Does doses and time of 2, 4-D application interfere in the physiology and wheat grains yield components?

The identification of the application stage and correct dose of 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide is important so that wheat is not harmed. In view of this, the objective of this study was to evaluate the effect of 2,4-D doses applied at different development stages of wheat crop. The experiment was conducted in a randomized block design, arranged in a 4 × 5 factorial scheme, with four replications. In factor A, the application stages (before tillering, tillering, first node and booting) were allocated and the doses of 2,4-D (0, 349, 698, 1047 and 1396 g.ha­1) were allocated in factor B. The variables evaluated were phytotoxicity at 7, 14, 21, 28 and 35 days after application of the treatments (DAT), photosynthetic activity, CO2 internal concentration, stomatal conductance, efficient water use and carboxylation efficiency. The number of spikes·m­2, spike length and number of full and sterile grains were determined in the preharvest. Thousand grain mass, grain yield and hectoliter weight were determined after harvest. The results demonstrate that the herbicide caused phytotoxicity to wheat, being greater in increasing doses and mainly before tillering, causing grain sterility and decreased productivity. The other yield components did not present difference when increasing the dose and application in different stages as well as the physiological variables. The increase of the 2,4-D doses applied before tillering and in the booting stage caused linear decrease in wheat grain yield.

Application of 2,4-D hormetic dose associated with the supply of nitrogen and nickel on cotton plants.

Growth traits, yield, N content, photosynthetic pigments, ammonia and amino acids were measured to verify the effect of the interaction between N, Ni, and 2,4-D applied in the cotton crop. The objective was to study the hormonal effect of 2,4-D associated with the application of N and Ni in coverage to improve yield. The N (0, 40, 80, and 120 kg ha-1) and Ni(0, 300, 450, and 600 g ha-1) were applied to the soil in the square phenological growth stage. The commercial 2,4-D DMA® BR (0 and 1.8 g a.e ha-1) was applied to the leaves at the same growth stage. The supply of N in cover fertilization up to 120 kg ha-1 was beneficial for cotton, providing greater yield and content of photosynthetic pigments. The application of 2,4-D in a hormetic dose, as a synthetic auxin during the beginning of flowering, proved to be a promising technique to improve cotton yield. This end-of-cycle response is related to the requirement for auxins during the cotton fruiting process.