VCR – Vegetable Crop Report – May 28th, 2026

Crop Updates

Brassica Crops – Transplants are starting to take off. Cabbage maggot has reached its first-generation threshold in Essex. Dig up wilted transplants, even in dry areas, to inspect roots for maggots. Flea beetles is low and cutworms are active. Products registered for cutworm management are most effective when they are applied early when the cutworm larvae are small. Keep an eye out for early season caterpillars. To determine if the threshold for management has been met for imported cabbageworm, diamondback moth, or cabbage looper (Figure 1), scout 5 plants in 5 locations and record the total number of each lepidopteran pest found (total number of egg or larvae found):

Multiply:

Diamondback moth x 0.2 = A

Imported cabbageworm x 0.5 = B

Cabbage looper x 1.0 = C

Then add and divide:

A+B+C divided by 25 = Cabbage Looper Equivalent

For cabbage, the threshold is 0.3 and for broccoli and cauliflower the threshold is 0.2.

**Figure 1 –** Eggs (inset) of diamondback moth (left), imported cabbageworm (middle), and cabbage looper (right). Larvae of diamondback moth (left) are pale green, leave window-pane damage on the leaf from feeding, wiggle frantically when disturbed and attach a silken thread and sometimes dangle over the leaf edge. Imported cabbageworm larvae (middle) are velvety in appearance and have a pale-yellow stripe along their back. Imported cabbageworm larvae photo: Dr. Mary Ruth McDonald. Cabbage looper larvae (right) are smooth with a thin white line along each side and two faint lines down the middle of the back.

**Figure 2 –** Broccoli field 3 days after transplant – May 25, 2026.

Carrots – Recent conditions have been good for carrot seeding. Early planted fields are establishing well but unfortunately so are weeds (Figure 3). An important reminder that Zidua is now registered on carrots for use on muck soils thanks to the Minor Use Program.

**Figure 3** – Carrots in competition with pigweed.

Cucurbits – Cucumber beetles become active as the weather warms up. They enter the fields soon after emergence/transplanting. Seeds treated with thiamethoxam insecticide do not usually require additional treatments for this pest. Scout all fields for beetle activity. They are less active during the heat of the day, so morning or evening scouting is ideal. The cucumber beetle threshold is 0.5-1 beetle per plant. Beetle escapes can result in the spread of bacterial wilt disease in the crop. All cucurbits are susceptible to this disease, but cucumbers are particularly sensitive. The bacteria live in the gut of the overwintering cucumber beetle adults (Figure 4). The disease is spread when bacteria in the feces enters the wounds caused from beetle feeding. The bacteria then colonize the vascular tissue of the plant causing it to become plugged and preventing the flow of nutrients and water to developing tissue.

**Figure 4** – Adult cucumber beetles feeding on a leaf.

A good preemergence herbicide program for pumpkins, squash and melons is Dual II Magnum/Komodo plus Command. It controls a broad spectrum of annual broadleaf and grassy weeds. Do not use Dual II Magnum/Komodo on cucumbers, it can cause excessive crop injury. Cucumber growers can use Command plus Sandea preemergence instead of Dual II Magnum/Komodo.

Sandea is registered for early post emergence broadleaf control, after the crop has 3-5 leaves or no sooner than 14-days after transplanting. It can be used on cucumbers, pumpkins, squash, cantaloupe, and watermelon. Do not apply directly over plastic mulch as the spray may run into the planter holes and cause phytotoxicity. See the product label for instructions specific to each crop.

Garlic – The majority of fields are between 8-10 leaves per plant. Look out for damage from Allium leafminer (Figure 5) and leek moth (Figure 6). Refer to this article for managing leek moth: https://onvegetables.com/2025/03/07/leekmoth-3/. Scapes will be emerging over the next 2–3 weeks. Snap scapes above the newest leaf and avoid using sickle bar mowers or any knife to remove scapes as they can easily spread garlic pathogens (including viruses) and often damage leaves during the scape removal process. Past research by John Zandstra has shown that by accidentally removing one leaf when the scape was removed, bulb sizes were reduced by 13% and the yield was reduced by an average of 17.5%. The same trial showed that yield was greatly impacted as the number of leaves cut during mowing increased. If the top two leaves were cut, the yield was reduced by approximately 25%, almost outweighing any potential gains you would expect by removing the scape in the first place.

Register for the Garlic Growers Association 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.

**Figure 5 –** Egg laying scars of Allium leafminer on a garlic leaf. Photo: B. McAuley – May 18, 2026.

**Figure 6 –** Leek moth larvae along with feeding damage that almost looks like green sawdust.

Onion – Direct seeded fields are between the flag and 4th leaf stage with the majority still in the third leaf stage. Onion and seedcorn maggots are active. Be on the lookout for wilted plants. Stake/count 50 or 100 plants now and count later in the seasons to determine how many onions make it to harvest. While scouting, continue to be on the lookout for cutworms, especially along field edges. Destroy volunteer onions in neighbouring fields, as this can be a source for fungi inoculum like Stemphylium or pests like onion thrips that will be seen in the coming weeks.

Potato – Planted fields are progressing quickly with this recent stretch of weather. Monitor for any emergence issues caused by the cool and wet conditions around planting. Common emergence issues include Fusarium Dry Rot, Blackleg/Soft Rot, and Rhizoctonia.

Tomatoes – Planting is more than 50% complete for processing tomatoes, and fresh market tomatoes are continuing with their staggered planting schedules. Be sure to keep scouting for early season insect pests like black cutworm, wireworm and Colorado potato beetle. The cooler weather will slow down the growth of transplants, making them vulnerable to these pests for longer than most years.

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***	290	242	119	63	23	155	242	44
Essex*	606	539	356	250	125	414	539	203
Chatham-Kent*	523	458	286	194	100	341	458	158
Norfolk**	465	405	258	180	92	301	405	146
Huron***	380	324	184	114	45	226	324	87
Wellington**	353	302	179	114	52	214	302	88
Simcoe County***	344	295	176	112	55	212	295	88
Durham***	371	318	187	118	53	227	318	92
Peterborough	360	309	184	120	54	223	309	94
Kemptville***	386	335	197	130	64	239	335	104
Sudbury***	203	168	91	56	23	114	168	42
Timiskaming***	177	143	79	50	21	96	143	38
Lambton**	465	402	244	169	76	292	402	136
Thunder Bay	133	103	43	25	11	57	103	19
Middlesex*	479	418	261	179	85	309	418	143
Renfrew	331	284	160	102	48	198	284	82