Manitoba Insect and Disease Update: June 25, 2013

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

Cutworms 
Cutworms continue to be an issue in some fields, although in many fields a higher proportion of the cutworms are now in their later stages as larvae and starting to change to pupae. So if assessing cutworm damage and populations consider the size of the cutworms and whether they are turning to pupae. The species of cutworms being found vary. The photo below shows a redbacked cutworm (centre) and 2 pupae of redbacked cutworms.  

 

Flea Beetles
Over the past week, flea beetles continued to be a problem on canola in many areas. Populations of flea beetles now seem to be dropping, however, and most fields of canola are now getting to the stage where they can compensate well for flea beetle feeding. 
 
Grasshoppers
Grasshopper emergence continues, and there are some areas where higher populations are being noted and some insecticides are being applied. The grasshoppers are still in their early nymph stages and it will be awhile before they can fly. So now is a good time to assess fields, and particularly the edges of fields, to see what the populations may be like. Areas that had lush vegetation late last summer would be favoured egg laying sites. So in many regions this will be areas like field edges, or possibly alfalfa fields or pastures. In most instances, higher populations will still be concentrated around the field edges. But there are a couple of instances already this year where whole fields have been treated with insecticides because of high populations of young grasshoppers, A field of soybeans near Starbuck was sprayed for grasshoppers, but in this case the field was perennial ryegrass last year, which may explain why higher levels were throughout the field and not concentrated along the field edge. Some alfalfa near Gladstone was reseeded because of grasshopper feeding. There are also a few instances where field edges have been treated.
 
Note when scouting for grasshoppers in the field edges that there are other non-economical insects that may be present in these areas that will hop when disturbed. So look carefully so proper identifications are made.
Some non-economical species of leafhoppers may be present in the ditches this time of year. These are not species that can spread aster yellows, and are not a threat to crops. Be careful not to confuse them with grasshoppers. The photo below is of a small grasshopper (left) and one of the non-economical species of leafhoppers (right).
 
 
 
 
Some have also been enquiring what grasshopper eggs look like. Below is a photo of grasshopper eggs.
 

Aster Leafhoppers
Aster leafhoppers are one of the two species of leafhoppers that can be a concern to field crops in Manitoba, but so far there are very few aster leafhoppers that have been found. Levels were also reported as low in last weeks North Dakota State University Crop and Pest Report. So the risk of aster yellow being economical to field crops in Manitoba in 2013 remains low. Those growing carrots and other sensitive vegetable crops should be monitoring for aster leafhoppers in and around their crops.  
 

Surveys and Forecasts

Diamondback moth

Trap counts for adult moths are highest in the Eastern part of Manitoba. Highest trap counts are:
 
Location Count from previous week Total Count
Steinbach 578
Beausejour 153 317
Oldenburg 37 306
Dencross 141 195
Morris 72 178
River Hills 48 163
Springwell 144
 
All of the counts in the table above are from traps in Eastern Manitoba.

The highest count from a trap in Central Manitoba is 73 from a trap near Carman.
The highest counts from traps in Western Manitoba are 
  The Pas - 44
  Durban - 31
  Miniota - 12
 
The high adult counts in some of the traps indicate that looking for larvae of diamondback moth should be considered a priority when scouting canola fields, particularly in Eastern Manitoba, but are not an indication that higher levels of larvae will occur. No high levels of larvae have yet been reported. High adult numbers in traps do not always result in high levels of larvae. Natural enemies, weather, or a combination of these factors can keep levels of larvae low.
 
A table showing the trap counts from the diamondback moth monitoring program can be found on the MAFRI website at: https://www.gov.mb.ca/agriculture/crops/seasonal-reports/pubs/diamondback-report-2013.pdf
 
 Traps for diamondback moth can be removed after counts are taken for this week.

Bertha armyworm

Trap counts for adult moths of bertha armyworm have been low so far, although it is still early in the monitoring period. Highest counts so far are:
  Carberry - 38
  Beausejour - 23
  Gladstone - 22
These cumulative counts are still well within the low risk zone, and it is too early to say what the risk will be for this year, as we may still be early in emergence of the moths.
A table showing data from the bertha armyworm monitoring program can be viewed on the MAFRI website at:
 

Fusarium Risk Maps

As winter wheat across the province is approaching the early flower stage, the Fusarium Head Blight risk maps have returned for the 2013 season. These maps will be updated daily until the end of the flowering period for spring wheat. The risk of FHB is influenced by the conditions over the last 7 days and these maps are created based on the temperature and precipitation data from the last week. Temperatures across most of the province have been in the ideal range for FHB infection and the recent rainfall over western Manitoba has increased the risk in that area to the ‘extreme’ level. These maps are meant as a guide, please consider localized weather events in your area as well as the stage of your crop when making management decisions such as a fungicide application. The maps can be accessed at the following link: https://www.gov.mb.ca/agriculture/crops/seasonal-reports/pubs/fusarium-report-2013.pdf