgrass cultivars recommended for Nebraska can be found on the UNL Extension Horticulture website at http://extensionhorticulture.unl.edu/ToDo/TurfCultivar07.shtml.
