VCR – Vegetable Crop Report – June 25th, 2020

Ontario DD Map_jun24 Temperature – Temperatures dropped towards the end of this past week but will increase again into the upcoming week. With the humidex, we may see temperatures reaching the high 30s throughout Ontario. All regions have similar GDD to the 10 year average and are following the same increasing trend. Onion maggot thresholds have been surpased in all regions except Essex, Chatham-Kent and Norfolk which exited the first stage. Seedcorn maggot is at threshold in all regions except Essex and Sudbury. Essex, Chatham-Kent, Norfolk and Durham regions are at the second threshold stage for Carrot Weevil. Degree day data for each region is shown below.

Rainfall – Rain showers are forecasted for most regions over the weekend. The chance is higher in South Western Ontario where there is also a risk of thunderstorms. No rain is expected for the remainder of the week. Huron, Simcoe, and Sudbury monthly precipitation are reaching the 10 year average levels while all other regions, particularly Durham and Kemptville regions, lag behind. Precipitation data for each region is shown below.

Crop Updates

Asparagus – Continue to scout ferns for insects and fungal disease. Be on the look-out for rust developing, especially on young plantings, which can then move to mature fields later this season.

Brassica Crops – See last weeks VCR for scouting for lepidopteran pests such as diamondback moth and imported cabbage worm. Flea beetle pressure has decreased in most areas. Dig up wilted plants with a trowel or shovel and inspect the roots. Wilting can be caused by several pest/pathogens including cabbage maggot, nematodes, clubroot or wireworm damage.

Carrot – Carrots are growing well now that they’ve received some rain and are enjoying this weather. We’re nearing the end of carrot weevil egg laying in most areas, so if the field was later planted and not yet at the 2^nd leaf stage the risk of damage is decreasing.

carrot_jun24 — Young carrots growing nicely between the protection of barley.

Celery – Tarnished plant bug and aster leafhoppers are active. Scout for Aster yellows and celery leaf curl and rogue out infected plants. Plants showing symptoms this early in the season will be a source of inoculum for infections later in the season.

Cucurbits – Now that we have had some precipitation, scout for wilting and test for bacterial wilt. Remove affected plants to control spread during second emergence of cucumber beetle. Look for virus symptoms so that infected plants can be rogued out before aphid populations start to build in July. A reminder that downy mildew has been confirmed in SW Michigan, so growers should switch to downy mildew specific programs. Click here to see our post on downy mildew in the Great Lakes region for more details. We are continuing to monitor for the arrival of both downy mildew spores and downy mildew symptoms in Ontario.

Garlic – Scaping is wrapping up and the amount of leek moth captures is increasing in several regions signaling the start of the second flight. 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 days after the date of peak moth capture and the second treatment 14 days later. Products such as Matador, Delegate, Entrust, Successs, XenTari and Bioprotec are most effective when they make contact with the larvae.

Leafy Greens – With the hot, dry conditions, germination has been uneven leading to large variation in plant maturity in some fields. Tip burn from dry weather has been observed in a few fields and cutworm pressure continues to be higher relative to other years. Rhizoctonia, Fusarium and Pythium continue to be issues as some fields have been experiencing extremes when it comes to soil moisture. Tarnished plant bugs and aster leafhoppers are active.

Onions – The warm weather has created favourable conditions for Stemphylium leaf blight. For the first application, Sercadis (group 7) or a product containing mancozeb (group M3) may provide protection. Mancozeb products such as Manzate Pro-Stick, Dithane Rainshield, and Penncozeb 75 DF Raincoat are registered for Botrytis and Manzate Pro-Stick is registered for Botrytis and Alternaria/Purple Blotch. Avoid applying products from the same chemical group one after the other. Research has shown that there is very high resistance in Stemphylium to one of the fungicides in Quadris Top (group 11/3) and high resistance to one of the fungicides in Luna Tranquility (group 7/9). The 2019 Muck Crops Research Station Greenbook Report has Stemphylium trial results starting on page 69. While scouting, dig up wilted plants and look for maggots, wireworms or pink root. The pressure of thrips is low but will increase dramatically as we see more hot and dry weather. 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. If the spray threshold exceeds 1 thrips/leaf, Movento 240 SC could be followed by two applications of Agri-Mek (group 6), and then two applications of Delegate (group 5) and two applications Exirel (group 28). 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.

onion_jun24 — Onion leaf with *Stemphylium* or *Alternaria* spores causing black spotting in tan lesion – June 24, 2020.

Potatoes – The crop is at varying growth stages across the province, from emergence to bulking. Many fields are filling the row or starting to flower and it’s a critical time for fungicide application. As rows close, with the recent rains and cooler weather, the risk of disease is increasing. If you used Velum Prime in-furrow, don’t use a fungicide that contains a Group 7 (Aprovia Top, Cantus, Sercadis, Vertisan, Luna Tranquility) for your first foliar application. Colorado Potato Beetle are out in full force right now. If you are seeing high levels and potential early breakdown of the at plant insecticide please contact Dennis (519-766-5337). The resistance testing of populations will continue in 2020 so that we can determine the best way to adjust our management strategies in the future.

CPB_jun24 — Colorado Potato Beetle larvae feeding ferociously.

Rhubarb – Widespread leaf spotting was observed on rhubarb last week. Temperature fluctuations have provided a challenge for rhubarb this year.

rhubarb_vcr20200625 — Photo by Katie Goldenhar

Sweet corn – Scout fields in the evening or on overcast days when armyworm is active; this pest has moved into sweet corn. Concentrate on the edge of fields, especially those that border grain crops. If scouting during the day look for ragged feeding damage, frass, and potentially armyworm larvae hiding in the whorl or in the soil at the base of the plant. Check for the presence of parasitoid eggs on the larvae, this indicates that parasitic wasps are active and sprays may not be required. Some fields have been sprayed: thresholds are low on seedling corn, mid-whorl corn will be more tolerant if the growing tip is not damaged before the V7 stage.

NOTE: Data as of June 24th, 2020

Pest Degree Day Forecasting

Pest	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*	947	852	613	492	339	685	852	438
Chatham-Kent*	835	746	532	420	258	595	746	370
Norfolk**	834	745	520	409	249	586	745	358
Huron***	692	620	439	335	192	493	620	287
Wellington**	685	607	421	322	188	477	607	278
Simcoe County***	689	613	432	333	201	488	613	288
Durham***	739	659	461	358	212	518	659	311
Peterborough	695	615	424	322	185	480	615	276
Kemptville***	725	648	453	353	215	509	648	308
Sudbury***	577	519	371	291	172	415	519	254