Agronomy Updates: June 9th

Hi everyone,

Thankful for those that have gotten some rain over the last 3-4 days.  Too bad that the whole province hasn’t received that rain.  It poured hard for a while in Charlottetown this afternoon, but I think that those thundershowers were quite spotty around the eastern half of the Island.

 The Time is Now for Herbicides

If you haven’t already, make sure you get those pre-emerge herbicides on ASAP.  I see lots of potato fields around the province where weeds are showing up.  Timing is everything with weed control, as is having sufficient soil moisture to activate the herbicide.

When looking at your herbicide program, it’s important to keep an eye to resistance management by rotating chemistries/chemical families and following the rates and instructions on the label.  If you are having an issue with weeds showing resistance to herbicides you routinely use, you may need to look at some different options.

The PEI Department of Agriculture has just updated the Pest Control Guide.  Consult the Guide for available herbicide options approved by PMRA.  The guide does a really good job of breaking down which products can be used at what time (before planting, before emergence, after emergence, etc).

There are some options out there beyond the traditional Sencor (metribuzin) and Lorox (linuron), if you are finding that you’re having a hard time getting control with those chemistries.  Last year, Dr. Andrew MacKenzie-Gopsill at AAFC did some really interesting evaluation of different herbicides at Harrington (with lots of weed pressure), comparing to both weedy and weed-free controls.  According to information presented at the PEI Soil & Crop meeting in March, the highest marketable yields were achieved with Sencor STZ (which includes sulfentrazone).  Other options from a different family of chemistry are Dual II Magnum (S-metolachlor) or Boundary LQD (S-metolachlor + metribuzin).  Both of these also performed well in the same AAFC trial last year.  Both of these need to be applied before ground crack.  An option after ground crack is Ignite (glufosinate ammonium), which has excellent ratings on annual grasses and broadleaf species.

For those using glyphosate (Roundup) for control of emerged weeds…be very careful to only use prior to potato emergence.  Glyphosate will injure potato plants and can also be translocated down into the tubers, often causing malformed tubers.  That being said, glyphosate has no soil activity, so it can be used if your potato plants are still below the ground and you have lots of emerged weeds.  Scout your fields before any herbicide application to make sure you’re using the right tool for the job!

A couple of other best practice notes:

  • If using Lorox, moisture is needed to get good weed control.  However, don’t apply Lorox before a heavy rainfall is forecast, as this can wash the chemical down to the growing sprout and damage the sprout/delay emergence.  The sandier your soil (with less soil organic matter) the higher the risk of injury to potatoes.
  • Moisture is also needed shortly after application for optimum pre-emerge effectiveness of Sencor (metribuzin).
  • Use of Prism (Rimsulfuron) with Sencor as a post-emergence herbicide is most effective on grasses.  It appears that it is quite ineffective on lambs quarters here in PEI according to reports from AAFC.
  • If you are planning to plant a cover crop in the next few weeks (ie. sudangrass, mustard, pearl millet, etc), it would be wise to control any weeds in your field before planting the cover crop to ensure that the cover crop doesn’t have to compete with weed pressure to get established.  After established, many of these cover crops do a great job of helping to control weeds for the following year.

Soil Building Crop BMPs:

I’m getting lots of questions about soil building crops.  There are lots of choices out there for different purposes.  I would encourage you to check out the presentation that I presented back in the winter that gives some pros and cons as well as helpful hints on some of these different crops/mixtures.  It is available HERE (PDF).

If you want to plant sorghum sudangrass and pearl millet (warm season grasses)…I recommend waiting until next week.  Waiting until June 15th is usually recommended for those grasses.  If the soil is warm and moist when you plant those grasses, growth will be usually be fast.  Planting too early will often retard growth and they don’t “grow out of it” as much as you’d like.  I hope that we get some more rain in the next couple of weeks to provide adequate moisture to get that seed germination happening quickly.

Also, if you want a handy tool to consult for establishment windows and BMPs for a number of different crops, check out the Eastern Canadian Cover Crop Decision Tool.  You can click on each individual crop name for a best management profile on each crop.

As I noted last week…don’t skimp on the fertilizer either.  Feed your cover crops so they can help you feed the soil and build your soil structure and soil health.  This is a good place in rotation to use manure or compost (if available).  If you are selling a crop of hay/silage off of your field, make sure you accounting for the nutrient removal in the value of the crop you are selling.  You can calculate your nutrient removal rates using the online calculator at or download a nutrient removal app for your smart phone (there are multiple free versions available, such as Ag PhD)

Cull Pile Deadline – June 15th

Just a reminder that the deadline to get cull piles covered is coming up on June 15th.  It is very important to have cull piles covered to prevent the spread of seed-borne diseases such as late blight, early blight, and PVY.  This is particularly important this year, as the improved spring weather should accelerate seed germination and there is a greater volume of unused seed/cull potatoes around the countryside.  Do your part to minimize the spread of disease!

I hope everyone gets the moisture they need in the next couple of weeks and that we have a great growing season here in PEI.  As always, I’m available for questions and discussion by phone/text/email.  Morgan and I are just about finished with spring trial setup, so I’ll have some more time to visit with growers in the next couple of weeks.  Feel free to reach out.