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 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
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.
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
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
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
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
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
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.