Reestablishing the use of buckwheat as a precise weed control tool

2005 Annual Report for LNE05-214

Project Type: Research and Education
Funds awarded in 2005: $103,235.00
Projected End Date: 12/31/2008
Region: Northeast
State: New York
Project Leader:
Dr. Thomas Bjorkman
Cornell University

Reestablishing the use of buckwheat as a precise weed control tool


Buckwheat is a traditional tool for weed control, but knowledge of how to use it effectively is being lost. Current guidance is overly general, missing important details needed to incorporate it effectively into farming systems. Through this project, more growers will use buckwheat effectively by knowing the situations where is works best and detailed procedures to succeed.
We will provide the needed information through four approaches.

First, we will document traditional knowledge of the art of weed control with buckwheat through interviews and gray literature. Second, we will identify the questions growers most need answered to try the method, and do field trials to provide answers with the degree of detail expected of other weed control methods. These include the target crop, the weeds that are controlled and not controlled, seeding rates, and the timing of use relative to the climate and to weed and crop development. Third, we will engage about 60 growers to test and demonstrate the effectiveness. Finally, we will produce a definitive grower-friendly information set for the Northeast that will be in archival form so that it is available indefinitely. It will be promoted through field days, grower conferences, mailings, and publications in trade magazines and extension newsletters.

We are examining the following best uses:

Bringing abandoned land or old pasture into production using buckwheat to suppress summer annuals and to make the soil friable.

Before a late-summer seeding of alfalfa or alfalfa/grass to suppress quackgrass and winter annuals, and to leave a weed-free friable soil for rapid establishment of small alfalfa and timothy seeds.

Between early-harvested vegetables and overwintered crops to suppress annual weeds and maintain tilth.

Before strawberries, in which weed control is a great expense. Used with a winter grain to disrupt perennial weeds, to suppress annuals, and to reduce the weed seed bank.

The performance target is to have 100 growers in the Northeast using buckwheat as a cover crop successfully in situations where they did not use it previously by the 2008 growing season.

Objectives/Performance Targets

The performance target is to have 100 growers in the Northeast using buckwheat as a cover crop successfully for weed management in situations where they did not use it previously by the 2008 growing season.


1. Five Core Advisors and 150 prospective Intensive Engagement growers consulted. (winter-spring 2005)

We consulted the Core Advisors on the primary issues, opportunities and information needs. We had identified four scenarios where buckwheat was likely to be important (see summary). The Core Advisors reinforced our original assessment.
We sent a mailing to 120 prospective growers to engage.

2. Five Core Advisors and 60 Intensive Engagement growers have identified unknowns. (Spring 2005)

Since the project was approved on May 3, when many growers were already in the field, a small number of growers were available for interviews. We identified 23 Intensive-engagement growers in the spring who contributed their key information needs through interviews. We identified 4 additional growers during fall meetings.

We discovered two additional expert users who have provided excellent guidance on practices that are essential and practices to avoid in order to get effective cover crop performance.

Our plan is to use the winter 2005-2006 season to identify an additional 33 intensive-engagement growers, largely through grower meetings that we attend.

Interviews were free-form, allowing growers to identify information needs first. Then, if appropriate, additional information was provided and evaluation sought for issues we or other growers had identified as of potential importance. The following subjects were the most important:

A. Where can I buy it and how much does it cost? We have most sources identified, but sources of locally produced buckwheat may be important for economical use.

B. When can it be planted as a cover crop? The optimum date for grain production is well known, but the range of planting dates effective for cover crop production is not. Some field research will be necessary to make that determination.

C. What is the necessary land preparation and seeding method? Minimizing tillage and cost is important for cover crops, so finding the simplest preparation requires a field trial and consultation with expert users. A field trial was conducted in 2005.

D. Which herbicides can carry over to injure buckwheat? Many herbicides have been screened, with atrazine known to be problematic. Data are needed for herbicides used on vegetables. A trial was conducted in 2005.

E. When is it better than Sudex, sorghum or sudangrass? Comparative trials have been conducted in warmer climates. General answers are available, but precise comparisons in northern climates would be valuable. One field trial was conducted in 2005, and further work is the subject of an independent grant proposal.

F. Which weeds does it control? Specific mention of chickweed, creeping charley, toadflax, bindweed, quackgrass, oxalis and Canada thistle. Buckwheat has a strong reputation for controlling the rhizomatous perennial quackgrass. Whether it can be effective on other perennials in unknown. Trials in 2005 identified annuals that were suppressed.

G. How do you manage volunteer buckwheat? Considerable information is available from expert users who find that volunteers are not a significant problem. The ability of immature fruits to form viable seed with different killing times and methods has not been sufficiently determined. A greenhouse trial showed that ungerminated seeds from the initial planting do not contribute to volunteers.

H. What is the proper maturity at mowing or plowdown to maximize organic matter and weed suppression? There is a relatively small (~1 wk) time window after organic matter plateaus before leaf loss and seed maturation. A field trial could determine the amount of leeway.

