Spring Barley Production Guide - College of Agricultural and Life ...

Figure 9. Russian wheat aphid damage causes lightcolored
streaks on leaves. Leaves often take on an
onion leaf (rolled) appearance which may cause head
distortion as the heads emerge from the leaf sheaths.
behavior. The rolling also interferes with the potential effect
of natural enemies such as predators and parasitoids.
Aphids secrete a toxin that causes white or purple streaks
on the leaves. Purple discoloration is more common in
cool weather, while white streaks and leaf rolling are prominent
in warm weather. Heads of infested plants may become
twisted and distorted or may not emerge. Heavy
infestations may cause severe yield losses due to aphid
feeding and toxic secretions. Russian wheat aphids do
not transmit viruses.
Unlike other aphids found on barley, the Russian wheat
aphid has a simple life cycle. No males or overwintering
egg stages can be found in the U.S. As long as temperatures
remain above 60°F, females continue to give birth to
living young. As colonies become crowded or the host
plant matures, winged forms are produced that move to
other hosts. Russian wheat aphids overwinter as live
aphids sequestered near the base of wheat plants. Winter
mortality is usually very high and appears to be a reflection
of the length of the winter more than the amount
of snow or extreme cold temperatures.
Russian wheat aphid infestations can spread rapidly. As
the colonies become crowded or the plant declines, wing-
IDAHO SPRING BARLEY PRODUCTION GUIDE
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less aphids move to neighboring plants. Winged forms
may also arise and rapidly infest other fields in the area.
Several cultural control practices such as controlling volunteer
wheat and barley plants, planting certified seed,
fertilizing correctly, and adjusting planting dates according
to suction trap data can reduce the need for chemical
control.
Planting dates can be adjusted according to suction trap
data to reduce the need for chemical control. A suction
trap system partially funded by the Idaho Barley and Wheat
Commissions to monitor aphids in Idaho has been in existence
for eighteen years. Insects are collected in canisters
placed in these suction traps and sent weekly to the
University of Idaho Aberdeen Research and Extension (R
& E) Center for identification. The information generated
is distributed throughout the growing season by means
of a free access website called the Aphid Flyer (http://
www.uidaho.edu/so-id/entomology/Aphid_Flyer.htm),
email, a newsletter, and the internet to alert growers to
potentially damaging cereal aphid populations and virus
epidemics.
Chemical control decisions for Russian wheat aphids
should be based on infestation levels from crop emergence
to the milk stage of kernel development. Early detection
and control minimizes losses. Several contact and
systemic insecticides are labeled for controlling Russian
wheat aphids. See University of Idaho publication CIS 817,
Russian Wheat Aphid, for current thresholds and insecticide
recommendations.
Greenbugs
Greenbugs (Schizaphis graminum) are short, oblongshaped
aphids with a lime green body color and a dark
green stripe along the back of the abdomen. Greenbugs
have pale green cornicles with dark tips that do not extend
beyond the rear tip of the abdomen. Their antennae
extend all the way to the rear abdominal tip. Greenbugs
appear to overwinter as eggs or as live aphids during mild
winters, although this is not known with certainty.
Greenbugs damage spring barley in two ways. First,
they are the most important vectors of barley yellow dwarf
virus (BYDV), particularly in the high mountain valleys of
eastern Idaho. Second, they feed on stems beneath the
emerging head while the barley plant is in the boot stage,
resulting in empty heads that do not fully emerge. Any
barley crop that is still in the boot stage after June 15
should be examined for greenbugs. Unfold the flag leaf
sheath and look for aphids on the stems below the emerging
head.