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Grasshoppers: The Hungry Ones
4/4/2008
Michael Fisher
Area Extension Agent
(Livestock)
Colorado State University Extension
Golden Plains
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It seems like grasshoppers have managed to find their way into my
conversations every few days for the past several weeks. Did you know that one
of the divisions of USDA-APHIS does an annual survey of grasshopper and Mormon
cricket populations on rangeland areas in Colorado? Plant Protection
Quarantine, the APHIS division responsible for the survey, conducts counts when
the insects are in the nymph stage and follow up with an adult count later
during the summer. That data is compiled and mapped to assist land managers in
decision making.
It seems that some of the counts taken in Colorado's
Golden Plains Area in 2007 were beginning to appear high. Additionally, a very
large section of western Nebraska had high population counts in 2007. This
brings about the questions of how many eggs did the 2007 grasshoppers lay and
how much of a problem will they be in 2008?
Some of you may be wondering
why a livestock agent is worrying about this. After all, the small pests will
attack crops, right? Well, grasshoppers can have a terrible impact upon
rangelands and the forages that livestock depend upon for grazing. There are
several grasshopper species that can become a problem. Each has its own
characteristics and statistics. Depending on the grasshopper, they can eat
between 30 and 250 percent of their bodyweight on a daily basis. Let's put this
into perspective. Researchers at the Noble Foundation suggest that 30 pounds of
grasshoppers will consume roughly the same amount of forage in a day, as what a
600 pound steer will. From a cow perspective, Montana State University suggests
that 80 to 104 pounds of grasshoppers will consume the same amount of forage as
what a 1250 pound cow will on a daily basis.
As you can see, the
grasshopper is an aggressive competitor for rangeland forage. So one is left to
ask, "How many grasshoppers does it take to be a problem?" Once again, this
varies depending on the species of insect and the crop that they are invading.
One can find reports ranging from as few as 3 to as many as 40 grasshoppers per
square yard is the point when the economic threshold is reached. In other
words, that is the point when the damage is costly enough to warrant
intervening with a control measure. In typical rangeland or pastures the
economic threshold is often considered to be 15 to 20 nymphs or 8 to 10 adults
per square yard. However, recent information distributed by the University of
Wyoming and USDA-APHIS states that treatment is rarely justified at less than
14 of the pests per square yard but would certainly be warranted if the density
reached 24.
In many cases, we assume that control is synonymous with
chemicals. True, there are a lot of effective pesticides on the market.
However, grasshoppers are very mobile. Therefore, large areas (10,000 acres+)
of treatment can prove to have a better result than spraying just a couple of
hundred acres. Also, if using chemical treatments, consider doing the
treatments in alternating strips. This will protect some of the insects that
play a positive role in your rangelands; while the mobile grasshopper is apt to
move through a treated strip and still be dosed.
A grasshopper control
that many people do not think about is rotational grazing. Dr. Jerry Onsager
did research with the USDA-ARS that evaluated controlling grasshopper outbreaks
by simply using that approach, compared to season-long grazing. He discovered
that nymph stage grasshopper populations in the rotational system developed
slower and had lower survival rates. Subsequently, the adult populations were
lower and appeared later in the season. This led to many of the pests not
reaching egg laying maturity before the end of the grasshopper season.
Additionally, there was a dramatic difference in forage use. In the rotational
grazing system, grasshoppers' forage consumption was 10 to 23 percent of the
cattle's forage consumption. However that range increased to 91 to 168 percent
in a season-long grazing system.
You can expect it to be roughly mid-May
before the nymphs began hatching, which is still a month away. Yet, this is a
good time to start thinking about the hungry little pest. Develop a plan to
watch for them in your pastures and rangeland. Choose some dates on your
calendar that you are going to make an asserted effort to check for
grasshoppers. As the growing season moves on, be observant and if you start
seeing a lot of grasshoppers tell your neighbors, your Pest District
Supervisor, your Extension Agent, or your NRCS Range Specialist. Communication
is one of the real keys to controlling a major grasshopper
problem.
Major grasshopper species of the western rangeland States
and Alaska
(From USDA-ARS website Grasshoppers: Their Biology,
Identification, & Management)
Grasshopper photos from USDA-ARS
NPARL website.
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Page Created and Maintained by: Perry D. Brewer, Area
Extension Agent (Technology Education/Youth)
4/9/2008 |
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