Potato Update for Ontario

Fields across Ontario are at very different stages ranging from flowering and bulking in south western Ontario to still emerging in late areas such as Shelburne-Melancton.

Most of the fields planted in early May in central Ontario are filling the rows, and tuber size is good! I saw leaf burning caused by heat and excessive evapo-transpiration. Plants overgrow this leaf burning lesions. Poor emergence has been noticeable in a few fields. Possible causes are crusted soil, differences in seed vigor, cold temperatures, and frost damage. In other jurisdictions, glyphosate carry-over in seed is being investigated as the cause of poor emergence in fresh market potatoes.

If insecticide resistance is ruled out, why are we seeing more Colorado Potato Beetles (CPBs) this season? A possible explanation is that pre-cutting seed is more common now than in the past. When the seed is pre-cut and treated with an insecticide, it remains in storage e.g. two weeks until is planted. Seed usually emerges in three weeks after planting and CPBs may start infesting plants a week after emergence. Thus, six weeks (42 days) after the seed treatment, the insecticide has lost some activity and CPBs are exposed to sublethal concentration of the insecticide? Something to think about.

There have been lots of alerts on true armyworms attacking cereal crops. Armyworms infest potatoes, but this season, there are no reports of potato fields being infested by this sporadic pest.

What Does Summer Have in its Agenda?

A grower told me: “Whatever summer will bring to potato production is in the hands of Mother Nature”. We can all agree on that!

Here is a table outlining the diseases and physiological disorders (PD) which are likely to develop depending on the weather.

Cool and Wet                                             Warm & Dry

– Late blight                                                     -Alternaria Brown Spot