PROJECT RESULTS

Weed Control/Herbicide Option Development of Legume Seed Crops

Applicant: 

Gerald Huebner
Manitoba Forage Seed Association
Arborg, Manitoba  R0C 0A0  Canada

Table of Contents:

• Background and Objective
• Procedure and Project Activities
• Results and Discussion
• Conclusions

ARDI Project:

#98-077

Total Approved:

Date Approved:

Project Status:

Completed February, 2002

Background and Objective:

Today, Manitoba has become a leader in both legume seed and leafcutter bee production. In the early 1970’s, this industry was virtually non-existent. As development occurred, successful production systems were developed through a cooperative industry approach. Alfalfa and other legume seed growers continue to struggle with perennial weeds. The forage seed industry has repeatedly identified this as a top priority. The yield damaging effects of perennial weeds on these crops is estimated at 20-25%. By reducing this effect by even 50%, both the increased farm gate value and increased productivity would be approximately 2 million dollars. This project looked at increasing effective registered herbicide options to enhance Manitoba’s legume seed production industry.

Procedure and Project Activities:

Year 1 (1998)
In 1998, herbicide trials on seedling forage seed crops were planned. Due to circumstances, plots were seeded late and did not establish well enough to continue the tests.

Year 2 (1999)
In 1999, herbicide effect on weed control in established alfalfa seed crops was examined. Herbicide treatments were applied with a bicycle sprayer and plots were located on commercial fields. Plots were 2 meters by 5 meters in size and treatments were replicated four times. The sprayer boom was equipped with a two-meter boom with 4 nozzles (8001) at 50-cm spacing. A pressure of 45 psi and a speed of 5 km/hr (3 mph) were used when spraying. The plots were sprayed with Matador on June 17, 1999, and with herbicide treatments on June 18, 1999. Herbicide treatments included:

1. Control (no chemical applied)
2. Basagran at 0.9 L/acre
3. Roundup at 0.5 L/acre
4. 2,4-DB (Embutox) at 0.9 L/acre
5. MCPA Na (sodium salt) at 1.7 L/acre
6. MCPB + MVPA (Tropotox plus) at 1.7 L/acre
7. MCPB (Tropotox)
8. MCPB (Tropotox) + Pardner at 1.7 and 0.5 L/acre
9. MCPA Na (sodium salt) + Pardner at 0.4 and 0.5 L/acre
10. 2,4 DB (Embutox) + Pardner at 0.9 and 0.5 L/acre

Plots were harvested October 12, 1999, by hand clipping ¼-meter squares (50 cm x 50 cm) from the front and back of each plot. This is not the most ideal method of harvesting as variability is quite high. Yields were ranked as follows, from highest to lowest:

• MCPB Tropotox
• Tropotox
• MCPA Na
• Tropotox + Pardner
• Embutox + Pardner
• Embutox
• MCPA Na + Pardner
• Roundup
• Basagran

Weed control was quite good in spite of the herbicides being applied a little later than the optimum window; however, crop tolerance was an issue with all chemicals. Alfalfa seed producers may have to put up with some crop damage in order to control weeds, as most herbicides used in alfalfa seed caused some crop damage. Given the low tolerance for certain weed seeds in alfalfa seed and that many of the weeds targeted are perennials, yield may have to be sacrificed some degree to eliminate certain weed species.

In the 1999 season, we also planned to have herbicide screening trials on seedling alfalfa, birdsfoot trefoil, red clover, alsike clover and sweet clover in two locations in Manitoba. Once the crops were established, these screening trials would be continued for the next two years to evaluate the herbicides. However, test plots did not get well established and could not be sprayed as crop growth was too variable to be able to compare the treatments. Problems were due to soil crusting at one site and wet soil conditions at the other.

Year 3 (2000)
In 2000, a number of herbicides were screened over a number of forage seed legume species to identify crop tolerance to herbicide products and to observe effect on seed yield and quality.

Seedling Tolerance Screening Trials
Seedling tolerance screening trials were conducted at Arborg, MB in 2000 on 6 legume crops: Algonquin alfalfa, Vector alfalfa, Leo Birdsfoot trefoil, red clover, Norgold sweet clover and Aurora Alsike clover. Twenty-three herbicide products and 1 untreated control were used in the trial (Table 1). This trial was initiated at two sites, but one had to be abandoned due to poor emergence as a result of adverse weather conditions.

Table 1.  Treatments for seedling herbicide screening trial.

The purpose of the seedling trial was to identify herbicides with potential to control both grass and broadleaf weeds during establishment of forage seed crops (Table 2).

Herbicide replicated screening trial plot size was 2m x 2m. The trial was seeded on May 26 and the herbicide treatments were applied on July 6, 2000.

Visual assessments were conducted at 5, 10 – 41 days after treatment (DAT). Herbicide tolerance ratings were done numerically on a scale of 0-9. For crop tolerance, 0 would mean complete kill of the crop while a rating of 9 would be complete tolerance. Water volumes were the maximum recommended for each herbicide.

Established Trials
The established trials consisted of two established legume species: alfalfa and birdsfoot trefoil. Plot size was 8m x 2m. On each trial site a total of 10 different treatments and 1 untreated control were applied (Table 3). These treatments were conducted on established forages in grower’s fields over 6 locations. Spray dates varied according to the appropriate crop stage at each location.

Table 3.  Treatments for established alfalfa and birdsfoot trefoil trial.

*ALF alfalfa, BFT birdsfoot trefoil

Note: Water volumes were the maximum recommended for each herbicide.

Crop stands were assessed for herbicide tolerance approximately four, seven and 37 DAT and seed yield was measured for alfalfa.

Results and Discussion:

The established herbicide trial included crop tolerance as well as seed yield. Established forage species often recovered from herbicide damage by 37 days after treatment that their seedling counter parts did not. In some cases, presence of visible crop damage did not translate into reduced seed yield. Alfalfa was less tolerant to 2,4 D amine than Odyssey, however, seed yield for alfalfa sprayed with 2,4 D amine was no different than that for alfalfa sprayed with Odyssey.

There was minor crop injury to established alfalfa when sprayed with 2,4 D amine, MCPB + MCPA and Pardner + MCPA, which are known to control top growth of Canada thistle and dandelion (2,4 D amine only) (Figure 1 and 2). Birdsfoot trefoil tolerated Embutox and MCPB + MCPA well, thus these products may provide the Canada thistle control trefoil producers are looking for (Figure 3). Unfortunately, significant crop injury occurred to alfalfa and birdsfoot trefoil when sprayed with Sundance, which means the search for good quackgrass control in these crops continues.

Conclusions:

Several herbicides of known efficacy on weeds were identified as having potential to control weeds in legume seed crops. Some of these herbicides may provide the answer to the weeds of biggest concern to forage seed producers. The herbicide screening trial was designed in such a way as to act as a sieve with fairly large holes. A large number of herbicides (23 on seedling crops) were screened over several forage species and cultivars. Once herbicides are identified as having no adverse effect on crop tolerance and answer specific weed problems in various forage seed crops will be entered into trials geared toward minor use registration.

In 2001, minor use trials will be conducted in cooperation with forage seed associations in Saskatchewan, Alberta and British Columbia.

Acknowledgements:

This research was initiated through the financial support of the Agri-Food Research and Development Initiative (ARDI), Covering New Ground (CNG), Manitoba Rural Adaptation Council (MRAC), and the Manitoba Forage Seed Association (MFSA).

ARDI Home - Contact ARDI