Posts filed under ‘weeds’

Dry Weather and Fall Herbicide Options

OSU’s Dr. Mark Loux provided an overview of dealing with fall herbicide applications during dry conditions in the most recent CORN Newsletter. I have summarized a few basic points below:

  • don’t be in a rush to apply. There is really no risk of less effective control by delaying treatment, even through mid to late November
  • herbicides are more effective on dandelion after a frost in late October or November
  • waiting until early November could also allow for a more informed decision on whether fall treatment is actually necessary

This same thinking can be applied to winter weed management in no-till wheat:

  • postemergence herbicides applied in November,  such as dicamba plus Express (or the equivalent generic product), can be an effective option
  • cautionary note: labels for many wheat herbicides specify that they should not be applied in the fall until wheat has 2 to 3 leaves, which does allow substantial time for growth of weeds that have already emerged

Full podcast available here:

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September 28, 2010 at 5:51 pm

Strategies to Control Marestail

This is easily one of the worst marestail years I have seen. Marestail is a weed that can follow a winter or summer annual life cycle. Marestail plants start out as a rosette, generally bolt in April/May, flower in July, and set and disperse seed from August to October. Each plant can produce up to 200,000 seeds that travel via the wind.

For those of us who deal with marestail, we know that post-emergence control of many marestail populations is close to impossible. As such, the goal of a marestail management program is to ensure that the combination of fall and spring burndown and residual herbicides results in a weed-free seedbed at the time of soybean emergence, and little to no emergence of marestail between soybean emergence and crop canopy closure. But keep in mind that even the most effective marestail management programs can fail to completely achieve this, but they often keep the populations low enough in the soybeans that they are not problematic.

For marestail control suggestions, OSU Extension Weed Specialist Dr. Mark Loux suggests the following as one possible approach:

Apply a combination of glyphosate and 2,4-D in the fall, followed by application of residual herbicide in the spring prior to soybean emergence. At the time of soybean planting, the field is likely to be infested with marestail that emerged earlier in spring, so include effective burndown herbicides to control emerged plants. Keep in mind these plants can be very small and not noticeable.

The idea here is to apply an herbicide treatment in the fall that adequately controls emerged marestail, but does not break the bank and allows use of residual herbicide in the spring. Canopy herbicide can also be used in the fall, but use of metribuzin in the fall preserves the option to plant corn the following spring. Follow the OSU Extension CORN newsletter for the latest updates at corn.osu.edu

September 7, 2010 at 3:04 pm 1 comment

Tips to Maximize Glyphosate Effectiveness

Christy Sprague, MSU Crop and Soil Sciences, wrote an article for the MSU IPM newsletter on maximizing glyphosate activity: http://www.ipmnews.msu.edu/fieldcrop/fieldcrop/tabid/56/articleType/ArticleView/articleId/2706/Tips-for-maximizing-glyphosate-activity.aspx

I’ve taken a few tips verbatim from that article:

  • Ammonium sulfate (AMS) should always be added to all glyphosate products. We recommend adding dry spray grade AMS at 17 lbs/100 gal. or the equivalent of 17 lbs/100 gal. of liquid AMS products. The addition of AMS minimizes the negative effect of hard water on glyphosate activity and is important for velvetleaf control, regardless of water quality.
  • Applying the appropriate glyphosate rate in glyphosate-resistant crops is important for consistent weed control. Proper glyphosate rates should be based on weed type, weed size and spray volume. In most cases, the appropriate rate to use for weed control in glyphosate-resistant crops is 0.75 lbs a.e./A of glyphosate. This rate will effectively control several annual weed species between two to eight inches tall. However, if weeds become larger or if harder to control species such as common lambsquarters or giant ragweed are present, increase the glyphosate rate to 1.13 lbs a.e./A to adequately control these weed species.
  • It is important to make timely glyphosate applications to minimize the chances of yield loss due to early-season weed competition and to maximize weed control. The optimum time for glyphosate applications in corn is before weeds are four inches tall, and when weeds are four inches tall in narrow-row (7.5 and 15 inches) soybeans and six inches tall in wide-row (30 inches) soybeans. Controlling weeds at these times reduces the chances for yield loss, as well as reduces the risk of weed control failures of larger weed that may be under stressful conditions (drought, stem-boring insects, coverage issue, etc.).

