Posts tagged ‘glyphosate’

Tips to Maximize Glyphosate Effectiveness

Christy Sprague, MSU Crop and Soil Sciences, wrote an article for the MSU IPM newsletter on maximizing glyphosate activity:

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

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

Glyphosate Management in Soybeans

The results of weed-crop interference studies show that weeds in soybeans should be treated with herbicide before they exceed a size of 6 to 8 inches in order to ensure that weed interference is not a limiting factor in soybean yield. Weeds may not have reached this size in later-planted soybeans, or where pre-emergence herbicide activity reduced weed populations and growth. In soybeans planted late May through June, POST herbicides can be applied sooner after planting when weeds are small, which maximizes POST herbicide activity and reduces the need for higher glyphosate rates.

Glyphosate rates should generally be based on weed size and age, environmental conditions, and the previous history of glyphosate effectiveness in the target weed population. You can use the lowest labeled rate of glyphosate, 32 oz/A Roundup Original and similar products, and achieve 100% control when the following are met: 1) weeds are less than 6 inches tall; 2) weeds have not survived tillage or a previous herbicide application; 3) glyphosate is applied following use of a pre-emergence herbicide; and 4) environmental conditions are extremely favorable for herbicide. Increasing the glyphosate rate to a range of 48 oz/A to 64 oz/A of Roundup Original and similar products can greatly increase effectiveness when weeds are more than 6 inches tall and/or other conditions are not optimum for herbicide activity.

Glyphosate-resistant corn increases the potential for volunteer corn problems in soybean when glyphosate is used for weed control. Fortunately, good volunteer corn control options exist in glyphosate-resistant soybean. Most postemergence grass herbicides are very effective in controlling volunteer corn. The exception is that Poast Plus can be less effective. Postemergence grass herbicides can be tank mixed with glyphosate, but the adjuvant requirements may be greater than the typical ammonium sulfate added with glyphosate and may depend if a glyphosate formulation requires no additional surfactant or if surfactant is required. The question of whether volunteer corn needs to be controlled depends both on the competition from the corn and the potential for dockage because of corn in the harvested soybeans. Based on previous studies from University of Wisconsin, soybean yield loss from volunteer corn is in the neighborhood of 1% yield loss for every 75 to 100 “clumps” of volunteer corn per acre.

June 17, 2009 at 7:30 am

Soybean Scouting and Stand Assessment Tips

Across the area soybeans are emerged and evaluation of the stand might be needed in some isolated cases. Even though soybeans have a capacity to compensate for low plant populations and gaps within the row, there is potential yield loss from stands that are too low in population.

There are a couple of different methods of determining soybean stand. One popular method to determine plant population is by using a hula hoop. This involves placing a circular device of known diameter such as a hula hoop on the ground and counting the plants contained within. Use the table here to calculate plants per acre:

When the soybean crop is planted in rows spaced 7.5 inches apart, the effect of plant population on yield is very small over the normal range of seeding rates and for any particular set of conditions. For a crop planted before May 20 in narrow rows, final populations of 100,000 to 120,000 plants per acre are adequate for maximum yield. Final populations for mid-June plantings should be in the range of 130,000 to 150,000 plants per acre. It is important to remember that soybeans can tolerate low populations very well, with only small reductions in yield potential across wide ranges in plant loss.

Recent research from University of Minnesota is consistent with OSU research that populations near 100,000 per acre are likely to produce maximum yields. Soybean stands with populations around 80,000 will yield about 90 percent of the maximum. However, expected yields drop more rapidly in stands below 50,000, with 39,000 plants per acre likely to produce about 75 percent of the normal yield. Researchers at U of M conclude that only those fields with remaining stands below 30,000 to 40,000 plants per acre are likely to produce greater yields when replanted.

Small, recently emerged soybeans (right) are dwarfed by large giant ragweed (left)

Small, recently emerged soybeans (right) are dwarfed by large giant ragweed (left). Click image for full size.

In addition to possible issues with thin soybean stands, there are some weed control challenges in soybeans due to lack of burndown applications prior to planting soybeans. It is not unusual now to see soybeans at 2-3” in height dwarfed by 12”+ giant ragweed or other tough-to-control weeds. Glyphosate is still the most effective herbicide on large weeds, with little risk of crop injury. However, be aware that it does not necessarily provide good control of large weeds in all situations, especially where the weed population has lost sensitivity to glyphosate over time.

Large weeds will require glyphosate to be used at a high rate, such as 1.5 lbs acid equivalent per acre in soybeans. OSU Extension Weed Specialist Dr. Mark Loux recommends increasing spray volume to 20 gallons per acre to improve coverage in dense weed infestations, or where spray needs to penetrate into the weed/crop canopy. Where the weeds are the same size or larger than the crop, be sure the nozzles are high enough above the weeds to obtain the full spray pattern distribution.

June 15, 2009 at 7:30 am

Weed Control in Winter Wheat – Fall is the BEST Time

Mark Loux, Ohio State University Weed Specialist, wrote an excellent article in the CORN Newsletter on weed control in winter wheat.  I encourage you to read the entire article, but I’ll give you Dr. Loux’s summary points:

  • apply glyphosate at 0.75 lb active ingredient/acre prior to planting wheat or immediately after wheat is planted
  • if timing/manpower does not allow for applying glyphosate prior to wheat emergence, plan for a early- to mid-November application of herbicide in emerged wheat (best: Express at 0.33 oz/acre plus dicamba at 4 oz product/acre)
  • fall herbicide applications in wheat are more effective than spring applications of herbicide in winter wheat

Listen to an excerpted version of the article in my podcast below

October 1, 2008 at 7:00 am

Delayed Planting Means a Change in Burndown Strategy

Wet weather has caused some fields to miss an early burndown.  I recommend increasing your glyphosate rate to attack large weeds.  There is one silver lining to the delay in planting with regards to weed control — find out about it by listening to my podcast here:

May 12, 2008 at 9:35 pm


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