There are two main ways allelochemicals are released. One is by release of the allelochemical by growing plants such as tall fescue, perennial ryegrass, or black walnut. The second is the release of the allelochemical by decaying plant residue such as rye or wheat used as a cover crop for a warm season crop such as corn, soybean, or vegetables. The following information is needed to understand the potential use of allelochemicals for weed management and the limitations of allelochemicals for total weed management. Allelochemicals are found in leaves, roots, stems, flowers and fruits.
Leaves are the major source in most species.
The roots generally produce smaller quantities and less toxic compounds compared to leaves. The location of the source is much less important than the total amount released. Several environmental factors have been shown to increase the amount of allelochemicals produced by plants. Generally, as the intensity, duration and quality of light increases, the more allelochemicals produced. Mineral deficiencies in soil, drought stress, cooler than normal temperatures, herbicides, and other allelochemicals will induce greater production of allelochemicals.