By Michael Fisher
Area Livestock Extension Agent, Golden Plains Area
As posted on the High Plains Journal Web site, May 26, 2008.

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 body weight 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 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 as 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 cattles' 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 begin 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.

This article appeared on High Plains Journal, www.hpj.com, on May 26, 2008.