VCR – Vegetable Crop Report – July 15th, 2021

Temperature – Daytime temperatures are forecasted to range from low to high twenties during the day for the next week in most regions.

Nighttime temperatures are forecasted to from mid to high teens over the next week depending on region. Onion maggots are at thresholds in all regions except Peterborough and Sudbury. Carrot Rust Fly is at threshold in Essex. Cabbage maggot and seedcorn maggot are at threshold in Huron, Wellington, Simcoe, Durham, and Kemptville. Degree Day data for each region is shown below.

Rainfall – Most regions, except Sudbury, are anticipated to have rainfall up to Wednesday of next week. The regions of Simcoe, Wellington, Durham, and Peterborough have received enough rain to match or surpass their 10-year averages and most other counties are close to matching pace of their 10-year averages. Precipitation data for each region is shown below.

Crop Updates

Beans – Potato leaf hopper have been observed in snap beans, however this pest is not usually problematic after the crop reaches the 3^rd trifoliate. See European corn borer comments (here). Temperatures above 26C during the period of blossom development and during pollen shed can impact bean pod development and even result in the abortion of the pods, causing split sets. High night time temperatures (above 20 C) have a great impact than daytime temperatures.

Brassica Crops – Alternaria and Sclerotinia white rot have been observed. For both pathogens, residue from harvested blocks should be incorporated as soon as possible to reduce inoculum. In drier years, allowing the top inch of soil to dry out between irrigation events can help with Sclerotinia development, but this year that does not seem possible in many areas. Managing chewing insects will also reduce the spread of Sclerotinia. Given all the precipitation over the past couple of weeks, some fields are showing symptoms of nutrient imbalances which have resulted in tip dieback, leaf edema and/or sun scorch.

Carrot – The risk of Alternaria and Cercospora leaf blights is high (Figure 1). You can use a 25% spray threshold for leaf blights.

Also, use the opportunity before the canopy closes to apply a white mold specific fungicide if you are planning on storing carrots. With the amount of soil moisture we now have, when the canopy closes it will be ideal conditions for white mold to develop.

**Figure 1**. Cercospora leaf blight on carrot leaves

Celery – Weather continues to be conducive for celery leaf curl development (Figure 2). Blackheart, leaf blights and bacterial rot are likely to develop in areas that have received access moisture. Avoid prolonged periods of leaf wetness and allow the canopy to dry out between irrigation events. Dig up stunted plants and examine the roots for nematodes, the hearts for carrot weevil damage or blackheart.

**Figure 2**. Celery leaf curl suspect, July 13^th, 2021

Cucumbers – Cucurbit downy mildew has been confirmed at one location in Norfolk County and two additional locations in Kent County. Disease severity is low at all locations where preventative fungicides have been applied. There have been a few reports of fruit rots. If you are seeing fruit rots in your field, please follow up with elaine.roddy@ontario.ca or ctrueman@uoguelph.ca. We would like to keep track of which pathogens are causing fruit rot problems in the field this year. With the extended wet conditions in several growing regions, we are concerned about the development of Phytophthora.

Garlic – Allow the crop to reach at least 40% yellowing/senesce before harvesting for better yields and increased storability. As the crop dies down, pay attention to leek moth counts. Leek moth peaks that occur later in the season will mean larvae that hatch between now and harvest will be searching for green tissue and may move to the bulb as they feed instead of remaining in the leaf tissue or stem. With the excess humidity over the past two weeks, garlic rust (Figure 3), has developed in some fields. If rust is a reoccurring issue every year, consider moving next year’s crop away from the field that’s currently infested, decreasing planting density and observing a four-year crop rotation. Other production practices to avoid rust are to avoid planting near hedgerows that shade the crop or in areas that are protected from the wind.

**Figure 3**. Garlic rust found on a few plants near a windbreak in 2018

Onions – Many areas are at a high risk of onion downy mildew. The 2017 Muck Crops Research Station Greenbook report summarizes downy mildew product efficacy on page 66. Past research at the 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 for controlling this disease and are most effective when they are applied as a protective application before infection can occur. Stemphylium (Figure 4), continues to develop and many fields are making great gains in bulbing given the adequate amount of soil moisture available. Levels of thrips remain low which makes sense given the amount of precipitation that has occurred in most regions. The second flight of leek moth is underway and onion fields that have not had a recent insecticide application may be at risk. Leek moth creates window-paning feeding damage in onions that can be mistaken for Botrytis or herbicide damage. Cut open leaves of suspect plants and look for leek moth frass and larvae (Figure 5). Many regions have also entered their second generation of onion maggot. Be on the lookout for onion downy mildew and stunted/wilted plants due to onion maggot over the next week.

