As swathing begins, now is a great opportunity to capture additional clues about the “why?” behind any underperforming acres, according to Derwyn Hammond, Canola Council of Canada senior agronomy specialist in Manitoba.
“During harvest many growers will be using their yield monitors and GPS technology to learn which areas yielded the best and which yielded poorly,” says Hammond. “But farmers will only gain from that knowledge if they correctly determine what contributed to the poor yields and then use that information to make changes in the future.”
Hammond says harvest is a good time to gather information because producers have greater access to all areas of the field, and a unique visual perspective of the plants that have survived to maturity and are contributing to yield.
“This year’s canola crop has faced a myriad of environmental stresses, ranging from drought to frost to excess moisture at almost every stage, so it would be easy to write off poor yields as strictly weather related. But taking that approach means missing the opportunity to collect the clues that can make managing a canola crop easier and more successful in the long run.”
Hammond advises producers to be on the lookout for areas in the field with wilted or prematurely ripened plants, stunted plants, or plants with poor pod and seed set. “Note the distribution of these symptoms, both within the field and on the plants, as this provides clues about when the stress occurred.”
For example, says Hammond, symptoms on upper pods and branches may indicate a late season nutrient deficiency as available soil reserves were depleted, or a late infection from disease. On the other hand, missing pods at the base of the main stem indicate stress that occurred earlier in the season, probably between bud formation and first flower.
Prematurely bleached plants often bring to mind sclerotinia stem rot, but any disease that cuts off moisture and nutrients can result in similar symptoms. Hammond advises growers to take steps to confirm the source of the problem. “Break open the stems of any bleached white plants and look for hard black sclerotia bodies forming inside the stem. Record the percentage of plants infected and severity of symptoms because this is important information for assessing risk in future years.”
If growers rule out sclerotinia, other disease possibilities include blackleg, clubroot or root rot. During the past few years, blackleg has been more prevalent in fields with tight rotations, especially where hail damage created points of entry for the disease. To check for blackleg, Hammond advises looking for black rimmed stem lesions and basal stem cankers. “Don’t forget to dig up some plants and check the roots for galls from clubroot or root rot symptoms. If clubroot is confirmed, proper equipment sanitation to prevent spread will be critical. Alternaria black spot is another disease to watch for as this disease will predispose pods to shattering, which may mean swathing a little earlier and avoiding straight combining.”
Producers are also advised to watch for signs of insect damage that may indicate missed opportunities for control and a need for more thorough scouting in future years. “Pod stripping and holes chewed in pods by bertha armyworm or diamondback moth larvae will be obvious; however, this year lygus bugs and cabbage seedpod weevils were the more prevalent late season insects. The tiny holes in pods and shriveled or devoured seeds beneath them that result from their feeding require a much closer look. Root maggots were also plentiful in many areas, so take a look for significant root maggot channels on the roots to determine if cultural control strategies should be considered in future years.”
Hammond notes there are already reports of high flea beetle populations emerging in some areas, so growers should take note of flea beetle pressure. While high numbers in the fall do not always correlate with trouble in the spring, these are the adults that will overwinter and emerge to feed on canola seedlings next spring.
For growers who don’t feel they have the time to stop the swather to scout, Hammond says that some good high resolution photos showing the symptoms, the ‘patches’ within the field and a comparison to some healthy plants may be a quick way to collect those clues and leave the sleuthing for later.
