Insects didn’t take a massive bite out of Manitoba crops in 2015, but there were some nibbling problems caused mainly by flea beetles and cutworms, says Manitoba Agriculture, Food and Rural Development entomologist John Gavloski.
Alfalfa weevil populations were high enough in many alfalfa fields to cause economic damage and army worms were a concern in many small cereal grain fields, Gavloski wrote in his Summary of Insects on Crops in Manitoba in 2015 released Nov. 6.
Soybean aphid numbers also reached economical levels in some soybean fields in August.
Spotted wing drosophila were a concern in many fruit crops, including raspberries from mid-July on.
European corn borer populations appeared to be higher in 2015 than the past few years. Some Central Region cornfields were sprayed with an insecticide to control the pest.
Corn hybrids with the Bt trait are protected from corn borer. This year about 45 and 14 per cent of the Manitoba grain and silage corn hybrids, were Bt varieties, according to data from the Manitoba Agricultural Services Corporation.
Corn borers turn to potatoes
Borers were also found in the stalks of some potatoes, edible bean and hemp this year. It’s not unusual to find corn borers in crops other than corn when populations are high or when the corn isn’t at the right stage to attract the borer, Gavloski said in an interview.
“Quite a few potato fields in Manitoba had ECB (corn borer) infestations in 2015, beginning in mid- to late July,” the summary says. “Many plants, in patches, were damaged at various stages of plant growth. Damage on main stems appears to have affected the tuber enlargement, but the injury on secondary branches appeared to have no apparent deleterious impact.”
While most canola seed is treated to protect seedlings from flea beetles, some farmers had to apply a foliar insecticide because of high flea beetle populations, the summary says.
“Some canola fields were reseeded because of high levels of damage from flea beetles, or a combination of flea beetle feeding and other stresses on the plants.”
Cutworm populations were generally a concern in Manitoba in 2015. There were reports of corn crops in the Central and Eastern regions damaged by cutworms in early June.
They were also a problem in some canola and soybean fields resulting in some farmers spraying to control them. A field of soybeans in the Central Region was reseeded due to cutworm damage.
“Cutworm damage was evident in some fields of sunflowers, and there were reports of insecticides being applied for cutworms in some fields in the Central Region,” the summary says. “A field of sunflowers near Sperling was reseeded because of damage from cutworms.”
Cutworm feeding was a concern in some soybean fields in the Eastern and Central regions. A soybean field in the Central Region was reseeded because of cutworm injury.
Alfalfa weevil larvae
Feeding injury caused by alfalfa weevil larvae was common in many alfalfa fields causing “quite severe damage” in some cases. That prompted some farmers to cut their alfalfa for hay early, the summary says. Insecticides were applied in many fields and there were reports of poor control.
Low levels of soybean aphids were noted in soybean fields in mid-July. Populations rose to economic levels in some soybean fields in the Eastern and Central regions in August, prompting some insecticide applications. However, high levels of soybean aphids’ natural enemies were found in some fields.
There were reports of lygus bug populations being high enough in some canola fields to cause economic damage in late July and August in the Northwest, Eastern and Interlake regions.
Many home and commercial Manitoba raspberry growers were surprised and disappointed by a poor crop this year. The culprit was the spotted wing drosophila. 2015 was the earliest and most widespread infestation of the insect in Manitoba, the summary says.
Drosophila were identified in traps three weeks earlier than the previous two years, starting in summer-bearing raspberry fields the second week of July in the southern international border region.
Drosophila were then identified extensively throughout southern Manitoba from mid- to late July in commercial and home raspberry fields and patches.
The last two years drosophila had been restricted to the south Red River Valley and south-central Pembina Valley regions. This year yield losses approached 50 to 75 per cent for many raspberry producers. There was little insecticide control as infestations occurred before drosophila was identified as a problem.
Drosophila were identified in June-bearing strawberries and dwarf sour cherries in late July as well. They caused 50 per cent yield loss for many sour cherry growers. Drosophila only affected the last June-bearing strawberry harvest so yield loss was minimal.
Day-neutral strawberry producers had to control drosophila for a second round of berry harvesting from mid-August until early October.
A province-wide monitoring program for spotted wing drosophila occurred from July to October in 2015.
Manitoba crops are susceptible to a wide range of other insects that caused little to no damage in 2015, the summary notes. For example, there were no reports of wireworm damage to corn. And levels of bertha army worm and diamondback moth were generally at low and non-economical levels.