Temperature – Extreme heat and high temperatures continue this week in all regions. Many regions are also beginning to surpass their GDD 10 year average. Onion maggot and Cabbage maggot have reached the second threshold level in Essex. Seedcorn maggot is at the second threshold in Essex, Chatham-Kent, and Norfolk counties. Degree day data for each region is shown below.
Rainfall – All regions received little to no rain over the past week with the exceptions of Essex county and Sudbury. Sudbury is on track to reach its 10 year average. There is a risk of thunderstorms and possible heavy rain over the weekend in all regions. Precipitation data for each region is shown below.
Brassica Crops – The dry weather has caused some heat stress that has resulted in wilt in many fields. Not only is wilt caused by extreme temperatures, it can also be caused by cabbage maggots, wireworms, clubroot and other pests/pathogens that are targeting the roots or a combination of several variables. It is a good idea to dig up wilted plants with a shovel and examine roots to see if any pests are present or if the wilt is caused from the heat. Lepidopteran pests are present many fields, mainly imported cabbage worm and diamondback moth. Refer to the newsletter from June 18 for information on thresholds. Softrot and white mould are active in some areas and Alternaria has been observed in some fields. Keep an eye out for thrips as the hot, dry weather can allow for populations to increase rapidly.
Carrots – It’s hot out there. Stands are all over the place. Pre-emerge activity was poor in later seeded carrots due to dry conditions. It’s shaping up to be a carrot oil year for weed control. The ‘carrot oil’ label can be found here: (info) (label). It might be a good time to think about investing in a band sprayer. Listen to our discussion on everything carrot weed control while you’re out checking irrigation this week (What’s Growing ON? Ep. 2 is also available on Spotify or Apple Podcast)
Cucurbits – Downy Mildew has been found in Ontario: it was found in Kent County on July 6th, (click here to read our post on Cucumber Downy Mildew Confirmed in Kent) Elgin County on July 7th and Norfolk County on July 7th. There are also confirmed cases in Michigan and New York. Check out our post (Cucumber Downy Mildew Confirmed in Great Lakes Region – June 22, 2020) for more details including spray recommendations: growers should be using downy mildew specific fungicide programs in the Great Lakes region. Hand-harvest of cucumbers is now underway in all cucumber growing regions.
Continue to scout for virus and bacterial wilt symptoms: infected plants should be rogued out before aphid populations build, and cucumber beetles continue to be active (Listen to our discussion on What’s Growing ON? Ep. 3 for more info on cucumber beetle. Also available through Spotify and Apple Podcasts) . Look for spider mite damage starting due to hot dry weather: because this can resemble drought stress, look for bronzing as well as the presence of mites, eggs, and webbing. Thrips have been problematic in several cucurbits during this hot, dry spell including pumpkins and watermelon.
Garlic – With some early cultivars being harvested and the bulk of the crop being harvested over the next couple of weeks there are a few things to keep in mind; the ideal time to harvest porcelain cultivars (such as Music) is when 50% of the leaves have senesced or turned yellow. Since it takes several days to harvest, many growers start at 40% and by the time the crop is fully harvested it may have reached 70%. Harvesting later you risk the plant lodging which makes it more difficult for bulbs to be picked up by belt harvesters. Leaving the crop in the ground longer is also a risk since moisture can degrade the bulb wrapper before trimming and cleaning. If black plastic has been used for weed control, cutting it open to allow the soil to dry before harvest can also help with harvesting and trimming; but be sure to check the weather forecast as opening up the plastic before a heavy rain could have the opposite of the desired effect. There are black spots on the leaf tips in some fields, this is likely Alternaria lesions colonizing the senesced parts of the leaves (picture below). If leek moth counts were high last week, consider targeting the larvae that are now feeding on the crop. While you may not have seen a lot of damage while scaping this year, by targeting these larvae on the crop now you are reducing the amount of overwintering moths and the potential damage to future crops. Products such as Matador, Delegate, Entrust, Successs, XenTari, and Bioprotec are most effective when they make contact with the larvae. Be sure to check the pre-harvest interval (PHI) of these products and ensure that the crop will not be harvested before the PHI has elapsed.
Onions – With adequate moisture plants are growing quickly with many direct seeded fields past the six leaf stage and some as far as 8 leaf. Stemphylium leaf blight has been observed in most fields. Refer to the newsletter from June 25 on information about Stemphylium. Purple blotch, pink root and onion smut have been observed. The second generation of onion and seedcorn maggot has reached its threshold in several regions. Keep an eye out for thrips as the hot, dry weather can allow for populations to increase rapidly. 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.
Potatoes – The drone of irrigation pumps are ringing in grower’s ears. We have started to see heat related disorders show up in fields; re-sprouting, tuber chaining and heat sprouts. Many fields are at a critical time of tuber initiation or bulking. The water demands are high and critical to fulfilling yield potential. Be on the lookout for a flush of potato leafhoppers if you have haying in the area.
Sweet corn – Sweet corn is experiencing moisture stress in many areas and current storms should provide some relief. Lepidopteran and other pest populations continue to build: for detailed information refer to the Great Lakes and Maritime Pest Monitoring Network for updates. Armyworm damage continues to be a concern in sweet corn fields that have not been sprayed, but corn is moving into maturity where this crop is more tolerant of armyworm feeding. Presence of parasitoid eggs on the larvae indicates that parasitic wasps are active and sprays may not be required. Look for European Corn Borer damage starting in Univoltine and overlap regions, as well as Corn Earworm, Western Bean Cutworm, and Corn Leaf Aphids. Common Stalk Borer has also been found so check areas adjacent to grasses.
NOTE: Data as of July 8th, 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: