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Resumo -Objetivou-se com este trabalho avaliar a atividade residual do herbicida 2,4-D sobre a emergência de soja em solos de texturas distintas. Os experimentos, um com cada classe de solo (textura média e argilosa), foram conduzidos em casa de vegetação, em delineamento inteiramente casualizado, no esquema fatorial 6x2+1, sendo os tratamentos constituídos pela combinação de seis épocas de aplicação: 0, 3, 5, 7, 10 e 14 dias antes da semeadura (DAS) da soja e duas dosagens de 2,4-D (502,5 e 1.005 g e.a. ha -1 ), mais uma testemunha absoluta sem aplicação do herbicida. A atividade residual do 2,4-D foi avaliada por meio do índice de velocidade de emergência (IVE), porcentagem de emergência (%), fitointoxicação visual (%), altura (cm) e biomassa seca (g) das plantas de soja aos 26 dias após a semeadura. Em ambos os solos, a atividade residual do 2,4-D foi observada, com variação em função da dosagem e do período de tempo entre a aplicação e a semeadura da soja. O efeito foi mais pronunciado nas plantas cultivadas em solo de textura média, onde houve maior fitointoxicação e redução da biomassa seca em relação à testemunha, principalmente, no tratamento onde o herbicida foi aplicado e a soja, cultivar V-Max, semeada em seguida.Palavras-chave: Herbicida, persistência, fitointoxicação.Abstract -This research aimed to evaluate the 2.4-D residual activity over soybean emergence in soils with distinct textures. The experiments, each one with a distinct soil type (clay sand and clay), were conducted in greenhouse conditions, in a randomized entirely design, in factorial scheme 6x2+1 with treatments constituted by the combination of six application period: 0, 3, 5, 7, 10 and 14 days before soybean sown (DBS) and two 2.4-D (502.5 e 1,005 g e.a. ha -1 ) doses,

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Field experiments were conducted during summer 2007 to determine a baseline information on crop and weed tolerance to broadcast flaming utilizing different rates of propane. The species evaluated were: maize (Zea mays), sorghum (Sorghum halepense), soybean (Glycine max), sunflower (Helianthus annuus), barnyardgrass (Echinocloa crus-galli), green foxtail (Setaria viridis), velvetleaf (Abutilon theophrasti) and redroot pigweed (Amaranthus retroflexus). The propane rates applied were 0, 12.1, 30.9, 49.7, 68.5 and 87.22 kg/ha. The response of the plants to propane rates were described by log-logistic models. Plant response to flame varied depending on the species, growth stage and propane rate. Broadleaf weeds were more susceptible to flames than grasses. Field maize and sorghum were less susceptible, while soybean and sunflower were severely injured. Of all crops tested, broadcast flaming has the most potential for use in field maize

Asiatic dayflower has recently become a troublesome weed in eastern Iowa. This weed demonstrates an extended emergence period and there is anecdotal evidence of glyphosate tolerance. Thus, Asiatic dayflower is difficult to manage in glyphosate-resistant (GR) corn and soybean. Greenhouse experiments were conducted to evaluate the response of Asiatic dayflower to glyphosate applied at different rates and growth stages. Field research was conducted in 2005 and 2006 to evaluate different herbicides for Asiatic dayflower control in soybean. PRE herbicides were applied at planting and POST herbicides were applied 21 and 42 d after planting (DAP). In addition, shikimate accumulation in response to glyphosate was compared among Asiatic dayflower and GR and non-GR corn and soybean. Under greenhouse conditions, a single application of glyphosate (0.84 kg ae ha−1) did not control Asiatic dayflower. Only the highest rate evaluated, 13.44 kg ae ha−1 (16X), was lethal to Asiatic dayflower. Even when applied at an early growth stage (two leaves) and using high rates (3.36 kg ae ha−1), glyphosate controlled Asiatic dayflower just 28%. In the field, metribuzin and KIH-485 controlled Asiatic dayflower 80 and 73%, respectively. Early POST applications (21 DAP) of cloransulam or lactofen controlled Asiatic dayflower 80 and 67%, respectively. A single glyphosate application of 0.86 kg ae ha−1 controlled Asiatic dayflower approximately 50%. Glyphosate-treated Asiatic dayflower and non-GR corn and soybeans accumulated shikimate after application. GR corn and soybeans did not accumulate shikimate in response to glyphosate. Twenty-one days after treatment, all the non-GR soybean and corn plants died; however, Asiatic dayflower plants survived.

Propane flaming could be an effective alternative tool for weed control in organic cropping systems. However, response of major weeds to broadcast flaming must be determined to optimize its proper use. Therefore, field experiments were conducted at the Haskell Agricultural Laboratory, Concord, NE in 2007 and 2008 using six propane doses and four weed species, including green foxtail, yellow foxtail, redroot pigweed, and common waterhemp. Our objective was to describe dose–response curves for weed control with propane. Propane flaming response was evaluated at three different growth stages for each weed species. The propane doses were 0, 12, 31, 50, 68, and 87 kg ha−1. Flaming treatments were applied utilizing a custom-built flamer mounted on a four-wheeler (all-terrain vehicle) moving at a constant speed of 6.4 km h−1. The response of the weed species to propane flaming was evaluated in terms of visual ratings of weed control and dry matter recorded at 14 d after treatment. Weed species response to propane doses were described by log-logistic models relating propane dose to visual ratings or plant dry matter. Overall, response of the weed species to propane flaming varied among species, growth stages, and propane dose. In general, foxtail species were more tolerant than pigweed species. For example, about 85 and 86 kg ha−1were the calculated doses needed for 90% dry matter reduction in five-leaf green foxtail and four-leaf yellow foxtail compared with significantly lower doses of 68 and 46 kg ha−1of propane for five-leaf redroot pigweed and common waterhemp, respectively. About 90% dry matter reduction in pigweed species was achieved with propane dose ranging from 40 to 80 kg ha−1, depending on the growth stage when flaming was conducted. A similar dose of 40 to 60 kg ha−1provided 80% reduction in dry matter for both foxtail species when flaming was done at their vegetative growth stage. However, none of the doses we tested could provide 90% dry matter reduction in foxtail species at flowering stage. It is important to note that foxtail species started regrowing 2 to 3 wk after flaming. Broadcast flaming has potential for control or suppression of weeds in organic farming.

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