Full podcast here: Maximizing Glyphosate Effectiveness

June 4, 2010 at 10:53 am

Tips and Suggestions for Controlling Marestail this Fall

The following is condensed from the October 6, 2009 OSU CORN newsletter written by Dr. Mark Loux on marestail control.

The goal of a marestail management program is to ensure that the combination of fall and spring burndown and residual herbicides results in a weed-free seedbed at the time of soybean emergence, and little to no emergence of marestail between soybean emergence and crop canopy closure. Even the most effective marestail management programs can fail to completely achieve this, but they often keep the populations low enough in the soybeans that they are not problematic.

Marestail plants that emerge in late summer or fall are easily controlled with a fall herbicide treatment. However, it’s essential to realize that a fall herbicide treatment is not likely to accomplish everything that’s needed in an effective marestail management program.

In those marestail-infested fields requiring a fall herbicide treatment for management of other winter annual annual weeds or dandelion, it is essential not to apply all of the residual herbicide in the fall. This also applies to those fields that are typically so wet that soybeans cannot be planted until mid to late May. In this situation, the goal of a fall residual herbicide treatment might be just to ensure that marestail are not too large when burndown herbicides are finally applied in May. Regardless of the type of herbicides applied in fall, an effective rate of a residual herbicide should still be applied in the spring, to maximize control of marestail that emerges in May and June. We suggest one of the following approaches [for marestail control]:

1. Apply a combination of glyphosate and 2,4-D in the fall, followed by application of residual herbicide in the spring prior to soybean emergence. At the time of soybean planting, the field is likely to be infested with marestail that emerged earlier in spring, so include effective burndown herbicides (2,4-D, Gramoxone, glyphosate, or Ignite or some combination as appropriate based on herbicide resistance, plant size and time until soybean planting) to control emerged plants.

2. Apply 2,4-D with Canopy DF or EX at fairly low rates (e.g. 1 oz of EX or 2 oz of DF) in the fall, followed by application of residual herbicide in the spring (with burndown herbicides if the residual from fall does not hold marestail through planting). It is possible to follow the fall Canopy application with a spring application of a chlorimuron-containing herbicide, as long as the total does not exceed the maximum labeled rate of chlorimuron for the soil type.

3. In ALS-resistant populations where Canopy will fail to provide any residual control of marestail, it may be possible to substitute a combination of 2,4-D with metribuzin in the fall. This combination should control most emerged winter annuals, but can be weak on dandelion. Follow with application of residual herbicide in the spring (with burndown herbicides if the residual from fall does not hold marestail through planting).

Full podcast here:

October 21, 2009 at 1:00 pm

Fall Ag Weed Control Tips

OSU Extension Weed Specialist, Dr. Mark Loux, put together a great article in the September 21 CORN Newsletter. Below, I have summarized the article:

Fall herbicide treatments can have a range of goals, from control of warm-season perennials prior to crop harvest to control of winter annuals that make for a messy seedbed next spring. Optimum timing can vary based on life cycle, but we can roughly lump the various life cycles into one of two categories:

1) Weeds that must be treated before frost, which pertains to all warm-season perennials, including: johnsongrass, pokeweed, milkweeds and hemp dogbane, and horsenettle. The first frost will cause these weeds to shut down, if they have not already matured and senesced. Herbicides are no longer effective after this occurs.

2) Weeds that should be treated after frost and in some cases even after a hard freeze. Winter annuals, biennials, and cool-season perennials fit into this category, and they are often most effectively controlled when herbicides are applied between mid-October and mid-November. Weeds that fall into this category include: chickweed, purple deadnettle, mustards, cressleaf groundsel, poison hemlock, wild carrot, Canada thistle, quackgrass and dandelion.

