Alexandre Gemelli

Selectivity of Herbicide Alternatives for Two Cassava Cultivars

It is important to evaluate the tolerance of cassava varieties under new weed chemical control alternatives. Thus, this study aimed to evaluate the selectivity of herbicides, applied at pre-emergence, for two important cassava varieties grown in the state of Parana, Brazil. The herbicides and respective doses (g a.i. ha-1) were: diuron (400 and 800), metribuzin (360 and 720), isoxaflutole (60), atrazine (720), S-metolachlor (1,920) and mixtures ametryn+clomazone (1,350+1,900), ametryn + trifluralin (1,500+1,350), isoxaflutole + metribuzin (60+320), isoxaflutole + diuron (60+400), combined with the use of a dual checkl adjacent to each treatment. The cultivars used were Fecula Branca and Fibra. Only herbicide S-metolachlor applied on both cultivars and metribuzin (360 g a.e. ha-1) applied on Fibra did not cause any injury. Atrazine reduced plant density only for Fecula Branca at 60 DAS (days after seeding) but no difference in plant height was detected. Atrazine reduced plant density for cultivar Fecula Branca at 60 DAS, but no plant height reduction was detected. Both atrazine (for both cultivars) and diuron at a dose of 800 g a.i. ha-1 (for Fecula Branca) affected root productivity. Thus, atrazine was considered non-selective for both cultivars and the highest diuron dose was also considered non-selective for the cultivar Fecula branca. Differences in tolerance were verified among the cultivars used in this experiment, with Fibra in general being more tolerant to the herbicides evaluated.

Grass straw mulching to suppress emergence and early growth of weeds

Sorghum, pearl millet, and Brachiaria ruziziensis have similar characteristics which have led to their use for mulch formation in no-till systems. This study was carried out to evaluate the potential of these three species as straw suppliers to suppress weed emergence. Initial findings led to the conclusion that both pearl millet and Brachiaria ruziziensis have similar or superior potential as weed suppressors, compared to sorghum straw, a species with recognized allelopathic potential. Subsequently, new trials were conducted under greenhouse conditions by sowing weed species in pots, followed by covering of the soil with the straw under evaluation. Independent experiments were conducted for Euphorbia heterophylla and Bidens pilosa. In each experiment, the factors analyzed were type of straw (pearl millet and B. ruziziensis), amount of straw (equivalent to 4 and 8 t ha-1 dry mass) and irrigation method (surface and subsurface). Both pearl millet and B. ruziziensis have shown to be species that can be cultivated to produce straw with allelopathic potential. These effects were effective in suppressing the emergence or early growth of E. heterophylla and B. pilosa. There was no difference in the suppression of emergence of these species when the soil cover level was alternated between 4 and 8 t ha-1 dry mass.

Plantas daninhas como hospedeiras alternativas para Pratylenchus brachyurus

Uma das acoes indiretas exercidas pelas plantas daninhas na interferencia sob especies cultivadas e o potencial de hospedar agentes causadores de enfermidades. O nematoide das lesoes radiculares (Pratylenchus brachyurus) vem causando uma serie de danos em diversas culturas no Brasil. Para o manejo deste fitoparasita, o cultivo de diferentes especies de crotalarias tem sido empregado. O objetivo deste trabalho foi avaliar a hospedabilidade de plantas daninhas para P. brachyurus, bem como o efeito de supressao de diferentes especies de crotalaria. Para isso, foi instalado um experimento em casa de vegetacao no delineamento inteiramente casualizado em arranjo fatorial (2x17), com seis repeticoes. O primeiro fator consistiu na presenca ou ausencia da inoculacao do nematoide. O segundo correspondeu a dezessete especies vegetais, sendo onze plantas daninhas, quatro crotalarias (C. breviflora, C. juncea, C. ochroleuca e C spectabilis) e duas variedades de soja, as quais serviram como testemunha sendo hospedeiras de P. brachyurus. A inoculacao do nematoide das lesoes radiculares nao influenciou a altura de plantas e massa seca de parte aerea das diferentes especies avaliadas. Portulaca oleracea, Amaranthus viridis e Sida rhombifolia foram as especies com maior numero de nematoides por sistema radicular, e apenas a S. rhombifolia apresentou comportamento semelhante a testemunha (variedade de soja BMX Potencia RR®). Com relacao ao numero de nematoides por grama de raiz, os maiores valores foram observados para A. viridis, seguido por P. oleracea. Excluindo-se a C. juncea, todas as demais especies de crotalaria apresentaram-se como boas opcoes para o manejo em areas infestadas com P. brachyurus.

