South Dakota Extension forage field specialist
In early July, large populations of Dectes stem borer were observed in some eastern South Dakota soybean fields. Since this time, the pest has been detected in nearly every southeast to central …
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In early July, large populations of Dectes stem borer were observed in some eastern South Dakota soybean fields. Since this time, the pest has been detected in nearly every southeast to central county. Some samples also contained high numbers of ash gray blister beetles (which also look somewhat similar to Dectes stem borer and are easy to confuse). This stem borer can reduce soybean yields and cause lodging in fields.
Dectes stem borer often have a prolonged emergence from June to July, making it difficult to reduce populations using foliar insecticides. There is no threshold for this pest currently; however, it is suggested to consider using an insecticide application if an average of 30 or more adults are observed from four sets of 30 insect net sweeps (using a 15” diameter sweep net). For a full list of insecticides on label for this pest, use the South Dakota Pest Management Guide for Soybean.
Infestations may be worse in no-till settings as tillage can disrupt the host stem. For no-till fields with infestation history, vertical tillage may be an option to disrupt larvae while attempting to minimally impact the no-till system. Diversifying crop rotations and reducing other hosts can help in dropping numbers as well; weeds such as wild sunflower, cocklebur, and giant ragweed are all hosts to Dectes stem borer.
Adult Dectes stem borers are light gray and about 3/8” long with long antennae that have segments that alternate gray and black. Larvae are cream colored and have an accordion shaped body. For more information on Dectes stem borer visit https://extension.sdstate.edu/dectes-stem-borer-adults-are-active-soybean.
In addition to Dectes stem borer, SDSU Extension entomologists have spotted potato leafhopper activity damage in alfalfa fields. The adult potato leafhopper is about 1/8” long and pale green. Their wings are translucent; nymphs (or immature leafhoppers) vary in size and look like adults without fully developed wings.
Scouting for leafhoppers this time of year is important to ensure serious crop damage does not occur. Large populations of this pest can cause stunted plants and lead to significant losses to alfalfa yield and quality. The first sign you may notice of a potato leafhopper infestation is “hopper burn” which occurs when leaves turn yellow.
Scout by checking for injury as well as using a sweep net. It is ideal to sample field edges because leafhoppers tend to be more of an issue in these areas. Sweep 25 times across the field in a “W” or “Z” pattern and count the total number of nymph and adult potato leafhoppers in the net. Measure the average height of the alfalfa stand, and then calculate economic threshold. Thresholds for alfalfa are based on height: 0-12”, 12-18”, 18-24”, and 24-30.” View the economic threshold tables to determine whether action should be taken and find more details on scouting and managing this pest here.
If management is deemed necessary after scouting, there are a few considerations:
For a more timely and comprehensive look at pests currently facing crops in our state, subscribe to the SDSU Extension Pest & Crops Newsletter here.
In other news, we have reached small-grain harvest for some growers. As harvest continues, good quality grain storage practices sometimes get pushed aside. In most situations, it’s not necessary to treat grain with a protectant insecticide before binning as long as it’s removed from storage by May or June of the following spring or fed to livestock within a year of harvest. However, if you plan to store longer than this, you should only apply a protectant after the grain reaches optimal storage moisture.
There are seven main steps to stored grain integrated pest management to consider:
1) Structural and maintenance components. Keep bins clean and repaired. Keep a 10 ft. perimeter around your bins free of vegetation and be sure to clean up grain spills outside of the bin. Before filling the bin check for any leaks that might allow precipitation or rodents in. Clean bins well, ridding them of as much old grain as reasonably possible (never put new grain on top of old grain).
2) Residual insecticide sprays. Residual insecticides can help protect grains, but be sure to follow all labeled instructions. Spray inside walls, ledges, floors, and sills. Spray outside walls and base.
3) Condition grain. Store clean, dry grain. For long-term storage corn should be at or below 13-14% moisture, soybeans at 11%, wheat at 13.5, and oil sunflowers at 8% or less.
4) Proper aeration. Run bin fans during cool, dry periods to ensure uniform temperatures and reduce moisture.
5) Use insecticide protectants. Treat grain as it is moved into storage.
6) Regularly inspect grain. Stored grain should be inspected often; at least once per week until it reaches 55°F or below, at which time inspections every two weeks should suffice.
When inspecting grain, don’t forget to follow safety procedures and always have another person outside the bin with a cell phone, wear a properly attached harness, and always break up crusted grain using a long pole or other tool from a distance.
7) Treat infestations when necessary. If there is an insect infestation, move grain and re-treat; cold weather can help kill insects when moving grain. Other options include feeding the infested grain, fumigating the bin, or selling at a reduced price.
For more details on preventing stored grain pests and insecticide application go here.
