Manitoba Insect and Disease Update: July 25, 2014

 Compiled by:
  • John Gavloski, Entomologist
    Manitoba Agriculture, Food and Rural Development
    Phone: (204) 745-5668
    Fax: (204) 745-5690.
  • Vikram Bisht, Plant Pathologist
    Manitoba Agriculture, Food and Rural Development
    Phone: (204) 745-0260
    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.
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Summary
Pathology: Goss’s wilt and leaf blight disease are showing up in corn. Ergot disease infection is now showing up in fall rye and grasses. Blackleg infection on lower stems/roots on canola is showing up. Downy mildew on sunflowers is reported.
Entomology: Grasshoppers are starting to mature to the adult stage. How much they move into crops from surrounding vegetation may partially depend on how lush the roadside vegetation remains relative to the crop. Still no soybean aphids found in Manitoba in 2014.
 
Corn
Goss’s wilt and leaf blight disease has been found in Southeastern Manitoba. The leaf blight stage development indicates that the disease initiated about 2-3 weeks ago. Rains accompanied with strong winds can carry the bacteria in the mist over long distances. This field appears to be near last year’s corn field, which may have had infected crop residue. It is also possible that infected corn residue got transported by spring water run overland. Burial of infected crop residue and GW tolerant varieties are the only economical management tools. Fungicide will not work on a bacterial disease.


Fig.1. Corn leaf with well developed leaf blight of Goss’s Wilt disease. Photo: Vikram Bisht, MAFRD
 
Canola
Pathogens: In many areas the canola crop is near the end of flowering. Fewer fields are at the early flowering stage. With the warm and moist canopy of densely growing crops there may still be some white mold inoculum within a crop and coming from outside. Flowering canola needs to be protected against white mold disease. Blackleg disease and what appears to be brown girdling root rot is being reported from a few fields (Fig 2 & 3).  The diagnosis is being confirmed in the lab. The incidence appears to be high in tight canola rotations. Many of the plants also are showing root maggot damage. Lodging appears high in such fields.
 

Fig. 2 & 3. Girldling on canola root, accompanied often with blackleg pycnidia in the lesion. 2014. Photo: Vikram Bisht, MAFRD.
 
Bertha armyworm: A network of pheromone-baited traps has been monitoring the relative abundance of moths of bertha armyworms. What the traps catch are specifically the male moths. Although the traps can not predict individual fields that are at higher risk (it would be wrong to use the traps in this regard) the combined results can be used to predict regions that may be at higher risk. Consistently getting cumulative counts under 300 moths over the trapping period for traps in a region indicates a lower risk. So far the risk of bertha armyworm is low in Manitoba, as shown by the table and map below.
 
 Highest cumulative counts of bertha armyworm in pheromone-baited traps in Manitoba in 2014
 0-300 = Low risk     300-900= Uncertain risk     900-1,200= Moderate risk  1,200+= High risk
Nearest Town Region Cumulative Count
Altamont Pembina 482
Tourond Eastman 289
Roseland Southwest 233
Ridgeville Eastman 231
Emerson Red River 198
  
 
Consider the value of Pollinators in Canola: Canola can yield quite well without pollinators. But research has shown that yields can be improved when pollinators are active in canola fields. Thus insecticides should only be used in flowering canola when crop feeding insects are above economic threshold levels. Otherwise you could be inadvertently resulting in a decrease in yield while not significantly reducing crop damage by crop feeding insects. So scout canola, and make wise decisions based on the level of potentially damaging insects that are present. Tank mixing an insecticide with a sclerotinia spray because the insecticide is cheap and the sprayers will be in the field anyway can end up reducing the yield potential of the crop if decisions are not made wisely.
 
Fall Rye
Ergot sclerotial bodies have been reported on fall rye and in grasses. Due to frequent rains, which may have match the flowering period, there could be a fair amount of ergot infection. It is important to scout susceptible cereal crops.
 

Fig.4 & 5. Ergot sclerotia on fall rye (Photo courtesy: TaoWang, Cargill) and grass (Photo: Vikram Bisht, MAFRD)
 
Sunflower
Downy mildew has been reported in Southwestern Manitoba on non-DM resistant varieties.
 
Wheat
Fusarium head blight: The Fusarium head blight risk forecast for the whole province has been low on July 21 but changed to moderate in the southern half of the province on July 22 due to overnight rains.  A lot of spring wheat fields have finished flowering and are in the milk stage.
 

The Fusarium Head Blight Risk Forecast webpage is available at https://www.gov.mb.ca/agriculture/crops/fhb/index.html
 
Wheat Midge: Emergence of wheat midge should now be 50% to 90% complete in many areas of southern Manitoba. Note the synchrony of the emergence of Macroglenes penetrans, the most important parasitoid of wheat midge, with that of wheat midge. Macroglenes penetrans wasps will also be emerging and looking for eggs of wheat midge to lay their eggs into.