VCR – Vegetable Crop Report – July 4, 2024

Welcome back to the next VCR Report of 2024! All counties continue to trend above their 10 year average GDD.

Crop Updates

Brassica Crops – Alternaria is active and early detection and management of Alternaria will reduce potential inoculum later in the season. Incorporate all left over plant tissue immediately after harvest to lower the amount of inoculum available to infect later plantings. With the hot, wet weather be on the look out for Sclerotinia/white mould. The mould tends to start near the ground on plants and as it infects it creates dark, water-soaked areas on the lower leaves near the base at the soil line. As the pathogen progresses you may see white mycelial growth. These water-soaked lesions enlarge and can cause the leaves to wilt. Infected cabbage heads will retain their shape but will be filled with a soft, watery rot. If conditions are favourable for the Sclerotinia, you will see the white mycelial growth followed by small, black spots/spores that look like mouse droppings within the fluffy white growth. These black spores can overwinter in the soil for up to 8 years and the best preventative management strategy is to rotate with non-susceptible crops such as beets, onions, spinach, corn, cereals or grasses. It is also helpful to decrease the plant density of the field to allow for adequate air circulation. Allow the top inch of soil to dry out between irrigation events and incorporate residue from harvested areas as deep as possible. Continue to scout for lepidopteran pests, aphids, and thrips. Thresholds for lepidopteran pests using the cabbage looper equivalent can be found here: https://onvegetables.com/2024/06/06/vcr2024-6/.

Carrots – Aster leafhoppers are active and infectivity is thought to be high this year. Monitor your fields using sticky cards and registered products can be found on the Ontario Crop Protection Hub.

Cucumbers – downy mildew is present in Norfolk, Elgin and Kent growing areas. Weekly applications of targeted downy mildew fungicides will be required to maintain control throughout the season. Always rotate between the three different fungicide families (Orondis Ultra, Zampro and Torrent) for resistance management.

Garlic – Harvest has started in some regions where the plants have had several leaves turn yellow and senesce. Allow the crop to reach at least 40% yellowing/senesce before harvesting for better yields and increased storability. Symptoms of Fusarium basal rot, Botrytis neck rot and stem and bulb nematode will cause pre-mature senesce (Figure 1). Depending on how quickly your soil dries out, avoid irrigating too close to harvest as soil stuck to the bulb will make it more difficult to achieve a clean wrapper. If black plastic has been used for weed control, cutting it open to allow the soil to dry before harvest can also help with trimming and wrapper cleaning. If leek moth counts were high last week, consider targeting the larvae that are now feeding on the crop. If mites or Fusarium were issues in storage last year, refer to this article with information about curing: https://onvegetables.com/2021/12/09/stored-garlic-might-have-mites/

**Fig. 1** Infected plants with Botrytis neck rot appear stunted and green leaves can develop water-soaked lesions, wilt and eventually turn yellow (A). Plants infected with stem and bulb nematode show similar symptoms with yellowing of the leaves from the bottom of the plant moving upward, but the leaves turn yellow before wilting (B).

Onions – The threshold for the second generation of onion maggot has been reached in many counties over the past week so be on the lookout for second generation onion maggot damage. Stemphylium has been observed in multiple fields across the province. 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, 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 against group 7 or group 29 fungicides so that they can be used to manage Stemphylium for future years.

Potatoes – Late blight has been confirmed in Elgin County. Even though it was a few plants in one field, growers in all regions should be vigilant and ensure plants are protected with a late blight specific fungicide. Disease risk remains high. Plants are growing vigorously and new growth needs to be protected. Lab testing has identified the strain as US-23. This strain is highly aggressive on tomatoes as well as potato tubers but less so on potato foliage. This strain should still be susceptible to Ridomil. Visit the Ontario Crop Protection Hub to view registered late blight specific products on potatoes. Review the potato late blight entry in Ontario CropIPM to refresh yourself on what late blight infection looks like.

Pumpkins and Squash – We have had early reports of powdery mildew in squash. This disease usually appears in late-July, however the early start to the hurricane season will bring a wide range of pathogens and insects into the Great Lakes region. Early control is essential. Apply preventative fungicides before row closure, to ensure good coverage of the lower canopy. Keep in mind that the group 11 fungicides are resistant to this pathogen.

Sweet corn – looking at the weather patterns, we can expect to see earworm moths moving into the Great Lakes region. At this time of year, populations tend to be sporadic with numbers increasing over the summer months. Any green silk is at risk of infestation. Target insecticide sprays at the silks, ensuring thorough coverage. Corn earworm populations have developed resistance to pyrethroid insecticides. The group 28 insecticides, Coragen and Voliam Xpress, are registered for earworm control.

Corn earworm larvae (figure 2) range in colour from green to beige to pink. Look for the double fine line running along the back of the larvae.

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***	952	852	589	435	244	670	852	367
Chatham-Kent*	1234	1126	833	663	425	925	1126	579
Durham***	1083	978	696	533	323	784	978	458
Essex*	1346	1234	926	745	498	1023	1234	660
Huron***	1053	948	664	500	302	754	948	426
Kemptville***	1082	978	711	555	348	793	978	482
Lambton**	1180	1076	786	617	397	878	1076	538
Middlesex**	1211	1102	804	632	404	899	1102	553
Norfolk**	1168	1059	759	590	366	853	1059	510
Peterborough	1007	904	632	472	274	718	904	401
Renfrew	1062	961	699	550	350	780	961	480
Simcoe***	1016	914	643	485	287	728	914	410
Sudbury***	814	729	506	374	209	576	729	313
Thunder Bay	656	573	358	242	103	423	573	191
Timiskaming***	832	750	530	400	237	599	750	340
Wellington Centre**	1040	935	662	504	300	746	935	431
Wellington North**	1022	921	650	495	299	735	921	423