VCR – Vegetable Crop Report – June 20, 2024

Welcome to this week’s VCR! All counties continue to trend above their 10 year average GDD.

Crop Updates

Brassica Crops – Harvest has started in early planted broccoli and cabbage this week. Be on the lookout for black rot, caused by the pathogen Xanthamonas campestris pv campestris (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 and heat canker will likely be observed on newly transplanted Brassicas next week. Dig up wilted plants and inspect roots for cabbage maggot larvae, nematodes, clubroot or damaged caused by wireworms.

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

Celery – Plants are establishing well in fields with adequate moisture available. Cutworms, tarnished plant bugs, aster leaf hoppers and slug damage have been observed. Scout for yellow/orange scratch marks along the stalk left by carrot weevils or downward cupped leaves that could be due to celery leaf curl. Rogue out yellow plants in the field that show aster yellows symptoms. Dig up stunted and/or wilted plants and gently knock of soil to inspect their roots for nematode cysts, or carrot weevil larvae.

Cucurbits – We are quickly approaching the time of year, where downy mildew typically arrives in Ontario growers of cucumbers and muskmelons should begin a preventative spray program before the disease appears in the crop. Broad spectrum sprays maybe used early in the season switching to targeted downy mildew products when there is a first report in the Great Lakes Basin. Continue to scout, pumpkins and squash for cucumber beetles. The overwintering generation should begin to tail off now, however bacterial wilt is a concern wherever they are feeding on the foliage.

Garlic – Ensure plants have adequate moisture and consider irrigating over the next two weeks while plants are bulbing in order to achieve optimal yields in these high temperatures. Dig up plants that show advanced leaf dieback from the base of the plant upward and inspect basal plate for damage caused Botrytis neck rot or stem and bulb nematode (Figure 2). Leaf yellowing from the top, newest leaves and progressing downward is often caused by Aster Yellows, nitrogen deficiency, Fusarium yellows or herbicide damage.

**Figure 2.** Infected plants with Botrytis neck rot show wilted leaves which turn yellow starting from the oldest leaves first (A). Leaves of plants infected with stem and bulb nematode yellow before they wilt (B).

Onions – The largest direct seeded onions are reaching the 8th leaf stage while most fields are still around the 6th leaf stage. Conditions for white rot development have been very favourable in some areas. Stemphylium leaf blight is likely to be observed over the next couple of weeks. If Penflufen (group 7) was part of the seed treatment, do not start foliar applications with a 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. For the second foliar product, Allegro 500F (group 29) or 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). Avoid applying products from the same chemical group one after the other to reduce the selection pressure group 7 or group 29 so that they can be used to manage Stemphylium for future years. 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. Over the next couple of weeks, monitor for damage caused by the second generation of onion maggot larvae.

Snap beans – early crop are beginning to enter the flowering stage. Consider the need for white mould controls at first flowering. Under drier conditions, and/or less-dense canopies controls may not be needed. This disease thrives in dense canopies where the threshold of 72 hours of leaf wetness is easily exceeded.

Sweet corn – Planting continues with first harvests expected within the next couple of weeks. Corn at the silking stage is most susceptible to corn earworm damage. Earworms typically migrate to Ontario from late June onwards often peeking in September. There is a higher risk of moth deposition in areas where there have been sudden, heavy storm activities.

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***	751	664	443	317	168	511	664	263
Essex*	1083	985	719	567	361	803	985	496
Chatham-Kent*	984	891	639	497	301	717	891	428
Norfolk**	923	828	570	429	247	650	828	364
Huron***	838	747	504	369	213	580	747	308
Wellington Centre**	813	722	492	362	200	562	722	303
Wellington North**	798	711	482	355	201	553	711	297
Simcoe***	793	706	477	346	190	548	706	285
Durham***	848	756	516	381	213	591	756	320
Peterborough	783	694	464	333	176	536	694	275
Kemptville***	846	757	532	403	238	600	757	345
Sudbury***	649	576	388	281	152	447	576	232
Timiskaming***	628	561	383	280	160	438	561	234
Lambton**	956	865	614	471	290	693	865	405
Thunder Bay	486	417	244	156	57	295	417	119
Middlesex**	967	873	617	472	286	697	873	407
Renfrew	840	753	530	407	245	598	753	350