ABSTRACT Images from unmanned aerial vehicles (UAV) can serve as a baseline for studies in weed science, complementing observations obtained in the ground. The objective of this work was to determine soybean (Glycine max (L.) Merr.) plant injury caused by pre-emergence herbicides in sandy and clayey soils, using a low-cost UAV. The experiment was conducted in a randomized complete block design, with four replicates and seven treatments consisted of herbicides (diclosulam, chlorimuron, sulfentrazone, flumioxazin, and S-metolachlor), hand weeded and untreated treatments. Ground-based evaluations were carried out to assess soybean crop injury, plant stand, leaf chlorophyll content, plant height, canopy distance and grain yield. Images were taken using a UAV equipped with an RGB (red green and blue) camera. Soybean plants sprayed with diclosulam had lower plant reflectance in the R (98.9), G (147.1) and B (74.3) range than the other treatments in sandy soil. In clayey soil, hand weeded treatment had higher plants (30.8 cm) and untreated favored smaller plants (24.9 cm) compared to herbicide treatments. In sandy soil, soybean yield of all treatments was similar, however in clayey soil, soybean yield treated with chlorimuron and flumioxazin was higher than 5000 kg ha-1 and better than the others treatments. The nutrient-poor soil (sandy) may have aggravated the plant injury caused by herbicides and explain the lower yield observed compared to clayey soil. It was determined soybean plant injury caused by pre-emergence herbicides with the use of unmanned aerial vehicles, providing complementary results to ground-based measurements, indicating the potential of this technology for low-cost evaluations in weed science.

ABSTRACT The objective of this research was to evaluate weed control in a successional soybean-sorghum system by using preemergent herbicides. Two trials were conducted in soybean and two in sorghum, in different soil types (sandy in Rio Verde city and clayey in Montividiu city). All trials were established in a completely randomized block design with five preemergent herbicides in soybean (rates in): diclosulam 35.3 g a.i.·ha–1, chlorimuron 20 g a.i.·ha–1, sulfentrazone 200 g a.i.·ha–1, flumioxazin 50 g a.i.·ha–1, S-metolachlor 1728 g a.i.·ha–1, and two controls (hand weeded and untreated). Treatments in sorghum trials were the same to the soybean plus atrazine 1250 g a.i.·ha–1 and atrazine 1250 g a.i.·ha–1 + S-metolachlor 1728 g a.i.·ha–1. All treatments had four replicates. Weed control was assessed at 7, 14, 21 and 28 days after planting (DAP) in both crops. In addition, yield was measured when grains reached physiological maturity. All preemergent herbicide treatments successfully controlled weeds, specially Commelina benghalensis, Cenchrus echinatus and Eleusine indica, in both soybean trials until 28 DAP. In some weeds of sorghum, sulfentrazone, diclosulam and chlorimuron sprayed at soybean preemergence performed better than atrazine sprayed at sorghum preemergence. All preemergent herbicides sprayed at soybean preemergence did not affect soybean and sorghum yield, showing similarity with the hand weeded treatment. The results of this research provide evidence that the mix of crop succession and preemergent herbicide applications can be a strong strategy for integrated weed management.

Resumo: O objetivo deste trabalho foi avaliar a sensibilidade de diferentes populações de Digitaria insularis aos herbicidas glifosato, cletodim e haloxifope-P-metílico, em áreas agrícolas, e elaborar mapas de infestação com base na resposta das populações aos herbicidas. Cento e sessenta e uma populações com suspeita de serem resistentes foram avaliadas e comparadas a uma população suscetível. Quando as plantas estavam com três a quatro perfilhos, as populações foram pulverizadas com glifosato (1.000 g ha-1 e.a.), cletodim (108 g ha-1 i.a. + 0,5% de óleo mineral) e com haloxifope-P-metílico (62,35 g ha-1 i.a. + 0,5% de óleo mineral); plantas sem aplicação de herbicidas foram usadas como controle. As populações foram classificadas como sensíveis, resistentes ou intermediárias (com plantas sensíveis e resistentes) aos herbicidas-teste. Todas as populações foram sensíveis ao cletodim; 97,5% foram sensíveis e 2,5% intermediárias a haloxifope-P-metílico; e 9,9% foram sensíveis, 21,1% intermediárias e 68,9% resistentes ao glifosato. Populações resistentes ao herbicida glifosato estão dispersas homogeneamente nas regiões avaliadas. Não há casos de resistência múltipla de D. insularis nas regiões amostradas; no entanto, detectou-se resistência cruzada a glifosato e a haloxifope-P-metílico.

Abstract: The objective of this work was to evaluate the sensitivity of different populations of Digitaria insularis to the glyphosate, clethodim, and haloxyfop-P-methyl herbicides, in agricultural areas, and to develop infestation maps based on the responses of these populations. One hundred sixty-one populations suspected of being resistant were evaluated and compared to a susceptible population. When plants displayed three to four tillers, the populations were sprayed with glyphosate (1,000 g ha-1 a.e.), clethodim (108 g ha-1 a.i. + 0.5% mineral oil), and haloxyfop-P-methyl (62.35 g ha-1 a.i. + 0.5% mineral oil); plants without herbicide application were used as the control. The plant populations were classified as susceptible, intermediately resistant (with susceptible and resistant plants), or resistant to the tested herbicides. All populations were susceptible to clethodim; 97.5% were susceptible and 2.5% were intermediately resistant to haloxyfop-P-methyl; and 9.9% were susceptible, 21.1% intermediately resistant, and 68.9% resistant to glyphosate. Glyphosate-resistant populations are homogeneously distributed throughout the evaluated regions. There are no cases of D. insularis multiple resistance in the sampled regions; however, cross-resistance to glyphosate and haloxyfop-P-methyl was detected.