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