Cold-tolerant hairy vetch and late planting can be key factors for successful organic no-till corn in the Northeast.
Managing for optimum weed-fighting and fertility contributions from cover crops pushes back plantings into peak risk times from voracious cutworms, but improved stands prove worth the wait at 153 bu/ac.

By Dave Wilson, research agronomist, The Rodale Institute

Posted January 17, 2008: Delayed planting, a higher seeding rate and super-winter-hardy hairy vetch varieties can combine to produce top organic no-till corn yields, allowing producers who carefully track cutworms to beat these bugs.

These findings from fields at The Rodale Institute in 2007 add new understanding of how to increase the positive impact of the Institute’s roller-crimper. This simple, rugged implement is a smart-technology bridge in two critical spheres: for organic farmers to move into no-till (saving tillage, labor, fuel and time in field prep and mechanical weed management); and for non-organic no-tillers (to add cover crops to cut their costs for purchased fertility and weed management, while increasing soil carbon additions).

Records show 2006 was the breakthrough year for our organic no-till yields of corn. (See an overview here with details here on the conditions and management that resulted in a yield report of 146 bu/ac.)

We realized even better yields in 2007, but also learned some valuable lessons about the interplay of cover-crop survival, corn-stand numbers and corn variety day-length variations. So here’s the 2007 story, starting from the beginning: cover-crop planting the previous fall.

First thing: cover-crop hairy vetch

In late summer 2006 the intended corn field was prepared with clean tillage (moldboard plowing, disking and cultipacking) and planted to a combination of hairy vetch (Vicia villosa) and spring oats (Avena sativa), drilled on September 8 at 18.5 lbs/ac and 47.5 lbs/ac, respectively.

In this trial we looked at hairy vetch with two seed-tag origins. One was purchased through Ernst Conservation Seeds with a seed tag origin of Nebraska and a 74-percent germination rate; the other was from our local farm-supply store (F.M. Brown, Fleetwood, Pennsylvania) and had a seed tag origin of Oregon, labeled “EarlyCover” with a germination rate of 85 percent.

The winter of 2006-2007 began mildly enough; the fall growth of both hairy vetch types produced about 1,000 lbs/ac of biomass (dry weight) before going dormant for winter. Then in February, the “EarlyCover” hairy vetch took a dive. A genetic cost for its prized early blooming trait—which has strong economic benefits in spring—seems to be lessened winter hardiness.

Conditions were harsh, and we had little snow cover to provide insulation. Early February temperatures dropped as low as O°F, and in mid-February we recorded low temps of 4°F. Temperatures warmed up above freezing for a short spell, but dipped as low as 0°F again by mid-March.

Vetch survival depends
on many influences
Sub-freezing temperatures during the winter period can cause serious stand losses in northern states, even in southeastern Pennsylvania. Winter survival of legume cover crops such as hairy vetch can be one of the most important determinants of successful biomass production the following spring (and of subsequent crop yields during the growing season).

Cover-crop plant losses during the winter are usually the result of low temperatures in association with moisture in or on the soil or in the plant itself, since in the absence of a snow buffer the plant tissue is directly exposed to the surrounding frost and ice. The crowns and roots of even the most cold-resistant forages cannot stand direct exposure for very long to temperatures as low as 5°F to 15°F without injury or death.

We typically plant spring oats with hairy vetch, both to cover the soil quickly after harvest in the fall (since the hairy vetch establishes more slowly) and to provide sheltering insulation to the hairy vetch and soil. In the winter of 2006-2007, the dead oat residue did not provide enough insulating effect for the “EarlyCover” hairy vetch. Since this variety puts on fall growth more rapidly than other vetches, that extra green matter makes it especially vulnerable to cold weather and in need of this sheltering residue. Our “EarlyCover” didn’t survive the Arctic blasts and left us with insufficient cover-crop biomass to roll in spring 2007 in those plots.

Fortunately, we had mixed in plots with the Nebraska-type hairy vetch, which turned out to be very winter hardy. It produced adequate biomass required for a rolled weed-suppressing mat for the following crop of organic no-till corn.

We began evaluating the hairy vetch stands for bloom and biomass in May 2007. One of our main objectives for the coming no-till corn trial was to evaluate four dates of rolling/planting of the no-till corn.

The first roll-and-plant date was May 30—delayed from normal local planting to allow greater vetch maturity, biomass and fertility, but early in the vetch season—with successive rolling and plantings taking place weekly on June 7, June 14, and finally on June 21. Bloom ratings were at 50 to 60 percent on May 7; 60 to 70 percent on June 7; and 100 percent on June 14. The last planting date was very late for our location in southeast Pennsylvania where conventional no-till corn planting typically takes place in early May.

Critical note: The major consideration in timing the mechanical killing of the hairy vetch cover crop is bloom stage. The vetch should be at full-bloom stage before rolling, which will ensure adequate kill by the roller’s crimping action and will also ensure that the hairy vetch will be mature enough that it supplies adequate biomass for both weed control and the nitrogen needed for the corn crop. The biomass making up the rolled mat restrains the weeds until the corn can start to grow enough to form a leafy canopy in the field, shading out weeds.

With this trial we wanted to compare the effect of the killing time of hairy vetch on weeds, pests and yield.

