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Manitoba Insect & Disease Update

Issue 10:  July 20, 2016

 
Summary
 
Insects: Pea aphid levels are still a concern in some pea fields, although many fields will be getting to the stage where management would no longer be economical. Aphid levels have dropped in many cereal fields where previously levels had been increasing. High levels of natural enemies have been noted in some of these fields, and some intense rains may have also contributed.
 
Plant Pathogens: Some infections of blackleg in canola and Fusarium head blight in cereals have been reported.
 
Disease update
 
Cereals: Low levels of Fusarium head blight (FHB) was reported in cereal crops. FHB was reported in oats in MCVET trials where no fungicides were used. Oats are less susceptible to FHB compared to wheat and barley. However, lack of fungicide use and prevalence of favourable weather conditions may have led to FHB development in oats.
 
Fig 1. Fusarium head blight in oats
 
A few cases of loose smut in barley were also reported.
 
Canola: Several cases of blackleg in canola were also reported.
 
Corn: Two positive identifications of Goss’s wilt in corn were made. The positive identifications were made based on immunostrips and/or polymerase chain reaction (PCR) assays.
For more information on Goss’s wilt, https://www.gov.mb.ca/agriculture/crops/plant-diseases/goss-wilt.html
 
Aphids in Peas
 
A reminder that research has found that should aphids in peas exceed the economic threshold, yield was enhanced most when a single application was made as soon as 50% of the crop had young pods. Control at the early pod stage provides protection through the pod formation and elongation stages, which are very sensitive to aphid damage.
 
Most of the damage that aphids do to peas is to the pods before they start to fill. If you think that most of the pods have already started to fill, spraying would be too late and would not be economical.
  
European Corn Borer
 
Egg masses of European corn corer are starting to be noted in some fields of corn. So far there are no reports of high levels, but now is the time to be checking fields for the egg masses. Figure 2 below shows two egg mass of European corn borer, the upper egg mass would be younger, whereas the bottom egg mass is a bit older and closer to hatching. Note the dark head capsules of the larvae are visible in the eggs just before they hatch.  

  Figure 2. Egg masses of European corn borer.
 
Canola fields needed for Lygus bug study
 
We are looking for canola fields with high levels of Lygus bugs to collect field data to help refine the economic threshold for Lygus bugs in canola. This study aims to test in commercial canola fields the thresholds derived from studies with cages and in plots. The study would be carried out in fields that need to be sprayed for Lygus bugs. What would be required is:
  • Check strips (areas where insecticide would not be applied) would be marked in the field with flags. These would be 30 m wide and 100 m long. Ideally 3 or 4 check strips would be established in a field, but a minimum of two. 
  • Ten sweep net samples will be taken in each strip (check and adjacent sprayed area) before and after insecticide application.
  • Yield data from the combine yield monitor would be collected in unsprayed check strips and adjacent sprayed areas.

If the fields are within 2 hours of Winnipeg, someone will come to sweep the fields and mark the check strips.

To have a field with high levels of Lygus bugs become part of the study, please contact:   Dr. Tharshi Nagalingam; phone 204-869-1215,  Email: kstlk2001@yahoo.com

This study is being done Alberta, Saskatchewan and Manitoba. Hopefully this will provide good data for assessing the impact of Lygus bugs on modern canola varieties. 

Thanks for helping us develop better insect pest recommendations.

 
Emergence of wheat Midge
 
The following map shows the percent of wheat midge that are expected to have emerged, based on models using degree days to calculate percent emergence. In some areas of Central and Southwest Manitoba, greater than 90% of the wheat midge are expected to have emerged (red on the map). In many areas of Manitoba about 50 to 90% of wheat midge are expected to have emerged.
                         
A reminder that wheat that has already produced anthers is no longer susceptible to feeding by wheat midge. Even if adults are still active in these more advanced fields, the larvae will not feed on the grain.
Note: Emergence may be 2–8 days later than expected at sites receiving more than 145 mm rain in May and June. 
 
 
 Insect Monitoring Programs 
  
Bertha armyworm: So far cumulative trap counts for bertha armyworm are mainly in the low risk range (less than 300). Out of 83 traps, 74 are currently in the low risk range, and 9 are in the uncertain risk range (300 to 900 moths). No traps are in the moderate risk (900 - 1,200 moths) or high risk range (1,200 plus moths). Most of the counts in the uncertain risk range are in the western regions of Manitoba. The table below shows the highest counts, all of which are in the uncertain risk category, as of July 19:
Location Count
Durban (NW) 885
Benito (NW) 569
Lena (C) 510
Kenville (NW) 462
Minto  (SW) 447, 361
Roblin (NW) 408
Tummel (NW) 388
Dunrea (C) 323
 
Weekly counts in most traps have now declined.
 
For uncertain risk the precaution we use is that economic levels of larvae may not be widespread, but fields that were particularly attractive to egg-laying females could have higher levels. Check your fields.
Note that there are times when we get to these levels, and no economic levels of larvae occur.
Also, higher levels of larvae, should they occur, may or may not be in the fields that the traps are in.
 
Compiled by: 
 
John Gavloski, Entomologist                    Pratisara Bajracharya, Field Crop Pathologist        
Manitoba Agriculture                                    Manitoba Agriculture
Phone: (204) 745-5668                               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.
 
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.
 

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