Four Early-Season Insects to Look For

Cutworms

  • There are different species, which will affect crops differently and may be present at different times.
  • Dingy cutworm overwinter as partially grown larvae, so will be ready to feed as the crop emerges. They will feed on emerged plant tissue, but don’t do a lot of clipping of stems.
  • Redbacked cutworms overwinter as eggs, so may not be noticed until later in May or June, when larger larvae are feeding on plants. They potentially will clip stems.
  • Cutworms can be patchy in a field. Areas of the field that had later flowering crop or weed patches last year may have higher levels of cutworms.
  • Cutworms are nocturnal, feeding during the night, then burrowing into the soil during the day. They will burrow deeper if the soil is dry.
  • If insecticides are needed to control cutworms, they should be applied as late in the day as practical, and may only be needed on patches, depending on how the population is distributed in the field.
  • More information on cutworms can be found at : http://www.gov.mb.ca/agriculture/crops/insects/cutworms-field-crops.html

Flea beetles in canola

  • The 2 main species of flea beetles in canola in Manitoba are the striped and crucifer flea beetles.
  • These are potentially a concern from the time canola emerges until about the 3 to 4 leaf stage in canola.
  • Seed treatments will provide early season control. None of the seed treatments currently registered work as well under cool, wet conditions as they do in warmer, drier conditions.
  • Insecticide effectiveness can vary with the species of flea beetle. Neonicotinoid-based seed treatments (Helix, Prosper) work well against crucifer flea beetle, but control will be less on striped flea beetle. This is not a developed insecticide resistance, just natural variation in effectiveness between species.

Wireworms

  • Are larvae of click beetles. Will have 3 small pair of legs at the front the body, but don’t have the fleshy prolegs at the back like cutworms.
  • Feeding is all underground.
  • Foliar insecticides will not be effective.
  • Seed treatments can stop wireworms from damaging young crops, however current seed treatments result in little mortality of the wireworms.
  • Are hard to monitor; bait balls can be used, but growing vegetation and other sources of CO2 near a bait ball will compete for wireworms and reduce effectiveness.
  • Practices that result in quick germination and early growth can help minimize damage form, wireworms.
  • More information on wireworms, as well as some insects that could be confused with wireworms, can be found at: http://www.gov.mb.ca/agriculture/crops/insects/wireworms.html

Grasshoppers

  • It will probably be early-June before we see much hatch of our potential pest species of grasshoppers this year.
  • Any larger grasshoppers seen in May will not be pest species.
  • Heavy rains and standing water will not kill grasshopper eggs. Newly hatched grasshoppers, however, are quite susceptible do being killed because of heavy rains. So heavy rains in April or May will likely do little to our pest species of grasshoppers. Heavy rains in June could potentially reduce populations significantly.
  • Areas that had lush green vegetation late last year, such as along field edges, are more likely to have higher concentrations of grasshopper eggs, and early-season grasshopper levels will be heaviest in these areas. These areas should be monitored in June.
  • If grasshopper control is needed:
    1. Control of young grasshoppers is more effective than controlling adults
    2. Control may only be needed along field edges or areas where they are concentrated early.
    3. Bran baits (with an attractant that lures the grasshopper to the bait) as well as foliar sprays are available.

Submitted by:  John Gavloski, MAFRD Extension Entomologist

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Grasshoppers – Common Questions

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
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