Crop Report – August 25, 2021

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 15^th, 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 28^th to August 4^th; 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 4^th. Grey county observed peak flight later than all other counties across Ontario (August 5th – 11^th). 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 1^st. 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.

County	Peak WBC Moth Flight Week		Accuracy of Prediction
	GDD3.3C Predicted	Observed
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 15^th 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 29^th-August 4^th) 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 21^st 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

Weather Data

Location	Year	Weekly August 16- August 22			Accumulated
		Highest Temp (°C)	Lowest Temp (°C)	Rain (mm)	Rain (mm) April 1st	GDD 0C April 1st	GDD 5C April 1st	CHU May 1st
Harrow	2021	31	14	9	438	2529	1827	2685
	2020	30	12	13	309	2431	1742	2669
	2019	29	14	35	405	2379	1687	2517
Ridgetown	2021	31	13	17	414	2391	1697	2532
	2020	31	9	17	315	2314	1640	2517
	2019	29	11	21	535	2252	1563	2373
London	2021	31	13	13	342	2371	1684	2499
	2020	29	9	8	338	2259	1587	2433
	2019	29	12	61	513	2153	1489	2291
Brantford	2021	32	12	10	300	2345	1655	2451
	2020	32	8	0	211	2285	1619	2420
	2019	30	11		274	2227	1550	2350
Welland	2021	30	13	3	306	2360	1667	2500
	2020	29	10	3	272	2317	1644	2529
	2019	29	15	38	400	2288	1595	2449
Elora	2021	30	11	1	266	2174	1493	2280
	2020	29	7	2	282	2097	1450	2265
	2019	28	12	53	411	1758	1155	1833
Mount Forest	2021	29	11	33	361	2178	1500	2300
	2020	29	8	9	396	2074	1440	2281
	2019	29	10		129	2006	1347	2143
Peterborough	2021	31	7	1	301	2184	1492	2268
	2020	29	5	18	220	2085	1440	2223
	2019	28	6	11	345	1988	1325	2042
Kingston	2021	29	10	10	248	2246	1555	2382
	2020	26	10	30	285	2267	1589	2488
	2019	28	12	12	359	2203	1514	2344
Kemptville	2021	33	9	2	266	2346	1649	2418
	2020	29	7	40	275	2240	1572	2403
	2019	31	11		203	2104	1437	2188
Earlton	2021	32	13	0	452	2042	1370	2086
	2020	27	10	11	323	1886	1301	2089
	2019	30	9	0	349	1652	1074	1760
Sudbury	2021	31	12	0	366	2095	1424	2183
	2020	24	7	18	399	1958	1348	2173
	2019	28	8	30	381	1699	1116	1819
Thunder Bay	2021	33	7	0	247	1932	1274	1983
	2020	26	6	39	219	1759	1180	1925
	2019	29	7	26	291	1601	1015	1685
Fort Frances	2021	33	4	13	215	2043	1379	2141
	2020	30	5	4	292	1917	1301	2085
	2019	29	7	79	372	1727	1112	1813
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.