Cereal Leaf Beetle and True Armyworm Update
Cereal leaf beetle (CLB), and true armyworm are common cereal pests in Ontario. To help support growers in their management of these pests and to better understand their prevalence, 28 fields across Ontario are being scouted weekly for cereal leaf beetle (CLB) and true armyworm (TAW). Crop growth stages are also being monitored.
CLB and TAW have been found at some locations but continue to be well below threshold (Table 1 and 2). All trap data can be found at The Great Lakes Pest Monitoring Network.
| Location (County) | Average CLB Counts |
| Brant | 1 adult |
| Bruce | 0 |
| Chatham-Kent | 2 egg masses |
| Peterborough | 0 |
| Haldimand | 1 adult, 2 egg masses |
| Halton | 7 adults |
| Essex | 0 |
| Simcoe | 0 |
| Middlesex | 0 |
| Lambton | 0 |
| Waterloo | 1 adult |
| Wellington | 0 |
| Location (County) | Average TAW Moth Counts |
| Brant | 1 moth |
| Bruce | 0 |
| Chatham-Kent | 0 |
| Peterborough | 0 |
| Haldimand | 0 |
| Halton | 0 |
| Essex | 0 |
| Simcoe | 1 moth |
| Middlesex | 0 |
| Lambton | 0 |
| Waterloo | 1 moth |
| Wellington | 1 moth |
| Stormont, Dundas and Glengarry | 0 |
The best time to scout for TAW is shortly after dusk when larvae are actively feeding. In cereals and mixed forages, examine 10 areas of the field, assessing the number of larvae per 30 cm x 30 cm (1 ft2). Pay particular attention to the border area directly adjacent to other grassy host crops. During the day, if it is cloudy and overcast, you might be lucky enough to see larvae on the head of the plant but on sunny days, they will be down on the ground among the crop debris or under soil clods. Brown frass may also be present on the plants and on the soil surface. Birds diving into your field is a good indication that there are good eats there so take a look.
When you do find larvae, look for any white eggs that may be attached to the backs of the armyworm larvae. This is a sign that the larvae have been parasitized by one of its parasites which have done the job for you. Avoid treating with insecticides when large numbers of parasitized larvae are present as they have already been controlled by parasitoids or when larvae are close to 2.5 cm in length, as insecticides will no longer be effective, and the larvae will soon stop feeding.
Chemical control for true armyworm is warranted if there are 4 to 5 un-parasitized larvae per square foot (30 cm x 30 cm). If a significant amount of wheat head clipping is occurring, spray may be warranted if larvae are still actively feeding, are smaller than 2.5 cm and pre-harvest intervals have not been reached.
For CLB, controls are needed if an average of three larvae per tiller are found before boot stage, or one CLB adult or larvae per stem after boot but prior to heading. Chemical control products for winter wheat against TAW and CLB can be found on the Crop Protection Hub. Currently, TAW levels are low across Ontario, and no insecticide treatments are recommended. CLB has been seen in select counties, with some higher prevalence in more southern regions compared to eastern and northern Ontario.
Winter Wheat Growth Stages
Winter wheat is progressing quickly through growth stages with fields in southern Ontario now reaching flag leaf which is approximately 10-14 days ahead of normal. Some fields near Harrow are now at the early boot stages. Once the flag leaf emerges herbicide applications should be avoided. While fields in southern Ontario are at or quickly approaching flag leaf, many areas further east and north are still in the early growth stages and are about 7 days ahead of normal (Table 3).
| Location (County) | Average Growth Stage (Zadoks) |
| Brant | GS 32 (2nd node) |
| Bruce | GS 31 (1st node) |
| Chatham-Kent | GS 33 (3rd node) |
| Peterborough | GS 30 (Stem Elongation) |
| Haldimand | GS 32 (2nd node) |
| Halton | GS 31 (1st node) |
| Simcoe | GS 31 (1st node) |
| Lambton | GS 32 (2nd node) |
| Middlesex | GS 32 (2nd node) |
| Waterloo | GS 31 (1st node) |
| Wellington | GS 31 (1st node) |
| Essex | GS 37 (flag leaf just visible) |
| Stormont, Dundas and Glengarry | GS 31 (1st node) |
Winter Wheat Growing Degree Days (GDDs) January 1 – May 5, 2024
Growing Degree Days (GDDs) can be a helpful tool to track cereal crop growth and development. GDDs are calculated by adding the average daily temperatures during the cereal crop’s growing season. If the daily average temperature is equal to or less than 0˚C, the degree-day value is zero and no GDDs were accumulated for that day. It takes approximately 100 GDDs for each new leaf to appear on a winter wheat plant, which is a period known as the phyllochron. The environmental conditions at planting plays a role in setting the length of the phyllochron, with early planted wheat generally having a longer GDD requirement than later planted wheat. Once winter wheat emerges, you can begin calculating the number of growing degree days accumulated. Since January 1, 2024, Growing Degree Day (GDDs) accumulations across Ontario have ranged from 175-300 GDDs in northern Ontario to 550-650 GDDs in southwestern Ontario (Figure 1 and Table 4). The Visual Guide to Winter Wheat Staging is a helpful resource for identifying crop growth stages.
| Location | 2024 | 2023 | 2022 | 10 Year Norm |
| Windsor | 649 | 521 | 391 | 401 |
| St. Catherines | 582 | 466 | 393 | |
| Ridgetown | 577 | 467 | 346 | 324 |
| Sarnia | 557 | 456 | 331 | 303 |
| Delhi | 549 | 404 | 328 | 292 |
| London | 544 | 394 | 307 | 294 |
| Hamilton | 533 | 447 | 349 | |
| Goderich | 489 | 358 | 288 | 237 |
| Elora | 421 | 289 | 256 | 218 |
| Kingston | 417 | 331 | 297 | 229 |
| Kemptville | 414 | 321 | 310 | 236 |
| Ottawa | 411 | 310 | 299 | 235 |
| Peterborough | 409 | 311 | 274 | 227 |
| Mount Forest | 406 | 290 | 248 | 200 |
| Moose Creek | 384 | 289 | 284 | |
| Barrie | 357 | 272 | 237 | 191 |
| Kenora | 205 | 120 | 76 | |
| Kapuskasing | 191 | 116 | 87 | |
| Dryden | 173 | 109 | 69 |
References:
Watch for True Armyworm and Cereal Leaf Beetle – Field Crop News
Managing Winter Wheat with Growing Degree Days – Field Crop News
Historical Data – Climate – Environment and Climate Change Canada (weather.gc.ca)
Growing-Degree Days and Development of the Wheat Plant
A Visual Guide to Wheat Staging
Haun, J. R. (1973), Visual Quantification of Wheat Development. Agronomy Journal, 65: 116-119.