Slugs In Corn And Other Crops; Armyworms In Corn
JACKSON, TENN.
April 19, 2012 – Slugs. There have been a few
calls about slug feeding in corn, and I
would expect some similar calls in other
crops as they emerge. Slugs, unlike snails, lack
shells and commonly feed on plants. They feed
on leaves and sometimes cut the stems of cotton
or soybean seedlings similar to cutworms.
Snails rarely cause economic damage to field
crops, and the ones typically encountered do not
even feed on the plants. There are no set thresholds
for slugs. The standard recommendation is
to treat when stands are being reduced below
acceptable levels. This requires some professional
judgment. Below are a few bullets for your
consideration.
The brown marsh slug is common in Tennessee.
It grows to about a length of ½-inch.
Slugs are almost exclusively a pest in reducedtillage
fields and are much more problematic
where there is a lot of plant residue on the soil
surface. Thus, it is common to see them following
corn, sorghum or behind cover-crop wheat.
Slugs feed mostly at night. A common symptom
is mysterious holes in the leaves or on the
leaf margins. Look under plant debris, in soil
crevices and other hidden locations if you suspect
slugs are present.
Warm and dry conditions go a long way in
helping plants outgrow slug injury. Thus, expect
the worst problems in wet fields and when
plants are growing slowly.
The worst problems I’ve encountered are when
the seed furrow does not close completely. This
typically occurs when the field is planted a little
too wet. This creates a highway for slugs down
the seed trench and allows themto feed on the
plant below the ground level and during the day.
In high residue fields, set your row cleaners to
throw most the residue off the row. Some research
has indicated this can reduce slug damage
as much as 40 percent.
No insecticides provide meaningful control of
slugs.
The only reliable control for established slug
infestations is use of granular baits containing
metaldehyde. Deadline M-Ps, from AMVAC, is
the most commonly used product (link to label).
The standard use rate is 10 lb of Deadline M-Ps
per acre. Thus, it requires some forethought and
effort to spread the bait evenly at such low rates.
You can use higher rates, but the product is relatively
expensive. Also, be advised that this
product will probably not be in stock at your
local distributor. It is necessary to find potential
problems quickly so you have time to react.
Armyworms in Corn. Yes, this is the same
armyworm that attacks wheat (often referred to
as the true armyworm). Although there have
been few calls in Tennessee about armyworms
in wheat, I’ve received some calls from the
Bootheel of Missouri and reports from surrounding
states. I’ve also know of armyworm
problems in corn from these same areas.
It is not uncommon for the true armyworm to
feed on corn. This often happens adjacent to infested
wheat fields or grassy areas. As their
name implies, the armyworms will sometime
move in numbers from wheat fields into corn.
Feeding in corn will typically be worst along field
edges. True armyworms will rarely if ever cause
economic damage to cotton or soybean. They will
feed on leaves and sometime totally defoliate the
above-ground parts of corn plants. Injury may
resemble cutworm or slug feeding, and like both
pests, they tend to hide underground or under
debris during the day. The good news is that
true armyworms are pretty easy to control with
relatively low rates of synthetic pyrethroid insecticides.
Often, treatment around field edges
is all that is needed. Like with slugs, I can’t give
you an exact threshold. Treatment is suggested
if corn stands are being reduced below acceptable
levels. Keep in mind that the growing point
of corn is below ground until plants are at the
3rd or 4th leaf stage. Even severely defoliated
plants often recover if the growing point of the
plant is not destroyed. Δ
DR. SCOTT STEWART: IPM Extension Specialist,
University of Tennessee
The brown marsh slug
Slug feeding in soybean
Armyworm