Allelopathy--Summary

Increased interest in allelopathy is fueled by the desire to reduce synthetic herbicide use in agriculture and to find or identify natural products or allelopathic processes to control HR weeds.

Allelopathic effects can be and have been measured in controlled environment settings such as a laboratory or greenhouse, but replicating the effects in the field has been and continues to be difficult.

Research has left little doubt that the presence of a phytochemical that is toxic to plants of another species will have an adverse effect on those plants. However, equating the toxicity of the phytochemical to its availability and effect in the natural environment of the target plant species is often not accomplished.

Research is needed to ascertain soil microbial involvement in allelopathy; e.g. do soil microbes transform allelochemicals to more or less toxic forms, does exposure of soil microbes to a particular allelochemical over a period of time increase their activity on the allelochemical, do allelochemicals change the soil microbial makeup.

Concerted research efforts have been made toward the development of wheat varieties with high allelopathic activity. However, in 2012, wheat varieties that may have been released with this trait are not advertised in the US.

Corn allelopathy has not been specifically identified as a factor in US corn production systems, especially as it relates to soybeans rotated with corn. There is no evidence that corn allelopathy will be utilized as a weed management tool in the near future.

There is strong research evidence that grain sorghum has an allelopathic effect on plants of a following crop, and on weed plants that may appear in a growing sorghum crop. It is anticipated that grain sorghum’s allelopathic effect will be the first to be exploited for use in production agriculture. However, the application of this trait has yet to be realized.

The variability in allelopathic effects from plant residues presently negates their consideration as a stand-alone weed control option in large-scale crop production systems.

Cover crops that are proven to physically or allelopathically suppress weeds to offset some herbicide use may be a consideration in a soybean production system. However, the costs associated with this practice and the uncertain magnitude of the effect from using this practice will affect its adoption.

The likelihood of weeds becoming resistant to allelochemicals is unknown, so if they become an important component in weed management, this will be a factor to consider.

Allelochemicals that may be forthcoming will have to be selective in their effect; i.e., they must only adversely affect targeted plants such as weeds.

Using transgenics to produce crop cultivars that have enhanced allelopathic properties is being undertaken, but this area of research is insignificant compared to that of using transgenics to develop herbicide resistance in crop species.

In the near future, there is little reason to expect the development of allelochemicals for use as natural herbicides.

The principle of allelopathy may have the greatest application in low-input agricultural systems.

The study of allelopathy and discerning its importance for agricultural production systems will only be advanced if current and forthcoming research results can be translated into new technologies that can be used for weed management and/or reduced dependence on synthetic herbicides.

Click here to read the entire series on allelopathy posted on this website.

Composed by Larry G. Heatherly, Nov. 2012, larryheatherly@bellsouth.net