Swede midge and imported cabbageworm observed in canola
At this time, canola exists in Ontario at almost every growth stage. Late planted or re-seeded spring canola is at the seedling stage in Northeastern Ontario. There is also spring canola approaching first flower, and some already in full bloom in the far north and Grey, Bruce, Dufferin, and Wellington. Winter canola is grown in many different areas, spread across counties south and east of Muskoka. It is fully podded and harvest will begin in a week or two in Essex and other southern counties.
Swede Midge
Spring canola producers should continue to monitor for swede midge. While injury has been limited in recent years, the pest has not disappeared. Agronomists have reported high numbers of adults trapped this spring. At a University of Guelph monitoring site in Dufferin County, the first adults of the year emerged June 3rd and there were over 100 on most traps between June 10 and 25th.
Swede midge damage to Ontario canola was a major problem from 2012 to 2016. Typically, swede midge adults emerge in late May to early June. Drs Rebecca Hallett and Angela Gradish and their team at the University of Guelph have continued annual trapping in Dufferin County over the past decade. At the Dufferin site in 2022 to 2024, the average trap counts never reached the first spray threshold (average of 20 adults across all traps on a field) or didn’t reach it until August when the crop is no longer susceptible to significant damage. Northern producers also reported little to no injury in the past few years. Some moisture is required to encourage adults to emerge from the soil. If a dry spring or other factors lead to early canola planting or late swede midge emergence, economic injury may be avoided. Beneficial insects, changes in the distribution of canola acres in Ontario, rainfall patterns and other weather conditions may all have contributed to a reduction in crop injury.
Swede midge is a pest of canola and other Brassica species including locally grown vegetables. Eggs are laid in canola growing points and the saliva of the larvae breaks down plant tissue. This can prevent bolting (stem elongation) when the main growing point of the plant is damaged, or it can limit branching off the main stem. Both adults and larvae are tiny. Pheromone traps are used to determine when adults first begin emerging from the soil, and when the control threshold is reached. Decisions around insecticide applications also depend on plant growth stage. Canola is most vulnerable when buds are starting to form in the center of the rosette, but if high numbers of midges are being caught control measures are recommended between emergence and early bloom.
Winter canola has usually bolted in May before swede midges emerge from the soil, so the risk of economic injury to winter canola is low. High numbers of swede midge emerging in September have been recorded by University of Guelph, but because winter canola does not produce buds prior to winter it is anticipated that the pest will not cause significant injury to the winter crop. Dr. Hallett has reported on this scenario in the past – midges were observed on traps in winter canola, but crop overwintering and yield were not impacted. Traps will be set on winter canola fields this year to monitor swede midge in late summer and fall.
Imported Cabbageworm
White butterflies have been observed in very high numbers in winter canola fields this year. Imported cabbageworm, sometimes called cabbage whites, are an invasive species from Europe and Asia. They are a significant and frequent pest of locally produced Brassica vegetables and are also observed in spring canola.
The larvae feed on leaves of Brassica species (Figure 1), and presence of their frass (feces) reduces the market value of Brassica vegetables. They are green, appear velvety and are 3cm long at maturity. They do not feed on other crops, including soybeans, winter wheat, oats and peas that might be planted after winter canola harvest. The Western Canada and Ontario experience with this insect would indicate it is not an economically significant pest. However, it’s possible that the increase in winter canola acreage in southern counties has led to higher populations than observed in the past.
The butterflies are white (Figure 2) with a few black dots on their wings and are very conspicuous flying around fields. They feed on flower nectar and are found on blooming weeds such as vetch and thistles, as well as other flowering plants in adjacent fields and yards. They have multiple overlapping generations beginning in May.
While there have been many reports of high populations of butterflies, producers have not reported finding larvae or significant defoliation. Canola can tolerate up to 50% defoliation in the vegetative stages. High levels of defoliation at the beginning of bloom may decrease yield and would be noticeable while scouting ahead of fungicide application. Leaf area becomes less important through flowering; up to 70% of the leaves are shaded by flowers and pods. Producers are encouraged to monitor seedling canola for feeding this summer/fall and report any pest observations to meghan.moran@ontario.ca .
