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FARGO, N.D. -- Sugar beet 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, Fargo, 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 because of 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 usually has infested sugar beets 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 one-quarter inch long and one-eighth
inch wide. Their color can range from dark greenish yellow to brown.
Older adults usually will 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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