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Manitoba Agriculture, Food and Rural Initiatives

Manitoba Insect and Disease Update

June 13, 2011                   

Compiled by: John Gavloski, Entomologist, Manitoba Agriculture, Food and Rural Initiatives
Phone: (204) 745-5668; Fax: (204) 745-5690
Holly Derksen, Plant Pathologist, Manitoba Agriculture, Food and Rural Initiatives
Phone: (204) 750-4248; Fax: (204) 745-5690

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 contact address.

To be placed on an E-mail list so you will be notified immediately when new Manitoba Insect and Disease Updates are posted, please contact John Gavloski at the address or numbers listed above.


 

Recent Insect and Plant Pathogen Activity

Canola

Flea beetles: There have been some reports of canola seedlings sustaining heavy flea beetle feeding and requiring foliar insecticide treatments. Even if Helix or Prosper seed treatments have been used, some minor feeding to leaves and cotyledons is normal, as the flea beetles needed to ingest the seed treatment to be killed. Such feeding is normally not heavy enough that further control would be needed. In years when germination and early development of the canola is delayed, seed treatments can lose their effectiveness before the canola reaches the 3 to 4 leaf stage, where it can better tolerate flea beetle feeding. When doing early-season scouting in canola, consider the level of feeding that is occurring and the stage of the plants. If seed treatments are losing their effectiveness, heavy feeding can occur if flea beetle populations are large, particularly on warm, calm days.

Some have asked whether we get flushes of flea beetles. For the species of flea beetles that feed on canola, there is 1 generation per year, although adult beetles appear twice. The beetles you see now are the ones that overwintered. They feed in the spring, lay eggs and then die. When the eggs hatch the larvae feed on the roots in early and mid-summer. This feeding is believed to not be economically significant. Then in late-summer adults will appear again, which will overwinter and emerge to feed on crucifer seedlings the following spring. So we don't really have flushes (as in multiple generations) of flea beetles, although the populations of different species peak at different times.

Cutworms: Cutworm damage to canola has occurred in some areas. Heavier feeding has been reported from the Swan River and Neepawa area. As we get into mid-June it is important to consider the size of the cutworms and how close they would be to pupating when making control decisions. The photo below shows a larva (centre) and 2 pupae of the redbacked cutworm.

Redbacked Cutworm

Forage Grasses

Brown Blight: Perennial ryegrass near Carman showed symptoms of infection by Drechslera sp. This fungus was identified on the stubble as well as the live leaf tissue. Symptoms of this disease begin as small circular or oval lesions on the leaves and can expand to larger lesions which may result in leaf dieback. This disease is normally observed in early spring or late fall as it thrives in cool, wet, cloudy conditions.

 

 

Surveys and Forecasts

Diamondback moth monitoring: Diamondback moth (Plutella xylostella) was first reported this year in a trap near Carman during the week of May 2-8, then more generally during the week of May 9-15th. There was an increase in the number of moths caught in some of the traps in the eastern region over the past week. The Eastern and Central areas of Manitoba have the highest trap catches so far.

Table 2. Highest cumulative trap counts for diamondback moth in Manitoba as of June 13, 2011

Location

Cumulative
Trap count

Sewell

68

Beausejour

67

Carman

33

Thalberg

28

St. Joseph

28

The full data set for adult counts of diamondback moth can be viewed at: https://www.gov.mb.ca/agriculture/crops/insects/db/pdf/2011diamondbackdata.pdf

The program for monitoring adults of diamondback moth was originally scheduled to end after the week of June 6th to 12th. But there is good reason to want to keep at least a subset of traps going. Counts in some of the traps in the eastern part of Manitoba have just started to rise. So I will add a few more weeks to the spreadsheet, and we can keep some traps going. Note that pheromone lures for the diamondback moth traps should be replaced after eight weeks of use. Some traps may be getting close to when the lures should be replaced. If you plan on keeping the diamondback moth traps up for a period that extends past 8 weeks, let me know and I will send replacement pheromone.

Bertha armyworm monitoring: For those setting up traps to monitor adult moths of bertha armyworm, the traps can be set up as soon as possible if they are not already up. Protocols for setting up the traps can be found at: https://www.gov.mb.ca/agriculture/crops/insects/fad59s00.html