Efficiency of different methods of cotton stubble destruction with different technologies

Cotton is a perennial plant, which means it survives after harvest and regrows during the off-season. The persistence of plant residues in the field allows the growth of larger stems that are more difficult to eradicate, causing interference in successive crops, which is aggravated when both have the same resistance technology to herbicide action mechanisms. When sprouting occurs, with plant development and production of reproductive structures, the organs become sources of inoculum for diseases and pests, such as angular leaf spot, fusarium, whitefly, aphids, thrips, caterpillar complex, mites, boll weevil, among others.

Thus, one of the difficulties encountered by cotton growers is the destruction of crop residues after harvest, since management occurs during a period of water stress (July-August), a time when herbicide translocation and absorption are lower, reducing their efficiency. Thus, after harvest, several control methods are adopted, usually mowing, followed by two or three applications of herbicides in mixtures or not. Aiming to further strengthen the cotton production chain in the state of Goiás, the IGA – Goiás Institute of Agriculture, has been working since 2017 to provide the best methods for managing ratoon crops, aiming to ensure that crop residues do not remain.

The three tables show the treatments tested in three agricultural harvests. All experiments were conducted in a randomized block design, with four replicates. The statistical analysis used was ANOVA (analysis of variance), followed by comparison of means using the Scott-Knott test.

The evaluation of dead plants was performed through destructive analysis. Plants located 5 meters from the two central lines of the plot were uprooted, and the outer layer (cork) was removed to observe signs of sap circulation and turgidity of the buds. Plants with brown coloration and buds without turgidity were considered dead, as shown in Figure 1.

The results described in the graphs represent the number of dead cotton plants according to the stubble destruction programs (Pgr.) tested in the respective harvests.

Through the results obtained, it is possible to identify that for good ratoon management, it is essential that the 1st application be carried out immediately after mowing, since greater control is observed in Pgr. 2 and 8 compared to Pgr. 9 in the 2018/19 harvest; as well as greater control in Pgr. 1 compared to Pgr. 2 in the 2021/22 harvest (Figures 2 and 4). The application immediately after mowing aims to increase the absorption of the herbicide by the conducting vessels that are still exposed.

The 2nd application should be carried out when the ratoon has 70% regrowth. This is to provide greater interception of the herbicide by the plant and facilitate control, since a greater number of dead plants were observed for Pgr. 1 compared to Pgr. 2 in the 2020/21 harvest (Figure 3).

Increasing the dose of DMA 806 BR or Aminol (2,4-D) from 2 to 3 L/ha in the first application and its association with Protox (protoporphyrinogen oxidase enzyme) inhibitor herbicides in the first or second application did not provide increases in ratoon control, as observed in the three agricultural harvests. However, parallel studies show that the association of 1-D with Protox inhibitors can provide increased control in areas where herbicide absorption is particularly difficult.

Carrying out 3 applications in ratoon management provides a higher percentage of dead plants, with the 1st application being with DMA 806 BR herbicide (2 L/ha), immediately after mowing; the 2nd with Aurora herbicide (0,07 L/ha), when 70% regrowth was observed; and the 3rd with Reglone herbicide (2,0 L/ha), as verified for Pgr. 5, in the 2021/22 Harvest.

Some nutritional products, when associated with herbicides for ratoon management, can provide better control, as observed for Pgr. 7 in the 2021/22 harvest (Figure 4).

Therefore, it can be said, through the research results obtained in the 3 agricultural harvests, that: (a) in the 1st application, the use of 2,4-D at a dose of 1.340 g of acid equivalent, immediately after mowing, is decisive; (b) in the 2nd application, the herbicide carfentrazone-ethyl can be used, at a dose of 28 grams of the active ingredient, or 2,4-D at a dose of 1.005 g of acid equivalent, when 70% regrowth is observed; (c) the 3rd application should occur 20 days after the 2nd application, with diquat herbicide, at a dose of 400 g of the active ingredient, before planting the crop.

In the destruction of ratoon crops, Protox-inhibiting herbicides can be associated with 2,4-D, with the aim of favoring the control of weeds remaining in the crop.

By Roberio Neves, Jhonatan Wendling, Carlos Joaquim, Leandro S. Pereira e Enderson Gama (IGA)

Article published in issue 291 of Cultivar Grandes Culturas Magazine