June 17, 2013
As canola gains popularity as a winter crop rotation in northern grains farming systems, researchers are working quickly to provide recommendations for pest management.
Dr Melina Miles, Department of Agriculture, Fisheries and Forestry Queensland (DAFFQ) principal entomologist, Toowoomba has trials underway with support from the Grain Research and Development Corporation (GRDC).
Aphids are the main focus of the research work as these are regularly occuring pests of northern grain crops and cause angst among northern growers, Dr Miles says.
“This is primarily because there is a lot of uncertainty about the thresholds and the need to control infestations. Monitoring the crop is a major challenge when it comes to assessing an aphid infestation.
“You can get very high numbers around the edge of the field but not as many into the field and that makes monitoring a very important part of assessing whether there’s likely to be any impact on yield.
“In a big crop of canola getting further than the first few metres into the crop can be quite a challenge.”
Beneficial insects can be extremely effective in controlling aphid infestations in some instances, but when aphid outbreaks do occur, beneficials generally take some time to reduce the aphid population, she says.
Dr Miles says aphids are highly variable in when and how they infest a canola plant.
“You can get single racemes that have early infestation and lots of aphids which stop that raceme flowering and setting pods or you can have every raceme on the plant with just a few aphids that seem to just slow down the flowering or stop the last few flowers and pods from setting.”
She says the key to estimating yield loss is the crop’s ability to compensate for damage.
“That comes down to the variety, the amount of moisture and time it has to compensate for earlier loss of flowers or pods.
“Potentially, canola has huge ability to put on extra racemes and increase the size of the seed inside the pods to compensate for the impact of aphids.
“That’s an area of work that we’ll be looking at this year, inflicting some simulated aphid damage to racemes with different varieties, at different stages of development and under different environmental conditions and looking at how much the plant will compensate or experience yield loss.”
Dr Miles and her team are running trials at several locations throughout the northern region.
“Last year we monitored fields in the northern region where there was a high instance of aphids.
“In one field the grower treated half the field and we assessed at the yield difference between the treated and untreated areas at harvest, and there was no significant difference.
“The conditions for that crop were fairly unconstrained due to a relatively cool, moist finish so the crop had plenty of opportunity to compensate.
“It will be interesting to see under a more restrictive growing environment, and different varieties whether we see the same level of compensation.”
Dr Miles says canola needs good establishment to thrive so growers should also be mindful of pests that threaten the early crop.
“The establishment of canola is probably the most critical part of getting the crop going and there are a number of insect pests that can impact on establishment.
“Most significantly among those are earth mites which can be an issue in the southern part of the northern region.”
She says factors that drive earth mite abundance include weedy fallows so growers considering sowing into this type of paddock and those who have left weed control to just before sowing will potentially need to manage blue oat mites.
“The earth mites may have built up in number during the previous spring, significantly increasing the risk of earth mites carrying over from a weedy fallow to the crop.”
Dr Miles says assessing risk is an important part of a crop protection plan and growers must decide if they will treat crop loss or pre-emptively use a seed dressing.
“In a high risk situation, if you are planting into a paddock that has come out of pasture or a weedy fallow or you are unsure of the pest levels, then a seed dressing is a wise option but, on the other hand, if it’s a low risk situation that might not be a requirement and monitoring during the first four weeks will detect emerging issues.
“One of the downsides of relying entirely on seed dressings is that under high pest the crop can still suffer significant damage because the mites have to feed on the seedling to get a dose of the chemical.
“So using a seed dressing doesn’t negate the need to monitor during that really critical stage of getting the crop from emergence through to establishment.”
Dr Miles says once the crop is established the spring flowering period is the next crucial time for pest monitoring and growers should look for leaf damage and defoliation.
“Depending on where you are and how much canola is being grown diamondback moth and cabbage moth may or may not be an issue,” she says.
“These pest populations are driven not only by environmental conditions (for example wet seasons and proliferation of brassica weeds that build up numbers) but the number of canola crops and volunteer canola plants across a district.”
Other pest threats include helicoverpa and Rutherglen bug which can affect podding and maturing crops.