Manitoba Insect & Disease Update

Issue 3:  June 7, 2017

 
Summary
 
Pathology: Wheat Streak Mosaic Virus detected in the Wawanesa area. FHB Risk Maps available starting today. 
 
Insects: Flea beetles in canola, and cutworms continue to be the main insects of concern. Hatch of the potential pest species of grasshoppers has started, but so far levels are quite low.
 
Wheat Streak Mosaic Virus
 
There was a report of spring wheat suspected to be infected with Wheat Streak Mosaic Virus (WSMV) near Wawanesa. The disease is showing up in patches in the field and dead winter wheat is evident in the same areas. The field was winter wheat in 2015 and soybeans in 2016. It is suspected that a flush of winter wheat volunteers emerged post-harvest last year. The key management technique for WSMV is breaking the green bridge. Ideally this mean making sure winter wheat does not emerge in the fall until after nearby spring wheat has ripened/been desiccated. This virus is spread by wheat curl mite that travels to nearby fields on wind currents. If you have a spring wheat field that is bordering a winter wheat field, be sure to check for WSMV.
 
Figure 1. Wheat Streak Mosaic Virus on spring wheat (photo courtesy Lionel Kaskiw)
 
Fusarium Head Blight Risk Maps
 
Winter wheat in the province is nearing or at the heading stage. The first Fusarium Head Blight (FHB) risk map for the season was produced today and is posted on the FHB Risk Map site. Maps will be posted on a daily basis (Monday to Friday) until the end of the spring wheat flowering period. Wheat is most susceptible to FHB infection during anthesis. The maps should be used as a guide as local conditions can vary and infection depends on the crop being at the susceptible stage.
 
Flea Beetles
 

There continues to be some foliar insecticide applications for flea beetles.

A reminder that once canola gets into the 3 to 4 leaf stage it can usually compensate well for flea beetle feeding.

Flea beetles will feed more aggressively on hot, calm days.

If it has been greater than 3 weeks since seeding, and your canola is still not at the 3 to 4 leaf stage, do scout canola fields for flea beetle feeding. The nominal threshold suggested is if greater than about 25% of the plant tissue is damaged, and flea beetles are still actively feeding, and the crop is not yet at the 3 to 4 leaf stage, then there is reasonable odds an insecticide application would be economical.

Remember that if using a pyrethroid insecticide for flea beetle control that this group of chemistry has temperature restriction - check the labels or the Guide to Crop Protection.

 

Cutworms

There continues to be some localized insecticide applications for cutworms.

Dingy cutworms will often remove plant tissue, but do less clipping than some other species. They feed at night, and are hidden during the day. So if you are seeing defoliation but no insect activity, dig around affected plants to see if dingy cutworms are the cause.

Dingy cutworms are turning to pupae, a non-feeding stage, in some fields.

 

Grasshoppers

There are 3 main grasshopper species in Manitoba that potentially can be pests, and many others that never get to pest levels.

Hatch has started for the potential pest species, but numbers are currently low.

Any grasshopper that is large this time of year is not a potential pest species. Those large grasshoppers you may see while hiking this time of year, that click as they fly away, are not potential pest species.

A good general guideline is that about 10 days after the lilacs are flowering, the egg hatch for our pest species of grasshoppers has begun. In a study in Montana, a comparison was made between the phenological phase dates of purple common lilac (Syringa vulgaris L.) and Zabeli honeysuckle, and 6 common species of rangeland grasshopper. Results indicated that spring hatch (75% of first instar) occurred about 10 days after the begin bloom phase of purple common lilac. Peak occurrence of grasshoppers for instar 2 coincided, on average, with the end bloom phase of Zabeli honeysuckle, whereas peak instar 3 occurred about 10 days later. About 75% adult stage occurred about 14 days after red berries first appeared on Zabeli honeysuckle (Journal of Range Management. 1991: 583-587). So when the grasshoppers are smaller and harder to scout and stage, some botanical observations may help.

 
Insect Monitoring Programs
 
Bertha Armyworm: A reminder for those setting up traps to monitor adults of bertha armyworm that traps should be set up the week of June 5 to 10.
 
Diamondback Moth: Diamondback moth monitoring with the pheromone baited traps has been underway since the beginning of May. Some moths have been caught in the traps, but levels so far have been low. Out of 86 traps, 34 still have cumulative counts of 0 as of June 6. Table 1 below summarizes the highest cumulative counts in Manitoba.
 
Table 1. Highest cumulative trap counts for diamondback moth adults over the trapping period May 1 to June 6, 2017.
 
Location Count
Minitonas 19
Ste. Agathe 17
Lockport 16
Ste. Elizabeth 15
Winkler 14
Altona 13
 
A more detailed update of diamondback moth counts in Manitoba is available in the Manitoba Agriculture website at: https://www.gov.mb.ca/agriculture/crops/insects/diamondback-moth-forecast.html
 
Insect Identification Quiz
 
The small insects in the photo below were found on soybeans. They jumped when disturbed. What are they and should you be concerned?
                             
                              Photo courtesy Jeremy Remple - South East Seeds
 
Answer: These are called springtails. This particular species belongs to a family of springtails known as globular springtails (Sminthuridae). There is a second family of springtails called elongate-bodied springtails that are similar but more elongate.
Springtails have a valuable role as decomposers, feeding on dead plant material and are not usually a pest.  Some species may do light feed on seedlings, but are not likely to be economical.
People sometimes confuse springtails with aphids; but springtails don’t have tailpipes (cornicles) like aphids. And although they are small and jump, they are not flea beetles.
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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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