Agronomy Updates – July 19th

Hi everyone.  Quite a bit of the Island got some welcome rain Wednesday night.  Sounds like more on the south shore and down east, with less in West Prince.  From my travels and conversations with growers, it appears that potato crops are progressing well across the Island and there isn’t much concern about moisture stress thus far.  Hopefully we’ll get some good periodic moisture through the next couple of months to keep the momentum going!  A few things to share with you today:

Late Blight and Early Blight Decision Tools

A number of growers across the Island are using one of three blight decision support programs this summer to help them in making decisions on their fungicide applications to best match applications to weather conditions, choice of fungicides, and in some cases, the absence or presence of spores.

This year, the Board has partnered with the PEI Department of Agriculture & Land, some participating growers, and a company from Quebec called AIR to collect spores three times per week at locations across the province.  The growers get location-specific weather data in real time as well as spore data three times a week.  Through these agronomy updates as well as the weekly pest update from the PEIDAL, we’ll be sharing results and severity indices with all growers during the season.

The first spore tests were taken on Monday of this week.  All samples came back negative for late blight (Phytophora infestans).  There were some spore counts for Alternaria (early blight/brown spot):

Community # of spores
Elmsdale 31
O’Leary 49
Tyne Valley 0
Evangeline 0
Summerside 0
Kinkora 0
Rustico-Oyster Bed 0
Meadowbank 84
Rollo Bay – Souris 0 to 138
Dundas 9
East Point 178

In conversations with folks in New Brunswick who have been working with this program for the past two years, these numbers are indicative of an “early blip” in Alternaria spore numbers that they usually see in July.  It’s interesting that so far we are seeing big variation in the numbers, and seemingly lower numbers in the middle of the province.   In NB, they’ve usually seen an early blip in late June to mid July, followed by a bigger spike in spore numbers in August.

What’s the advice?  Firstly…these numbers are for monitoring purposes and shouldn’t be the sole data you plan your fungicide sprays on.  However, there are spores around in many communities, and early blight/brown spot affect primarily the lower leaves in the canopy at this time of year, so getting effective fungicides on that control early blight and brown spot before row closure would be prudent.  Particularly for varieties that are more susceptible (ie. Ranger Russet).  If you see any foliar symptoms, it’s a good idea to send a sample to the Plant Lab in Charlottetown for diagnosis.  Last year, all of our samples came back positive for brown spot, not early blight.  This is important to know, because the list of fungicides that are effective on brown spot is much smaller.  Spend your money wisely by using the most suitable product!  If you are unsure what products are available, contact your agronomist or consult the PEI Potato Pest Control Guide.

Status of the Crop:

Generally, folks I’ve been talking to (growers, agronomists, scouts) are quite positive about how the crop looks thus far.  There have been a few findings of Colorado Potato Beetles, but not much.  At the Fieldworkers Meeting on Tuesday, there was mention of finding some Corn Borer egg masses and that there definitely moths around.  For managing corn borer, timing is critical, so consult closely with your scouts and agronomy support to make sure that if you need to spray (above threshold) that you are doing it at the right time!  There hasn’t been much reporting of foliar disease to date, and generally emergence rates are quite good.  There have been a few reports of herbicide injury in a few fields, causing stunting of the crop.  This can occur when pre-emergence herbicides are applied before a significant rain on sandy/low OM soil, moving the herbicide down into the root zone of the growing potatoes.  With some of the big rains in mid-June, this makes sense that we would see some cases of herbicide injury.

As many of you know, it’s a weedy year.  This has impacts not only in the potato crop but in your rotation crops as well.  After emergence there is only so much that can be done to manage weeds outside of managing grasses with metribuzin (ie. Sencor) and additional hilling.  However, if you have a weedy forage crop…do what is necessary to not let those weeds go to seed!  Consult with your agronomy supports on whether there is value in a herbicide application, depending on what you are growing.  Particularly for fast growing grass and legume species, you have the option to mow/mulch that crop before the weeds can set seed.  Minimizing the weed seed bank in rotation years makes life a lot easier in the potato years!

Keeping an Eye on the Weather

We’re definitely into the time of year when we’re all keeping an eye on the weather and tracking rainfall totals.  A couple of tools to assist you, for those that don’t already have on-farm weather stations:

PEIDAL Weather Stations:  WeatherCloud (now with 24 hr rainfall per station)

AgWeather Atlantic:  Full data for each station is no longer available for PEI, but if you visit the Nova Scotia page, PEI stations are included in the maps for rainfall and GDD.  Good for getting a picture of the whole Island.  (Must select Nova Scotia in drop down menu on top right).

AAFC Extreme Weather Indices:  AAFC has an online tool which produces maps showing probability maps of Greatest Daily Precipitation and Probability of Daily Precipitation above 2 mm, 10 mm or 25 mm.  These are weekly maps generated every 4 weeks during the growing season.  There are also maps for temperature and wind.  An interesting tool to explore.

AAFC Satellite Soil Moisture map and Canadian Drought Monitor map.  AAFC also has a cool tool for generating agroclimate maps (ie. Accumulated rainfall in last 60 days) to compare across the province or the region.

Thinking About Sugar Ends

For those that missed it, there was an interesting webinar this week hosted by Spud Smart on the topic of Sugar Ends and Stem End Chip Disorder.  You can watch a recording of the webinar here.

What are the key factors causing sugar ends in susceptible varieties?

  • High soil temperatures, particularly at tuber initiation.  The threshold temperature seems to be about 72 degrees F (21 C) at tuber depth in the soil.
  • Water stress, particularly at tuber initiation.  Less than 60% available soil moisture has shown to be the threshold in past research.
  • Exposure to cold, such as harvest below 45 degress F (7.2 C) or extreme cold in storage early in the storage season (cooling down too quickly).  Sugar ends/cold sweetening does not tend to improve with time in storage.

Preventing sugar ends/dark ends is largely dependant on the weather, but there are some things that can be considered to help prevent them, including:

  • Reducing soil compaction, allowing plants to develop greater root mass in order to access more water.
  • Take steps to reduce Verticillium wilt/early dying complex, which causes early senescence which warms up the soil
  • Avoid excess Nitrogen application, which can cause excess foliar growth at the expense of root growth
  • Minimize the amount of time that tubers are in warm soil without green plants
  • Explore varieties that are less susceptible to sugar ends, where possible.

A couple of upcoming events:

  1. Island Agrology Workshop – August 19-20th in Stanley Bridge (details and registration form on the website)
  2. 2019 Regional Precision Agriculture Conference – August 22nd at UPEI, Charlottetown (link to Eventbrite registration form.  Registration is free!)

Is there something you would like to see in future agronomy updates?  Do you have questions about a field or a research trial or anything else agronomy related?  Please feel free to contact me.