Staying one step ahead of the pests in your alfalfa can save you big, in terms of yield and quality. And the best way to do that is knowing where to look for them.
Researchers at Michigan State University think they're on to a better way of predicting insect movement in alfalfa fields.
Over the last three years, forage specialists there, including crop and soil scientist Richard Leep and graduate student James De Young, have been applying precision ag principles to alfalfa management, including pest control.
Using a backpack global positioning system (GPS), they mapped field perimeters and grids on five Michigan farm fields. Then they used some old-fashioned field sampling to track infestations and movement of alfalfa weevils and potato leafhoppers.
That data was turned into insect density maps, which not only helped to determine whether insecticide treatments were necessary, but also served as a benchmark to compare with future sampling.
Each summer, the researchers set out every seven to 10 days with sticky traps and sweep nets for the tedious task of sampling and counting insects per their two grid sizes — 1 acre and ⅓ acre.
“We compared our grid results to the more traditional zigzag pattern of sampling across a field, and found there were hot areas that were sometimes not even detected with the latter approach,” says Leep.
What surprised the researchers was the amount of variation in insect damage across a field.
“You can see the average of the amount of insect damage when looking across a field, but there may be areas requiring individual management,” notes De Young. “For instance, potato leafhoppers tend to move within a field, and they usually appear in the same area of a field each year, especially on southerly sides of slopes and ridges.”
“We saw a direct correlation between elevation maps and where the leafhoppers showed up first,” adds Leep. “If we can recognize where they show up first, we can begin monitoring that area initially, before scouting the rest of the field.”
That approach can reduce the overall amount of pesticide needed by spraying only those areas of heavy infestation, he adds.
The limiting factor in establishing this type of program is time, says De Young.
“Most hand-held GPS equipment is fairly affordable (a palm-type computer with GPS insert sells for around $1,000) and there's plenty of good mapping software available, such as SSToolbox Stratus. It's just very time-consuming to do the initial field sampling.”
The precision project also included sampling and monitoring of soil fertility, crop quality and yield. And based on those results, four of the five farms they worked on showed a positive economic return from grid sampling.
“We didn't expect as much return on the fifth farm because it didn't have as much soil-type variation,” says Leep.
“This project helps to put the pieces of alfalfa management together,” he adds.