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.

Tank mixture of glyphosate and 2,4-D applied on RR® maize crop.

Herbicide tank-mixing is often carried out by farmers aiming to control weeds in crops. Thus, it is important to evaluate the effects of these mixtures regarding the selectivity of crops. The aim of this work is to assess the selectivity of increasing doses of herbicides (glyphosate and 2,4-D), applied alone or as a mixture, on maize crop. Two experiments were carried out in randomized blocks, with four replications, during two crop years. The evaluated variables were: phytotoxicity, plant height, stem diameter, ear length, number of rows per ear, number of grains per row, mass of 1,000 grains and grain yield. The herbicide, 2,4-D, when applied in mixture with glyphosate caused severe phytotoxicity symptoms on maize. Grain yield and growth characteristics were not affected by the herbicides applied alone or as a mixture. Increasing doses of 2,4-D caused severe phytotoxicity symptoms on hybrid Status VIP3. Increasing doses of glyphosate did not show phytotoxicity symptoms and are not directly correlated to any injury caused by 2,4-D in the SX 5885 VIP3 maize hybrid.