Weather and insect populations go together like soup and marriage, horse and sandwich, love and carriage.
“The weather certainly has an impact on insect populations. It affects different insects in different ways,” said John Gavloski, Manitoba provincial entomologist.
The cool wet spring followed by a hot dry summer affected the 2011 insect population and is already shaping insect trends for 2012.
“Grasshopper and insects like that which overwinter are right now taking advantage of this weather for mating and laying eggs. They’re more active in these kinds of conditions,” he said.
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“Hot dry weather gives them the opportunity to lay the maximum number of eggs. Current conditions are what they need to start re-building their populations.”
Gavloski said insect populations can’t go from low to high in one year. He said it would take a number of hot dry years for grasshoppers to reach high levels.
It is hard to predict what to expect next year for spider mites, he said. Their populations are influenced greatly by the weather. Hot, dry conditions generally favour higher mite populations. In most years, spider mite populations are controlled by natural factors to the point where they are barely noticeable.
The cutworm is another insect basking in the hot dry Manitoba weather.
“The moths are flying right now. They’re mating and laying eggs. To lay the maximum number of eggs, they need nectar to feed on and warm dry evenings. And that’s what they’re finding.
“There’s nothing a farmer can do about any of this right now. Just keep it in mind because it might be important next summer.”
When asked if the big cracks in the fields might allow frost to go deeper and perhaps destroy some eggs, Gavloski said he doesn’t know of any research on that subject.
“However, there is a lot of research indicating that the level of snow is a factor. More snow provides better insulation and keeps the ground warmer.”
Lygus bugs in canola
High levels of lygus bugs are reported in the eastern and central regions. Canola remains vulnerable to lygus bug feeding injury from late flowering to mid pod. Lygus bugs in the later podding stages will cause less injury.
Late summer flea beetles
The fall population of flea beetles has recently become noticeable in some canola fields. No economic thresholds are available for fall populations of flea beetles in canola. Spraying in the fall to reduce the risk the following spring is not recommended. Flea beetles are mobile enough that farmers could still have problems in the spring. There can be big differences between fall and spring populations.
A reminder that when applying insecticide in canola, the shortest pre-harvest intervals are seven days to swathing or direct combining. Once a canola crop is within seven days of harvest, insecticides cannot be applied.
Canola storage
Malathion cannot be used to treat bins where canola will be stored or to treat canola going into storage. These applications can result in residues that are unacceptable in some of Canada’s key export countries.
Most insects in stored canola will not feed on sound, healthy seed. Moisture-loving fungus feeders such as foreign grain beetles, psocids and mites may be found in canola in poor condition.
Primary stored product insects can be found if there is cereal grain mixed with stored canola.
Winter wheat diseases
Another factor is the risk of wheat streak mosaic virus spread by mites, and barley yellow dwarf spread by aphids. Both can be transmitted to winter cereals in the late summer and overwinter in the crop. The risk can be reduced by delaying seeding until later in the range of recommended seeding dates.
It’s important that a field be free of all volunteer wheat plants and grassy weed hosts for at least two weeks before planting.
Spider mites
In this drier year, there is some feeding by spider mites, particularly on soybeans and in some cornfields. In many instances, there are edge effects.
Some soybean fields have already reached the full seed (R6) stage, where the seeds in the upper pods fill the pod cavity. In most instances, the feeding by the mites will not be severe enough or the crop will be advanced enough that control would not be economical.
Contact: John Gavloski, MAFRI extension entomologist, 204-745-5668 or John.Gavloski@gov.mb.ca.
