VCR – Vegetable Crop Report – July 20th, 2023

Welcome back to the VCR! Precipitation is up throughout the province in every county, and will continue to rise over the weekend.

Brassica Crops – Alternaria and Sclerotinia white rot have been observed. For both pathogens, residue from harvested blocks should be incorporated as soon as possible to reduce inoculum. Managing chewing insects will also reduce the spread of Sclerotinia. Cabbage aphid and Swede midge populations are increasing. Swede midge lays it’s eggs on the main growing point. The larvae hatch out and feed on the tissue which can result in multiple heads (Figure 1) or bacterial symptoms (Figure 2) months later. Swede midge damage is often found in early-transplanted fields where the first insecticide application for other pests was delayed.

Figure 2. Swede midge damage on kale – photo by A. Quinn.

Garlic – Harvest continues across the province. Always avoid leaving harvested bulbs in direct sunlight after they have been pulled. Take the time to cull/remove bulbs with rots or defects before they go into storage. If you are seeing rot around the basal plate, consider getting the bulb tested to rule out stem and bulb nematode. Be vigilant about reducing mechanical injury during harvest. The excess moisture will make it easy for pathogens to colonize wounds and lower quality and storability. Controlling humidity is the most important variable to control when curing. Forced air at less than 50% relative humidity is key for removing moisture from the crop quickly before it is stored. Curing over a long period of time (eg. 14+ days), can allow storage pathogens and bulb mites to acclimatize and cause problems in storage. Curing under a week is less favourable for pests and should allow the crop to be stored longer. The higher the quality of crop that goes into storage, the longer it will last.

Onions – Most fields are showing some level of Stemphylium pressure now. Allegro 500F (group 29) is now registered for suppression of Stemphylium, Botrytis leaf blight and purple blotch. A product containing mancozeb (group M3s, such as Manzate Pro-Stick, Dithane Rainshield, and Penncozeb 75 DF Raincoat) may provide protection against Stemphylium if it is being applied to manage onion smut, Botrytis or Alternaria/Purple Blotch. Allego 500F and products containing a group 7 show the best efficacy, such as Sercadis, Aprovia, or Miravis Duo (group 7/3). Avoid applying products from the same chemical group one after the other to manage Stemphylium. Research has shown that there is very high resistance in Stemphylium to one of the fungicides in Quadris Top (group 11/3) and in Luna Tranquility (group 7/9). Levels of thrips are climbing in some fields even given how wet it’s been. Apply no more than two consecutive insecticides from the same IRAC crop as thrips have a relatively short life cycle with multiple generations through the summer months and are at a high risk of developing insecticide resistance. The next generation of onion maggot and seedcorn maggot are active in many areas across the province. Be on the lookout for onion downy mildew and stunted/wilted plants due to onion maggot over the next week.

Pest Degree Day Forecasting

County	Carrot Rust Fly	Onion Maggot	Carrot Weevil	Aster Leafhopper	Tarnished Plant Bug	Cabbage Maggot	Seedcorn Maggot	European Corn Borer
THRESHOLD	329-395, 1399-1711	210-700, 1025-1515	138-156, 455+	128+	40+	314-398, 847-960, 1446-1604	200-350, 600-750, 1000-1150	See legend below
Bruce***	1054	958	688	525	324	775	958	455
Essex*	1383	1265	947	765	514	1046	1265	679
Chatham-Kent*	1293	1179	873	694	454	970	1179	612
Norfolk**	1271	1158	859	683	445	953	1158	599
Huron***	1126	1022	745	579	362	832	1022	501
Wellington**	1133	1033	759	592	373	848	1033	515
Simcoe County***	1141	1040	759	596	379	848	1040	520
Durham***	1236	1129	837	667	439	927	1129	588
Peterborough	1159	1056	767	597	375	858	1056	520
Kemptville***	1269	1165	877	701	466	970	1165	616
Sudbury***	1073	981	726	570	367	809	981	497
Timiskaming***	1049	958	697	541	346	783	958	470
Lambton**	1237	1127	825	652	418	920	1127	569
Thunder Bay	881	795	557	421	239	634	795	356
Middlesex*	1273	1164	869	692	452	962	1164	610
Renfrew	1274	1174	888	714	484	981	1174	634