3. Answers to growers key questions discovered through field trials (summer 2005- Fall 2006)

Trial A. Establishment of alfalfa/timothy. A replicated randomized complete block trial was established to test buckwheat before alfalfa/timothy. Weed suppression and effect on crop will be determined in spring. The treatments are with and without buckwheat before seeding, and also buckwheat sown as a nurse crop and killed by frost. Dry conditions resulted in weak buckwheat growth before forage seeding.

Trial B. Tillage requirement for establishment and weed suppression

i. How much tillage is necessary after early vegetables to establish buckwheat and suppress weeds following a spring vegetable? Incorporating crop residue with a disk was necessary and sufficient tillage. No-till stunted the buckwheat, but plowing had no effect.

ii. How long after incorporating the crop residue must one wait to sow the cover? Sowing immediately after incorporation was too soon, resulting in a low population and spaces where weeds could grow. One week later was enough of a wait, less may be all right. A longer wait allowed weeds to germinate.

iii. How much weed control can be achieved? A good buckwheat stand eliminated all weeds. Where the ground was disked, then planted after 1 week, weed biomass was reduced by 99% relative to the weedy control.

iv. Which weeds are suppressed, and which weeds escape? Galinsoga, purslane and nightshade were completely suppressed. The first weeds to escape where the buckwheat stand was weak were redroot pigweed, lambsquarters and barnyardgrass.

Trial C. Biomass production and weed suppression in the field.

i. Compare biomass production and weed suppressive ability of two legume (soybean and cowpea) and two non-legume (buckwheat and sorghum-sudangrass) cover crops grown in late summer. Biomass production at the appropriate cutting time for buckwheat (39 d) was 4,500, lb/ac for buckwheat and 4,800 lb/ac for sorghum-sudangrass. The Sorghum-sudangrass was allowed to grow until 63d, when it produced 7,400 lb. (In trial B, biomass production was 3,600 lb DW/ac at 42 d). Legumes grew poorly in combinations with these cover crops, they did not increase biomass or weed suppression.

ii. Test whether mixtures of legumes with non-legumes could improve weed suppression and legume nodulation relative to legumes grown alone. Buckwheat reduced weed biomass by 98%, compared to 78% for sorghum-sudangrass and 71% for the legumes. Pigweed overran the legumes, producing about 150,000 seeds/m2; it produced 20,000 seeds/m2 in the sorghum-sudangrass at 63 d.

iii. Evaluate the effect of fertilization on growth, nodulation, and weed suppressive ability of cover crops both alone and in mixture. Mixtures of legumes with non-legumes tended to be dominated by the non-legume, resulting in low legume biomass and poor nodulation.

Trial D. Annual weed suppression

i. Emergence of barnyardgrass and hairy galinsoga in fall wheat were equal in plots with a buckwheat cover crop and fallow controls when the weeds were sown at the same time as the cover crop. Buckwheat residue had no significant effect on wheat emergence, but reduced wheat height and biomass, especially when wheat was planted into fresh buckwheat residue.

ii. In growth chamber testing, fresh buckwheat residue significantly reduced emergence and biomass of all weed species except barnyardgrass, but buckwheat residue allowed to decompose for 15 days had no effect on emergence (with the exception of pigweed) or dry weight of any of the weed species

Trial E. Effect of seeding depth on emergence and latent germination.

i. What is the optimal seeding depth? Time to emergence increased rapidly with seeding depth, with a delay of one day per 2 cm of depth. Emergence in potting mix was 85% with no effect of seeding depth from 1 cm to 9 cm. Emergence in soil was 80% at 1 cm and declined linearly with depth to 35% at 9 cm.

ii. Do deep seeds remain dormant and germinate at the next disturbance? Deep seeds (5 to 9 cm) had lower emergence due to abnormal seedlings, but equal germination. At all depths, seeds that failed to germinate (approx 8%) rotted. There were no viable seed to germinate later.

4. Intensive Engagement group tries buckwheat cover crop and reports reasons for success or failure, and identifies new information needs. (Ten in 2006 and 30 in 2007).
One tried buckwheat in 2005.

5. Five hundred growers have heard about project through early publicity (Fall 2006)
An article on the project reached 130 farmers subscribing to NY Berry News in summer 2005. Presentations are scheduled at the February 2006 NY Expo’s sessions for Peas & Beans and for Berries.

6. 2000 have heard about project results. Definitive literature is generally available in grower homes, extension and consultant offices, libraries and online archives. (Fall 2007)
Pending results

7. 100 growers in the Northeast use buckwheat as a cover crop successfully for weed management in situations where they did not use it previously (Summer 2008)

Impacts and Contributions/Outcomes

None yet


Robin Bellinder

Cornell University
Department of Horticultre
134a Plant Science
Ithaca, NY 14853
Office Phone: 6072557890
Russell Hahn

Associate Professor
Cornell University
Department of Crop and Soil Sciences
238A Emerson Hall
Ithaca, NY 14853
Office Phone: 6072551759