Glyphosate-Based Weed Management in Alfalfa


  • Determine glyphosate treatment effects on tonnage, NDF and crude protein of Pioneer® brand alfalfa varieties with Genuity® Roundup Ready® technology.
  • Investigate stand longevity, yield, and quality with glyphosate-based weed management.

Study Description

Locations: Chazy, NY, and Ithaca, NY
Research locations
Plot Layout:        20 ft x 50 ft plots, 4 replicates
  Pioneer® Brand
  54R01(RR), 54R02(RR)
  Treatments:       Non-treated
      3-5 Trifoliate (recommended timing)
  • Glyphosate was applied in seeding year.
  • Due to delayed seeding in 2011, only 1 cutting was taken.
  • Second cutting was not taken at the Ithaca location in 2012.

Weather Conditions

  • 2011 (Seeding year) - Prolonged spring rains delayed planting until the third week of May. Continued rains, followed by hot dry weather the remainder of the summer, resulted in 1 cutting.
  • 2012 - Hot and dry most of the growing season; tonnage was reduced with limited moisture.
  • 2013 - Adequate rainfall and timely cuttings in established stands.

Yield Results

  • Weed pressure from unsprayed plots contributed to overall tonnage in the seeding year for both 54R01 and 54R02 (Figure 1).
  • Aside from the seeding year, glyphosate-treated plots of 54R01 consistently demonstrated increased dry matter tonnage over unsprayed plots and were at parity in 2013 third cutting (Figure 1).
  • Total dry matter yield from 2011-2013 (Table 1) was 0.94 ton/acre greater in glyphosate-treated plots of 54R01 and similar between treated and non-treated plots of 54R02, despite weed biomass contributing to greater tonnage for first cutting; in some cases accounting for 15% of total dry matter.
    Table 1. Total dry matter yield, 2011-2013 all cuttings.
    Variety Non-Treated 3-5 Trifoliate App
      ————— tons/acre —————
    54R01 9.94 10.88
    54R02 10.73 10.77
Dry matter tonnage per cutting of 54R01 and 54R02 with and without glyphosate treatment at 3-5 trifoliate (2011-2013)

Figure 1. Dry matter tonnage per cutting of 54R01 and 54R02 with and without glyphosate treatment at 3-5 trifoliate (2011-2013).

Quality Results

  •  First cutting quality in the seeding year (Table 2) demonstrated a positive response to glyphosate application at 3-5 trifoliate, with a 9% decrease in NDF and 8.6% advantage in crude protein for Pioneer® variety 54R01.
  • Likewise, 3-5 trifoliate glyphosate application to Pioneer® variety 54R02 resulted in a 10.9% decrease in NDF and a 5.8% advantage in crude protein when compared to unsprayed
  • Table 2
    Table 2. Weed control effect on NDF and crude protein;
    2011 first cutting.
    Treatment NDF Crude Protein
      —————— % ——————
    54R01 Non-treated 46.1 15.1
    54R01 3-5 Trifoliate 37.1 23.7
    Difference -9 8.6
    54R02 Non-treated 44 19.1
    54R02 3-5 Trifoliate 33.1 24.9
    Difference -10.9 5.8
  • First cuttings over all years demonstrated improved forage quality for both NDF and crude protein when a glyphosate application was applied at 3-5 trifoliate growth stage (Table 3).
  • Weed populations in the non-treated plots were suspected to contribute to lower quality forage, as weeds accounted for up to 15% of samples even into the third year (2013).
  • Glyphosate-treated 54R01 showed a positive response in quality with 3.9% lower NDF and 3.67% higher crude protein compared to the unsprayed.
  • 54R02 treated with glyphosate had a positive response in NDF (5.43% lower) and crude protein (2.73% higher) when all first cuttings were averaged.
Table 3. Weed control effect on NDF and crude protein;
first cuttings 2011-2013.
Treatment NDF Crude Protein
  —————— % ——————
54R01 Non-treated 44.60 17.97
54R01 3-5 Trifoliate 40.67 21.63
Difference -3.93 3.67
54R02 Non-treated 44.00 19.77
54R02 3-5 Trifoliate 38.57 22.50
Difference -5.43 2.73


  • 1 recommendation for glyphosate-tolerant alfalfa has been timing the application (3-5 trifoliate) to ensure null plants are removed early in establishment rather than later, causing gaps or reduced stand.
  • Null plants have been reported to be as high as 10%; however, after application and counts in this study, null plant percentages were 2.72% in 54R01 and 2.05% in 54R02 after glyphosate application (Table 4).

    Table 4. Null plants during establishment following glyphosate treatment at 3-5 trifoliate and 15-inch height.

    Variety 3-5 Trifoliate 15-inch
      —————— % ——————
    54R01 2.72 4.72
    54R02 2.05 1.94
    Total 2.39 3.33
  • Results indicate the primary value of glyphosate-tolerant alfalfa is improved forage quality obtained in seeding year cuttings.
  • Table 2 demonstrates these advantages despite tonnage from the seeding year cutting being 0.28 and 0.18 DM tons/acre lower for 54R01 and 54R02, compared to non-treated plots.
  • Forage quality of the treated plots was greater for all 3 first cuttings from 2011-2013.
  • Final stand counts in this 3-year trial demonstrated a 2 plant/ft2 advantage for both 54R01 and 54R02 plots that were maintained with glyphosate, compared to the controls.
  • Stand longevity could be greater for glyphosate-tolerant alfalfa compared to conventional alfalfa.
Alfalfa fields - Non-treated (left) vs. 3-5 trifoliate spray (right) prior to the first cutting of 2011.

Figure 2. Non-treated (left) vs. 3-5 trifoliate spray (right) prior to the first cutting of 2011.

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PIONEER® brand products are provided subject to the terms and conditions of purchase which are part of the labeling and purchase documents. 2011-2013 data are based on average of all comparisons made at two locations through Nov. 15, 2013. Multi-year and multi-location is a better predictor of future performance. Do not use these or any other data from a limited number of trials as a significant factor in product selection. Product responses are variable and subject to a variety of environmental, disease, and pest pressures. Individual results may vary.

HERBICIDE RESISTANCE: Monsanto Company is a member of Excellence Through Stewardship® (ETS). Monsanto products are commercialized in accordance with ETS Product Launch Stewardship Guidance, and in compliance with Monsanto’s Policy for Commercialization of Biotechnology-Derived Plant Products in Commodity Crops. This product has been approved for import into key export markets with functioning regulatory systems. Any crop or material produced from this product can only be exported to, or used, processed or sold in countries where all necessary regulatory approvals have been granted. Do not export Genuity® Roundup Ready® Alfalfa seed or crop, including hay or hay products, to China pending import approval. It is a violation of national and international law to move material containing biotech traits across boundaries into nations where import is not permitted. Growers should talk to their grain handler or product purchaser to confirm their buying position for this product. Always read and follow pesticide label directions. Crops that contain the Roundup Ready gene confer tolerance to glyphosate, the active ingredient in Roundup® agricultural herbicides. Roundup agricultural herbicides will kill plants that are not tolerant to glyphosate. Excellence Through Stewardship® is a registered trademark of Biotechnology Industry Organization.

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