VCR – Vegetable Crop Report – June 23rd, 2022

Temperature – Though many counties experienced a heat wave this past week the week GDD continues to match or be slightly above the GDD 10 year average. Daytime temperatures continue to run high this week with forecasts ranging in the twenties to thirties across the province and peaking over the weekend.

Precipitation – Most counties received little to no rain over the past week except for Durham, Peterborough and Kemptville. Some counties may see rain towards the end of the weekend, some with a chances of thunderstorms, and also again midweek.

Crop Updates

Brassica Crops – Harvest has started in early planted broccoli and cabbage this week. Black rot, caused by the pathogen Xanthamonas campestris pv campestris, is being observed in multiple locations this season (Figure 1). Black rot spreads rapidly during warm, humid weather and enters other plants through wounds or natural openings on the leaf tips. The Xanthamonas bacteria often finds it’s way to farms in infected seeds and then bacterial cells overwinter on used trays, propagation equipment and crop debris for up to three years. Infected plants have characteristic ‘v’ shaped lesions and systemically infected plants have chlorotic areas anywhere on the leaf. When leaves are held up to the sun, veins filled with Xanthamonas bacteria are stained black in the chlorotic areas on the leaf. The best management strategy is prevention through certified clean seed, sanitation of propagation equipment/tools, a four-year crop rotation, and roguing and then burying all crop debris. To read more about black rot, refer to CropIPM. Damage from imported cabbageworms, cutworms and diamondback moths continues to be observed. Dig up wilted plants and inspect roots for cabbage maggot larvae, nematodes, clubroot or damaged caused by wireworms. Check transplants for bacterial leaf spot and in the field be on the lookout for Alternaria, heat canker, aphids and thrips.

Figure 1. Black rot leaf on cauliflower with characteristic ‘V’ shaped lesion on leaf tip.

Celery – Plants are establishing well. Tarnished plant bugs and aster leaf hoppers are active, and some fields are showing cutworm, Leafminer and slug damage. Scout for yellow/orange scratch marks along the stalk left by carrot weevils. Rogue out yellow plants in the field that show aster yellows symptoms. Dig up stunted and/or wilted plants and inspect roots for nematode cysts, or carrot weevil larvae.

Garlic – Scaping continues across the province. Ensure plants have adequate moisture and consider irrigating over the next two weeks while plants are bulbing for optimal yields. The populations of leek moths in traps is increasing this week which will likely result in an increase in larvae feeding/damage to leaves over the next two weeks. If applying insecticides, a single insecticide application is most effective when it is applied 10 days after the date that corresponds to the peak moth capture. If you plan on two applications, make the first application 3 to 7 days after the date of peak moth capture and the second treatment 14 days later. Dig up plants that show advanced leaf dieback from the base of the plant upward and inspect basal plate for damage caused by stem and bulb nematode (Figure 2) or Fusarium basal rot. Leaf yellowing from the top, newest leaves and progressing downward is often caused by Aster Yellows, nitrogen deficiency, Fusarium yellows or herbicide damage.

Register for the next Garlic Production and Pest Management workshop near Janetville, ON, that takes place Friday, August 19th from 9:30-4:30. Register by calling 1-877-424-1300 or filling out this online form: https://survey.clicktools.com/app/survey/go.jsp?iv=1y59n0qcz8rld.

Figure 2. Various degrees of stem and bulb nematode damage on garlic. Look for stunted plants with leaf yellowing from the bottom leaves of the plant moving upward.

Onions – The largest direct seeded onions are reaching the 6th leaf stage while most fields are still around the 4th leaf stage. Transplant onions are taking off with some fields at the 8th leaf stage. The pressure of thrips has continued to be low in direct seeded onions, but higher levels are being observed in transplants. Be mindful that onion fields next to hay or overwintering rye are at a greater risk to thrips once they are cut and include counts from at least one location near the field border when scouting for thrips. Past research has shown that Movento 240 SC (group 23) has some residual activity that works better against larvae when it is applied earlier in the season. If the spray threshold exceeds 3 thrips/leaf, Movento 240 SC could be followed by two applications of Delegate (group 5) or Agri-Mek (group 6). Malathion 85E (group 1B), Dibrom (group 1B), Entrust (group 5), Success (group 5), and Exirel (group 28) are also registered. Using a penetrating surfactant can be useful to maximize the effectiveness of products against thrips. 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. Stemphylium leaf blight is likely to be observed over the next couple of weeks. If Penflufen was part of the seed treatment, do not start with a foliar group 7 fungicide. For the first application, 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. Avoid applying products from the same chemical group one after the other to manage Stemphylium. For the second foliar product, products containing a group 7 show the best efficacy, such as Sercadis, Aprovia, or Miravis Duo (group 7/3). 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). Over the next couple of weeks, monitor for new cutworm damage, wilt caused by onion maggot larvae, and white rot as conditions have been favourable for white rot development in some areas.

Pest Degree Day Forecasting

*NOTE: Data as of June 22, 2022

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
Essex*	1010	921	675	539	372	752	921	479
Chatham-Kent*	867	783	556	432	264	628	783	379
Norfolk**	881	798	571	439	263	644	798	382
Huron***	764	685	469	348	190	536	685	294
Wellington**	742	665	451	332	179	519	665	283
Simcoe County***	749	671	461	340	189	527	671	290
Durham***	801	718	496	371	202	566	718	315
Peterborough	737	660	447	330	169	514	660	277
Kemptville***	803	718	498	378	208	564	718	323
Sudbury***	611	551	380	280	144	435	551	236