Dr. Bob Hartzler, professor of agronomy and an extension weed specialist, and Meaghan Anderson, field agronomist in central Iowa posted this recent Integrated Crop Management blog on the impact of cover crops on weed management.
One benefit of planting cover crops is their contribution to weed management. While several factors contribute to the inhibition of weeds by cover crops, the physical barrier of cover crop residue on the soil surface is most important. Research has shown a strong relationship between the amount of cover crop biomass at termination and the level of weed control provided by the cover crop.
Because of the importance of cover crop biomass, it is essential to manage the cover crop to maximize growth when using cover crops to aid weed management. The following practices have a major influence on cover crop biomass:
1) Planting and termination date.
2) Cover crop species.
Due to the risk for negative effects of cover crops on corn yield, there is greater potential for using cover crops for weed suppression in soybean. The longer termination is delayed, the greater accumulation of biomass, and the more benefit in suppressing weeds. In most years, delaying termination until mid- to late-May will allow sufficient biomass for consistent weed suppression.
Increasing the seeding rate of cereal rye above recommended rates generally has little impact on the quantity of biomass when termination is delayed, except in cases of very late planting. The tillering ability of rye is responsible for the lack of responsiveness to seeding rate. Higher seeding rates may result in more rapid ground coverage in the fall and early spring, but the impact of seeding rate on biomass is diminished when termination is delayed until stem elongation.
Be sure to read the full blog here to learn more about potential reductions in herbicide use and allelopathy considerations.