We have started to see Lygus Bugs in sugarbeet here in the northern valley. This insect has been reported in the southern Valley last week. There are Lygus in sugarbeets every year, but rarely do their populations get large enough to be a problem. This year, we're probably seeing more Lygus immigrate into beets because of the dry conditions. Lygus bugs attack more crop species than any other insect pest in the US, and they are likely moving in from other crops, weeds, and grasses as they are harvested or dry off. Unfortunately, sugarbeets represent one of the last sources for a decent meal for these bugs. Lygus (also called Tarnished Plant Bug) is 1/4" long when grown, adults are brown with a yellowish white "V" behind their heads (although this sometimes appears as only 3 white spots). The adults will darken as they get older and end up being a dark bronze color. Immatures are yellow to green, with 4 black spots on their backs. Adults and immatures move quickly on leaves and the adults readily fly, generally in a wandering flight path close to the top of the canopy. The species currently attacking beets in the Red River Valley likely has 3 generations per year which overlap, causing a continuous presence of immatures and adults. They overwinter as adults in leaf litter or under bark.
Lygus feed by piercing the plant and sucking plant juices. In addition, they inject saliva into the plant to pre-digest plant sap in the plant before they suck it up. This saliva is toxic to the plant and acts like a growth regulator, causing curled, yellow leaves. Feeding locations often appear as black dimple. In addition, there is a black, tarry substance associated with Lygus that stains leaves. This is caused by a fungus that grows on Lygus excreta.
Lygus feed preferentially on new growth and will kill new leaves in sugarbeet. To scout for Lygus, randomly select plants in the field, and quickly open the canopy to examine new growth near the crown. Lygus bugs move quickly and the adults will readily fly. If there are more than one Lygus bug per plant, count the plant as infested. If more than 30% of the plants are infested, treatment is considered economically viable.