June 1998
Don't overlook aphids as a pest problem, says new U of M entomologist
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Prairie Grains is the
official publication of
the Minnesota
Association of
Wheat Growers,
North Dakota Grain
Growers Association,
South Dakota Wheat,
Inc., and the
Minnesota Barley
Growers Association.
"I think aphids will be a greater problem to watch for in small grains this growing season." MacRae says aphids can be described as a "snowbird" insect: Populations develop in the southern regions of the US and are blown north in spring and summer weather systems from the south. This year, thanks to El Nino which hastened those warm jet streams, aphids will likely arrive early, says MacRae. Scouting on young plants should begin in late May and continue through plant maturity, when aphids tend to abandon wheat for other crops.
MacRae, originally from Prince Edward Island, Canada, was hired by the U of M last August to replace David Noetzel, who retired. MacRae is based out of the Northwest Experiment Station on the U of M's Crookston campus, rather than the St. Paul campus. This decision, urged by the Minnesota Association of Wheat Growers, suits MacRae fine. "This way, I feel more responsive to the growers. They're right in my backyard," he says. "I also have the potential to do collaborative work with the folks across the river at NDSU, as we often have the same pest problems."
One of the first items of business upon hitting the fields for his first growing season in northwest Minnesota will be to determine whether an insecticide for aphids (Penncap-M or Lorsban) can be tank-mixed with Tilt and applied on wheat to improve yields.
The Russian wheat aphid was one of MacRae's primary areas of research during his three years of post-doctoral research at Colorado State University. MacRae also worked on tracking grasshopper populations within various cropping systems, the results of which he would like to apply to northwestern Minnesota. This spring, MacRae co-wrote the "Minnesota Grasshopper Management - 1998" guide. The guide can be obtained by calling him at 218-281-8611, or by linking to it from the Northwest Experiment Station's web site at http://www.nwes.umn.edu. It is also available at county extension offices in Minnesota.
MacRae says he doesn't expect the orange wheat blossom midge to be a major problem this year. Earlier planting should help wheat development get ahead of the midge. Evening winds would also help: dusk is when female midge fly about looking for wheat heads to lay eggs on, and winds above six miles per hour hamper their flying ability. In areas where midge does merit spraying, however, MacRae notes that Lorsban 4E SG is a treatment option. (For more information on midge scouting and treatment, see NDSU extension small grains specialist Mike Peel's column on the next page).
One insect that MacRae would like to bring under control is the sunflower midge, which has effectively chased the sunflower crop out of northwest MN. Spray treatments are minimally effective; spraying chemical on the midge kills only the adult sunflower midge, while larvae lay protected underneath the flowers' bracts.
Under a federally-funded project, MacRae is helping to develop-in a collaborative project with NDSU entomologist Gary Brewer, USDA-ARS sunflower entomologist Larry Charlet, and South Dakota State University entomologist Mike Catangui-a degree-day model using climatic and emergence data from three locations in the Red River Valley to refine the timing of adult emergence and the insect's distribution in sunflower fields.
Making sampling easier
MacRae would also like to refine sampling methods and thresholds for aphids in wheat. Not enough growers sample consistently because the sampling process can be tedious, he says, and simplifying the methods would promote scouting and help eliminate unnecessary spraying. New methods may include the use of yellow sticky-traps (aphids are attracted to yellow). He is also looking into developing a way to scout for more than one insect at one time.
Eliminating unnecessary spraying is one potential result of using Integrated Pest Management (IPM), says MacRae. IPM employs various pro-active techniques growers can use to keep pests below yield-impacting population levels. MacRae is currently putting together a CD-ROM (a compact disc with information that can be viewed on your computer) with IPM information for soybeans.
"Since soybeans are a relatively new crop in the Northern Plains, most information available is written for Central Plains growers," says MacRae. The CD-ROM will provide information pertaining to the Northern Plains, including an integrated pest-solving key with pictures. MacRae plans to make the guide available on the Internet in the future. n
Gauging Rainfall Effects on Grasshoppers
Heavy rains during emergence - Kills young grasshoppers by trapping them in the soil or physically washing them away.
Drought or lack of rain - Poor egg hatch; hoppers starve from lack of food, low egg production by adults.
Scout for hoppers
Although some entomologists suspect grasshoppers won't be as pervasive this growing season as was predicted last fall, vigilance in scouting and taking control measures is still needed.
Phil Glogoza, NDSU Extension entomologist, says growers should scout areas where adult grasshoppers were present last fall. Inspect carefully for newly-hatched hoppers, which are only about the size of a kernel of wheat. To estimate populations, move through an infested area and count the number of grasshoppers that jump or move within a one square foot area. Keep a record of the counts, then divide the total number of grasshoppers by the total number of samples. Multiply the result by nine to get the number of grasshoppers per square yard.
For more information about controlling grasshoppers or other pests, consult the 1998 North Dakota Insect Management Guide, which is available on the Internet at http://www.ext.nodak.edu/extpubs/plantsci/pests/e1143w1.htm.