Reestablishing the use of buckwheat as a precise weed control tool

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)

We interviewed 27 intensive engagement growers identified in dentified 23 Intensive-engagement growers in the Spring (23) and Fall (4). They contributed their key information needs through interviews. 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.

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.

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. We found that 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.

In 2006, sequential plantings were done every 2 weeks from May 18 to August 18, 2006. 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.

In 2007, biweekly plantings were made from May 15 to September 15. Early seeding resulted in slow initial growth, with initial growth increasing in each successive planting until mid-August. Ground cover at 3 weeks increased from 50% in the first planting to 85% in the last. Seeding from mid-June through mid-August produced maximal buckwheat biomass. Planting in mid-August resulted in good early growth, but plants stopped growing in September. One June planting did poorly because the soil was too dry for germination. Therefore, buckwheat cover crops can be planted to control weeds any time from late May until 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. A replicated randomized complete block trial was established to test buckwheat before alfalfa/timothy in fall 2005 and fall 2006. In the first year, dry conditions resulted in weak buckwheat growth before forage seeding.
In the second year, the treatments were 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. First-cutting hay data will be collected this summer. However, buckwheat has no benefit when grown before seeding alfalfa and timothy.

Trial B. Establishment after early vegetables.

i. How much tillage is necessary? Replicated field trials in 2005, 2006 and 2007 showed that incorporating crop residue with a disk was necessary and sufficient tillage. No-till planting stunted the buckwheat.

ii. How long after incorporating the crop residue must one wait to sow the cover? In the dry years (2005 and 2007) 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 wet year (2006), 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 wet year (2006) had about 4 times as heavy weed pressure.

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 barnyard grass, 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.

Issue 3. Which herbicides carry over to injure buckwheat?
Field trial. In 2006, 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.
In 2007, buckwheat was seeded after spraying the soil with 13 different herbicides used in early vegetables. Carryover was simulated by waiting seven weeks after spraying, lightly disking the soil and sowing to buckwheat. The amount of stunting of buckwheat was measured one and two weeks after sowing, and the dry weight at 2 and 4 weeks measured. Buckwheat was not stunted significantly by carryover of ten of the herbicides. It was stunted severely by Refex, Sandea and Pursuit.

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?
Over three 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, lambs quarters and barnyard grass. Ragweed suppression was excellent, yet populations were high in the subsequent crop.
The only weed suppressed after buckwheat incorporation is Powell amaranth, perhaps by allelochemicals.

One concern we discovered was that summer pea emergence was suppressed if sown immediately after incorporation of buckwheat.
In growth chamber testing, fresh buckwheat residue significantly reduced emergence and biomass of all weed species except barnyard grass, 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.

Weeds observed in buckwheat stands that were sown biweekly through the season. were primarily lambsquarters in stands planted before late July; in later plantings, pigweed and grasses became more common in general, weed growth in these stands was very low.

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 vegetable, two strawberry and two idle. Thirty four growers participated in 2007.

5. Five hundred growers have heard about project through early publicity (Fall 2006)
Through newsletter articles and grower presentations, we reached 350 farmers in 2005 and 150 more in 2006 to inform them of project goals, and engage more growers.

NY Fruit and Vegetable Expo (100 growers, Feb 2006),

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 were presented in a workshop at the following meetings:
NOFA-NY Winter meeting (70 growers, Jan 2007),
NY Fruit and Vegetable Expo (50 growers, Feb 2007),
New England Vegetable and Fruit conference (200 growers, Dec 2007),
Niagara Fresh Market Vegetable Meeting (50 growers, Jan 2008)
Empire State Fruit and Vegetable Expo (70 growers, Jan 2008)
Capital District Small Fruit and Vegetable Growers Meeting (100 growers, Feb 2008)
Northeast Buckwheat Field Day (32 growers, August 2008)
Cornell Ag and Food In Service (20 extension educators, Nov 2008)
Mid-Atlantic Fruit and Vegetable Conference (100 growers, Feb 2009)
Ontario Fruit and Vegetable Conference (30 growers, Feb 2009)
Finger Lakes Grape Growers Conference (200 growers, March 2009)

Articles were published in extension newsletters throughout the Northeast in late spring and early summer 2007, 2008 and 2009, reaching 1000 to 2000 growers.

The Northeast Buckwheat Cover Crop Guide was written based on the information obtained in this project. It was distributed to 1450 growers by mail, at conferences or by extension field staff. The online version has been accessed by 2,683 times during the last year of the project. It is in the Library of Congress and through interlibrary loan from Cornell. It is also available online, where it has been downloaded by 3125 different visitors, of whom 1085 were from the Northeast Region.

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)

We conducted a survey to assess the amount of adoption.

Intensive Extensive
Have you heard anything at recent conferences or read in publications about using buckwheat as part of your weed management program 96% 100%
Have you received a copy of the Buckwheat Cover Crop Handbook, or accessed it online? 72% 19%
After you heard about it did you consider trying buckwheat as a cover crop? 72% 81%
Did you try using buckwheat as a cover crop in a situation where you did not use it previously 56% (average 6.4 acres) 67% (ave. 4.6 ac)
Was it successful 57% 79%
Do you think you might use it in the future? (Asked of non-users) 52% 69%
Do you use buckwheat cover cropping as a regular part of your weed management? 32% 53%

We have two ways of estimating the size of the target population for this project. We distributed to all the Intensive Engagement group, and three quarters remembered receiving it. We distributed the 1450 handbooks to the Extensive engagement group. If they have similar recall, those handbooks were received by about a quarter of the population our survey audience sampled. That audience is therefore about 6000 growers.

There are 6000 vegetable farms over 5 acres in the Northeast according to the 2007 Census of Agriculture. We suspect that very few of the ~8000 smaller farms (<5 ac) were on the lists from which we obtained contact information.

Thus we have two estimates of 6000 growers in the target audience that was surveyed.

Intensive engagement.
This group included 60 targeted growers.
The goal was to have 30 growers use buckwheat as a cover crop successfully in situations where they did not use it previously
Of the 56% (~34) who tried buckwheat, 57% (~19) felt it was successful.

Extensive engagement:

2000 growers and crop consultants to see at least one communication.

We estimate that 6000 growers and crop consultants were reached.

400 growers to see at least three communications, including the main extension publication and one conference presentation.

We estimate that 1500 growers received the handbook, based on our mailings ad conference distribution. The recollection of publications suggest more than 400 had multiple impressions.

70 try using buckwheat as a cover crop successfully in situations where they did not use it previously.

Of the 67% (~4,000) who tried buckwheat, 79% (~3000) felt it was successful, thereby well exceeding the target of 70 growers. Of the 33% who did not try it, 27% (~500) expect to try it in the future. The mean area reported was 4.6 acres, implying 18,000 acres were planted.

We suspect that the intensive group had higher expectations and was more critical of the results than the extensive group. Several in the intensive group currently used buckwheat and will continue to use it for their old situation.