Authors: Buyung Hadi, Jan Knodel and Ken Ostlie
Wireworms are the larval stage of click beetles (Coleoptera: Elateridae). Melanotus species, Agriotes mancus and Limonius dubitans are among click beetles species reported from soybean.
As the name implies, wireworms look wiry with conspicuous segments, anywhere between 0.23-1.5 in. (6-38 mm) and yellowish brown in color. The adult beetles have two characteristic rear-facing pointed corners of pronotum.
Life Cycle and Seasonal History
Female click beetles deposit their eggs in the soil of grassy or cultivated areas. The larvae hatching from these eggs require 2-6 years to develop into adults, depending on the species. There is a generational overlap, so larvae of all instars may be found at one time. Wireworms move up near the soil line when the temperatures reaches 55˚F (12.8˚C) and move deeper into the ground when the temperatures rise above 75˚F (23.9˚C). Thus it is difficult to find wireworms near the soil surface in hot and dry conditions. Wireworms typically pupate in the soil during the fall. Pupation lasts for two weeks. The emerging adults survive the winter in the soil and surface in the following spring.
Plant Injury and Damage
Wireworms may injure soybean by feeding on germinating seeds and soft stem tissue underground. Since wireworms seem to prefer cool and humid soil conditions to move to the upper soil layer, low lying parts of soybean fields where moisture gather may experience higher wireworms problem. Economic damage due to wireworms feeding in soybean is rare.
Scouting and Threshold
Injuries due to wireworms feeding appear to be more prevalent in soybean following sod, such as pasture or Conservation Research Program (CRP) land that was reclaimed for soybean production. To determine whether the wireworms population in a particular field warrant management action, bait stations should be placed in the field before planting. A bait station consists of 4- to 6- inch deep hole with one cup of untreated wheat or shelled corn in it. Cover the grain with soil and then an 18-inch2 piece of black plastic to increase soil temperature and seed germination. Baits should be placed in grassy areas in the field or parts of the field with wireworms history. Between 5 and 10 bait stations should be scattered in the field if the field is larger than 12 ha. A few days before planting, the bait stations should be checked for wireworms. The economic threshold is an average of 1 wireworm per bait station for the whole field. If this population level is reached, soybean seed treatment against wireworm is recommended.
Other Online Resources
For information regarding labels of chemical control options, please visit Agrian.com