OMAFA Weather Summary: Thurs June 26—Wed July 2, 2025
| Location | Highest Temp (°C) | Lowest Temp (°C) | Rain for Week (mm) | Rain Since April 1st (mm) | GDD0C April 1st | GDD5C April 1st | CHU May 1st |
| HARROW | |||||||
| 2025 | 31.6 | 17.0 | 7.3 | 291.5 | 1360 | 918 | 210 |
| 2024 | 28.3 | 10.2 | 37.9 | 258.7 | 1522 | 1056 | 166 |
| 2023 | 27.4 | 13.9 | 48.7 | 202.8 | 1323 | 869 | 189 |
| 10 YR Norm (2011-2020) | 27.8 | 15.1 | 26.3 | 288.4 | 1347 | 884 | 193 |
| RIDGETOWN | |||||||
| 2025 | 30.1 | 14.8 | 0.7 | 208.4 | 1284 | 844 | 192 |
| 2024 | 28.5 | 7.4 | 60.8 | 339.8 | 1428 | 966 | 151 |
| 2023 | 29.3 | 11.9 | 95.8 | 281.9 | 1253 | 807 | 182 |
| 10 YR Norm (2011-2020) | 28.3 | 13.6 | 17.3 | 237.9 | 1258 | 801 | 183 |
| SARNIA | |||||||
| 2025 | 32.0 | 15.2 | 27.0 | 263.5 | 1237 | 802 | 194 |
| 2024 | 30.5 | 9.2 | 13.8 | 218.1 | 1406 | 947 | 154 |
| 2023 | 30.2 | 12.3 | 7.7 | 183.1 | 1208 | 764 | 180 |
| 10 YR Norm (2011-2020) | 27.1 | 14.7 | 15.2 | 264.0 | 1211 | 756 | 182 |
| LONDON | |||||||
| 2025 | 29.4 | 13.4 | 15.0 | 249.6 | 1206 | 788 | 185 |
| 2024 | 28.5 | 8.4 | 32.0 | 301.4 | 1406 | 940 | 150 |
| 2023 | 29.0 | 8.1 | 26.0 | 271.6 | 1251 | 807 | 173 |
| 10 YR Norm (2011-2020) | 27.3 | 14.0 | 15.9 | 266.3 | 1235 | 781 | 179 |
| BRANTFORD | |||||||
| 2025 | 29.4 | 13.1 | 35.6 | 289.2 | 1232 | 805 | 179 |
| 2024 | 26.9 | 8.7 | 27.7 | 244.6 | 1349 | 888 | 149 |
| 2023 | 29.7 | 9.4 | 37.2 | 224.0 | 1242 | 795 | 178 |
| 10 YR Norm (2011-2020) | 28.0 | 13.2 | 15.1 | 250.2 | 1214 | 764 | 173 |
| WELLAND | |||||||
| 2025 | 30.7 | 13.2 | 55.1 | 205.3 | 1275 | 838 | 184 |
| 2024 | 25.9 | 10.2 | 35.3 | 307.0 | 1403 | 939 | 161 |
| 2023 | 27.7 | 10.7 | 59.9 | 239.5 | 1242 | 790 | 178 |
| 10 YR Norm (2011-2020) | 26.6 | 14.3 | 20.6 | 268.6 | 1236 | 781 | 181 |
| GODERICH | |||||||
| 2025 | 30.4 | 13.3 | 47.8 | 214.6 | 1162 | 736 | 182 |
| 2024 | 25.5 | 6.6 | 2.9 | 200.6 | 1255 | 801 | 127 |
| 2023 | 26.6 | 7.0 | 8.2 | 146.7 | 1130 | 702 | 168 |
| 10 YR Norm (2011-2020) | 24.9 | 13.5 | 11.3 | 230.8 | 1103 | 658 | 167 |
| ELORA | |||||||
| 2025 | 28.4 | 10.8 | 52.4 | 257.9 | 1128 | 711 | 167 |
| 2024 | 26.0 | 8.2 | 9.2 | 259.7 | 1254 | 803 | 139 |
| 2023 | 27.5 | 7.4 | 25.5 | 188.2 | 1143 | 714 | 166 |
| 10 YR Norm (2011-2020) | 25.7 | 12.2 | 19.7 | 265.6 | 1096 | 655 | 162 |
| MOUNT FOREST | |||||||
| 2025 | 28.6 | 11.0 | 52.0 | 238.7 | 1123 | 710 | 172 |
| 2024 | 24.4 | 8.0 | 4.1 | 241.8 | 1237 | 790 | 134 |
| 2023 | 27.0 | 7.6 | 21.3 | 232.5 | 1139 | 715 | 163 |
