Grasshoppers have been a sporadic pest of seedling cotton for 10 or
more years.
Growers reported observing high numbers of adult grasshoppers during
harvest season in fall 2017. Overwintering populations are influenced by
environmental conditions. Rainfall is likely more important than
temperatures. Dry winters are favorable for grasshopper population since
they overwinter as eggs in the soil. Grasshopper problems are sporadic
and almost always associated with reduced tillage fields.
The
primary grasshopper that damages cotton is the differential species
which also overwinters as eggs in the soil. Eggs hatch from late March
throughout April, May and June as soil temperatures rise and spring
rains occur. The first nymph to leave the egg pod makes a tunnel from
the pod to the soil surface through which the succeeding nymphs emerge.
Nymphs feed and grow for 35 to 50 days before becoming adults which can
then fly. The nymphs or immatures can only jump. Their development
proceeds most rapidly when the weather is warm but not too wet. Mature
grasshoppers mate and continue feeding on plants. About 2 weeks later,
females begin to deposit clusters of eggs in the soil. Soil particles
are glued together around the eggs to form a protective pod. Each pod
may have 25-150 eggs. Most grasshopper species only complete one
generation per year.
In fields with historical grasshopper
problems, growers may want to take a more preventative approach by
adding a grasshopper insecticide to their burn down herbicide. Since not
all grasshoppers emerge from the egg stage at the same time, a long
residual IGR (insect growth regulator) insecticide could also be
utilized. Dimlin has proven to be a good management tool for
grasshoppers. It has extended residual that provides good control of
immature grasshoppers but will not control adults.
There are no
established thresholds for grasshoppers in cotton and will likely never
be since their feeding habits are so unpredictable. Some fields and some
years may have grasshopper damage while other fields and years have the
same level of grasshoppers but no damage. Preventative insecticide
applications for grasshoppers are a judgment call. When grasshoppers are
observed, and cotton is in the susceptible stage, treatments can be
based on the risk level that an individual grower is willing to take.
Grasshopper
problems are greater in lighter soils or soils with higher sand
content. Damage often occurs in the same fields or farms from year to
year. Grasshopper damage as stated is unpredictable but can potentially
threaten a stand. Grasshoppers may feed on foliage, but most economic
damage occurs when grasshoppers feed on the main stem of emerging (in
the crook or cracking stage) seedlings. In some cases, grasshoppers may
completely sever the stem, but
more often they will chew partially through the stem weakening the plant which will fall over at the feeding site.
Most
all cotton insecticides will control immature grasshoppers when applied
at a low labelled rate. Later into the spring, adult grasshoppers are
very difficult to control with any insecticide, even at a high labelled
rate. Acephate (Orthene) at 0.6 lb. active per acre has proven to be the
most effective grower treatment for adult grasshoppers.
