Agronomy Update – July 20

Hi everyone,

Another hot, muggy week in PEI.  In looking at weather data, it looks like just about all parts of the province have had ~35 mm of rain in the last 10 days, with a little more in West Prince (closer to 50 mm).  Most of the province has had 85-95 mm since Canada Day.  This moisture, plus the warm temperatures, is fueling very rapid plant growth.  A lot of fields are fully closed in now and are in flower.  Some of the late-planted fields are starting to catch up a bit now and are growing quickly.


Crop Update:

Our second Crop Update Meeting of the season was held Tuesday in Charlottetown.  Some comments shared at that meeting and in chats with producers and agronomists since:

  • Plant growth is very rapid, filling the rows quickly.
  • There is lots of PVY inoculum around. Rogueing potatoes has been a challenge, due to the heat and the amount of positive plants.
  • Not too many reports of early blight or brown spot yet. Most growers with susceptible varieties have one or two sprays of targeted fungicides on now.
  • There is worry about late blight, despite the lack of spores detected in PEI. There have been spores detected in NB and Quebec in recent weeks.
  • Grey mold spores are showing up earlier than normal, so some growers have already adjusted fungicide products to address this.
  • European corn borer moths and egg masses are being reported. One person recorded finding hundreds of moths in one trap after finding few in 2022. There are samples being taken in PEI to be submitted to the University of Guelph for Bt resistance
  • There are some fields with Colorado potato beetle pressure, as we start to see the neonic in-furrow or seed piece control time out. Growers should be diligent to watch for CPB and rotate chemistries to maximize control.


Spore Trapping Update:

Spornado, collection date July 18th

  • Late blight: Negative at all 12 locations
  • Grey mold (Bortrytis): Negative at 10 locations, positive at two locations (Elmsdale and Freetown)


Airspore, collections from July 17th to 19th

No late blights spores detected in PEI.  Late blight spores detected in Quebec on July 17th.

Early Blight Brown Spot Grey Mold
West Prince 17 3 6
East Prince 2 2 8
Queens 54 3 64
Kings 33 4 23

Early blight spores have generally increased since last week, particularly in the eastern half of the province.  However, about half of the individual spore samples had no early blight spores, so a few individual samples have the highest impact on the averages.

Brown spot continues to be not detected in about 75% of samples.  Since brown spot is mostly an opportunistic pathogen, we would not expect to see a lot of it if the crop is not under much other stress.

Bortrytis (grey mold) spore counts are down on average by about half from last week, and there was a significant drop in fields from Monday to Wednesday of this week.  This is also reflected in the reduced number of positives from Spornado sampling.  Hot, sunny weather will slow down progression of grey mold in most cases.


Late Blight Refresher Webinar:  Friday, July 21 at 9:00 am

Given the weather of recent weeks, the finding of late blight spores in other provinces (QC, NB) in recent weeks, and the length of time since we’ve had late blight in PEI, we thought it was the right time to do a short “refresher” webinar on late blight.

Dr. Rick Peters of AAFC Charlottetown, an expert on late blight (Phytophora infestans) is going to do a webinar at 9:00 am this Friday, July 21st on Zoom.  The Zoom login details are available by request.  This webinar will be recorded, but all growers are encouraged to attend, especially if you have any questions on managing late blight.

Thanks to Dwayne McNeill with Cavendish Farms for helping to facilitate this webinar.  I will also be applying for CEUs for CCAs for this webinar.


Aphid Alert and Insecticide Options:

So far this season, aphid numbers have been relatively low in PEI.  So far this season, only “other aphids” (non-colonizing aphids) have been detected in PEI.  Here is the trend for the first three weeks, expressed in aphids per trap:

Week 2020 2021 2022 2023
1 2.5 1.1 8.1 0.9
2 7.3 0.7 5.7 0.6
3 3.1 0.4 5.8 1.2

So far, aphid numbers in 2023 have been much lower than in 2022, and more similar to 2021.  However, we also know that a lot of the issue with PVY spread in 2022 was historically high numbers of green peach aphids in August.  So far, green peach aphids have not been found in PEI, but they have been found in Maine already.  For the last few weeks, much of our warm, humid weather has been coming from the US seaboard, where green peach aphids overwinter, so it would be not a surprise to see them arrive soon.

Under AIM, we have engaged with Mathuresh Singh and Tyler Mackenzie at the ACS Lab in Fredericton to look at aphid alert samples from 2022 to assess for signs of insecticide resistance.  While this work is not yet complete, we do have some preliminary results.  Aphids tested from early in the season (non-colonizing aphids) do not show any genetic signs of resistance to pyrethroid insecticides.

However, samples from green peach aphids from late in the season showed a 100% incidence of genetic mutations associated with resistance to Group 3 pyrethroids.  Therefore, these same insecticides will not be effective against green peach aphids and should be substituted with other products.

Group 3 pyrethroids include:

  • Matador
  • Labamba
  • Silencer
  • Decis
  • Pounce
  • Ambush
  • Perm-Up

Some non-pyrethroid options: (list may not include all available options)

  • Assail (group 4)
  • Beleaf (group 29)
  • Closer (group 4C)
  • Lagon/Cygon (group 1B)
  • Exirel (group 28)
  • Movento (group 23)
  • Sefina (group 9D)
  • Sivanto Prime (group 4D)
  • Vayego (group 28) (suppression)

We will be sharing more with you from the aphid insecticide resistance work as it is completed.  Thank you to the PEI Department of Agriculture for their partnership on Aphid Alert…we will share those results with you as we have them.


Robert Larkin Presentation:

AAFC will be hosting a presentation by Dr. Robert (Bob) Larkin on “Maximizing the Use of Organic Amendments in Potato Rotations” at the Charlottetown Research Centre  on July 27th at 10:30 am.  Dr. Larkin was a previous guest speaker at AIM workshops a few years ago to talk about his work on crop rotation and compost work in potato rotations in Maine.  Growers and industry partners are welcome to attend.

FYI:  I’m going to be very busy with the PAA meetings being held in PEI starting this Sunday through Thursday of next week, in case you’re trying to get ahold of me.  Next week’s Agronomy Update will go out next Friday.

Have a great rest of the week.