It is safe to say that western bean cutworm (WBC) is a pest that we can rely on entering corn and dry beans every year in Ontario. Though a frustrating pest to scout for, using traps to monitor moth flight has helped us better predict when to expect peak moth flight occurs, which is shortly followed by peak egg laying. For several years now, moth flight has started to ramp up in Ontario during the week of July 15th, three weeks prior to peak flight. Based on average trap counts from the 500+ traps in Ontario on the Great Lakes and Maritimes Pest Monitoring Network (GLMPMN) this year, peak moth flight occurred during the week of July 28th to August 4th; the same week it has been doing so since 2018 (Figure 1).
Peak flight occurred the same week for both field corn and dry bean traps while sweet corn traps peaked a week earlier. As always, dry bean traps captured more moths during that period than traps next to field and sweet corn fields (Figure 2).
When we look more closely at trap counts by county however, peak flight timing varied and wasn’t entirely dependent on geography or degree day (DD) accumulation (Figure 3). Some counties peaked the week of July 22-28, while others peaked the week of July 29 – August 4th. Grey county observed peak flight later than all other counties across Ontario (August 5th – 11th). Several DD models have been developed to help predict WBC flight activity. Hanson et al. 2015 is considered the most reliable so far by many states. It uses 3.3C as the base temperature, calculating degree days starting on March 1st. According to the model, 50% of moth flight (peak flight) occurs when 1502 DD have been accumulated. Using weather data and trap counts for Ontario this year, the model accurately predicted peak flight for some locations but not all. Table 1 shows the predicted versus observed peak flights by county across Ontario. Predicted peak flight was too early or too late for some counties. We hope to make refinements to this model to predict WBC development more accurately in Ontario. This will help improve both scouting and application timing to enable the most effective management possible.
Table 1. WBC predicted versus observed peak moth flight by county using the Hanson et al. 2015 model and trap counts from the GLMPMN.
|Peak WBC Moth Flight Week||Accuracy of Prediction|
|Essex||July 15 – 21||July 22 – 28||Too Early|
|Chatham-Kent||July 22 – 28||July 22 – 28||Accurate|
|Lambton||July 22 – 28||July 22 – 28||Accurate|
|Middlesex||July 22 – 28||July 29 – Aug 4||Too Early|
|Elgin||N/A||July 22 – 28||N/A|
|Norfolk||July 22 – 28||July 22 – 28||Accurate|
|Haldimand||N/A||July 29 – Aug 4||N/A|
|Niagara||July 22 – 28||July 22 – 28||Too Late|
|Brant||July 22 – 28||July 22 – 28||Accurate|
|Oxford||N/A||July 29 – Aug 4||N/A|
|Perth||N/A||July 29 – Aug 4||N/A|
|Waterloo||July 29 – Aug 4||July 22 – 28||Accurate|
|Wellington||Aug 5 – 11||July 29 – Aug 4||Too Late|
|Huron||July 29 – Aug 4||July 29 – Aug 4||Accurate|
|Bruce||Aug 5 – 11||July 29 – Aug 4||Too Late|
|Grey||N/A||Aug 5 – 11||N/A|
|Dufferin||Aug 5 – 11||July 29 – Aug 4||Too Late|
|Simcoe||Aug 5 – 11||July 29 – Aug 4||Too Late|
|Kawartha Lakes||Aug 5 – 11||July 29 – Aug 4||Too Late|
|Northumberland||Aug 5 – 11||July 29 – Aug 4||Too Late|
|Prince Edward||Aug 5 – 11||July 22 – 28||Too Late|
|Lennox and Addington||N/A||July 22 – 28||Too Late|
|Frontenac||Aug 5 – 11||July 22 – 28||Too Early|
|Renfrew||July 22 – 28||July 29 – Aug 4||Too Early|
|Leeds and Grenville||July 29 – Aug 4||July 29 – Aug 4||Accurate|
|Lanark||N/A||July 29 – Aug 4||N/A|
|Ottawa||July 22 – 28||July 29 – Aug 4||Too Early|
|S, D and G||N/A||July 29 – Aug 4||N/A|
|Prescott and Russell||N/A||July 29 – Aug 4||N/A|
|N/A = no weather data available for this county|
With peak flight consistently occurring for the last four years during the last week of July, it is safe to plan to start scouting corn no later than the week July 15th each year, starting first in fields that are approaching tasseling stage. Scout weekly, looking for egg masses, up to the peak flight period or until R3 stage of corn has been reached. If during those scouting periods, 5% of the plants have had egg masses on them, an insecticide is required. Soon to be published Ontario research indicates that some WBC insecticides provide up to 2 weeks of protection against WBC. Therefore, an application made the week prior to peak flight (i.e. July 22nd-28th) or during peak flight (July 29th-August 4th) will provide the most protection during the critical period of WBC development.
Over that two-week period, many of the eggs will be laid in these fields and larvae will have hatched. Keep in mind however, no insecticide provide 100% control and larvae will still be found in some ears later in the season. Egg laying does continue after peak flight, especially in later planted fields still in R1 or R2 stage. Some escapes should be expected. Yield loss is not the main concern with this pest. The concern is the wounds they leave in the ear that helps encourage ear mould development.
In a year like this one, with ideal weather conditions for ear mould development, scouting in early to mid-September is important, regardless of whether an insecticide or fungicide application was made. Any fields found to have larvae in the ears or ear mould developing should be harvested early. Plan to segregate the grain from these problem areas from the rest of the field to avoid contamination.
WBC management in dry beans is different, given that this pest is nearly impossible to scout and successfully find eggs or larvae in the field. Dry bean fields with trap catches of 150 or more moths should receive an insecticide application 10 to 21 days after peak moth flight if pods are developing on the plants. This would mean somewhere between August 10 and 21st would be a good time to apply an insecticide to protect from WBC feeding, targeting the earliest planted fields first.
Always make sure to rotate your management tools annually for this pest. Don’t rely solely on one particular insecticide or Bt corn trait (i.e. Vip3A) as this pest has great potential for developing resistance to these tools.
More information western bean cutworm can be found at:
Great Lakes and Maritimes Pest Monitoring Network: https://arcg.is/0Lry5a.
Canadian Corn Pest Coalition: https://cornpest.ca/corn-pests/western-bean-cutworm/
Ontario Dry Bean Agronomy: https://drybeanagronomy.ca/insects/
WBC Degree Day Prediction Model Paper: https://academic.oup.com/jee/article-abstract/108/4/1728/2379857?redirectedFrom=fulltext
Field Crop News: https://fieldcropnews.com/
OMAFRA Publication 812, Field Crop Protection Guide: http://www.omafra.gov.on.ca/english/crops/pub812/p812toc.html
Weekly August 16- August 22
|Highest Temp (°C)||Lowest Temp (°C)||Rain (mm)||Rain (mm) April 1st||GDD 0C April 1st||GDD 5C April 1st||CHU May 1st|
|Report compiled by OMAFRA using Environment Canada data. Data quality is verified but accuracy is not guaranteed. Report supplied for general information purposes only. An expanded report is available at www.fieldcropnews.com.|