10 Aug Agronomy Update – August 10th

Hi everyone,

A somewhat shorter agronomy update today…just to get everyone up to speed.

It’s been a week of broken weather, with variable rainfall across the province and more rain forecast for tomorrow.  Temperatures are forecast to go up starting this weekend with a bit more sun, but still some shower chances this weekend and early next week.

I’ve had a number of producers comment that they don’t know if they’ve ever seen tops as large as they’ve seen this year.  The potato plants have generally built a big factory…now we just need them to start bulking tubers.  In general, I would say that average tuber number appears to be average…slightly less than last year.  Hopefully we’ll have a good chance to bulk those tubers up over the next 4-6 weeks.  Some seed fields and early varieties are now starting to settle down in the rows.  As the canopy starts to lay down, this will be an even greater reason to watch for signs of fungal disease.

Spore Trapping Update:

Spornado – Collection on Tuesday, August 8^th:

Late Blight:  negative at all 12 sites

Grey Mold:  positive at 9 of 12 sites

Airspore:  collections on Aug 7 and Aug 9:

Late blight spores detected in Evangeline region on August 7^th (13 spores).  No other positive spore samples in PEI.

Some thoughts:

• Any finding of late blight spores heightens the alert level for producers, but a detection in the same community two weeks in a row increases that even more. While it is still quite possible that late blight spores are blowing in from New Brunswick, growers should be very vigilant to look for evidence of foliar late blight, especially with the wet conditions and cooler temperatures of the past week.
• Late blight spores are routinely being detected in NB, ME, and QC in recent days. No reports have crossed my desk yet of foliar late blight in NB or ME.
• Early blight spore levels have exploded in West Prince, with multiple locations having > 1000 spores per sample. This also tracks with the reports of heavy early blight symptoms on certain susceptible varieties, mostly West Prince.  The lack of moisture until this week in West Prince may have made plants more stressed, and therefore more vulnerable to infection.
• Brown spot continues to be at very low levels across the province.
• Grey mold spore numbers are increasing again, particularly in the east and west.
• Not on this table was a marked increase in Fusarium spore counts. While Fusarium doesn’t often cause severe foliar disease in potatoes, it can cause Fusarium wilt, which can look a bit like Verticillium wilt but with a severe darkening of the lower levels of the stem, as well as a bronzing/yellowing of the top leaves.  I’m also hearing about lots of Fusarium head blight in the wheat crops, so this is likely a prime reason we’re seeing spores detected during grain harvest.

Crop Update Meeting:

Next Crop Update Meeting is Tuesday, August 15^th at 8:00 am at the PEI Potato Board office in Charlottetown.

Folks are welcome to join in person or by Zoom.

Join Zoom Meeting

https://us02web.zoom.us/j/8108591566?pwd=R3BmSnM5UXM3V3dQTXRYMFMreFdYUT09

Meeting ID: 810 859 1566

Passcode: potato

Aphid Alert:

Aphid numbers are still relatively low compared to last year; however, we have detected Green Peach Aphids 5 weeks earlier than last year.  Green peach aphids are the most effective vector to transmit PVY.  With warmer and drier days forecast in the next week, I would expect GPA numbers to increase.  Seed producers should be very vigilant and be spraying with non-pyrethroid insecticides to target GPA.  Potato aphid numbers are also increasing recently…they are also a colonizing aphid capable of effectively transmitting PVY.

The Mancozeb frequency pinch:

Most of you would be well aware by now that due to label changes in the last couple of years, growers can now only apply products containing mancozeb (Manzate, Dithane, Penncozeb, etc) a total of 8 times per season.  In the last couple of years, this wasn’t as bit of an issue, as cooperative weather plus low late blight spores/cases meant many were lengthening out their fungicide sprays, with good reason.  This year, the more frequent spray schedule is more than justified.

In order to maintain full coverage for your crop until top-killing/senescence, you will undoubtedly need to look at additional products for your spray schedule.  Approved options for late blight include:

• Chlorothalonil products (Bravo, Echo). Max 3 applications per season.  Chlorothalonil also targets grey mold, so might be best timed for when grey mold (Bortrytis) pressure is highest.
• Orondis Ultra (groups 40+49). Longer-acting late blight prevention, moves upward in the plant.  Max 4 applications/season
• Ridomil Gold (group 4). Recent strains of late blight have shown reduced susceptibility to Ridomil.  The same goes for pink rot.
• Elaborated contact fungicides such as:
  • Ranman 400 SC (group 21). 6 applications/season.
  • Allegro 500F (group 29) 10 applications/season, also targets white mold
• Phosphorus acid products (systemic for tuber blight control and pink rot), such as:
  • Phostrol
  • Rampart
  • Confine
• Translaminar products (usually combined with a contact fungicide), such as
  • Reason (group 11).
  • Revus (group 40).
  • Tanos (group 11+27).
  • Zampro (groups 40 + 45)
  • Forum (group 40)
  • Curzate (group 27)
  • Evito 480 SC (group 11)

This may not be 100% complete list, but these are some of the products available.  My suggestion if you are nearing your limit on mancozeb products would be adding back in Bravo/Echo (along with a translaminar product if you see fit), Orondis Ultra, and Ranman/Allegro as enhanced contact products. The phosphorus acid products will not likely do much to prevent foliar late blight, but they are proven to limit late blight in tubers and are also very valuable at preventing pink rot infection, which I also expect to be an issue this year. Hopefully a mix of these products will get you through to the end of the season with a healthy crop.

I will be off on vacation next week, but we will get an agronomy update out to you by late next week.  Have a great weekend.

Ryan