Efeito de subdoses de 2,4-D na produtividade de uva Itália e suscetibilidade da cultura em função de seu estádio de desenvolvimento

Field experiments were carried out in Maringá - PR, Brazil, during 2002/2003 and 2003/2004, with the purpose of evaluating the potential damage of sublethal rates of 2,4-D on grapeyard, simulating drift events. For the first trial, application of 2,4-D was accomplished 30 days after winter pruning of a grapeyard of cv. Italia. Rates were 6.72; 13.44; 26.88; 53.76 and 107.52 g of acid equivalent (a.e.) per hectare of 2,4-D, equivalent to simulated deposits of 1.0%; 2.0%; 4.0%; 8.0% and 16.0% assuming a commercial application of 1 L ha^-1 (670 g a.e. ha^-1). At this point of crop cycle, plants were at stage 15 (bunch formation/flowering). Visual phytotoxicity symptoms were immediate and proportional to applied rates. Crop yield was affected by all rates within this range. Nevertheless, even with severe injuries observed at highest rates, plants were able to recover after two pruning for the usual regional management (two harvests per year). For the second trial, rates equivalent to drifts of 1.0 and 2.0% (6.72 and 13.44 g a.e. ha ^-1) were applied at three stages of crop cycle. After reaching the stage of 50% development of bunches, rates ≤ 13.44 g e.a. ha^-1 (up to 2.0% simulated drift) of 2,4-D had no negative effect on crop yield or plant development.