Dodging cutworm damage with timing

The black cutworm (Agrotis ipsilon)—the cutworm moth in its caterpillar stage—has been a major pest of our organic no-till corn in past years. This moth is also called “Dark Sword-grass.” How much damage they do depends on the stage of corn development and local environmental conditions. The larvae cut off many more plants than they consume—and they consume a lot.

While some cutworms may develop from overwintering pupae or adult moths, most come from adult moths blown into the area with storm fronts during April and May. Moths fall out of the sky, laying eggs where they land. We see eggs on grasses, broadleaf weeds, crop residues and on our hairy vetch cover crop in the early spring, usually before the corn is planted.

For many insects, no-till agriculture represents a major positive change in their immediate ecosystem. Full tillage typical of organic agriculture is extremely disruptive of soil-insect habitat and produces high mortality of many of the crop pests—including these moths. Generally organic no-till ensures greater survival of many pests as well as many beneficial-insect species that remain within the no-till field or move to surrounding fields or crops.

Black cutworms are a significant threat to the young corn crop in Pennsylvania. They produce more than one generation of offspring per year, but it’s the first generation that tends to cause the most significant damage to corn.

Seed corn producers rate maturity on the number of equivalent growing degree days (GDDs) or heat units. The most common formula for calculating GDD averages the maximum temperature plus the minimum temperature for the day, minus 50. (Note: 86°F is the highest temperature recorded, even if the temperature exceeds 86°F.)

GDD units for the black cutworm are calculated in the same way. In Pennsylvania the black cut worm requires between 200 to 300 heat units to develop from an egg to the fourth-instar stage, which is the stage when the larvae begin cutting corn seedlings. The onset of this damage—which lasts for another 400 to 500 accumulated GDDs—can be accurately predicted to guide planting decisions.

In Pennsylvania the cutworm spends about one month in the larval stage, during which they can severely reduce the stand of corn plants by cutting them off at or just below the soil surface. We have lost entire fields to cutworm damage. In the 2006 trial, we discovered many cutworm larvae in early June and decided to delay corn planting a week, until June 9. We therefore managed to avoid the peak of the cutworm damage.

The design of the 2007 trial with the four weekly planting dates allowed us to quantify the corn plant population decrease due to the cutworm damage in the period of May 30 to June 21.

The graph below shows the relation of planting date to corn-plant population. Fields on all four dates were planted with a rate of 36,624 seeds per acre at 95 percent germination, which would ideally translate into 34,793 plants per acre. I purposely increased seeding rates this year in an effort to increase the final stand of corn after loss to cutworm damage and to compensate for other factors, including more-challenging seed placement in the no-till system.

The first planting date had a stand of 15,616 plants per acre. The cutworm damage was peaking during the second planting date and we experienced the largest decrease, with a stand of only 7,569 plants per acre. As the planting date got later in June, the cutworm damage decreased and stands improved dramatically. Populations for the third and fourth planting dates were 27,998 and 29,991 plants per acre, respectively. This was a result of the larvae maturing out of their cutting stage and growing into moths.

Farmers growing no-till corn realize it’s all about achieving a good stand. In the no-till roller/crimper system, proper planter modification is absolutely necessary to:

      • Cut through the heavy mat of a living, rolled cover crop.
      • Place seeds at the proper depth.
      • Provide good seed-to-soil contact.
      • Leave as much residue as possible over the row to prevent
        in- and near-row weed seed germination.

Weed management in this no-till roller/crimper corn system depends on the mulching effect of the rolled mat of hairy vetch and a competitive corn-plant canopy. Early rolling—before full-bloom—does not adequately kill the hairy vetch, and some of the rolled cover crop pops back up and continues to grow, failing to provide desirable weed control. This occurred with the May 30 and June 7 roll/plant dates.

In addition, the decreased stand of corn from cutworms in the earlier-rolled hairy vetch led to a sparser canopy from the corn, reducing its competitive shading effect on the weeds. The higher corn populations and increased weed suppression from the later plantings are illustrated in the weed biomass graph below.

Corn is a population-sensitive crop. Competitive yields are dependent on sufficient population, and plant loss is directly influenced by seeding rate, planter setup and pest damage.

For this year’s trial, I recommended increasing the seeding rate to 36,000 seeds per acre, up from our previous 32,000 seeding rate. The actual calibrated rate was about 36,624 seeds per acre. We increased the seeding rate with the goal of offsetting some of the loss due to cutworm damage. Increased seeding rate and late planting gave us an advantage over the environmental conditions, enabling us to increase our stand of corn and produce a satisfactory yield—even at very late planting dates for this region.

The corn variety we used in this trial was certified-organic hybrid field corn provided by Blue River Hybrids, which had a Relative Maturity Rating of 95 (commonly called “95-day corn”). The graph below shows the yield corresponding to the four planting dates.

Variety selection, plant population, planting accuracy (influenced by adding extra weight on planting units and adjusting planter depth to cut through cover-crop residue) and date of planting may greatly influence the corn stand in this organic no-till system. Seeding at higher rates allows for some cutworm loss, and by planting later we avoid the peak of the damaging cutworm population, which in turn contributes to a more-competitive corn stand. Later planting also contributes to quick germination and vigorous seedling growth because soil and air temperatures are warmer at the later dates, which also helps to optimize corn populations and resulting yields.

I was very happy with our 2007 no-till yields. Despite the late planting, this shows another situation where the “no-till roller/crimper with cover crops” approach can be integrated into an organic system as a strategy to reduce tillage, labor, energy and time—and still produce competitive yields of field corn.