Temperature – Temperatures are expected to rise again moving into the weekend. All regions remain above their GDD 10 year average. Onion maggot has reached threshold in all regions except Essex and Sudbury. Carrot rust fly is at its second threshold in all regions except Essex, Chatham-Kent and Norfolk. Degree day data for each region is shown below.
Rainfall – Simcoe region has already received significantly more rain than its 10 year average for August and many other regions are also nearing their 10 year averages. There is a chance of rain and thunderstorms across the province beginning Monday (or Sunday in some areas). Precipitation data for each region is shown below.
Beans & Peas – Cooler wet conditions have been favourable for the start of white mold in beans caused by Sclerotinia sclerotiorum. Apothecia may be visible where sclerotia have germinated (Figure 1): sclerotia can survive for up to 5 years in soil which can exceed shorter crop rotations. Look inside the canopy for white cottony mycelial growth, especially in fields that have dense canopies from close row spacing or nitrogen fertilization. Initial infections often occur on flower petals that have fallen into the canopy. As noted for peppers, European corn borer is active.
Brassica Crops – Conditions have been favourable for Alternaria, Sclerotinia, clubroot, bacterial rot and downy mildew development in some areas. High temperatures from 3-4 weeks ago has been hypothesized to be the reason there is uneven growth in broccoli or cauliflower heads that are currently being harvested. If heads are uneven and trap water droplets, bacteria may enter and cause rotting in the heads. If irrigating, allow the canopy to dry out quickly by irrigating in the morning opposed to the late afternoon/evening. The level of lepidopteran pests remain high in most areas and thrips have been observed in high numbers in some fields.
Carrots – Leaf blights remain important to stay on top of. As canopies close it may be helpful to get in a white mold specific fungicide if the field has a history of Sclerotinia white mold.
Celery – Bacterial leaf spot and blackheart/calcium deficiencies have been observed. Conditions have been conducive for celery leaf curl. tarnished plant bugs, wireworms, and aster leafhoppers are active.
Cucurbits – Downy mildew pressure remains high (Figure 2), and has now been confirmed on cucumbers as far North as Wellington county. Early detection of downy mildew this year increases the possibility of fungicide resistance. If you think that you may have downy mildew that is not well controlled by rotating Orondis Ultra, Torrent, and Zampro, please contact Andrew C Wylie (email@example.com) or Katie Goldenhar – Pathologist-Horticulture (firstname.lastname@example.org).
Cucumber beetles continue to be active, if you haven’t reviewed the usage details in our earlier VCR for Harvanta (cyclaniliprole), this has been registered as an alternative insecticide labelled for this pest.
Wet weather increases the risk of Phytophthora in cucurbits and other crops: Examine wet areas for wilted or stunted plants, looking for dark crown lesions on zucchini, squash, and pumpkin, and for water-soaked lesions with white spores developing on the fruit in cucumbers and melons.
Powdery mildew is developing on several cucurbits, particularly squash and pumpkin. Infection with this pathogen can affect yield and fruit quality. High humidity increases the spread of powdery mildew although it does not need leaf wetness for infection. Scouts should inspect 10 leaves at 20 random locations in the field to determine % infection – 2% of leaves with one lesion is the control threshold. Powdery mildew is sometimes confused with downy mildew: See Figure 3 for a comparison of signs and symptoms.
Garlic – The Garlic Growers Association of Ontario has just announced that it is taking orders from members for clean planting material from the SPUD unit at the New Liskeard Agricultural Research Station, University of Guelph. E-mail email@example.com for the roundel order form and if you are not a member, the membership form as well. The cut-off to become a member and order this year is August 15th, 2020. Roundels are expected to ship in September. For more information, see the recent article on garlic clean seed program here: https://onvegetables.com/2020/08/05/spud/
Onions – Transplant onions are starting to lodge and seeded onions are bulbing. Tip dieback is becoming more prevalent with Stemphylium, purple blotch, botrytis and bacterial leaf spot being observed as well. Conditions over the past week have been favourable for Stemphylium and be on the lookout for downy mildew as plants have been experiencing prolonged periods of leaf wetness. The level of thrips has been low.
Peppers – continue size, set new fruit, and some varieties are starting to be hand harvested this week. The second generation of European corn borer is flying and laying eggs so be sure to be on the lookout for adults and scout for larval entry holes in the peppers. As of Wednesday, August 6th 2020, no pepper weevil have been caught on any outdoor traps in our pepper weevil monitoring program. A couple specimens have been brought for identification, but no populations of pepper weevil have been reported. Recently there have been a number of inquiries about sprays for pepper weevil in field peppers. With limited options for pepper weevil control, sprays should only be used when pepper weevil is present in your field, which is why monitoring traps and scouting regularly is so important. Pepper weevil can look similar to other native weevil species so if you think you have pepper weevil adults on traps, or damage in your crop, please confirm the ID by send pictures or specimens to Cassandra Russell (firstname.lastname@example.org) or Cara McCreary (email@example.com). Another helpful tool for correctly identifying pepper weevil adults on sticky cards can be found here: What weevil warrants worry.
Potatoes – Vines are collapsing in many fields as tubers really bulk up with the recent rains. The early regions of the province are ramping up harvest in the next week or two. Some early reports of bacterial rots, scab and secondary growth. All not very surprising considering the stretch of hot and dry weather we had at a critical time with little the growers could do to mitigate. No cases of late blight have been reported in the area but stay vigilant.
Tomatoes – The rains have been welcomed by field tomato growers, but in certain varieties fluctuations of soil moisture (heavy rains followed by hot and dry) will favour disorders such as leaf curling and blossom end rot. Some fruit are showing signs of bacterial spot/speck. It’s important to remember that prevention is the best tool against bacterial diseases in tomatoes. Late blight has not been reported anywhere further north than North Carolina so far this season. Spores that cause this serious disease in tomatoes tend to move up from the southern US throughout the season and will cause brown, greasy-looking spots on developing fruits. If you are looking for a refresher on scouting and identifying diseases in tomatoes, you can click here to watch this lecture by OMAFRA pathologist, Katie Goldenhar.
Sweet corn – Sweet corn is being harvested and lepidopterans continue to build. Monitor the Great Lakes and Maritime Pest Monitoring Network for up-to-date reports of pest levels. Traps have been filling with gypsy moth adults. Identification of gypsy moth adults can be difficult because when they are collected in large numbers their scales can rub off. This reduces their markings and creates a red spot on their back.
NOTE: Data as of August 5th, 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|
*- Bivoltine region for ECB. First Peak Catch: 300-350 DD, Second Peak Catch 1050-1100 DD
**- Overlap region for ECB. First Peak Catch : 300-350 DD Second Peak Catch 650-700 DD, Third Peak Catch 1050-1100 DD
***-Univoltine region for ECB. Peak Catch 650-700 DD
Use these thresholds as a guide, always confirm insect activity with actual field scouting and trap counts.
Select a region below for the latest weather, crop and pest degree day information: