VCR – Vegetable Crop Report – May 14th, 2026

Crop Updates

Asparagus – Overnight frosts resulted in more harvest losses this week. With warmer temperatures in the immediate forecast, we should start to see fields resume growth. Warmer temperatures also bring with them increase insect pressure. Scout for cutworm activity. Keep in mind that cutworm insecticides have a 2-day PHI. Information from the University of Wisconsin suggests that asparagus beetle adults begin to emerge when the redbud trees are in full bloom. Watch for egg laying on emerging spears. Once younger plantings begin to fern out, the adults are often attracted to those fields where they can cause considerable damage to the developing plants.

Asparagus beetle thresholds vary depending on the stage of the crop and the stage of the pest:

2% of spears with eggs
5-10% of plants infested with adults
50% of plants with larvae present (ie: an average of 50 larvae on 100 plants)
10% defoliation

Brassica – Transplanting continues. The first generation of cabbage maggot has should be reached soon in Exeter. Tray drenches of Success (Group 5), Entrust (Group 5), and Verimark (Group 28) are registered against cabbage maggot in broccoli, Brussels sprouts, cabbage, and cauliflower. Always up wilted plants and inspect the roots for wireworm, maggot or millipede feeding damage.

Carrots – Planting in the South-West is mostly completed while the central region of the province is just getting started after onion planting. We have started to enter the emergence period for carrot rust fly in the Southern tip of the province. Use yellow/orange sticky cards to monitor for carrot rust fly.

**Figure 1** – Carrot rust flies on an orange sticky card, identified by their black bodies and orange legs.

Garlic – The warmer weather is helping plants size up. Yellow leaf tips continue to be prevalent across the province with very few fields showing green right to the tips. Dig up any wilted plants you find and inspect cloves for seedcorn maggot larvae, wireworm or millipede feeding damage. The Garlic Growers Association of Ontario is hosting the 2026 field day Saturday, June 6th at Great Lakes Family Farms near Grand Bend, Ontario. Equipment from multiple manufacturers will be on display, along with products from fertilizer and pest control product suppliers. The agenda includes presentations on results from past garlic trials, industry, and minor use updates as well as a tour of a new garlic curing and storage facility. Registration starts at 9:00, the agenda starts at 9:30 and goes until 4:30. Lunch will be provided. Great Lakes Family Farms is located at 70748 B Line, Grand Bend, Ontario, and all are welcome to join, rain or shine. Please register for the field day by going to https://www.eventbrite.ca/e/field-day-2026-tickets.

Onion – The first generation of onion and seedcorn maggot fly has been reached in many locations across the province, eggs will be hatching out and larvae will be feeding on small plants. Dig up wilted transplants and inspect the roots for maggots. Some areas have seen dry weather making some seeded fields germinate unevenly. Once seeded onions have emerged, count out 25 plants per row, put a marker at each end and record the number of plants every week. These damage plots will be valuable to monitor the amount of damage due to maggot flies or other pests. The extended forecast looks good for transplant onion establishment over the next couple of weeks.

Potatoes – Planting continues in the central region of the province with many fields already planted in the SW counties and along Lake Erie. With the forecasted “warmer” weather this weekend, planting will be full steam ahead. Ensure you seed is properly healed and suberized before planting to avoid rot in these conditions. Available seed treatments can be found on the Crop Protection Hub. Potato Scout training is scheduled for Wednesday May 27^th, sign-up if you plan on scouting potato fields this season.

Sweet corn – Cooler temperatures can have an impact on the development of early planted sweet corn, even under covers. Corn is most susceptible to cold soils during the initial imbibition of water into the seed (immediately after planting). Cold water entering the seed damages enzymes resulting in poor early vigour and the potential for stand losses. Sh2 varieties have very little cold tolerance. Avoid planting them when soil temperatures are below 18°C. In general, se and synergistic varieties tolerate slightly cooler soil temperatures. Use a 16°C soil temperature threshold for these varieties. Slow early season growth may also result in an increase in pest activity. Seed treatments typically last about 3 weeks. If they wear out while the plant is still drawing reserves from the seed, fungal pathogens or seed insects can further impact stand establishment. Use a hand trowel to assess the health of the emerging seedlings and to look for insects such as wireworm and seedcorn maggot. Wireworm will become more active as the soils continue to warm up. Under drier conditions they will migrate back down below the root zone and become dormant, leaving behind damaged plants that struggle to catch up to their neighbours. Based on the growing degree days, the first generation of seedcorn maggot adults is occurring in Southwestern Ontario. The adult flies are attracted to the smell of organic matter such as manure applications or terminated cover crops. If a cover crop has been recently terminated or plowed under, avoid planting sweet corn for at least two weeks. This will allow the seedcorn maggot to complete their life cycle and move on from that field.

**Figure 2 –** 3-leaf sweet corn plant with symptoms of early die-back caused by wireworm feeding. Effected plants will often be undersized compared to their neighbours.

**Figure 3 –** Wireworm larvae and a corn seedling. Feeding damage is evident on the seed. At this stage of growth, the plant is still drawing reserves from the seed and damage can impact overall growth and vigour.

Tomatoes – Planting has started for tomatoes this week. Growers who have planted before nighttime temperatures are above 10°C should expect to see chilling, or even frost, injury on transplants. Chilling/Frost injury can have long term effects including reduced growth rates and issues with flower development, pollination, and fruit set. It is advised to wait to plant tomatoes until nighttime temperatures are appropriate.

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***	168	134	52	18	2	75	134	9
Essex*	417	364	224	146	60	268	364	113
Chatham-Kent*	351	300	170	106	44	211	300	83
Norfolk**	302	256	151	100	43	180	256	78
Huron***	239	197	96	50	9	127	197	33
Wellington**	209	172	90	50	13	113	172	34
Simcoe County***	188	153	76	37	7	98	153	23
Durham***	212	173	83	42	8	110	173	28
Peterborough	199	162	79	42	8	104	162	28
Kemptville***	217	180	84	44	12	112	180	31
Sudbury***	71	50	15	4	0	24	50	2
Timiskaming***	52	33	7	2	0	12	33	0
Lambton**	302	253	137	87	27	171	253	65
Thunder Bay	49	32	6	1	0	10	32	0
Middlesex*	312	266	150	97	37	185	266	74
Renfrew	172	139	57	26	6	82	139	18