This study examined the affect of targeted mowing of rye in the fall and spring on its suppression of germination, growth, and reproduction of redroot pigweed (Amaranthus retroflexus). This targeted mowing allowed rye to re-grow before being killed by sickle bar mowing. The hypothesis being tested is that mowing induces an increase in allelopathic activity, which enhances ryeís weed suppression ability. The design was a split-split plot complete block design with the presence or absence of rye root residue as whole plots; mowing treatments consisting of no mowing, fall mowing, and spring mowing as split plots; and rye shoot residue treatments consisting of no shoots, leached shoots, and unleached shoots as split-split plots. Rye shoot residues were bioassayed for allelopathic activity using lettuce seeds (Lactuca sativa). Redroot pigweed seeds were broadcasted in the split-split plots and covered with rye shoot residue. Pigweed emergence was monitored for four weeks, and cylindrical plant volume was used as a surrogate for above-ground biomass. As plants matured, seeds were collected and weighed. Results showed that spring mowing significantly reduced redroot pigweed emergence compared to no mowing, or fall mowing treatments in rye root residue plots. This suggests that targeted mowing operates to increase weed suppression by increasing the allelopathic activity of rye roots. Indeed, the effect of spring mowing on emergence was most noticeable in no shoot residue split-split plots in which pigweed seeds were exposed to root residue only. Mowing did not have a significant effect on pigweed biomass or seed production.
In conclusion, targeted mowing in early spring may be used to manipulate the allelopathic activity of rye roots, thus decreasing weed emergence. Since redroot pigweed emergence was affected while its biomass and seed production were not, targeted mowing may be more effective when weed plants are most sensitive to allelopathic chemicals, namely at the seedling stage of growth. Currently I am conducting an experiment to determine if spring mowing can reduce weed emergence sufficiently for a tomato crop to be more competitive and thus produce higher yields.