NEWS for North Dakotans
Agriculture Communication, North Dakota State University
7 Morrill Hall, Fargo, ND 58105-5665
August 17, 2000
Sugarbeet growers and crop consultants should be monitoring fields closely for Lygus bugs, also known as tarnished plant bugs, for the next few weeks to determine if treatment is necessary, according to Mark Boetel of the North Dakota State University entomology department. Lygus bug populations are increasing in a variety of plant habitats in the Red River Valley, he says.
Boetel says as of mid August Lygus numbers are not yet at economically significant levels. Significant infestations were seen in Pembina and Grand Forks counties of North Dakota and Polk, Red Lake and Kittson counties of Minnesota during the 1999 growing season. Sugarbeet fields in those counties could be at risk this year, as overwintering conditions were very conductive to Lygus bug survival, Boetel says.
Beets in areas where other crops such as sunflowers, soybeans and dry beans are stressed and dying due to summer flooding may be more at risk, because Lygus bug adults may move out of the stressed fields to search for food.
There is no established economic threshold for Lygus bug control. However, says Boetel, if growers check 30 to 50 plants in a field and find one or more adults or nymphs on at least a third of the plants, treatment may be justified. If fields are within two weeks of harvest, significant injury is not likely with infestation levels at the 33 percent level.
This insect has usually infested sugarbeets in August, so preharvest interval may be a critical factor when choosing an insecticide. Border treatments may be effective if the majority of insects are along the edges of a field.
Adult Lygus bugs are about a quarter inch long and an eighth inch wide. Their color can range from dark greenish yellow to brown. Older adults will usually have a distinctive mottled coloration with light wing tips and a pale yellow V-shaped mark near the middle of the back. First-stage nymphs are very small, wingless and bright green in color. Both adults and nymphs are very active, elusive, and usually hide or drop off the plant as soon as the canopy is disturbed.
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Source: Mark Boetel, (701) 231-7901
Editor: Gary Moran, (701) 231-7865
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