Plant Cover Crops

Learning about the benefits of planting cover crops.

cover crops becoming weeds

Can Cover Crops Become Weeds?

In a previous post I wrote that cover crops can suppress weeds.  And many farmers are planting them with that primary benefit in mind.

But, can cover crops become weeds?

Unfortunately, the answer is “yes, they can.”  Obviously we never want this to happen on our farm.  And with good management practices, we can lessen the possibility that it will.

Two species that require precise management are annual ryegrass and radishes. Both annual ryegrass  and radishes benefit the soil tremendously and have been shown to increase profit per acre, but both must be carefully managed as well. Specifically, there must be a comprehensive plan for terminating annual ryegrass. If you are not absolutely clear on how you are going to do this, you should not plant it. Likewise, with cover crop radishes, you need to be absolutely clear on what you are buying and when the seed should be planted.

It only takes a few annual ryegrass plants that produce seed to create a weed problem - especially if wheat is in the rotation.
It only takes a few annual ryegrass plants that produce seed to create a weed problem – especially if wheat is in the rotation.

This is why Hans Kok, from the Indiana Conservation Cropping Systems Initiative often tells farmers that are trying cover crops for the first time to start with a few acres of oats and radishes as a cover crop.  His thinking is that because both oats and radishes die over the winter that farmers will not have to worry about terminating the cover crop in the spring.  And I agree with Hans on this.

However, cover crops are becoming more popular and many producers are convinced that they are excellent at killing weeds and cover crops.  While Ag Chemical companies have shied away from making too many recommendations on killing cover crops, farmers are confident in their abilities to “figure it out” and make cover crops work on their farm.  Why use “boring” oats and radish?  Let’s use Annual Ryegrass!

Don’t get me wrong, Annual Ryegrass is a fabulous cover crop with tremendous value as a cover crop and forage.  But, it does take more management than many other cover crops.  Annual Ryegrass provides high reward with some additional risk.  On our home farm we sprayed our soybeans three times to make sure all annual ryegrass was killed.

Planting Radishes too early or planting the wrong Radish can create a problem with seed production on the radishes...and you don't want that!
Planting Radishes too early or planting the wrong Radish can create a problem with seed production on the radishes…and you don’t want that!

I’d love to hear your “formula” for annual ryegrass control. Have you noticed any difference with terminating annual ryegrass on different soil types? Different temperatures? Different additives? Different times of the day?

 

Terminating Cover Crops – Use Residual Herbicide

Terminating cover crops is part of the “stepped-up management” that using cover crops requires.  Over the past month I shot videos about killing annual ryegrass, killing crimson clover, and about the difference of killing cereal rye and annual ryegrass.  In each of the videos I examined the importance of killing the cover crop…and killing it dead.  Overall, most of the cover crop fields that I have seen had a very good burn down.  In more than a couple of instances it was obvious that the applicator missed a few (if not many) spots or strips.

Terminating Cover Crop Radishes

In the cover crop plots where Radishes were in the mix we now have plenty of Radishes in the corn!

But burndown is not all that we need to be concerned about.  In 2011 I saw photos from fields in Michigan that almost made my heart stop!

A corn field in southern Michigan had radishes that were taller than the knee high corn. And a field of soybeans had large radishes in it at harvest time.  Thankfully the corn field yield was not affected, but areas of the soybean field could not be be harvested.  At $12-13/bu soybeans that was an expensive lesson.

Applying glyphosate once a season without using a residual herbicide does not provide adequate weed control. These radishes germinated after the spring glyphosate application.

So how did these situations happen?  In both instances the producers used glyphosate for their burndown and did not  use (or had not yet used) residual herbicide.  Of course the radishes were not the only “weed” in the field, but it was the focus of the growers!

Terminating Cover Crops at Robison Farms

At Robison Farms in Central Indiana we have two issues going on in our fields this spring of 2012:

#1) Radishes are coming in the corn and soybeans, even though we did apply a residual herbicide!

#2) There are more annual ryegrass escapes than I’d ever like to see. We actually had very good burndown and we used residual herbicide too.  Note that these are NOT the only “weeds” that we have growing in the fields.  I cannot remember a year when we’ve seen so many winter annuals and broadleaf weeds survive residual herbicide.

My brother Don has been scouting our fields and he reports seeing ragweed, morning glory, cocklebur, Queen Anne’s lace,  and a variety of other broadleaf weeds across our 300 plus acres.  The weeds aren’t thick, but there are too many of them. So we’ve concluded that it is not “just the cover crops” that are escaping.

So what is the advice here?  Make a commitment to scout your fields for weeds, whether they be “cover crop species escapes” or other weed pressure.

  • Excellent weed control is vital for top profits in cash crops.
  • Use residual herbicide in corn and soybean fields.
  • Scout fields looking for escapes and other weed issues.
  • Terminate all escapes before they produce viable seed.
  • Realize that cover crop radishes do have hard seed and you most certainly will see radishes in the spring.
  • Oilseed crops (brassicas like radishes, turnips, rape, canola, kale, mustards) can stay viable in the soil for years. Scout each year in fields where you have had these brassicas.
  • Scout for brassicas later in the season as well.  This should not be an issue but don’t take a risk of losing acres of soybeans.  The soybean field in Michigan had no residual herbicide applied but the radishes that caused the problems came up later in the season (probably late July or early August gauging from their size at harvest).
  • In some years like 2012 (even if you did not use cover crops), you will have more weed pressure than other years.  Eliminating all weed pressure is important!
The casual drive-by look at this plot looks like we achieved a great kill on this annual ryegrass cover crop. The corn looks great, the grass looks brown and dead, but...
...in more than one area I found annual ryegrass "escapes" that are heading out or nearly heading out. These plants need to be sprayed right away so they will not produce viable seed.