Abstract
The objective of this study was to evaluate the selectivity of cassava cultivar ‘Santa Helena’ and the efficiency of weed control using herbicides applied alone or tank mixed with and without sequential applications. Two experiments were carried out, both in a randomized block design with four replications. The treatments for the 1st experiment were: Hand hoeing (weed-free control); No hand hoeing (non-weeded control); sulfentrazone (500 g ha-1); sulfentrazone/[clomazone + clethodim] (500/[1125 + 120] g ha-1); sulfentrazone/mesotrione (500/240 g ha-1); S-metolachlor (1920 g ha-1); S-metolachlor/[clomazone + clethodim] (1920/[1125 + 120] g ha-1); S-metolachlor/mesotrione](1920/240 g ha-1); [sulfentrazone + S-metolachlor]/[clomazone + clethodim] ([500 + 1920]/[1125 + 120] g ha-1); [sulfentrazone + S-metolachlor]/mesotrione ([500 + 1920]/240 g ha-1). The treatments of the 2nd experiment were: Hand hoeing (weed-free control); No hand hoeing (non-weeded control); glyphosate (360 g ha-1) + hand hoeing; glyphosate + sulfentrazone (360 + 500 g ha-1); glyphosate + flumioxazin (360 + 50 g ha-1); glyphosate + clomazone (360 + 1125 g ha-1); glyphosate + S-metolachlor (360 + 1920 g ha-1); glyphosate + sulfentrazone + clomazone (360 + 400 + 900 g ha-1); glyphosate + sulfentrazone + S-metolachlor (360 + 400 + 1440 g ha-1); glyphosate + flumioxazin + clomazone (360 + 40 + 900 g ha-1); glyphosate + flumioxazin + S-metolachlor (360 + 40 + 1440 g ha-1). In the first experiment, only the treatments S-metolachlor, S-metolachlor/[clomazone + clethodim] and S-metolachlor/mesotrione did not present efficient weed control, causing reduction in yields; the other treatments were crop selective and efficient. In the second experiment, all treatments showed excellent levels of weed control up to 65 DAA and were crop selective. It is concluded that applications of tank mixtures, sequential mixtures and the use of glyphosate mixed with pre-emergent herbicides constitute excellent alternatives of weed management strategies in ‘Santa Helena’ cassava.
Highlights
Cassava has been largely cultivated in many parts of the world such as Asia, Africa, South America, Central America and Oceania, mainly because of the high adaptability and rusticity of this plant (FAO, 2018)
During the phytotoxicity evaluation period (Table 3), at 19 Days After the 1st Application (DA1stA), the cassava plants did not exhibit any toxicity symptom caused by pre-emergent application of sulfentrazone and S-metolachlor, but at 33 DA1stA, the Treatments/sequential applications
At 46 DA1stA, all injury symptoms caused by the first herbicide application disappeared completely in all treatments
Summary
Cassava has been largely cultivated in many parts of the world such as Asia, Africa, South America, Central America and Oceania, mainly because of the high adaptability and rusticity of this plant (FAO, 2018). A great problem occurs due to the interference of weed plants, which can cause reductions of up to 100% (Biffe et al, 2010). Chemical control has been used as the main method of weed management (Silveira et al, 2012). In Brazil, there are few herbicides registered, which limits the options that producers have to develop management strategies using pre-emergent or post-emergent herbicides during the critical growth period of cassava (Costa et al, 2013a). Considering the registered herbicides, it can be seen that there are no alternatives for the control of non-grass dicot or monocot species at post-emergence; in
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