| FALSE
CHINCH BUG
 The
false chinch bug (Nysius raphanus) and/or its damage to potato plants
has been seen throughout the mid High Plains states.
Description
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.
Life
Cycle
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.
Damage
 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.
Scouting
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.
Control
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.
Quick
Review
Appearance:
Adult
- brownish-gray with silvery wings; 1/8 inch long
Life
Cycle:
- 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
Damage:
Wilting
of young top leaves
Control:
- Scouting
after grain or alfalfa harvest
- Treat
during early bulking if adult population is enormous
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