Volume
4 Issue 9
July 17, 2007
Watch for Variegated Cutworms in Sugar beets
Several weeks ago, alerts went out about watching for armyworm
and variegated cutworms due to large numbers of moths captured in
the region.
http://nwroc.umn.edu/Cropping_Issues/2007/Issue6/06_26_07_no1.htm
The armyworm threat appears to have passed with only minor
infestations found. Regarding the variegated cutworm, we now have
received reports of infestations in sugar
beet. We've seen this before, back in August 2001, when both
variegated and black cutworm were a late season (July/August)
problem in beets.
Variegated cutworms are climbing feeders and it is not uncommon
to see them feeding in the daytime, unlike our other common cutworm
species. At this point, damage is generally minor, but with large
populations, feeding damage can be significant to the younger growth
in the beet crown.
At least with this species, there's less likelihood you'll be
digging in the dirt to find them - they're a climber, feed in the
canopy and are more likely to be out in the daytime than other
species (although they still prefer a late evening supper). Look in
the canopy and in the crown; look for worms (figure 1)and for frass
(variegated cutworms are, apparently, very regular and leave quite a
messy dining area).
The
caterpillars (figure
1) are medium to dark grey with a light stripe on the side. They
also have several small, diamond-shaped yellow spots on top near the
head. Younger larvae are about 1/4 inch long while the mature, ready
to pupate worms can be 1 1/2 - 2 inches long. When scouting, pay
close attention to land adjacent to grassy borders and to weedy
patches neighboring or in the field. The easily seen feeding injury
includes irregular shaped holes in leaves to complete skeletonizing
of leaves (figure
2).
Because
it feeds in the canopy, it is susceptible to foliar applications of
insecticides. Some research indicates pyrethroid insecticides may be
more effective but remember possible efficacy issues with these
chemistries if applying at high temperatures (in the 90's F).
Control is recommended when populations reach 3-5 larvae/sq.ft. in
late season beets, post canopy closure.
Ian MacRae, Extension
Entomologist
NWROC, Crookston
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