The potato crop in southwestern Ontario has benefited enormously from the 1 to 1.5 inches of rain that fell on July 17. However Alliston, Shelburne and Eastern Ontario continue to be dry. Potatoes are showing signs of stress in the non-irrigated fields, especially leaf burn.
According to Ontario Potato Distributing, the first new potatoes from Leamington will arrive at the Alliston packing plant on July 22.
Joe Lach reported that a few potato producers near Delhi, Ont., have started topkilling the earliest varieties. The hot, humid weather has slowed tuber sizing. “We had over one inch of rain on Wednesday, which took the pressure off irrigating” he said.
There is not much early blight in fields indicating that there has been good control.
Colorado potato beetles have been found in the earliest planted fields where the neonicotinoid applied at planting is breaking down. A grower near London has reported very good control of CPB with the insecticide Delegate. Coragen and Exirel are also registered for CPB control.
Once again, the filters from the spore traps in Simcoe and Dufferin counties have tested slightly positive for late blight. There are spores around, but the number of spores is very low. This is probably due to the prevalent hot, dry weather.
There are reports from parts of New York and Pennsylvania of outbreaks of Phytophthora nicotianae, a “cousin” of late blight. The symptoms are very similar, but P. nicotianae lesions do not produce as much mycelium and spores like those of late blight. (See attached photos)
P. nicotianae is soil-borne and attacks all parts of the plant, including the roots. Infected plants are usually found in low, wet spots of fields. Fungicides registered for late blight also control P. nicotianae.