**Figure 4**. Stemphylium leaf blight development in some 8-10 leaf stage plants, July 13, 2021

**Figure 5**. Leek moth larvae feeding damage on onion leaf, July 7, 2021

Potatoes – Late blight, late blight, late blight. Keep spraying those late blight specific fungicides any way you can because risk remains high. Spores have been caught in spore traps, the crop is lush and healthy and it’s late blight weather. All the ingredients needed for late blight to develop (Figures 6 – 9). Continue to scout diligently for signs of late blight in the crop. Check the growing point of the plants and in the canopy for signs of dark water-soaked lesions with a yellow halo, usually at the margins of the leaves. Look for white fuzzy sporulation on the underside of the leaves as well. Late blight can develop on any part of the potato plant.

**Figure 6.** Late blight lesions on the underside of potato leaves (Photo courtesy of Eugenia Banks)

**Figure 7.** Late blight infecting stem and leaves (Photo courtesy of Eugenia Banks)

**Figure 8.** Late blight damage to potato leaves

Late blight symptoms on potato leaf — **Figure 9.** Late blight damage to potato leaves

Continue to monitor for insects as high numbers of Colorado Potato Beetles from this spring may be re-emerging to feed. Leafhopper counts have also been high for most of the season so look for symptoms of hopperburn and adults/nymphs on the underside of the leaves (Figure 10).

**Figure 10.** Leafhopper adults/nymphs on the underside of potato leaves

Pumpkins and Squash: Squash bugs are active. The adult resembles a stink bug, and the nymphs are a powdery grey colour with black legs. They often congregate in large groups with various life stages feeding together. The eggs are bronze coloured and bullet shaped, they are laid in clusters (Figure 11). The threshold for eggs is and average of one egg cluster per leaf (inspect a minimum of 100 leaves across the field). This pest is not usually a big problem, unless they start feeding on the developing fruit.

**Figure 11.** Squash bug eggs on the underside of leaf

This is a good time to scout pumpkin and squash fields during the early morning hours for bee activity (Figure 12). The bulk of pollination activity occurs prior to 9am. Count the number of bees on 25 blossoms, and repeat the process in 4 areas of the field. Counts should be taken between the hours of 6 and 8 am. Research done by Dr. Susan Chan, University of Guelph, suggests that if you have an average of 7 bees per 25 blossom, you have sufficient pollinators. Survey work in commercial pumpkin and squash fields across Southwestern Ontario from 2016-2018 indicates that many fields have good populations of the native pollinator, the hoary squash bee.

**Figure** 12. A bee pollinating a pumpkin/squash leaf

Sweet Corn – Based on the growing degree days for European Corn Borer, we are approaching peak flight in the univoltine regions. However, the Great Lakes and Maritime Pest Monitoring Network is not reporting any significant EBC catches at this time. In the bivoltine regions (Kent and Essex) we have not yet reached the growing degrees required for the start of the second generation. The GLMPMN is not reporting any corn earworm activity at this time either. Great Lakes and Maritimes Pest Monitoring Network 2021 (arcgis.com)

Pest Degree Day Forecasting

*NOTE: Data as of July 14th, 2021

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*	1447	1330	995	806	572	1100	1330	723
Chatham-Kent*	1306	1193	885	709	457	982	1193	629
Norfolk**	1297	1186	879	703	454	977	1186	622
Huron***	1195	1090	804	638	398	892	1090	563
Wellington**	1153	1045	757	591	360	847	1045	516
Simcoe County***	1186	1076	779	612	382	871	1076	537
Durham***	1206	1097	793	632	397	886	1097	559
Peterborough	1089	978	681	520	302	772	978	447
Kemptville***	1221	1111	799	621	379	899	1111	543
Sudbury***	996	901	651	514	304	727	901	449