Grasshoppers continue to be a concern in many areas. Below are some of the more common questions on grasshoppers that some have been asking:
Will they feed on the heads of wheat? Possibly. The initial feeding is likely to be on the leaves. As the plants get more mature and start to senesce, grasshoppers may move and look for more suitable hosts. But at times they will feed on the head or clip heads. So when assessing populations of grasshoppers, consider what they are feeding on as well as the levels.
Grasshoppers are present in the field but not causing a lot of damage to the crop; how concerned should we be? There are lots of different species of grasshoppers, but only 4 that we consider to be potential crop pests. Of these 4 species, the preference for food choices varies. There may be some weeds in or around the field, or vegetation around the field that is more preferred than some crops. We have seen situations before where grasshoppers have been present in a field, but feeding mainly on weeds in a field but not the crop. So once again, consider what they are feeding on as well as the levels. The lush vegetation around fields this year, due to good moisture conditions, may help prevent some crop feeding.
Will fungal diseases potentially reduce the grasshopper population? There are a few different types of fungal diseases that can potentially reduced grasshopper populations. One that is quite visible, and hence many are aware of is a fungus called Entomophaga grylli. This is the disease that in its terminal stages will cause the infected grasshoppers to climb to the top of the vegetation, where they remain clinging after they die. There are different pathotypes of this fungus, which affect different species of grasshoppers differently. One of the predominant species of grasshoppers this year, at least in the central region, seems to be the twostriped grasshopper, Melanoplus bivittatus. This species of grasshopper can be quite susceptible to pathotype II of this fungus. So if the proper pathotype of the fungal is prevalent, and the humidity levels are sufficient for the fungus to establish, this can result in some of the population being killed by this fungus. But it this point in the season it is hard to estimate how significant disease, or predators and parasites, may be in reducing grasshopper numbers and damage. The photo below show a dead grasshopper infected with Entomophaga grylli.
If insecticides are needed to control grasshoppers, remember to check the preharvest interval of the insecticides, which is the number od days that must pass between the insecticide application and swathing. For some products it will be too late in the season to use them on some crops.
Submitted by John Gavloski, MAFRI Entomologist
Taken from the Manitoba Insect and Disease Update for the Week of July 22, 2013: http://www.gov.mb.ca/agriculture/crops/seasonal-reports/insect-report-archive/insect-report-2013-07-23.html