Manitoba Insect & Disease Update
Issue 3: June 13, 2018
Summary
Diseases: No disease incidence to report this week. Growers interested in participating in the disease surveys in 2018 should contact their local MB Ag office or Holly Derksen.
Insects: Flea beetles and cutworms continue to be the main insect concerns. Flea beetles are becoming less of a concern in many field as canola advances to more tolerant stages.
Cutworms are getting larger and assessing the stage of larvae, as well as feeding damage, is becoming important in decision making.
2018 Disease Surveys
Manitoba Agriculture is conducting disease surveys for Fusarium head blight in winter wheat and spring wheat and all diseases in canola and soybean. If you or anyone you know is interested in participating in the 2018 disease surveys please contact your local MB Ag office or Holly Derksen at (204)750-4248 or holly.derksen@gov.mb.ca. We are particularly interested at this time in sourcing winter wheat fields for the FHB survey.
Cutworms
Many of our cutworm species, such as redbacked cutworm, will get to about 38 mm (about 1.5 inches) when they are a fully grown caterpillar. They feed for part of this final stage, then will stop feeding and prepare themselves to turn into a pupa. Once most of the cutworms in a field are about an inch long or more, they will be pupating soon. The economic gains from an insecticide application would be less when they are already in these more advanced stages. So consider stage of the cutworms when making decisions regarding cutworm management.
Figure 1. Redbacked cutworm larva and pupae.
Adult Grasshoppers Seen in the Spring
There have been reports of grasshopper activity, although mainly low levels of newly hatched grasshoppers so far. But occasionally you will see a larger or adult grasshoppers this time of year. Should this be of concern? The short answer is that any grasshopper that’s large by early-June is not a pest species.
None of the species of larger grasshoppers you see early in the spring cause economic damage, so they should not be controlled or used as indicators of later season grasshopper problems. Although there are numerous species of grasshoppers in Manitoba, there are 4 species that, given the right conditions, can cause significant damage to crops. These are the migratory grasshopper (Melanoplus sanguinipes), twostriped grasshopper (Melanoplus bivittatus), clearwinged grasshopper (Camnula pellucida), and Packard grasshopper (Melanoplus packardii). The species of grasshoppers that are considered crop pests all overwinter as eggs.
Regarding the early season appearance of large grasshoppers, there are a few species that overwinter as nymphs and emerge early in the season. So with these species you see large grasshoppers early. Not to worry though, none of these are pest species. All our pest species overwinter as eggs, and don’t start emerging usually until late-May.
The brown-spotted grasshopper (Psoloessa delicatula) is one of the species that overwinters as nymphs (it overwinters as 4th or 5th instar nymphs). It is an important food item for the survival of the nestlings of grassland songbirds. The specklewinged grasshopper (Arphia conspersa) overwinters as 5th instar nymphs, so this is another grasshopper that may be seen in a more advanced stage early in the season.
There is also a species called the club-horned grasshopper (Aeropedellus clavatus) that can confuse those keeping an eye on the grasshopper hatch. The club-horned grasshopper overwinters as an egg, but hatches more than a month earlier than pest species. The pasture grasshopper (Melanoplus confusus) is also a species that hatches very early, hatching in early spring. Any grasshopper you see flying by early- June is not a threat and has no relevance to the ones that are a threat.
Regarding the early season appearance of large grasshoppers, there are a few species that overwinter as nymphs and emerge early in the season. So with these species you see large grasshoppers early. Not to worry though, none of these are pest species. All our pest species overwinter as eggs, and don’t start emerging usually until late-May.
The brown-spotted grasshopper (Psoloessa delicatula) is one of the species that overwinters as nymphs (it overwinters as 4th or 5th instar nymphs). It is an important food item for the survival of the nestlings of grassland songbirds. The specklewinged grasshopper (Arphia conspersa) overwinters as 5th instar nymphs, so this is another grasshopper that may be seen in a more advanced stage early in the season.
There is also a species called the club-horned grasshopper (Aeropedellus clavatus) that can confuse those keeping an eye on the grasshopper hatch. The club-horned grasshopper overwinters as an egg, but hatches more than a month earlier than pest species. The pasture grasshopper (Melanoplus confusus) is also a species that hatches very early, hatching in early spring. Any grasshopper you see flying by early- June is not a threat and has no relevance to the ones that are a threat.
Insect Monitoring Programs
Bertha Armyworm: Trap counts are just starting to come in. All counts reported have been low, with the highest count so far being 13 from a trap near Morris.
Diamondback Moth: Monitoring adults of diamondback moth with pheromone baited traps has been underway since the beginning of May. Overall counts have generally been low. Highest counts have been in the Central region and Interlake. Lowest counts have been in the Southwest, where the highest cumulative count so far has been 2. Table 1 summarizes the highest cumulative counts in Manitoba.
Table 1. Highest cumulative trap counts for diamondback moth adults over the trapping period April 29 to June 12, 2018.
| Location | Count |
|---|---|
| Oak Bluff | 101 |
| Morris | 80 |
| Winnipeg Beach | 68 |
| Warren | 62 |
| Bowsman | 33 |
| Balmoral | 31 |
A more detailed update of diamondback moth counts in Manitoba is available on the Manitoba Agriculture website at: http://www.gov.mb.ca/agriculture/crops/insects/diamondback-moth-forecast.html
Insect Identification Quiz
While searching in the soil and under debris for cutworms you disturb this larva that quickly runs along the ground for cover. What is this? Hint - recall in last week's quiz we looked at a ground beetle. There is a connection between this weeks quiz and last weeks's.
Answer: This is a ground beetle larva. They are predators. Note the big mandibles on the larva in the photo. There are about 350 species of ground beetles in Manitoba, and appearance may vary with the species. Some are much lighter than this.
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Compiled by:
John Gavloski, Entomologist Holly Derksen, Field Crop Pathologist
Manitoba Agriculture Manitoba Agriculture
Phone: (204) 750-0594 Phone: (204) 750-4248
To report observations on insects or plant pathogens that may be of interest or importance to farmers and agronomists in Manitoba, please send messages to the above contacts.
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