Reestablishing the use of buckwheat as a precise weed control tool

2006 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)


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 2005-06 identified annuals that were suppressed.

G. How do you manage volunteer buckwheat? Some growers have had enough volunteers to interfere substantially with their crops. However, considerable information is available from expert users who find that volunteers are not a significant problem.

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)

Issue 1. What is the effective range of seeding times?

The range of planting dates over which buckwheat cover crops can be established was tested by making sequential plantings every 2 weeks from May 18 to August 18. Later seedings were not possible due to continuous rain. Early seeding resulted in slow initial growth, with initial growth increasing in each successive planting. Ground cover at 3 weeks increased from 50% in the first planting to 85% in the last. Seeding June and July produced maximal buckwheat biomass. Weed suppression was nearly complete (highest biomass was 10 g/m2, versus 300 g/m2 of buckwheat and 400 g/m2 of weeds in control plots). Weed suppression was effective even in those plantings where buckwheat growth was sub-optimal due to cool temperatures or heavy rain after seeding. For volunteer management, it is notable that the time until green seeds formed was 40 d in the July seedings and 50 d in the June seedings. Therefore, buckwheat cover crops can be planted to control weeds any time from mid-May until at least mid-August. If it is used as part of full-season cover cropping, June planting is ideal.

Issue 2. What is the necessary field preparation to obtain good growth and weed suppression?

Trial A. Establishment of alfalfa/timothy. A replicated randomized complete block trial was established to test buckwheat before alfalfa/timothy. The treatments are with and without buckwheat before seeding, and also buckwheat sown as a nurse crop and killed by frost. Buckwheat treatments inhibited fall growth of the forage crops by 50 to 80%, and provided no better weed control in the fall than treatments without buckwheat. Establishing a stale seedbed with herbicide was superior for crop growth and for weed suppression. Replacing the herbicide with tillage or with buckwheat stimulated subsequent weed growth. Following the stale seedbed with a buckwheat nurse crop only inhibited crop growth but not weed growth. Where weeds had been managed by cultivation before seeding, a buckwheat nurse crop did suppress fall weeds. If the forage species catch up in the spring, a buckwheat nurse crop may be useful for growers who control weeds with cultivation rather than herbicides before planting their forage. However, buckwheat has no benefit when grown before seeding alfalfa and timothy.

Trial B. Establishment after early vegetables.

i. How much tillage is necessary? Incorporating crop residue with a disk was necessary and sufficient tillage. No-till planting stunted the buckwheat. Chisel plowing was used to increase infiltration, and thereby reduce stunting from waterlogging. Plowing had no effect in either year.

ii. How long after incorporating the crop residue must one wait to sow the cover? In the dry year (2005) sowing immediately after incorporation was too soon, resulting in a low population and spaces where weeds could grow. One week was enough of a wait, less may be all right. In the wetter year, no wait was necessary.Waiting more than one week was undesirable, because it 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% (dry year) or 90% (wet year) relative to the weedy control. The wetter year (2006) had about 4 times as heavy weed pressure.

Trial C. 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.

Issue 3. Which herbicides carry over to injure buckwheat?

Field trial. Buckwheat was seeded after harvest of beans in a trial to test different bean herbicides. At 4 weeks, the amount of stunting of buckwheat was estimated. Buckwheat was not stunted by carryover of basagran or Bolero. It was stunted severely by atrazine and pursuit, and rendered ineffective for weed suppression by trifluralin and sulfonylurea.

Trials by others. Carryover problems can be expected with same-season use of Command.

Issue 4. When is buckwheat better than Sudex?

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.
Buckwheat suppressed summer weeds much better than Sudex, and produces comparable biomass at ~40d.

Issue 5. Which weeds are suppressed, and which weeds escape?

Trial A. Over two years of trials, we found that purslane and nightshade were completely suppressed. Galinsoga suppression was complete in some trials and poor in others. The first weeds to escape where the buckwheat stand was weak were redroot pigweed, lambsquarters and barnyardgrass. Ragweed suppression was excellent, yet it was common after buckwheat.

Trial B. 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.

Trial C. 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 D. Weeds observed in buckwheat stands were primarily lambsquarters is stands planted before late July; in later plantings, pigweed and grasses became more common.

Issue 6. Management of volunteer buckwheat.

Trial A. Effect of seeding depth on latent germination. (Greenhouse) 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.

Trial B. Effect of seeding depth on latent germination. (Field) Seed sown too deep to germinate immediately does not germinate after cultivation brings it into the proper zone. Seeds were sown either deep (~3″) or shallow (control) with either a disk or a drill. Plots were mowed after full emergence (3 weeks), then harrowed to bring up ungerminated seed. The deeps seeded plots had no more volunteers than the shallow controls, in both cases about 3% of the seeding rate. Therefore, volunteers are not derived from seeds that remain dormant after the initial sowing.

Trial C. (Funded by NYS IPM Program) The ability of immature fruits to form viable seed with different killing times and methods was determined. Most of the biomass is accumulated between 30 and 45 days after sowing. When the crop was mowed before any seed was formed (30 – 35 d) there was substantial regrowth from the lowest nodes. This regrowth produced new seeds approximately 30 days after mowing. Later mowing (40-45 days) gives no regrowth. However, by 45 days there was enough seed to give ~10 seedlings per square meter. These seedlings were killed by frost. When the cover crop was incorporated immediately after mowing, there was no regrowth. Incorporation early (30-35 d) resulted in little weed suppression, whereas later (40-45 d) incorporation resulted in weed-free conditions into the fall. Incorporation at 45 d also resulted in ~10 seedlings per square meter and an unknown number in the soil. In those cases where buckwheat seedlings will not be controlled by frost and field preparation, and the number of seeds must be minimized, the recommended practice is to let the crop grow for 35 to 40 days (long enough for weed-suppressive action), then mowed or incorporated (to prevent seed formation).

Trial D. A cooperating grower let the cover crop go to seed in the fall. The first-year strawberry crop that followed had no buckwheat volunteers.
Expert growers. Growers experiences with buckwheat cover crops report that complete elimination of buckwheat volunteers is obtained with atrazine, glyphosate, or early cultivation.

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. Ten tried buckwheat and our draft instructions in 2006. Six weere vegetable growers, two strawberry growers, and two bringing idle land into production. We are in the process of recruiting 30 for 2007.

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 were made at the February 2006 NY Expo’s sessions for Peas & Beans and for Berries, reaching approximately 200 farmers.

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)
Project results will be presented in a workshop at the NOFA-NY Winter meeting (Jan 2007) and the NY Fruit and Vegetable Expo (Feb 2007).

Literature will be prepared during winter 2007 based on results to date

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)

To be completed in coming years

Impacts and Contributions/Outcomes

Nine Northeast growers have used buckwheat as a cover crop in a situation where they have not tried it before.


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