VCR – Vegetable Crop Report – August 4th, 2022

Temperature – Most regions continue to match or surpass their 10 year average GDD with the exception of Peterborough which lags below but still follows the upward trend. Daytime temperature remain high in the mid-20s to low 30s over the next week, starting higher over the weekend before dropping slightly into the week. Nighttime temperatures are expected to range in the mid-teens to mid-20s across the province.

Precipitation – Many regions received at least some rain over the past week. Huron in particular received ~63mm yesterday and has now received almost its total cumulative precipitation for August just over the past 3 days. Rain with a chance of thunderstorms is in the forecast over the weekend and into next week in most regions.

Crop Updates

Brassica Crops – The dry weather has led to lower levels of Alternaria and other fungal pathogens, but has led to smaller stunted plants in some fields and tip dieback in others. Nutrient disorders have been common with head brassicas. In areas that have received adequate levels of moisture, white mould has been observed and the chance of bacterial rot is higher. 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. After blocks are harvested, be sure to incorporate all crop residue in the soil to reduce the amount of inoculum available to infect later plantings.

Celery – Early plantings of celery are being harvested. Blackheart/calcium deficiencies have been observed in low levels and conditions have been conducive for celery leaf curl. Avoid working in fields when the humidity is high, and the leaves are wet as celery leaf curl spores will stick to clothes and equipment. Leaf hopper counts are moderate to high in some areas, but the amount of Aster yellows remains low. Continue to dig up stunted plants weekly to examine the roots for nematodes, the hearts for carrot weevil damage or blackheart.

Garlic – Monitor humidity levels while you are curing the harvested crop. Curing / drying is often associated with an increase in temperature, however, when it comes to curing garlic, relative humidity should be the primary focus. Heating air increases the amount of moisture that the air can hold per cubic metre. A cubic meter of air can hold ~17 grams of water vapour at 20°C, while at 30°C it can hold ~30 grams. In most years, when the ambient air’s relative humidity is low, increasing the temperature greatly increases the water holding capacity of the air. Keeping the relative humidity low and curing the crop quickly has shown to be the best way to avoid garlic mites, fusarium development, and improve storage longevity. Good air circulation through totes, pallet boxes or baskets that reach all bulbs evenly will help to reduce over-curing some bulbs or under-curing others. Curing is complete when the bulb wrappers are crispy, the middle of the cut stem is hard, and the base of the stem is dry when cloves are removed. After harvest, incorporate field debris to reduce the likelihood of leek moth completing it’s lifecycle.

The Garlic Growers Association of Ontario (GGAO) is taking orders from members for clean planting material from the SPUD unit at the New Liskeard Agricultural Research Station, University of Guelph. GGAO members should E-mail garlicgrowersofontario@gmail.com as soon as possible to place an order. Roundels are expected to ship in September. For more information, see the garlic clean seed program here: https://onvegetables.com/2020/08/05/spud/.

The next garlic workshop is August 19^th from 9:30-4:30 near Janetville, ON. This workshop will focus on production and pest management of growing garlic in Ontario. Topics include clean seed production, cultivar selection, seeding spacing and density, crop insurance, weed control, pathogen and insect identification and management, crop rotation, scaping, upgrading equipment, cleaning, grading, curing and storage. Please register by contacting OMAFRA’s Agricultural Information Contact Centre by calling 1-877-424-1300 or filling out this registration form online: https://survey.clicktools.com/app/survey/go.jsp?iv=1y59n0qcz8rld.

Onions – Some early transplanted fields are lodging. Tip dieback is becoming more prevalent with Stemphylium, purple blotch, and bacterial leaf spot being observed as well. Areas with cooler nights, higher humidity and prolonged leaf wetness, have had favourable conditions for downy mildew development (Figure 1). Research at the Ontario Crops Research Centre – Bradford (Muck Station) has shown that Orondis Ultra (groups 40/49), Zampro (groups 45/40) and Ridomil Gold MZ (groups 4/M3) are the most effective at preventing disease development. Products containing mancozeb have shown to be effective if they are applied prior to downy mildew infection. The level of thrips have been low to moderate in most areas.

Figure 1 – Onion downy mildew will start as a tan lesion with purple-grey, velvety growth. Diseased leaves turn pale-green, yellow, and then collapse. Usually starts as a small patch then quickly spreads throughout the field – August 22, 2019.

Pumpkin and Squash – Powdery mildew infections are starting to increase. Powdery mildew is usually the most significant disease in pumpkins and squash, not to be confused with downy mildew which is more prevalent in cucumbers and melons. The fungicide controls for the two diseases are quite different, downy mildew fungicides will provide little control of powdery mildew (and vice versa). Powdery mildew controls are most effective if applied at the first sign of disease. Look for lesions of white fungal hyphae on the lower leaf surface or the leaf petioles.

Sweet corn – With August comes increased insect pest pressure. Summer storms originating in the southwest often carry both corn earworm and fall armyworm moths into the Great Lakes basin. These 4^th instar fall armyworm larvae were found in sweet corn near Ridgetown (Figures 2 and 3). Scout regularly for signs of feeding, frass or egg masses. For sweet corn in the pre-tassel stages, pyrthroid sprays offer control of fall armyworm and western bean cutworm. For corn earworm control during silking, either a group 28 insecticide (Coragen or Voliam Xpress) or Lannate (group 1A). There is widespread resistance to pyrethroids in the corn earworm population.

Figure 2 – Fall armyworm larvae found recently on sweet corn in Ridgetown

Figure 3 – Fall armyworm damage and frass on sweet corn in Ridgetown

Pest Degree Day Forecasting

*NOTE: Data as of August 3rd, 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*	1824	1693	1321	1101	808	1440	1693	999
Chatham-Kent*	1636	1510	1157	949	638	1271	1510	854
Norfolk**	1618	1493	1140	924	606	1255	1493	825
Huron***	1436	1316	974	768	469	1083	1316	673
Wellington**	1409	1290	950	746	451	1060	1290	656
Simcoe County***	1433	1313	977	772	478	1085	1313	680
Durham***	1522	1397	1050	841	529	1161	1397	743
Peterborough	1352	1232	894	695	408	1002	1232	603
Kemptville***	1535	1408	1062	858	546	1170	1408	761
Sudbury***	1258	1156	859	675	396	957	1156	589