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Manitoba Agriculture, Food and Rural Initiatives

Manitoba Insect Update

June 10, 2008                   

Compiled by: John Gavloski, Entomologist, Manitoba Agriculture, Food and Rural Initiatives,
Crops Knowledge Centre, Phone: 204-745-5668; Fax: 204-745-5690

To report observations of insect activity or control that may be of interest or importance to others in Manitoba, please send messages to the above contact addresses.

To be placed on an e-mail list to be notified when new Manitoba Insect Updates are posted, please contact John Gavloski at the address or numbers listed above.


Summary

Cutworms continue to be a problem in some fields, affecting a variety of crops. Flea beetles have become a concern in canola in some fields. In addition to the insecticide in the canola seed treatments, foliar insecticides have been applied to control flea beetles in some fields. In many fields it is just the edges that have been treated. Grasshopper nymphs, for the species that potentially can be pests, are starting to emerge.

Recent Insect Concerns and Observations

Cutworms: More reports have come in regarding cutworm control being needed. The central part of the province seems to have the highest cutworm activity, with sunflowers being one of the crops most heavily affected.

Effect of rains? One of the questions some are now asking is what effect all this rain will have on cutworms. There have been a few studies looking at the effect of rainfall and excess moisture on cutworms. A study of the effect of wet soils on larvae of cutworms in the genus Euxoa (which includes redbacked and army cutworms) found that “wet soil conditions during the larval stage promote fungus diseases among cutworms and also forces them to feed at the soil surface where they are subject to the attack of parasites and predators” (The Canadian Entomologist. 1971. pg: 1217-1235.). Cutworms generally don’t do as well in wet soils, however what effect rains this late in the larval stages will have on cutworm populations is not uncertain.  

Stage of Growth. When deciding whether cutworm control would be economical, consider the stage of the cutworms. Some species that overwinter as larvae, such as dingy or army cutworms, may be fully grown larvae or starting to pupate already. If this is the case, control is not likely to prevent enough yield loss to make it economical. Species that overwinter as eggs, such as redbacked cutworms, may still be small enough that if there are high enough levels in the field, control would prevent enough yield loss to be economical. 

Flea beetles: Canola growers are dealing with multiple stresses on their canola crop this year. The frost on May 27th reduced plant stands in some fields. These reduced stands will be even more vulnerable to flea beetles and need to be watched carefully. Foliar insecticides have been applied to many fields, mainly around the edges in a many cases, to control flea beetles. There is still a fairly even mix of striped and crucifer flea beetles in the population overall. Often striped flea beetles dominate early in the season, and the crucifer flea beetle is the dominant species by the point. The overall cooler spring may have delayed the emergence of crucifer flea beetles somewhat.  

Note that flea beetles must begin to feed on a canola plant to be killed by the seed treatments. So because there is some pits by flea beetles on the cotyledons or leaves does not mean the seed treatment is not working. Unless at least 50% of the leaf and cotyledon material on average is damaged, the plants will still develop with little yield loss. However, because flea beetles can damage plants quickly, the suggested economic threshold is to apply a foliar insecticide if 25% or more of the plant material is damaged and flea beetles will still be actively feeding. In the photo below, if most of the plants looked like this it would not be advised to apply a foliar spray; the plants will compensate for this amount of feeding and do fine without the added expense of an insecticide application, providing the damage does not increase much more.

Striped flea beetles and feeding pits
Striped flea beetles and feeding pits.

Grasshoppers: Grasshopper nymphs, for our potential pest species, are starting to emerge. When they first emerge they are quite small, about the size of a wheat kernel. At this stage they are very susceptible to adverse conditions, such as heavy rains. Seeing as many of the eggs for our pest species get laid in locations that have green vegetation late in the season, such as field edge and roadside ditches, the heavy rains last Friday may potentially harm some of the early hatch. Also note, we are still early in the hatch of the potential pest species of grasshoppers.

I have heard of some wondering about tank mixing an insecticide with their herbicide to control grasshoppers at the same time. The timing for this is not likely to work in your favour. Unless there are some older nymph stages present, it is likely that the hatch is not far enough along that this will provide satisfactory results; more will be hatching out. We will are currently surveying the grasshopper populations and determining abundance and stage. Currently most of the grasshopper species that can potentially be pests are still in their first growth stages. Don’t be fooled by the odd grasshopper that already looks fully grown. These are not species that potentially could be crop pests. Any species with wings fully developed this early is not one of our potential pest species.  

 

Surveys and Forecasts

Diamondback moth: Counts of adult diamondback moth have remained very low across Manitoba. The highest counts so far are from the eastern part of Manitoba; 11 and 7 moths caught in traps northwest of Steinbach. Thus the risk from diamondback moth is currently low.  Data from the diamondback moth trapping program and an interpretation of the data are available at: https://www.gov.mb.ca/agriculture/crops/insects/db/index.html

Bertha Armyworm: A reminder that traps for monitoring adults of bertha armyworm can now be set up. The protocol for setting up traps to collect bertha armyworm is on the MAFRI website at: https://www.gov.mb.ca/agriculture/crops/insects/fad59s00.html

Wireworm Survey: Thanks for all the wireworm samples that have been collected and sent in so far. This will provide valuable data. A reminder that if you find wireworms, you can place them in a container (pill bottle, film canister, etc.) with a bit soil and send them to: Dr. Bob Vernon, Pacific Agri-Food Research Centre, P.O. Box 1000 – 6947 #7 Highway, Agassiz, B.C., V0M 1A0. Remember to include some details regarding the location the sample is from, the date it was collected, and the crop that was being grown in the field. Samples can also be dropped off or sent to me at the MAFRI office in Carman.

Insect Identification Quiz:

Question: You are out walking a field edge and notice a lot of insects jumping around. Does this mean you have a grasshopper problem?

Answer: Not necessarily. Grasshoppers are not the only insects that will be hopping in these field edge areas. Often these areas are a great habitat for certain species of leafhoppers, which are not necessarily pest species (potato leafhopper and aster leafhopper are the only leafhoppers of concern in field crops in Manitoba). If you are uncertain what it is doing all the hopping as you walk the grassy field edges or ditches, take a sweep net and catch a few and have a look. In the photo below, the insect on the left is a juvenile grasshopper, the insect on the right is a leafhopper; one of the many species that are not crop pests.

 Juvenile Grasshopper (left), Leafhopper (right)
 Juvenile Grasshopper (left), Leafhopper (right)