Download Grasshoppers

agronomy
P L A N T S C I EN C E
M A R C H 2 013
Arthropod Pests of Wheat:
Grasshoppers
Adrianna Szczepaniec | Entomology Specialist
Description and Life Cycle
Grasshoppers are a large group of insects that belong
to the family Acrididae (Orthoptera). They have short
antennae and large hind legs responsible for the grasshoppers’ ability to jump. Newly hatched nymphs can
be as small as a ¼” while fully-grown adults of many
species can reach several inches in size. Their powerful
chewing mouthparts allow these insects to consume
even very tough plant tissues. Grasshoppers are ubiquitous and can feed on many different plant species.
Grasshoppers develop through an incomplete metamorphosis (egg, nymph, and adult). There is no larval
or pupal stage in grasshopper development. Eggs are
laid in the fall and are buried approximately 2” into the
soil in what is referred to as an egg pod. Each pod contains 15-40 ovular, white-yellow, eggs. Depending on
the grasshopper species, eggs can begin hatching in
early spring (late March- early April). Nymphs emerge
from the egg pods and begin feeding on green plant
material near the field edges. As they move through
their four instars (growth stages), they begin moving
further into the field. Four to five weeks after hatching, the nymphs reach their adult stage, which is distinguished by fully developed wings. Adults are very
active and extremely mobile, allowing them to move in
and out of fields with relative ease. By mid-June, adult
grasshoppers are present within the fields. Grasshopper adults lay eggs in the fall before temperatures are
consistently below 48°F. Most species overwinter as
eggs in the soil.
Damage and Management Guidelines
Over the past few years, grasshopper populations have
consistently reached economically significant numbers
in the field, and have resulted in high yield losses.
Scouting for grasshoppers should start early, in late
March or early April when temperatures break 48°F.
There are several scouting methods including visual
estimates, but the most effective approach to scouting
for grasshoppers is done using visual estimates. Scouting is usually done in 3 locations in the field (away from
the field edge). All thresholds given below are based
on the number of grasshoppers per sq. yd.
Rating
Grassho pp er. Pho t o c r edit : Jona t ha n Nixon
Nymphs/sq. yd.
Adults/sq. yd.
Margin
Field
Margin
Light
25–35
15–23
10–20
Field
3–7
Threatening
50–75
30–45
21–40
8–14
Severe
100–150
60–90
41–80
15–28
Very Severe
over 200
over 120
over 80
over 28
Mechanical management: Tilling fields in early spring
can destroy grasshopper eggs that are laid in the soil
during the previous fall. Tilling can also kill any nymphs
Page 1
iGrow | A Service of SDSU Extension
agronomy
or adults that may have overwintered within the field.
Grasshoppers have also adapted to combat tillage by
overwintering or laying eggs in and around drainage
ditches and field borders away from the reach of tillers.
Cultural practices: Doubling the seeding rate around
the edges of the field will help to decrease the overall
yield loss from early edge feeding from grasshopper
nymphs. The use of trap crops is also a very useful tool
to pull grasshoppers away from valued crops.
Biological management: There are several biological
control agents that target adult and nymphal stages.
Multiple species of wasps, ground beetles, and true
bugs target this pest. Pathogens such as fungi, bacteria, protozoans, and viruses naturally present in the soil
are very effective at suppressing grasshopper populations during cool wet weather conditions.
Chemical management: Only after sampling and establishing that the economic threshold has been reached
should chemical management options be used. Applying pesticides before economic thresholds have been
reached can result in reduced beneficial insect populations and trigger outbreaks of grasshoppers and other
pests during the season. The recommended management option would be the use of an insect growth regulator early in the season to stop nymph development.
This class of chemical along with the Reduced Agent
and Area Treatment strategy or RAATs has had great
success in managing grasshopper populations in South
Dakota as well as surrounding states.
Source: University of Nebraska, Lincoln (Extension
Publication G1627).
South Dakota State University, South Dakota counties, and USDA cooperating. South Dakota State University adheres to AA/EEO
guidelines in offering educational programs and services.
Publication: 03-2010-2013
Page 2
iGrow | A Service of SDSU Extension