Scattered Insect Observations From Around The State
URBANA, ILL.
University of Illinois professor of entomology
and crop sciences Extension coordinator
Mike Gray usually gets the first reports of
the emergence of adult western corn rootworm
during the July 4 festivities.
However, on May 29, Joe Spencer, an entomologist
with the Illinois Natural History Survey,
observed second instar corn rootworm
larvae northeast of Urbana in his research plots.
Spencer anticipates that the first beetle emergence
will occur in approximately two weeks
(June 11-12), which is very early.
“If the hot and dry weather persist in areas of
the state more prone to corn rootworm damage
– the northern two-thirds of Illinois – heavy infestations
of larvae could take their toll on small
root systems,” said Gray. “Because of the early
hatch and accelerated development of larvae
this spring due to very warm temperatures,
even Bt hybrids may sustain more root injury
than expected. The lack of soil moisture in
many fields will speed up larval development
due to the more rapid heating of dry soils.”
Also during the last week of May, adult Japanese
beetles were observed in southern, southwestern,
and south-central Illinois. Ron Hines,
a former University of Illinois Extension employee
and crop consultant, saw Japanese beetles
in Massac County on May 28. Robert Bellm,
University of Illinois Extension commercial agriculture
educator, observed Japanese beetles in
Fayette and Madison counties over the Memorial
Day weekend. He estimates that these sightings
are about two weeks ahead of normal.
The suggested economic threshold for Japanese
beetles in soybeans is based upon a defoliation
level of 30 percent before bloom. Soybean
fields that are under severe moisture stress may
suffer greater yield loss due to defoliation, and
this needs to be considered in making treatment
decisions. Japanese beetles tend to concentrate
their numbers along field margins. Scouts are
encouraged to examine plants in five separate
areas of the field’s interior.
“Don’t base rescue treatment decisions on
quick looks of defoliation in border rows,” Gray
advised. “With the mild winter we experienced
followed by the hot and dry spring, I anticipate
overall good survival of Japanese beetles and
encourage vigilant scouting for this insect
throughout the growing season.”
Gray also notes that potato leafhoppers are
now frequently observed in stands of alfalfa and
should be monitored using a sweep net. These
insects can inflict significant yield losses, especially
in dry years. Field perimeters are often the
first areas to shown signs of injury. The regrowth
of stands following a cutting should be
examined carefully for leafhoppers because as
few as 0.2 leafhoppers per sweep in alfalfa 0 to
3 inches high can significantly stunt further
plant growth.
“Don’t assume that the dry weather is solely
responsible for delayed plant development following
a harvest,” Gray said. He recommends
consulting the information about the life cycle,
biology, and management of the potato leafhopper
on the Department of Crop Sciences Extension
website:
http://extension.cropsci.illinois.edu/fieldcrops/alfalfa/potato_leafhopper/.
Finally, producers are observing higher-thannormal
numbers of beet and yellowstriped
armyworms in both corn and soybean fields
during the late days of May, probably due to the
mild winter, warmer than average spring, and
suitable migratory conditions this spring. Gray
recommends scouting of both corn and soybean
fields for these species for the next several
weeks.
Armyworm species are associated mainly with
damage to corn and wheat. However, in the
Handbook of Soybean Insect Pests published by
the Entomological Society of America (ESA), the
fall armyworm, beet armyworm, and yellowstriped
armyworm are listed as occasional pests
of soybeans. ESA's suggested economic threshold
for these armyworm species in soybeans is
“when larvae threaten to reduce stands below
the optimum plant population, typically to six
or fewer plants per row-ft (19.7 per row-m).”
Kevin Black, an insect and plant disease technical
manager at Growmark, Inc., observed beet
armyworms on corn in western and northwestern
Illinois on May 29. The threshold for armyworms
in seedling corn is when 25 percent of
plants are damaged, larvae are three-fourths of
an inch long or smaller, and some plants are
being killed. Δ