The false chinch bug (Nysius raphanus) and/or its damage to potato plants has been seen throughout the mid High Plains states.
The false chinch bug adult is 1/8 inch and brownish-gray with silvery-gray wings. Their body shape is cylindrical. It congregates on the leaves where it sucks the sap. As many as 100 adults may be on a single leaflet often crawled inside the curl. The adults crawl or fly to other plants after killing the plant top. The adults seem to be the primary concern on potatoes. The nymphs have a brownish-gray head and thorax with a light-tan longitudinal stripe and light tan abdomen with some tiny reddish spots. Nymphs are smaller than adults and are wingless.
False chinch bugs overwinter as nymphs and adults under debris near winter annuals especially mustards which also act as hosts. Eggs are laid in loose soils or in soil cracks. They hatch in four (4) days. Nymphs feed for about three weeks and reach adulthood. Adults live for several weeks congregating on hosts. There are three or four generations per season with peak populations in July and early August. Crop hosts besides potatoes include small grains, alfalfa, etc. The bugs have even been seen damaging sugar beets. Wild hosts include mustards, kochia, Russian thistle, and sagebrush. Heavy populations build up in these hosts.
Symptoms seen in fields look like wind burn to upper young leaves. The young top leaves first appear wilting and possibly slightly curled while the rest of the plant appears normal. These leaves rapidly turn brown along the edges and curl. This rapidly progresses with the leaves turning darker and curling tighter until they dry out and are dead. This can occur in a matter of a few days. Fully formed leaves are not affected by these bugs only new growing leaves are attacked. Affected areas can be along field's edge, spots in the field, strips or swathes through the field and in weedy areas.
Adults damage by sucking water from stem. Usually they are found in grains and alfalfa, their preferred hosts, but when these are harvested during the summer the false chinch bugs move to near by potato fields, even a few miles away. In general, the window for potato damage is about three weeks.
Yield losses may occur if large parts of the field are damaged during early to mid bulking when young leaves contribute water and nutrients. Although not reported, some tuber deformation might result from a severe attack at the right time interfering with water movement in the plant.
Adults prefer cooler temperatures and are seen on leaves during late evening, 6-8 pm, and somewhat in the early morning. During daytime temperatures, they crawl on the ground under the canopy and into the soil. They are difficult to see because of their brown coloring against the ground. This suggests that the best application of a chemical treatment is by air in the evening.
The best application of control products is during the week after nearby grains or alfalfa are harvested. At that time the false chinch bug will be moving looking for a new temporary home. After a couple of weeks, they will leave potato, looking to return to grains and alfalfa. The damage to young leaves, however, will remain after they leave as there is no recovery. However, new leaves forming after their departure are unaffected.
Little is known about chemical efficacy for control. However, the only product with this insect on the label is Thiodan. A number of growers have given it high marks for its effectiveness. The EC formulation would be applied at 11/3 qt/acre, the highest rate for Col. potato beetle, aphids or leafhoppers. Pyrethroids were suggested in Colorado from work on (true) chinch bugs. A few growers reported poor to fair results. Dimethoate , an inexpensive general foliar insecticide has been effective. Others effective products include Monitor and Provado.
Adult - brownish-gray with silvery wings; 1/8 inch long
Overwinters in debris near winter annuals
Three to four generations /season
Population peaks in July and early August
Move into potato after grain or alfalfa harvest
Wilting of young top leaves
Scouting after grain or alfalfa harvest
Treat during early bulking if adult population is enormous