From ONvegetables
By Dennis Van DYK
Insect Degree Days
| Weather Station Location | Onion Maggot | Seedcorn Maggot | Cabbage Maggot | Carrot Weevil | Carrot Rust Fly | Aster Leafhopper |
| (base 4°C) | (base 4°C) | (base 6°C) | (base 7°C) | (base 3°C) | (base 9°C) | |
| Harrow | 613 | 613 | 467 | 400 | 690 | 283 |
| Ridgetown | 534 | 534 | 394 | 333 | 611 | 231 |
| Delhi | 519 | 519 | 380 | 321 | 593 | 220 |
| Goderich | 414 | 414 | 292 | 239 | 479 | 164 |
| Guelph | 396 | 396 | 278 | 227 | 463 | 149 |
| Bradford* | 438 | 438 | 318 | 266 | 501 | 178 |
| Kemptville | 409 | 409 | 302 | 254 | 471 | 175 |
| Sudbury | 261 | 261 | 179 | 146 | 314 | 91 |
Summary and IPM Update
Onion thrips have been seen on transplants in the Grand Bend area but at this point numbers are low.
Onion maggot flies have emerged and are active in most areas of the province. Current trap counts are low in the Holland Marsh area* and low to moderate in the Grand Bend area.
Cabbage maggot has reached the DD threshold for emergence in Harrow, Ridgetown, Delhi and Bradford. It is nearing the DD threshold in Goderich, Guelph and Kemptville.
The 2nd generation of seedcorn maggot flies have reached the DD threshold for emergence in Harrow. In most other areas of the province, we are just getting over the 1st generation or are currently between generations.
Carrot weevil adults are currently laying eggs, if they are present.
The 1st generation of carrot rust fly has begun to emerge in almost all areas of the province.
Most of the province (Ridgetown, Delhi, Goderich, Guelph, Bradford, Kemptville) have reached the DD threshold for overwintering Aster leafhopper eggs to hatch. Harrow is nearing adult emergence of the local population of Aster Leafhopper adults.
Use these thresholds as a guide, always confirm insect activity with actual field scouting and trap counts.
Below are the various insect DD thresholds for reference.
Thresholds
| Degree Days | |||
| 1st generation | 2nd generation | 3rd generation | |
| Onion Maggot | 210 | 1025 | 1772 |
| Seedcorn Maggot | 200 | 600 | 1000 |
| Cabbage Maggot | 314-398 | 847-960 | 1446-1604 |
| Carrot Rust Fly | 329 – 395 | 1399-1711 | n/a |
| Carrot Weevil | 138 – 156 | Egg laying (oviposition) begins | |
| 455 | 90% of the egg-laying (oviposition) is complete | ||
| Aster Leafhopper | 128 | Overwintering eggs hatch | |
| 390 | Local adult emergence | ||
*Bradford weather, degree day data and information courtesy of the University of Guelph – Muck Crops Research Station
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