Canola: slow emergence and flea beetles

Growing degree days for everywhere outside southern Alberta are way lower than normal. The maps here show the growing degree days (GDD) for this year (top map) versus the normal (bottom) levels for April 1 to May 25. Click on them to enlarge. Prince Albert, Sask., for example was at 72 to 92 GDD as of May 25. Normal is 122 to 144. Morden, Man., was at 113 to 133 when normal is 214 to 236.

These maps are based on a GDD Base 5 reading. That means it doesn't start counting until average temperatures reach 5°C for the day. To calculate a GDD, add the high and the low and divide by two to get an average.  For example, if the high is 15°C and the low is 1°C, add them to get 16 then divide by 2 to get 8 GDD for that day. Thanks to Trevor Hadwen, agroclimate specialist with Agriculture and Agri-Food Canada, for providing the maps and explaining them. See more maps at  AAFC's Drought Watch page.

This confirms what we already know. It has been a cool spring. And that means crops emerge slowly. The Canola Council of Canada's Canola Watch No.4, issued this week, says:

"The number of days to 50% germination is a useful benchmark as the first half of plants to emerge usually accounts for the majority of crop yield. Research has shown much lower and slower canola germination at low temperatures. Soil temperatures above 5°C have little effect on the time to 50% germination, however the number of days to 50% germination increases dramatically at temperatures below 4°C (with germination taking as long as 9 days at 3°C or over 12 days at 2°C)."

Flea beetle protection running out

Canola Watch also warned farmers to watch for flea beetles. With such slow emergence, seed treatments to protect young canola plants from flea beetles have used up a lot of their usefulness before the plants break through the soil surface. The CCC report says:

"Entomologists warn that flea beetle pressure will intensify in the coming days, especially if the warm temperatures predicted arrive. Seed treatment protection starts when the seeds are first put into the soil (not when the plant emerges). As a result, protection may be tapering off in some of the earliest seeded fields. As canola emerges in the coming days, be prepared for significant flea beetle activity. Scout thoroughly and often as canola is most vulnerable to flea beetle feeding at the cotyledon to two-leaf stage.

"If flea beetles are present, check affected fields daily as problems can escalate quickly, especially if canola plants are growing slowly or are under stress. Be prepared in case additional control measures are required. The economic threshold for flea beetle control is when 25 per cent or more of the cotyledons are damaged. If 25 per cent defoliation is reached, foliar insecticide application may be needed if plants are growing slowly or are under stress, and if beetle feeding activity is increasing.

"Evidence of feeding does not automatically mean spraying is warranted. Unwarranted spraying can cause harm to beneficial insects and can also contribute to the development of insecticide resistance. With current seed treatments, flea beetles must feed on leaf material and ingest the insecticide for control so some feeding damage is normal. Flea beetles make their way into canola crops from the edges of fields. By catching a problem with flea beetles early, producers can often spray the perimeter of their fields and stop the infestation before it becomes widespread.  Growers are advised to be particularly careful in areas that saw high flea beetle populations around swathing time last fall as this can be used as an indicator for spring pressure. These areas include: Lethbridge, Alberta; Vauxhall, Alberta; St. Albert, Alberta; parts of southern Saskatchewan; and south central Manitoba.

The report also provided this links for more information on flea beetles:
http://www.gov.mb.ca/agriculture/crops/insects/fad09s00.html
http://www.gov.mb.ca/agriculture/crops/insects/fad52s00.html
http://www.agriculture.gov.sk.ca/Default.aspx?DN=3eb86279-cec4-4718-b3a6-9b7e71736bf2
http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/faq8031