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How to manage glyphosate-resistant Italian ryegrass

How to manage glyphosate-resistant Italian ryegrass

Residual herbicides in fall offer best chance for reliable control. Dual Magnum, Treflan, Command most consistent at Stoneville. Agressive tillage or Gramoxone Inteon for emerged ryegrass. Control on ditch banks, turn roads, field borders. Scout early to determine spring options.

In Fall residuals for glyphosate-resistant Italian ryegrass, I wrote that I expected to see Italian ryegrass emerging soon based on the weather around the Mississippi Delta at that time.

Three weeks have passed with practically no rainfall, so there is still little to no Italian ryegrass emerged. I did find a few plants at one of our ryegrass emergence monitoring sites in Coahoma County, Miss., on Oct. 4. However, it is still too dry for this weed to be a problem yet this fall.

At Stoneville, Miss., the weed science group has worked extensively on developing management programs for glyphosate-resistant Italian ryegrass over the last few years. The best chance for reliable control is with residual herbicides applied in the fall.

The following contain management suggestions for 2010-11, based on research and others, are personal observations.

Apply residual herbicides when weather permits between mid-October and mid-November.

Based on research from 2009-10, fall residual herbicides can be applied too early when rainfall is high through the fall and winter months. This year, we began our fall residual herbicide programs on Sept. More than likely, the treatments applied in September will fail again this year, but this time it will be because the herbicide applications have received no rainfall for incorporation.

In previous years, applications in early-November provided excellent ryegrass control until spring. Historically, rainfall totals (and the chances of not being able to apply a herbicide) increase in November.

Because the probability of good days for field work decrease later in the fall, I suggest monitoring the 10-day weather forecast over the next couple of weeks and applying a residual herbicide one or two days prior to a day with a good potential chance of rain (if there is a day like that).

Dual Magnum, Treflan, and Command have performed most consistently for controlling glyphosate-resistant Italian ryegrass in fall residual herbicide research at Stoneville. Dual Magnum or Treflan should be utilized in fields that will be planted to cotton or soybeans the following year. Dual Magnum is the only fall residual herbicide for ryegrass that may be safely applied if the field will be planted in corn.

In fields where the 2011 crop will be rice, Command (2 pints per acre) is the only fall residual herbicide option. Do not apply Command or Treflan in the fall prior to planting corn and avoid use of Dual Magnum or Treflan in the fall prior to planting rice.

The Dual Magnum rate should be at least 1.33 pints per acre on lighter-textured soils, but it will need to be increased to 1.5 pints per acre on heavier soil. Treflan has performed well at 3 pints per acre on glyphosate-resistant Italian ryegrass, but 4 pints per acre was common in the past when Treflan was applied in the fall for rhizome johnsongrass control. Regardless of the rate, Treflan requires incorporation within 24 hours of application.

Tillage, Gramoxone Inteon

Control emerged glyphosate-resistant Italian ryegrass in the fall with aggressive tillage or application of Gramoxone Inteon.

None of the residual herbicides available for glyphosate-resistant Italian ryegrass have postemergence activity. Should the current weather pattern change and ryegrass begin emerging, these emerged plants must be controlled before the residual herbicide is applied.

If the field has not already been tilled in preparation for next year, then the first flush could be destroyed during this tillage operation. When relying on tillage to control emerged Italian ryegrass, pay close attention to the clods behind the disk.

To completely kill Italian ryegrass seedlings, the clods must be crumbled and not just turned over. Emerged glyphosate-resistant Italian ryegrass will survive on the clods if they are not sufficiently crumbled.

Because destroying glyphosate-resistant Italian ryegrass with tillage in the fall may require an additional, unplanned pass across the field, then controlling emerged plants with Gramoxone Inteon (plus a crop oil concentrate or nonionic surfactant) may be a better option. Because ryegrass seedlings are small in the fall, the Gramoxone Inteon rate does not need to be as high as required in the spring.

Gramoxone Inteon should be applied at 4 pints per acre in the spring while 2 to 3 pints per acre should be sufficient to control glyphosate-resistant Italian ryegrass in the fall.

Gramoxone Inteon may be tank-mixed with Dual Magnum or Command. If you choose to use Treflan and emerged Italian ryegrass has been completely destroyed by tillage, then Gramoxone Inteon should not be required.

However, if the field has been worked once or twice and glyphosate-resistant Italian ryegrass emerges before the Treflan application and its subsequent incorporation, then Gramoxone Inteon will be needed.

Keep in mind that hippers often just bury emerged plants rather than killing them. Additional tillage will be required to control emerged plants prior to bedding in these situations.

When tank-mixing Gramoxone Inteon with Treflan, wait four to six hours between spraying and incorporation.

Regardless of how you choose to control emerged glyphosate-resistant Italian ryegrass in the fall, this is an absolutely critical component of the management plan and should not be overlooked or skimped on. Dual Magnum, Command, or Treflan will not kill even the smallest ryegrass seedlings. Escapes of just a few scattered one- to two-leaf seedlings in October will tiller and expand into large clumps in the spring, potentially resembling herbicide failure.

Ditch banks, field borders

Manage glyphosate-resistant Italian ryegrass on ditch banks, turn roads, and field borders.

Where glyphosate-resistant Italian ryegrass was only present on the turn roads or edges of the field last year, spot-treating these areas is a practical way to save on herbicide cost and possibly prevent the problem from becoming more severe in the future.

You may choose to wait and spray field borders and turn roads with clethodim (Select Max or various two-pound clethodim products) or Gramoxone Inteon after glyphosate-resistant Italian ryegrass emerges.

Another option would be treating these areas with a residual herbicide in the fall. Either of these practices could be an economical option in fields not completely covered with ryegrass.

Be very cautious if you choose to spot-treat areas with a residual herbicide. Italian ryegrass has extremely stiff straw that does not rapidly deteriorate. It is not uncommon to see Italian ryegrass residue complete with seed still standing in the fall. This seed from the previous year can be spread by a combine or it may spread into the field where land planes or dirt buckets were utilized.

Scouting fields

Scout fields in early- to mid-January to make spring management decisions.

If glyphosate-resistant Italian ryegrass escapes the fall residual herbicide application and is present in January, then the field should be treated with Select Max at 12 to 16 ounces per acre or 6 to 8 ounces of a 2-pound clethodim product.

Fields should be scouted again four to six weeks after clethodim application. Any surviving glyphosate-resistant Italian ryegrass should be treated with Gramoxone Inteon at 4 pints per acre.

Regardless of the program utilized, all ryegrass should be completely controlled prior to planting.

Unfortunately, there is little good news concerning glyphosate-resistant Italian ryegrass. The problem seems to be spreading every year. Few herbicides effectively control it, and most of these are expensive for burndown options.

Multiple herbicide applications are often required to completely control ryegrass, and the best herbicide application timings occur when most people are just not thinking about weed control for the next season.

The one positive right now is the dry weather has delayed emergence, so hopefully glyphosate-resistant Italian ryegrass will be more easily managed this year compared with last year.

Jason Bond

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