Jun 14, 2017 by Lee Hart

Updates and reminders on weeds and insects

I didn’t actually hop through the plots at Farming Smarter’s first field day of the year near Lethbridge, AB last week, but I did walk fairly briskly because I knew their were donuts and a great lunch waiting at the end of the tour of nicely established research plots maintained by the southern Alberta applied research association.

There weren’t any press-stopping revelations in the research updates presented to about 50 farmers and agronomists who participated in the Plot Hop, but even from my perspective, I find there is always something interesting and probably more useful to producers, there are always some good reminders of crop production practices. Here are a few of the highlights.

GET ON THOSE WEEDS EARLY

Bob Blackshaw, weed specialist and research scientist with Ag Canada’s Lethbridge Research Station reminded folks to tackle weeds early and use chemicals with varying modes of action to reduce the risk of selecting weeds for herbicide resistance.

Ten years ago about 10 to 15 per cent of Western Canadian fields had some level of herbicide resistant weeds, whereas today it is

Researcher Bob Blackshaw talks about weeds

Researcher Bob Blackshaw talks about weeds

more like 60 per cent of fields have weeds with herbicide resistance. Most are weeds that have developed resistance to Group 1 and 2 chemistries. So far the only glyphosate resistant weed in Western Canada is kochia, but the operative words there are “so far”. Farmers need to be vigilant to reduce the risk of selecting more weeds that have developed glyphosate resistance.

Here are a few of Blackshaw’s key points:

  • When applying a glyphosate pre-seed treatment always tank mix with another herbicide (different mode of action) to increase the level of weed control.
  • Also look at using some of the “old” chemistries, which are new again — products such as Treflan, Edge and Avadex — that control weeds with different modes of action. Blackshaw says even if they only achieve 70 or 80 per cent weed control that still helps to reduce over all weed numbers. If needed you can follow with another treatment to get the other 20 to 30 per cent.
  • And herbicide resistance is a numbers game. If a field is polluted with weeds the risk of there being one, two or five plants with herbicide resistance increases. So try to keep weed numbers low.
  • Pay attention to crop staging information on herbicide labels and aim to apply products earlier rather than later. Blackshaw says if producers wait for every weed to emerge before applying, the damage to crop yield is already done. As a rule “10 days late can mean a 10 to 15 per cent yield loss.” So apply products when there is that first flush of weeds. That should give the crop a better chance to establish. If more weeds emerge later, the crop should be robust enough to close canopy choking out those later weeds.
  • And know your weeds. For proper herbicide selection, scout your fields and identify weeds. On that front, Ken Coles, Farming Smarter research manager says work is underway to develop a weed ID app for a Smart phone. Much like facial recognition software, farmers will be able to use the app to scan a weed and the app will tell you what weed it is.

DEALING WITH PULSE AND CANOLA BUGS

ON THE PEA FRONT….

Hector Carcamo, an Agriculture Canada pest management research scientist says don’t panic if adult pea leaf weevils are eating leaves on field peas and faba beans. The adults can take up to 20 per cent of foliage and the plants will recover. The real problem with this weevil is the larvae. They are busy underground eating  the root area. Those little buggers zero in on nitrogen fixing nodules on the roots.

Best line of defence for the larvae is to always apply a seed treatment to pulse crop seeds. Carcamo says seed treatments may not be 100 per cent effective —  there still may be some damage — but the chemistry also affects the egg-laying ability of the adults

Hector Carcamo, with Agriculture Canada trying to keep a step ahead of crop pests

Hector Carcamo, with Agriculture Canada trying to keep a step ahead of crop pests

meaning there will be fewer eggs and fewer larvae.

If producers haven’t applied a seed treatment, one possible approach is to apply nitrogen to the crop. Since the larvae are attacking the crop’s ability to produce nitrogen, supplemental nitrogen will keep the crop growing. Actually,  applying nitrogen does an end-run around the pest.

Carcamo says it seems counter productive to apply nitrogen to a crop that is often being grown because it produces its own nitrogen. But if you haven’t used a seed treatment and the pest is prevalent in the field apply nitrogen. He agrees applying nitrogen is sort of a “desperate measure”, but if you apply nitrogen, the crop doesn’t produce nitrogen-fixing nodules so the larvae have nothing to feed on. “Apply nitrogen and prayer for rain,” he says.

ON THE CANOLA FRONT…

The striped flea beetle has become the No. 1 insect pest for Western Canadian crops, says Carcamo. It used to be the crucifer flea beetle was the leading pest for canola and other crops, but now the evil stepsister of the species has become more dominant across the prairies.

Seeding crops early was one effective management tool to avoid the impact of the crucifer flea beetle, which was slower to appear in spring. However, the striped flea beetle is a much earlier pest, so it is hard to avoid with time of seeding.

Seed treatments and chemical treatments can be somewhat effective against the pest. But again, where the crucifer flea beetle produced one new generation per year, the striped flea beetle can produce up to four generations. Repeat treatments of insecticide can help control it, but those treatments also destroy all the beneficial insects —  it can be a poor trade off.

Carcamo says research really hasn’t established a solid treatment threshold for the pest. The best recommendation is  25 per cent of leaf damage as a treatment threshold. He notes, however, Montana researchers have reduced the threshold to 15 per cent. Damage at the plant’s cotyledon stage is the most critical.

Since there are no effective biological control measures (natural enemies of the flea beetle) available, Carcamo says research continues to find the best management practices to reduce the impact of the pest. He noted too that research is underway to attempt to develop a hairy canola trait which would discourage pests from feeding, but that option is still some ways away.

Lee Hart is a field editor with Grainews based in Calgary. Contact him at 403-592-1964 or by email at [email protected]

 

 

 

 

 

 

 

 

 

Lee Hart

Lee Hart


Lee Hart is a long-time farm writer, and honorary member of the Alberta Institute of Agrologists, with many observations on the agriculture industry, who never hesitates to admit he is wrong (should that ever happen.)


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