VCR – Vegetable Crop Report – August 12th, 2021

Temperature – Daytime temperatures are forecasted to drop to around 25°C moving into the weekend. Most regions remain above their GDD 10-year average.

Carrot rust fly is at its second threshold in all monitored regions below except for Essex, Chatham-Kent, and Norfolk. Onion maggot is at its second threshold in Wellington, Peterborough, and Sudbury. Cabbage maggot is at its third threshold in Essex. European Corn Borer is at the univoltine threshold in Sudbury.

Rainfall – Most regions are forecasted to see some rainfall on Friday with clearer skies over the weekend. Precipitation data for each region are shown below.

Crop Updates

Brassica Crops – Cabbage maggot will be active in the upcoming weeks and has already reached the threshold for the third generation in Essex county. Keep levels of Alternaria low by incorporating all plant material after harvesting a block and avoid irrigating in the evening to reduce the time that leaves are wet. During the hot weather, dig suspect plants with a shovel and inspect the roots for clubroot, root knot nematode. Pulling the plants will often result in weak roots being left in the soil and then both of these pathogens may be hard to correctly identify. Thrips, aphids, imported cabbageworms and diamondback moths remain elevated in many areas. The threat of downy mildew and bacterial pathogens remains high given the high humidity and colder nights.

Carrot – Cercospora and Alternaria leaf blights have been showing up in carrot fields. More incidences of aster yellows are also showing up. Be aware that we have reached the degree day threshold for carrot rust fly in many regions of Ontario. Monitor with orange sticky cards to time the peak flight.

Celery – Early plantings continue to be harvested. Bacterial leaf spot, Cercospora and celery leaf curl have been observed. Blackheart/ calcium deficiencies continue to take down plants and rotted hearts from carrot weevil damage continue to be found. If celery leaf curl has been identified in the field, avoid walking through while the canopy is wet. Celery leaf curl spores will stick to clothes and equipment. Tarnished plant bugs, leafminers and aster leafhoppers continue to be active.

Garlic – Monitor humidity levels within the crop while it is being cured. In a closed environment, simply increasing the temperature may not pull enough moisture from the crop to cure it successfully. The Garlic Growers Association of Ontario is taking orders from members for clean planting material from the SPUD unit at the New Liskeard Agricultural Research Station, University of Guelph. GGAO members should E-mail garlicgrowersofontario@gmail.com to place an order by August 15th, 2021. Roundels are expected to ship in September. For more information, see the garlic clean seed program here: https://onvegetables.com/2020/08/05/spud/.

Onions – Transplants are being harvested and some direct seeded fields are starting to lodge. Stemphylium is starting to move into the leaf tips of some fields. The threat of downy mildew remains high, especially if inoculum is present from previous years. If the DOWNCAST forecasting model is not available to predict outbreaks for your area, a protective fungicide program for downy mildew is recommended during the humid weather we have been experiencing. Currently, downy mildew has been confirmed in a commercial field within the Holland Marsh. As fields of transplants start to dry down, be mindful of younger, direct-seeded onions in border fields as the level of thrips may surge as they move to a greener crop. We are currently looking for Botrytis samples. If you are finding Botrytis lesions in your onion field, please call 519 835-3382 or E-mail travis.cranmer@ontario.ca.

Potatoes – With the finding of late blight on tomatoes in Norfolk County it’s a reminder to remain vigilant in your fungicide applications. Luckily many fields have been top-killed or will be top-killed shortly. There are still fields that have a ways to go yet so remember to keep fields protected right up until top-killing.

Potatoes have been bulking remarkably well. Some fields have been bulking up a little too well and hollow-heart is beginning to show in some varieties. Keep an eye on susceptible varieties and think about adjusting late-season fertility and irrigation management. In some cases, Royal MH can be used to slow down growth and prevent hollow-heart although it may be too late for this point in the season.

We’re starting to see common later season fungal diseases show up in fields where the crop is senescing. Early blight (Figure 1), brown spot (Figure 2), Botrytis and white mould (Figure 3) have all be seen recently. Check between the rows in fields where the vines have collapsed.

**Figure 1.** Early Blight on potato leaves

**Figure 2.** Brown spot on upper leaves of the potato plant

**Figure 3.** White mould developing under the canopy of potatoes

Pest Degree Day Forecasting

*NOTE: Data as of Aug 12th, 2021

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
Essex*	1946	1803	1390	1150	838	1522	1803	1041
Chatham-Kent*	1805	1664	1272	1040	693	1397	1664	933
Norfolk**	1788	1649	1258	1026	681	1383	1649	916
Huron***	1661	1527	1157	936	600	1274	1527	833
Wellington**	1607	1471	1099	877	551	1217	1471	774
Simcoe County***	1654	1516	1135	912	587	1255	1516	809
Durham***	1696	1559	1171	954	624	1293	1559	853
Peterborough	1548	1409	1028	811	499	1148	1409	710
Kemptville***	1655	1520	1133	905	578	1257	1520	802
Sudbury***	1440	1317	983	790	485	1088	1317	697