Velvetleaf interference

The remainder of this discussion examines the possibility of a direct feedback mechanism in response to light as an explanation for crop yield reduction from early weed presence. Three types of data will be examined 1) results of our research on velvetleaf interference with light in soybeans 2) a comparison of observed and estimated soybean yield reductions for weed presence versus leaf removal and 3) the poor correlation between weed control and crop yields. 

Velvetleaf interference in soybeans. In 1984, a field study was conducted on the Agronomy farm near Columbia, Missouri to examine the effect of velvetleaf height and duration on soybean yields. 

Phenolic acids interfere with many major physiological processes of higher plants (35). These disruptions of function include an alteration of plant water balance. We found depression of leaf water potential to be an early indicator of allelochemical stress from ferulic and p-coumaric acids (42). Likewise one mechanism of allelopathic action by cultivated sunflower, velvetleaf Abutilon theophrasti Medic.), Koahia [Koahia saoparia (L.) Schrad.], and several other weeds was water stress (43-45). Since some allelochemicals interfere with plant-water relationships, it seemed logical that their action might be most critical at times when plants are under water stress from other causes. 

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