Insect Pest and Crop Degree Day Update – May 26

Ontario DD Map May 25

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 468 468 342 285 535 189
Ridgetown 408 408 288 237 475 155
Delhi 391 391 271 222 455 141
Goderich 308 308 206 164 363 108
Guelph 284 284 186 145 342 87
Bradford*  318 318   205 172  369  112
Kemptville 304 304 217 179 356 119
Sudbury 168 168 105 82 210 47

 

Summary

Onion and seedcorn maggot flies have begun to emerge in most areas of the province except for Northern Ontario.

Cabbage maggot has reached the DD threshold for emergence in Harrow and is nearing the DD threshold in Ridgetown and Delhi.

Carrot weevil adults have reached the DD threshold to start laying eggs, if they are present.

The 1st generation of carrot rust fly has begun to emerge in almost all areas of the province.

The southern areas of the province (Harrow, Ridgetown and Delhi) have reached the DD threshold for overwintering Aster leafhopper eggs to hatch.

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 and DD data courtesy of the University of Guelph – Muck Crops Research Station

 

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