All Things Organic - Biological grasshopper control needed

By Ian Cushon
September 5, 2002

Grasshoppers are causing considerable damage on many farms this year. Unfortunately we have not likely reached the peak of the current cycle. Grasshoppers are going to challenge some organic farmers' commitment to organic crop production for the next couple of years. The last major grasshopper out break occurred in 1985 and 1986. The majority of today's organic farmers began organic farming after that outbreak, so many farmers have limited experience with this pest.

Most farmers associate grasshopper outbreaks with droughts. Many of the conditions that support population increases are drought-related, but grasshopper cycles are not dependent upon drought. Damage may be more severe during drought periods because there is generally less plant growth and droughts are usually associated with warmer temperatures that increase insect activity.

Pesticides can provide some protection from grasshopper damage but most grasshopper populations decline naturally with cooler, wet summers and colder autumn weather. Diseases and predators also keep numbers in check. Wet, cool weather is important because it can increase naturally occurring diseases and discourage egg laying.

Not all grasshoppers are crop pests. Some types cause more damage than others and certain crops are less prone to damage. Choosing crops that are less susceptible is the first line of defense. Chickpeas are usually least susceptible to grasshoppers followed by peas, oats, mustard, canola, barley, wheat and sunflowers. Flax and lentils are the most susceptible crops. Crops with grassy weeds may provide some diversion in crops such as flax and lentils. Fallow tillage also helps control grasshoppers. Early spring tillage will minimize green growth and starve newly hatched grasshoppers. When grasshoppers do not have a food source on fallow, they do not lay eggs later in the year. Most damage on fallow-seeded crops occurs on field borders or when mature grasshoppers migrate.

On early harvested crops, fall tillage may discourage egg laying. Stubble cropping in moderate to severe infestations may be a high risk. Summerfallow may be a better option. Fortunately most organic farmers still have significant acreages of fallow that will reduce potential damage.

Early seeding is also recommended. Crops that are planted early and get a strong start will have a better chance of outgrowing grasshopper damage. As well, these crops are harvested earlier which makes them less prone to migrating grasshoppers. In some cases, fall-seeded crops can provide an advantage. But autumn damage can stifle fall-seeded crops.

Hopper traps
Farmers can use trap strips to attract and hold migrating grasshoppers. Strategically placing the strips on the borders of early harvested crops may reduce migration to more sensitive crops. Scouting fields for grasshopper numbers this fall will give an indication of next year's potential damage. This will allow farmers to place crops according to their tolerance of grasshoppers.

With limited control options, organic farmers face potentially devastating crop losses. In the 1980s, Canada was a world leader in developing biological control of grasshoppers. A lot of research was focused on the Nosema Locustae (N. Locustae), a microsporidian parasite. N. Locustae was the first microbial agent to be developed as a bio-pesticide for locust and grasshopper control. It is sprayed on wheat bran and used as a bait. N. locustae has been extensively field-tested in the United States and Canada, and releases were also conducted in Argentina, Cape Verde, China, and Mali. It is currently registered for use in the U.S. but not in Canada. Dan Johnson, an Agriculture Canada scientist in Lethbridge, Alta., is one of Canada's leading experts on grasshoppers. Johnson said N. locustae was not registered in Canada because regulators were concerned by its low level of effectiveness. They were also concerned because the wheat bran was contaminated with too many bacteria. According to Johnson, N. locustae can result in 10 to 50 percent mortality. On average, it is about 25 percent effective. N. locustae is not a fast acting pesticide. Its main benefit may be that it reduces feeding and egg laying. Overall it is not an effective solution, but for all types of farmers and especially organic farmers, it may provide another tool for controlling grasshoppers.

There are other biological control methods that could offer protection for organic farmers. One is Metarhizium anisopliae var. acridum FI 985, which has already been registered for organic farming in Australia. This fungal disease organism offers 70 to 90 percent control of some types of grasshoppers. To be registered here, Johnson said it will need to be evaluated under Canadian conditions. Johnson said it is difficult to register bio-pesticides in Canada. Elsewhere in the world there is greater willingness to register bio-pesticides. It is not clear why Canada is lagging in this area of development. Perhaps a conservative pesticide registration process is discouraging these developments. There has also been a decline in funding for biological grasshopper controls.

Critics of organic farming like to characterize organic farmers as using out of date, low-yielding farming techniques. Contrary to this opinion is the view that many broad spectrum insecticides that kill all insects including beneficial ones are unsophisticated technologies that should be avoided. Organic farming is about developing ecologically based production methods that use advanced science such as biological-control methods and selective bio-pesticides. Developing effective biological control of insects would be good for everybody, except maybe the insects and the companies who manufacture chemical insecticides.

Ian Cushon
Moose Creek Organic Farm Inc.
P.O. Box 85
Oxbow, Saskatchewan
Canada, S0C 2B0

Tel. 306-483-5034
FAX 306-483-2799
Cell 306-483-8257
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