Critical Period for Weed Control in Grafted versus Nongrafted Tomato

The critical period for weed control (CPWC) is an important component to develop integrated weed management strategies. One sustainable approach to reduce CPWC could be to use grafted plants that may have enhanced competitive ability against weeds for utilizing resources and hence improve yield. The objective of this study was to determine the effect of grafting on CPWC in fresh market plasticulture tomato. Field studies were conducted in summer 2013 at the Horticultural Crops Research Station, Clinton, NC. The removal and establishment studies were conducted to determine the maximum period of weed competition and minimum weed-free period, respectively after tomato planting. Tomato plants used in the study included nongrafted Amelia and Amelia grafted onto Maxifort tomato rootstock. In the establishment study, weeds were transplanted at 1, 2, 3, 4, 5, 6 and 12 wk after tomato transplanting (WATT) and remained until tomato harvest. In the removal study, weeds were transplanted on the same day of tomato transplanting and removed at 2, 3, 4, 5, 6, 8, and 12 WATT. Weed removal at 12 WATT was considered the weedy all-season treatment and weed establishment at 12 WATT represented the weed-free treatment. Each planting hole contained one grafted or non-grafted tomato plant and six weed seedlings [2 yellow nutsedge (Cyperus esculentus), 2 common purslane (Portulaca oleracea) and 2 large crabgrass (Digitaria sanguinalis)]. The experimental design was randomized complete block with four replications. The weed above-ground biomass was measured (dried at 55C) at the time of weed removal from the removal study or at the end of tomato harvest from the establishment study. At 8WATT, one tomato plant per plot was harvested and dried at 55C to measure dry weight. In both grafted and nongrafted tomato treatments, plant biomass increased as establishment of weeds was delayed and grafted plants had significantly higher biomass at 4 and 12 WATT. However, plant biomass decreased when removal of weeds was delayed and no difference was observed between grafted and nongrafted plants at any removal time. In both grafted and nongrafted plants, the delay in establishment and removal of weeds resulted in weed biomass decrease and increase of the same magnitude, respectively. To avoid 5% yield losses, it is sufficient to keep grafted and nongrafted tomato plants weed free for first 3.25 WATT. Overall, results show that grafting does not have a positive effect in reduction of CPWC. The study will be repeated to confirm these findings.