Avaliação da eficiência de herbicidas no controle de plantas daninhas em alfafa

Abstract

RESUMOObjetivou-se neste trabalho avaliar a seletividade e a eficiência de herbicidas no controle de plantas daninhas na cultura da alfafa. Foram desenvolvidos dois experimentos em Anápolis, GO. No primeiro, avaliaram-se oito herbicidas (imazethapyr, MSMA, fomesafen, bentazon, chlorimuron-ethyl, imazamox) aplicados em pós-emergência da alfafa, e no segundo, seis misturas de herbicidas [(diuron + MSMA), (diuron + MSMA), (diuron + paraquat), (diuron + paraquat)] aplicados um dia após o corte da alfafa. Em ambos os experimentos, foram incluídas duas testemunhas (capinada e sem capina), sendo os tratamentos distribuídos em blocos ao acaso com quatro repetições. Os herbicidas como imazethapyr, MSMA, fomesafen, bentazon, chlorimuron-ethyl e imazamox foram seletivos à cultura da alfafa e eficientes no controle de plantas daninhas. As misturas dos herbicidas (diuron + MSMA) e (diuron + paraquat) aplicados logo após o corte da alfafa causaram danos às folhas e aos caules remanescentes. As brotações, todavia, surgiram isentas de toxicidade, apresentando crescimento e desenvolvimento normais. Essas misturas promoveram eficiente controle de plantas daninhas, e não afetaram o acúmulo de biomassa seca e altura de plantas em relação à testemunha capinada. O não-controle das plantas daninhas reduziu a produção de biomassa seca e a altura das plantas de alfafa em 74,5% e 42,8%, respectivamente. Termos para indexação:Medicago sativa, seletividade, mistura de herbicidas. ABSTRACTThe objectives of this study were to evaluate the efficiency and selectivity of herbicides on the weed plants control at the alfalfa crop. Two experiments were carried out at the Experimental Station of Agenciarural, located in Anápolis, GO. In the first experiment it was evaluated eight herbicides (imazethapyr, MSMA, fomesafen, bentazon, chlorimuron-ethyl and imazamox) post emergency and in the second experiment six different mixed of herbicides [(diuron + MSMA), (diuron + MSMA), (diuron + paraquat), (diuron + paraquat)] applied one day after the alfalfa harvesting date. For both experiments were included two checks (weedy check and no weedy check) and it was used a randomized block design, with four replications. The herbicides imazethapyr, MSMA, fomesafen, bentazon, chlorimuron-ethyl and imazamox were selective to the alfalfa crop and efficient for the weed plants control. The mixed of herbicides (diuron + MSMA) and (diuron + paraquat) applied after the harvesting date were responsible for damage on leaves and stem remaining. Although the new alfalfa budding did not show any signal of toxic and the development and growth was normal. These mix of herbicides showed an efficient weed plants control and did not affect the harvest dry matter and plant height comparing to the weedy check. The no weedy check reduced the plant dry matter and height in 74,5% and 42,8%, respectively.

Herbicide selectivity in alfalfa crops

“…This behavior explains the fact that no significant difference occurred across treatments of this herbicide for plant height, shoot dry mass and root dry mass ( Figure 3D). A similar result was found by Silva et al (2004). However, the phytotoxicity symptom found by Mello et al (2000) was considered as average, with decreased dry mass and lower plant development.…”

“…There was no statistical difference in plant height across treatments, but a reduction was observed in shoot dry mass at the highest dose of the herbicide applied ( Figure 4D). For Silva et al (2004), the plants treated with fomesafen at 21 DAA still showed symptoms of toxicity; however, these injuries were restricted only to younger leaves, and not in the apical meristem, as verified by Silva et al (2001). However, Mello (2000) observed a decrease in dry matter accumulation when fomesafen had been applied to alfalfa, as well as lower height compared to the control.…”

“…Mello et al (2000) also reported phytotoxicity and reduction in plant size and in dry matter yield. However, in an experiment conducted by Silva et al (2004), plants treated with bentazon showed initial symptoms of phytotoxicity with full recovery after 14 DAA and 90 DAA. There were no differences between plants treated with this herbicide and the control for the parameters shoot dry biomass accumulation and height.…”

“…It was observed that at the commercial dose, the plants recovered after at 14 DAA, when phytotoxicity reached 60%. Silva et al (2004) showed that alfalfa treated with chlorimuron-ethyl showed initial symptoms of phytotoxicity with full recovery after 14 DAA. Mello et al (2000) obtained the same result, with less negative effects on alfalfa between the first and second cuts.…”

Flamethrower Application Time in Weed Control1

“…Ascard (1995), comparing the response of different weeds subjected to several dosages of propane for thermal treatment, observed that it was necessary to use dosages of 10-40 kg ha -1 to reach 95% of control on the number of plants from species that were sensitive during the stage with 0-4 real leafs; while plants with 4-12 leafs required 40-150 kg ha -1 . Silva (2008b), when testing direct radiation flamethrowers to control two large-leaf species, black-jack (Bidens pilosa) and morning glory (Ipomea triloba), and two thin-leaf species, signal grass (Brachiaria decumbens) and guinea grass (Panicum maximum), observed a high efficiency of the treatments both for large-leaf plants, getting to 100% in the case of black-jack, and for the other plants, which showed injuries that assure the control efficiency. Rahkonen & Vanhala (1993), studying the application of different doses of thermal treatment to a community of plants constituted by Chenopodium album, Matricaria inodora and Phleum pratense, verified that M. inodora showed lower injury levels when compared to two other species, which culminated on greater vigor to sprouting again and fast occupation of the room left by more sensitive species.…”