| 10 YR Norm (2011-2020) | 25.4 | 12.9 | 13.3 | 261.7 | 1078 | 646 | 164 |
| BARRIE | |||||||
| 2025 | 28.8 | 10.2 | 22.8 | 219.0 | 1118 | 702 | 171 |
| 2024 | 26.4 | 7.0 | 8.3 | 383.0 | 1195 | 747 | 136 |
| 2023 | 26.9 | 8.6 | 34.5 | 260.9 | 1119 | 689 | 162 |
| 10 YR Norm (2011-2020) | 25.9 | 11.1 | 13.3 | 248.4 | 1056 | 627 | 164 |
| PETERBOROUGH | |||||||
| 2025 | 29.5 | 12.7 | 4.8 | 202.8 | 1160 | 734 | 173 |
| 2024 | 25.8 | 5.6 | 20.3 | 287.5 | 1227 | 774 | 141 |
| 2023 | 28.4 | 8.5 | 12.2 | 203.3 | 1152 | 711 | 168 |
| 10 YR Norm (2011-2020) | 27.1 | 10.8 | 13.6 | 247.6 | 1110 | 668 | 162 |
| KEMPTVILLE | |||||||
| 2025 | 30.6 | 9.9 | 7.8 | 188.6 | 1218 | 789 | 178 |
| 2024 | 27.4 | 6.2 | 12.2 | 299.9 | 1296 | 843 | 154 |
| 2023 | 29.5 | 13.4 | 1.9 | 245.4 | 1217 | 781 | 185 |
| 10 YR Norm (2011-2020) | 27.4 | 12.4 | 26.5 | 262.3 | 1164 | 724 | 176 |
| SUDBURY | |||||||
| 2025 | 27.3 | 10.9 | 31.1 | 202.0 | 964 | 580 | 155 |
| 2024 | 25.7 | 8.2 | 27.4 | 354.4 | 1084 | 661 | 124 |
| 2023 | 28.9 | 7.3 | 30.8 | 314.3 | 1042 | 654 | 154 |
| 10 YR Norm (2011-2020) | 26.8 | 11.6 | 21.2 | 239.7 | 958 | 579 | 163 |
| EARLTON | |||||||
| 2025 | 29.1 | 10.5 | 13.9 | 188.0 | 926 | 559 | 159 |
| 2024 | 26.9 | 6.6 | 42.5 | 315.2 | 1076 | 659 | 124 |
| 2023 | 29.2 | 5.4 | 10.7 | 203.7 | 1028 | 639 | 149 |
| 10 YR Norm (2011-2020) | 25.8 | 10.0 | 15.0 | 214.7 | 882 | 526 | 153 |
| SAULT STE MARIE | |||||||
| 2025 | 27.0 | 10.0 | 27.8 | 219.0 | 920 | 529 | 147 |
| 2024 | 21.6 | 7.1 | 51.2 | 343.0 | 994 | 556 | 104 |
| 2023 | 26.3 | 7.3 | 25.5 | 206.9 | 1005 | 615 | 140 |
| 10 YR Norm (2011-2020) | 24.8 | 9.1 | 17.2 | 243.6 | 841 | 463 | 144 |
| THUNDER BAY | |||||||
| 2025 | 29.3 | 7.2 | 21.6 | 210.2 | 834 | 471 | 149 |
| 2024 | 24.0 | 4.9 | 28.9 | 245.8 | 893 | 479 | 96 |
| 2023 | 28.3 | 9.2 | 19.5 | 176.4 | 906 | 539 | 147 |
| 10 YR Norm (2011-2020) | 26.6 | 8.6 | 22.7 | 234.9 | 805 | 437 | 145 |
| FORT FRANCES | |||||||
| 2025 | 28.9 | 7.2 | 0.3 | 189.3 | 1011 | 613 | 158 |
| 2024 | 25.9 | 3.2 | 62.4 | 308.0 | 955 | 531 | 106 |
| 2023 | 29.7 | 7.7 | 18.0 | 153.5 | 1089 | 715 | 148 |
| 10 YR Norm (2011-2020) | 26.5 | 9.8 | 17.2 | 224.6 | 918 | 531 | 154 |
This weather summary is compiled by OMAFA using Environment Canada weather station data provided by Agriculture and Agri-Food Canada. Data quality is verified but accuracy is not guaranteed and should be used for general information purposes only. For additional locations and weather analysis, visit the OMAFA Pest and Weather System (PAWS)