Ontario Grain Farmer February 2021

10 WESTERN BEAN CUTWORM (WBC) was first identified in Ontario in 2008 and has quickly become one of the most challenging pest issues encountered by farmers growing corn in Ontario. Recently, WBC has undergone a range expansion across Eastern Canada and now overwinters in the Great Lakes region. With the help of researchers Dr. Jocelyn Smith, Dr. Yasmine Farhan, and Dr. Art Schaafsma at the University of Guelph Ridgetown Campus, it is becoming a more understood and manageable pest. WBC feeds on corn ears resulting in yield loss, and in some years, increased ear mould infection via Gibberella ear rot (GER). This can result in deoxynivalenol (DON) and zearalenone (ZON) contamination of grain corn which can cause huge financial losses for farmers. Corn inOntario is frequently at risk for mould infection due to favourable environmental conditions, making the management of WBC crucial. In 2018, high DON levels were due to environmental conditions more than WBC, but in prior years (2016) WBC caused high DON and ZON in grain corn. RESEARCH A recent study focused on the pest had five objectives; to evaluate thresholds for WBC and mycotoxin control, determine insecticides that were effective for control of WBC, maximize the effects of transgenic insecticidal proteins, measure how susceptible WBC is to Vip3A (an insecticidal protein), and to provide recommendations for resistance management for WBC. “Throughout the study it was found that different areas of the cob, when insect injury was replicated, resulted in higher DON and ZON accumulation,” says Smith. Cobs that had insect damage on the side of the ear at the R3 (kernel milk) or R5 (kernel dent) stage had the highest levels of DON and ZON in the grain. Whereas ears that had silk clipping, injury to the tip kernels at R1 (silking stage) and R2 (kernel blister stage) or grazing injury at R6 (physiological maturity) had little effect on DON and ZON levels. “It was also found that the severity of the injury had no effect on mycotoxin levels, a single insect feeding point was just as detrimental to mycotoxin contamination as a highly injured cob with many feeding points,” notes Smith. RECOMMENDATIONS From these findings Smith recommends farmers manage WBC and GER with a combined approach. Insect resistance management WESTERN BEAN CUTWORM Laura Ferrier “Monitor individual fields for infestation and apply an insecticide and fungicide that targets GER at full silking. This would be recommended for the threshold of five per cent egg masses, although hybrids with lower tolerance to GER and in years with ideal environmental conditions, the WBC thresholds could be lowered.” Vip3A is the only insecticidal protein that controls WBC currently. Field research to evaluate transgenic control Research WESTERN BEAN CUTWORM. PHOTO COURTESY OF TRACEY BAUTE.