1988 Annual Report for LNC88-021
Utilization of the Allelopathic Properties of Winter Rye as a Method of Weed Control in Soybean Production
Summary
Rationale:
Winter rye (Secale cereale) is an annual grass species that has the potential to control weeds
through the release of allelopathic chemicals from its residues. Farmers could take advantage of
these properties and significantly reduce the use of herbicides by incorporating rye into their
crop rotations. Other benefits of sowing rye in the fall would include controlling soil erosion,
keeping nitrogen residues from leaching into the groundwater, and adding organic matter to the
soil.
Objectives:
1) Conduct a series of trials on seven commercial-scale farms and three small plot trials on a
university research farm, testing the use of allelopathic properties of rye as a weed control
method for soybeans under different management and climatic conditions.
2) Study and assess other benefits of rye as a cover crop.
3) Compare the economics of using rye to conventional and mechanical methods of weed
control.
4) Conduct an effective outreach program with farmers and extension personnel.
Methods:
In 1989, trials were conducted at the Arlington Research Station located near Madison,
Wisconsin, to determine the feasibility of obtaining adequate weed control from fall-planted rye
which was killed at three growth stages (tillering, boot, and pollination) by three means
(glyphosate, mowing with a cycle bar mower, and chisel plowing.) Rye was planted on
September 7, 1988, in a wheat stubble field at 75 lb/acre in a silt loam soil prepared with
conventional tillage methods. Rye was killed on May 4 (tillering stage), May 19 (boot stage),
and June 2 (pollination stage) Soybeans were planted with a no-till drill in 8-inch rows. Half of
each plot received no other means of weed control than the rye, and the other half was treated
with an appropriate postemergence herbicide to control weeds as they appeared. Soybeans were
seeded into plots without rye both in no-tillage and conventional tillage systems the same days as
the other plots. Half of each non-rye plot also received either no herbicide or herbicides to
control weeds. Each treatment was replicated four times. Weed control evaluations were taken
several times during the season, and soybean yields were measured at the end of the season. The
trial was repeated in 1990 with only minor changes in techniques.
Results:
Results indicate that several of the systems tested offer great potential to reduce the amount of
herbicide used in a no-till soybean system. Mowing rye in the tillering and boot stages did not
prevent rye from retillering, and this regrowth behaved as a competitive weed. Rye mowed in the
pollination or heading stages had very little regrowth, but planting in early June is later than
ideal, especially if an early frost occurs as it did in 1989. Rye gave adequate annual weed control
when it was killed in the boot and pollination stage by glyphosate or by mowing and leaving the
forage in the field. Even when the rye was removed as forage at theses growth stages, weed
control was acceptable. Killing rye with a chisel plow at any date essentially removed the
allelopathic effect of the rye on weeds.
In 1989, soybean yields in plots with rye that did not receive additional herbicide were highest
when rye was killed with glyphosate in the tillering and boot stages or with plyphosate or
mowing when rye was in the pollination stage. However, the overall highest yields were
obtained in the treatments without rye and with herbicides. The use of herbicides in addition to
rye increased yields for each method of killing rye in the tillering stage, for the mowed and
chisel plowed plots in the boot stage, and for the chisel plowed treatment at the pollination
stage.
Potential Contributions and Practical Applications:
The use of the physical and allelochemical properties of rye as a weed management approach in
no-till soybean production systems may allow a reduction in herbicide use. However, there are
many questions yet to be answered before wide spread adoption of this system occurs.