VCR – Vegetable Crop Report – June 30th, 2022

Temperature – All counties continue to match or surpass their 10 year average GDD.

Precipitation – Most regions received some rain over the past week. Kemptville’s total June precipitation is now just below it’s 10 year average. Peterborough, Simcoe, and Huron* are the only counties that have met or surpassed their 10 year averages. Most fall below however Wellington county only received approximately half it’s 10 year average rainfall for June.

(*Note: Due to unavailable data for Huron county last week, values from the closest available weather station were used. They have now been replaced with generated predictive weather data that better reflects the area. With this update Huron region has surpassed it’s 10 year average precipitation)

Crop Updates

Brassica Crops – Harvest continues for broccoli, cabbage and kale with early cauliflower fields starting soon. In areas that received adequate moisture, conditions have been more favourable for Alternaria (Figure 1). Reference the Ontario Crop Protection Hub to determine what products are registered for Alternaria depending on the Brassica. Alternaria resistance has been documented in other regions outside of Ontario and it is important to rotate FRAC groups after every Alternaria application. Cabbage maggot damage has been observed and is relatively average compared to other years. The degree day threshold for the second generation of cabbage maggot has been surpassed in Essex and shortly in Chatham-Kent and Norfolk. Diamondback moth and imported cabbageworms are the predominant insect pests currently with some fields showing very low levels of aphids and thrips. While scouting, dig up a few plants with a trowel and inspect the roots for nematodes, clubroot and cabbage maggot larvae. Cut open the stem and inspect for discolouration due to Fusarium yellows, Verticillium or Xanthamonas. Over the next week, look closely for thrips as well as Alternaria lesions.

Figure 1. Older cauliflower leaf with an Alternaria lesion. Alternaria often develops circular rings within leaf lesions.

Celery – Plants are establishing well. Aster leaf hoppers are active and in some fields the numbers are reaching the lower threshold of 10 leafhoppers/card. Scout and rogue plants showing yellow leaves/symptoms of aster yellows. It is unknown what percentage of aster leafhoppers may contain the aster yellows phytoplasma, but it is early in the season and the percent infected is likely to be low. If suspicious plants showing symptoms of aster yellows are found in or around the field, and the level of leafhoppers is high, it may be time for an insecticide application. Scout for tarnished plant bugs and scratch marks along the stalk left by carrot weevils. Dig up stunted and/or wilted plants and inspect roots for nematode cysts, or carrot weevil larvae or if plants were unable to establish properly after transplanting due to a lack of adequate moisture.

Cucumbers – looking at the calendar, this is typically the time of the year when we get the first report of cucurbit downy mildew in field cucumbers. To date we have not had any confirmed reports, but it is important to scout regularly. Broad spectrum fungicide sprays before the canopy closes are one of the best preventative management tools. While daytime temperatures above 30 C are not conducive to infections, consider nighttime temperatures and the duration of dewfall when planning your spray program. For more information, see https://onvegetables.com/2022/06/14/cucurbit-downy-mildew-get-out-and-scout-2/

Cucurbits Weeds – under dry conditions the performance of pre-emergence herbicides may be limited. If using Sandea post emergence keep in mind that it must be applied prior to the crop flowering.

Garlic – Plants with adequate moisture are bulbing up nicely. Drought and in some cases, excess moisture stress, can lead to virus symptoms (such as stunting, mottling or streaking) to be more pronounced than in early in the season. Adult leek moth counts have risen sharply this week which will result in an increase in feeding damage to leaves this week and next. 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 after peak moth capture. Multiple fields, in several areas across SW Ontario, are showing stunting in plants where the planting date was delayed after the bulb was cracked into cloves. Many of these fields were planted with bulbs that were cracked in late September or early October and planted 6-10 weeks later. Bulbs that have been cracked into cloves should always be planted within a week of cracking to avoid colonization of pathogens on wound sites. These pathogens (such as Fusarium and Penicillium), can weaken root establishment in the fall which may lead to increased winterkill and stunting the following year. Now is a good time to rogue out plants that show symptoms of viruses (like leaf mottling or stunting) in areas of the field where harvested bulbs will end up as planting stock for the 2022-2023 season.

Onions – The largest direct seeded onions are reaching the 7^th-8th leaf stage while most fields are still around the 5-6th leaf stage with transplant onions starting to form bulbs. The threshold for the second generation of onion maggot has been reached in Essex county, and other southern areas will likely reach this threshold later in the week. The level of thrips continue to be low, but are likely to reach threshold within the next two weeks in most onion growing regions if the weather is hot and dry. 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 as the first insecticide. If the number of thrips exceeds 3 thrips/leaf, Movento 240 SC (two applications) 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 has been detected and will likely be observed over the next two 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). Conditions were favourable for white rot over the past few weeks in some areas (Figure 2). Dig up plants that are wilting from the bottom/up and inspect the base of the plant for white mycelium with black sclerotia (Figure 3).

Figure 2. White rot of onion in a transplant onion field with lower leaves turning yellow and wilting – June 2022

Figure 3. White mycelium growing on onion bulb with black sclerotia present – June 2022.

Pest Degree Day Forecasting

*NOTE: Data as of June 29, 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*	1135	1039	771	622	433	856	1039	554
Chatham-Kent*	982	891	643	505	312	722	891	444
Norfolk**	993	904	655	510	310	735	904	446
Huron***	850	765	528	392	212	602	765	332
Wellington**	844	760	526	392	215	600	760	336
Simcoe County***	853	768	538	403	228	611	768	345
Durham***	912	823	580	441	248	657	823	378
Peterborough	842	758	523	393	209	597	758	333
Kemptville***	920	828	588	454	260	661	828	392
Sudbury***	712	644	453	338	178	515	644	287