GrainsWest Fall 2019

Fall 2019 grainswest.com 13 “In the Peace, when we had that big outbreak many producers went to that midge-tolerant wheat and the results have been spectacular.” —Scott Meers BY CULLEN BIRD • PHOTOS COURTESY OF TYLER WIST, AGRICULTURE AND AGRI-FOOD CANADA use 100 per cent midge-resistant wheat it would eliminate all wheat midge except those with a resistance to the Sm1 gene. These surviv- ing “virulent midge” would then be able to eat Sm1 wheat. To prevent this, scientists from Agriculture and Agri-Food Can- ada (AAFC) decided to use a “refuge” system in which midge-re- sistant seed is mixed with non-resistant wheat. About 90 per cent of the seeds are of the midge-resistant variety, while 10 per cent are non-resistant. Allowing the wheat midge to eat some of the non-resistant wheat ensures the wheat midge population remains susceptible to Sm1. “There is going to be some small amounts of wheat midge that are out there damaging the non-resistant variety, but that’s the only way we can maintain the Sm1 gene,” said Chapman. Farmers must buy the seed from a certified grower and sign a contract to do so. It’s best for farmers to avoid growing their own midge-resistant seed, since it’s difficult to mix the two wheat vari- eties together, according to Chapman. “If we want to maintain the system, we have to follow the rules,” he said. PEST CONTROL Macroglenes penetrans is a parasitic wasp active in Alberta that can make a big dent in midge populations. Unfortunately, the tiny wasp doesn’t instantly kill the midge, so its benefits are generally only felt the following year. Spraying for wheat midge requires correct timing application with the insect’s emergence. The most effective and commonly used chemical for the job is chlorpyrifos, commonly known as Lorsban, as it kills both adult midges and their eggs. However, Canada’s Pest Management Regulatory Agency published a re-evaluation of the pesticide in May. The report rec- ommended banning it except for a few small-scale uses. Banning chlorpyrifos would create a bad situation, said Meers. “In certain uses, there is nothing to replace it,” he said. The other alternative is dimethylate, which is less effective as it only kills the adult midges, not the eggs. PLANNING FOR THE FUTURE Currently, there is no Plan B if the Sm1 gene fails or wheat midge populations become resistant. However, there are potential control measures being studied, said Tyler Wist, a field crop entomologist with the AAFC Saskatoon Research and Development Centre. One is an egg-laying deterrent being studied by a multi-organiza- tion partnership mostly conducted at the University of Manitoba. Launched in 2018 and concluding in 2023, the study is examining the effect of airborne chemicals produced by wheat—essentially odours—that deter wheat midge from laying eggs. If the researchers can determine the key components of an effective odour, it could be bred into Sm1 wheat as an additional deterrent, added Wist. “So, you’ve got less egg laying and then if the eggs do get laid the Sm1 gene kicks in and takes care of them,” he said. Wist is involved with a study researching two potential coun- termeasures. The first is a wheat variety that has especially hairy glumes. These may form a “mechanical deterrent” that would hopefully discourage wheat midge from landing on the wheat heads, he said. The second is one he calls egg antibiosis. One breeder line of non-commercially available winter wheat exhibits this trait. “The eggs of the wheat midge just don’t even hatch,” he said. A quick and deadly response to egg-laying is not unheard of in other plants, said Wist. The plant recognizes eggs have been laid and quickly creates a chemical response that kills the eggs. The study began in April of this year and will continue for three years. In the meantime, Meers said his team will continue carrying out surveys and keeping farmers informed of the wheat midge threat. “The industry really wants us to be doing this, and that’s our plan,” he said. The insect’s larvae can cause substantial crop damage.