03 Aug Agronomy Update – Aug 3rd

Hi everyone,

After hot and muggy weather last week, we’ve moved into a lower humidity trend with cooler night-time temperatures.  While this has made it much easier to sleep at night (temperature-wise)…it changes the story on fungal diseases a bit.  We’ll delve into that a little more in this update.

Humna did up a report on July weather across the province.  For precipitation, West Prince was actually down 12 mm from historical average in July, and most of that came the first weekend.  The rest of the province was well above average…+50 mm in Summerside, +75 mm in Charlottetown, and +95 mm in Souris.  For the growing season, the western half of the province has had about average rainfall (15% deficit for West Prince, 5% deficit for East Prince), while Charlottetown is 22% above average and Souris is 30% above average.

July was also much warmer for growing degree days (GDD) than average, with 20-28% greater accumulation of GDD across the province in the month.  This largely explains the rapid growth in all of the crops over the last few weeks, allowing a lot of late seeded potato fields to catch up.

Spore Trapping Update:

Spornado – Collection on Tuesday, August 1^st:

Late Blight:  negative at all 12 sites

Grey Mold:  positive at 7 of 12 sites (mostly in western half of the Island)

Airspore:  collections on July 31 and Aug 2:

Late blight spores detected in Evangeline region on July 31^st.  No other positive spore samples in PEI.

Early blight counts are swinging a lot from one collection to another.  It should be noted that there is a lot of variation from field to field, with a few high counts in individual fields spiking the averages higher.  Brown spot numbers are starting to jump in a few places…again, high counts in individual fields having a big impact on averages.

That said, we are getting increasing reports of aggressive levels of early blight and brown spot infection in certain susceptible varieties.  Early blight is being seen even in fields with multiple applications of systemic, targeted fungicides.  Growers are recommended to stay on top of their fungicide programs and rotate chemistries to stay ahead of resistance.

Registered chemistries for both early blight and brown spot (may not include all available products)

• Aprovia Top (Group 29)
• Cevya (Group 3)
• Luna Tranquility (Group 7 + 9)
• Miravis Duo (Group 7 + 3)
• Proline Gold (Group 7 + 3)
• Propulse (Group 7 + 3)
• Quadris Top (Group 11 + 3)
• Veltyma (Group 11 + 3)

A more complete list of registered fungicides is available here.  Please talk to your service provider for the list of products available here.

Late Blight:
There was a spore detection of late blight early this week in PEI through Airspore, but nothing since.  Significant foliar late blight has been found in Ontario and Quebec, and spores have been detected in both Maine and New Brunswick.  Although the turn to drier air is an advantage in slowing late blight infection, the cooler night time temperatures also are in favour of late blight.  Growers are encouraged to remain vigilant and consistent with their fungicide programs.  A number of growers are making use of anti-sporulant fungicides as well as phosphite products in the last couple of weeks to ensure their crop is protected.

Aphid Alert:

In the most recent update from the Department of Agriculture, total aphid numbers per trap continues to be below 1 per trap, lower than in the last few years.  However, last week saw the first detection of green peach aphid in PEI, a full five weeks earlier than last year.  Green peach aphids have also been detected earlier than normal in Maine.  Green peach aphids are the most efficient vector for spreading PVY in-season, and are also the main vector for potato leafroll virus (PLRV).

As noted in previous updates:  pyrethroid insecticides like Matador and Silencer will not be effective at controlling green peach aphids, due to high levels of resistance detected.  Rotate other chemistries along with frequent mineral oil applications to keep your seed crops protected!

Crop Update Meeting:

In addition to some of the points raised above, here are some of the other points that were raised at the Crop Update meeting on August 1^st in Kensington (which was very well attended):

• Colorado potato beetle (CPB) continue to be found, but recent foliar insecticide applications have generally been effective. There are some pockets around the province with significant CPB pressure.
• European corn borer (ECB) pressure appears to be much higher this year, due in part to the higher GDD accumulation. Moths have been numerous and many egg masses found.  PEI Department of Agriculture is collecting samples for Bt resistance.
• Grey mold (Bortrytis) is being found but levels of damage appear to be low in most varieties.
• Rate of growth has been rapid, rows filled in quickly, and most fields have large canopies. With some cooler nights, it is hoped that some varieties will be starting to bulk tubers.
• Early harvest for chips is starting this week in Eastern PEI

Preparing for Fall Cover Crops:

I’ve been talking with quite a few growers in recent days about prepping fields destined for potatoes next year, including use of cover crops.  A few timely reminders:

• If using glyphosate (Round-Up) to terminate a forage crop ahead of fall tillage and cover crop establishment, it will be most effective if sprayed on forage with at least 2 to 3 weeks regrowth after cutting.
• Budget for 10-14 days after spraying of glyphosate to do vertical tillage (Lemken/Synkro), possibly longer if it’s been dry.
• If you are seeding brassica species like tillage radish or mustard, the earlier you can plant, the better! Aim to have those crops planted before the first week of September.
• A mix of a brassica and a cereal (oats/barley) generally provides the greatest amount of biomass for the longest time in the fall if you aren’t using a winter species.

Let’s make 2023 our industry’s best year yet for cover crop establishment!  They are a benefit to your farm but also to the environment.

Have a great weekend!

Ryan