Grasshoppers are a concern this year for many soybean growing areas. The decision process to spray, not to spray, when to do it, and how much of the field should get covered, requires scouting to get an average number.
Brunel Sabourin of Antara Agronomy joins Kelvin Heppner in this episode of Soybean School to discuss strategies for keeping grasshoppers under control.
Hatching is concentrated in grassy areas where the eggs were laid, so typically along ditches and field borders, which is where the most damage to the crop will happen first.
When making a decisions to spray, Sabourin says it can be hard to determine the population, as they’ll jump away, but the threshold is 10 to 12 in a metre square. It’s best to walk a zig-zag pattern, as a straight line will push hoppers away in a wave.
This early in the hatch, grasshoppers don’t have wings yet; and while Sabourin says you could use a sweep net to help determine the initial population number and what size they are, it’s not the preferred method for scouting.
Is it better to spray strips along field edges early, or take the chance of not spraying and have the grasshoppers take over more of the field?
Sabourin says that there are different products and tactics to control grasshoppers, one of which is a bait that can be spread in the ditch or near roadways to slow them down.
Another option is a product with a high residual rate, but will only protect the part of the plant that’s grown, and not protect any new growth. Once the crop is more advanced, and more grasshoppers have hatched or the existing population has grown, that’s the time to look at spending the big dollars says Sabourin.
Another technique in the toolbox is to spray every second strip, with a product that has high residual, a recommendation from Dr. John Gavloski, provincial entomologist at Manitoba Agriculture and Resource Development.
There are a variety of insects that can take out grasshoppers, so if possible, consider the beneficial insect population and choose an insecticide option that is easy on them. There’s also a fungus that can infect grasshoppers under wet, humid conditions, but the dry conditions over the past few years, especially in Manitoba, mean the fungus won’t have an effect on grasshoppers this year.
For areas that haven’t received a lot of precipitation, it might not make economic sense, but for future years Sabourin says it’s recommended to spray if grasshopper numbers get high enough later in the season.