In general, mixtures of 2,4-D and glyphosate work well.  One of the most problematic weeds in my area is dandelion.  For dandelion, combinations of 2,4-D and glyphosate are recommended, but combinations of 2,4-D with Basis or Canopy are also among the most effective treatments on dandelion.

Full audio podcast here:

October 1, 2009 at 1:00 pm

Soybean Burndown Options When 2,4-D Cannot Be Used

Unfortunately, the weather has not been the most cooperative this spring for fieldwork.  Cool, wet conditions are delaying field work and as we get closer to May many growers may drop 2,4-D from their soybean burndown.  Dr. Mark Loux, OSU Weed Specialist, suggests that where it’s not possible to use 2,4-D in a soybean burndown consider applying a combination of glyphosate plus products such as Canopy EX or DF, Valor XLT, or Envive. The addition of one of those products to glyphosate in a soybean burndown will provide generally broad-spectrum control of no-till weeds in the absence of 2,4-D. In addition, adding one of those products to glyphosate will help on the tough to control dandelion. But there are other products that will work well too. Mixtures of glyphosate with Gangster or Sonic/Authority First, are also more broad-spectrum than glyphosate alone. Actually, these products can be more effective for control of emerged ragweeds and marestail (as long as they are not ALS-resistant), but overall Gangster or Sonic/Authority First are less effective on a number of winter annual weeds including dandelion.

In addition to adding one of those soybean residual herbicides mentioned above to glyphosate, Dr. Loux recommends increasing the glyphosate rate from 0.75 lbs ae/A (22 – 24 oz of newer glyphosate formulations and 32 oz of generic glyphosate formulations) to 1.1 or 1.5 lbs acid equivalent per acre.  This increased glyphosate rate will help improve control in mixtures with soybean residual herbicides. But keep in mind that even mixtures of high rates of glyphosate and ALS-based soybean residual herbicides will not control populations of marestail or ragweeds that have developed resistance to both glyphosate and ALS inhibitors. In summary, for growers that cannot use 2,4-D in a soybean burndown OSU strongly recommends using one of the residual soybean herbicides mentioned here plus glyphosate at a rate of at least 1.5 lb acid equivalent per acre.

Full podcast available here:

April 23, 2009 at 7:30 am

Don’t Forget To Include 2,4-D in Burndown Applications

A little over a week ago about the only weed I noted in corn stalks was dandelion.  Now, I see that summer annual weeds such as giant ragweed, lambsquarters, and a few others have started to emerge in central  and north-central Ohio. The emergence of these weeds increases the need for appropriate preplant (burndown) herbicide mixtures in no-till crops.

This past winter you may have been considering whether or not you need to add 2,4-D with your burndown applications.  Because of the prevalence of dandelion and glyphosate-resistant weeds the addition of 2,4-D in preplant herbicide burndown applications is very important in achieving effective weed control prior to planting.  Unfortunately, there are several weeds that have expressed glyphosate resistance (or tolerance, whatever you want to call it).  Just a few examples of glyphosate tolerant weeds in our area include marestail, common/ giant ragweed, and lambsquarters.  Of these, I am most concerned with marestail (Conyza canadensis).  This weed is difficult to control in the best of situations, let alone when it gets > 8″.  OSU Weed Scientist Mark Loux recommends controlling this weed when it is 4″-6″ or smaller.  I completely agree, as I have observed the difficulting in controlling this weed once it bolts. And, unfortunately, postemergence control options with this weed are usually not overly successful.

We are still early enough in the season that it is more important to include 2,4-D in preplant herbicide applications rather than planting the crops and controlling weeds long after planting. For the latest updates on weed control strategies, visit the OSU C.O.R.N. newsletter at http://corn.osu.edu/.

Full podcast available here:

Edit (04/08/09): I was asked ‘What is a burndown?’  Good question, and I apologize for using the ag jargon.  A burndown is a herbicide application made to an ag field several days (or even a couple of weeks) prior to planting.  Burndown applications are made in no till fields.

April 8, 2009 at 7:30 am

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