Temperature – Temperatures are expected to remain below 30C this upcoming week and may even drop to the low 20s in many regions. All regions have surpassed their GDD 10 year average. Carrot rust fly is at its second threshold in Essex, Chatham-Kent, Norfolk, and Durham regions, and Kemptville. Onion maggot has reached threshold in all regions except Essex which has now passed the second threshold range. Cabbage maggot and Seedcorn maggot are at threshold in Sudbury. Degree day data for each region is shown below.
Rainfall – Many regions received precipitation levels near their 10 year averages in July but still lag marginally behind. Exceptions include Durham and Peterborough regions, which received around half their 10 year precipitation averages, and Sudbury, which received more than double the 10 year average. There is a chance of thunderstorms starting Sunday and chances of rain continuing into the week throughout Ontario. Precipitation data for each region is shown below.
Brassica Crops – Lepidopteran pests continue to be an issue across the province. For information on scouting thresholds, see the VCR post from June 18. 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. Alternaria is starting to show up in some fields. As blocks are harvested, incorporate residue to lower the overall spore load. Often bacterial rots enter broccoli or cauliflower heads where an insect has chewed or where fungi have damaged the cell wall. With uneven heads and trapped water droplets, it’s likely that there will be bacterial rot observed over the next few weeks. Given the high humidity and colder mornings, be on the lookout for downy mildew.
Carrots – Leaf blights continue to show up in some fields. Alternaria leaf blight will look like the leaves are burnt. Cercospora leaf blight will be spotty with elliptical lesions on the stems. Not all fungicides will work on both blights. Use a 25% incidence spray threshold. Some areas of the province are at risk for the second generation carrot rust fly. It’s easy to monitor for carrot rust fly with yellow or orange sticky cards around the edge of the field.
Celery – Bacterial rot is taking down infected plants in some fields and celery leaf curl has been observed in several fields. Tarnished plant bugs are active.
Cucurbits – Harvanta (cyclaniliprole) is now labelled for cucumber beetle suppression. Refer to last week’s VCR for usage details – cucumber beetles remain active. We are continuing to track this year’s downy mildew epidemic, if you are observing symptoms of downy mildew on any crops including melons (including watermelon), pumpkin, and squash we would be interested in hearing from you.
Squash bugs are increasing, but do not usually cause problems in commercial fields as they are susceptible to several insecticides. When scouting, take note of egg masses like the ones in Figure 6, the threshold is one egg mass per plant.
Continue to scout for Phytophthora in cucurbits and other crops: Examine low lying or poorly drained areas noting any wilted or stunted plants, and look for lesions. Phytophthora usually presents as a foliar blight or a crown rot in zucchini, squash, and pumpkin, so look for dark lesions on the crown. In cucumbers and melons Phytophthora usually causes fruit and stem lesions so look for water soaked lesions with white spores developing on the fruit. Maintain good biosecurity practices, and please contact Andrew Wylie (firstname.lastname@example.org) or Katie Goldenhar – Pathologist-Horticulture (email@example.com) if you observe symptoms resembling Phytophthora.
Garlic – Thinking of planting a new cultivar? Take a look at last year’s garlic cultivar trial that summarizes 22 cultivars grown at three field sites – Click here to visit the 2019 Garlic Cultivar Trial post. Be sure to test all planting stock for bulb and stem nematode before planting in your field. Low levels of nematodes can be found in planting stock that otherwise looks great.
Onions – Be on the lookout for downy mildew given the high humidity, heavy dews and colder mornings. The 2017 Muck Crops Research Station Greenbook report summarizes downy mildew product efficacy on page 66: Click here to visit page 66 of the 2017 Greenbook. Stemphylium, purple blotch, botrytis, onion smut, pink root have been observed.
Potatoes – Second generation of CPB seem to be emerging in some fields. If numbers are above threshold don’t use a foliar neonic (Assail, Alias, Admire, Actara, Clutch) if you used a neonic at planting (Actara, Titan, Cruiser Maxx). No reports of late blight in the region but protectant sprays are still important. Starting to see some early blight show up on older leaves. Localized outbreaks of leafhoppers have been seen in some fields. Keep an eye out for European corn borer in some regions of the province (check table below for your region).
Sweet corn – Sweet corn harvest is underway and lepidopterans are numerous. Click here to listen to last week’s interesting podcast on caterpillars in sweet corn from the Great Lakes Vegetable Producer’s Network (also available on Spotify and Apple Podcasts) and check out the Great Lakes and Maritime Pest Monitoring Network for up-to-date reports of pest levels.
NOTE: Data as of July 29th, 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: