VCR – Vegetable Crop Report – August 8th, 2024

Welcome back to the next VCR of 2024!

Almost all counties continue to trend above their 10 year average GDD, with the exception of Thunder Bay which is on trend with its 10 year average.

Crop Updates

Brassica Crops – Nutrient disorders have been common with head brassicas including sun scald, edema and splitting. In areas that have received excess moisture, white mould and downy mildew have also been observed. The second and third generation of cabbage maggot are active different regions. When scouting blocks, continue to dig up wilted plants and inspect the roots for maggots, clubroot or nematodes. The Cimegra (Group 30) label was temporarily expanded to help manage cabbage maggot in head Brassicas this year. Switch 62.5 WG (Groups 9/12) was recently registered for use on head Brassica’s for suppression against Alternaria leaf spot. After blocks are harvested, be sure to incorporate all crop residue in the soil to reduce the amount of surviving of larvae and inoculum available to infest and infect later plantings.

Carrots – Leaf blights are starting to show up so the ensure the crop is protected with a fungicide. Monitor for carrot rust fly as we have just passed a peak in most regions. Aster leafhopper infectivity remains elevated so monitor for flushes into the field.

Garlic – Most garlic has been cured and is going into storage. Once cured, table stock can be kept at a temperature of 0.5°C at a relative humidity of 50-70% and planting stock can be kept above 14°C (up to 18°C) at a relative humidity of 55-65%. Some harvested fields are showing bulbs with fat necks or internal rot above the cloves within the neck . The bacterial pathogen Pseudomonas fluorescens may be responsible. Pseudomonas is the same genus of bacteria that causes café au lait in garlic found in other garlic growing regions. In café au lait, there is sheath necrosis that rots bulb wrappers and leaves brown streaking on the remaining wrappers once the bulb is cured. Some plants show fat necks (Figure GP1), and there is rotten tissue above the cloves within the stem above the cloves (Figure GP2). To reduce the incidence of bacterial rot, implement at least a 4-year crop rotation. Rogue out infected bulbs and inspect planting stock prior to planting and avoid planting in poorly drained fields or parts of the field that encounter shade or poor air movement. Throughout the season, avoid overhead irrigation and late applications of nitrogen after the 5^th leaf stage.

**Figure GP1** – Plants with a fat neck showing bacterial infection within the neck identified as *Pseudomonas fluorescens.*

**Figure GP2** – Bacterial rot above the cloves within the bulb sheaths identified as *Pseudomonas fluorescens.*

Onions – Transplants are being harvested and some direct seeded fields are starting to lodge. The threat of downy mildew remains high, especially if inoculum is present from previous years (Figure 3). If the DOWNCAST forecasting model is not available to predict outbreaks for your area, a protective fungicide program for downy mildew is recommended during the humid weather we have been experiencing. Past research at the Ontario Crops Research Centre – Bradford has shown that Orondis Ultra (groups 40/49), Zampro (groups 45/40) and Orondis Gold (groups 4/M3) are effective for controlling this disease and are most effective when they are applied as a protective application before infection can occur. Stemphylium leaf blight is slowly causing tip dieback, but it is not as severe relative to previous years for mid-August. As fields of transplants are harvested, be mindful of younger, direct-seeded onions in border fields as the level of thrips may surge as they move to a greener crop.

**Figure 3** – Onion downy mildew – July 19^th, 2024.

Potatoes – Vines are collapsing in many fields as tubers continue to bulk. Seeing signs of early dying in some fields as the stress of excessive rainfalls early in the season and high temperatures are catching up to some varieties. Late blight should still be a main concern although infections have been well controlled with late-blight specific fungicides and the drier weather has helped dry lesions up. Expect early blight to set in as lower leaves start to yellow and senesce.

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***	1535	1400	1032	808	512	1148	1400	704
Chatham-Kent*	1883	1741	1342	1103	759	1470	1741	984
Durham***	1741	1599	1212	979	664	1335	1599	869
Essex*	2026	1879	1466	1216	863	1599	1879	1096
Huron***	1658	1519	1129	895	592	1254	1519	786
Kemptville***	1743	1604	1233	1006	694	1350	1604	898
Lambton**	1854	1714	1316	1075	747	1444	1714	960
Middlesex**	1868	1725	1322	1079	747	1451	1725	965
Norfolk**	1819	1675	1270	1030	702	1399	1675	916
Peterborough	1636	1498	1121	892	588	1242	1498	785
Renfrew	1753	1616	1246	1025	717	1363	1616	919
Simcoe***	1636	1499	1124	895	592	1243	1499	785
Sudbury***	1446	1324	989	782	505	1096	1324	683
Thunder Bay	1219	1100	780	594	350	880	1100	508
Timiskaming***	1407	1291	966	766	498	1070	1291	670
Wellington Centre**	1643	1504	1126	898	589	1245	1504	790
Wellington North**	1622	1486	1109	885	584	1230	1486	778