Persistence of Biological Activity and Leaching Potential of Herbicides Aminocyclopyrachlor and Indaziflam in Soils with Different Textures1

Herbicides aminocyclopyrachlor and indaziflam are under development in Brazil. Information about the behaviors in Brazilian soils and climate is scarce. Thus, the present work has aimed to evaluate the persistence of biological activity and leaching potential of aminocyclopyrachlor and indaziflam in contrasting textured soils by means of bioassays. For the evaluation of persistence, four experiments were performed, in which soils with different textures were studied in different time periods between herbicide application and bioindicator sowing (beet and soybeans). To determine leaching potential, three blades of rainfall (0, 30 and 60 mm) were simulated, each constituting a single experiment in soils with different textures and five bands of depth in the columns. The bioindicator used for the leaching tests was beet. The persistence of biological activity of aminocyclopyrachlor and indaziflam was greater than 150 days. In clayey soil there was less persistent aminocyclopyrachlor than in the loam texture. For indaziflam there was no difference in persistence between the two soils. Regarding the leaching potential, it was observed that the precipitations have the capacity to interfere with the leaching of herbicides aminocyclopyrachlor and indaziflam. Aminocyclopyrachlor has greater potential for leaching than indaziflam. The first one has its mobility increased when applied to soil of loam texture in relation to very clayey soil. As for indaziflam, marked differences between soils with different textures have not been noticed.

Dose-response curve to soil applied herbicides and susceptibility evaluation of different amaranthus species using model identity

Greenhouse studies were conducted in 2008-2009 with the objective of adjusting dose-response curves of the main soil-applied herbicides currently used in cotton for the control of Amaranthus viridis, A. hybridus, A. spinosus, A. lividus, as well as comparing susceptibility among different species, using the identity test models. Thirty six individual experiments were simultaneously carried out in greenhouse, in a sandy clay loam soil (21% clay, 2.36% OM) combining increasing doses of the herbicides alachlor, clomazone, diuron, oxyfluorfen, pendimethalin, prometryn, S-metolachlor, and trifluralin applied to each species. Dose-response curves were adjusted for visual weed control at 28 days after herbicide application and doses required for 80% (C80) and 95% (C95) control were calculated. All herbicides, except clomazone and trifluralin, provided efficient control of most Amaranthus species, but substantial differences in susceptibility to herbicides were found. In general, A. lividus was the least sensitive species, whereas A. spinosus demonstrated the highest sensitivity to herbicides. Alachlor, diuron, oxyfluorfen, pendimethalin, S-metolachlor, and prometryn are efficient alternatives to control Amaranthus spp. in a range of doses that are currently lower than those recommended to cotton.

Selectivity of chemical weed control systems in conventional cotton

Cotton is highly susceptible to the interference imposed by weed community, being therefore essential to adopt control measures ensuring the crop yield. Herbicides are the primary method of weed control in large-scale areas of production, and usually more than one herbicide application is necessary due to the extensive crop cycle. This study aimed to evaluate the selectivity of different chemical weed control systems for conventional cotton. The experiment took place in the field in a randomized block design, with twenty nine treatments and four replications in a split plot layout (adjacent double check). Results showed that triple mixtures in pre-emergence increased the chance of observing reductions in the cotton yield. To avoid reductions in crop yield, users should proceed to a maximum mixture of two herbicides in pre-emergence, followed by S-metolachlor over the top, followed by one post-emergence mixture application of pyrithiobac-sodium + trifloxysulfuron-sodium.

Seletividade do Clomazone no Manejo Químico de Plantas Daninhas da Cultura do Algodão LL(r)

O amonio-glufosinate e um herbicida de amplo espectro de controle de plantas daninhas, porem nao apresenta controle residual no solo, o que limita sua utilidade quando usado isoladamente na cultura do algodao, havendo a necessidade de combinar diferentes herbicidas em mais de uma modalidade de aplicacao. O objetivo deste trabalho foi avaliar a seletividade de diferentes sistemas de controle quimico de plantas daninhas contendo clomazone na cultura do algodao LL(r). As misturas triplas em pre-emergencia apresentaram maior potencial de reducao no porte do algodoeiro. Recomenda-se utilizar misturas de dois herbicidas em pre-emergencia na cultura do algodao, com aplicacao de S-metolachlor em over the top, seguido de duas aplicacoes em pos-emergencia de amonio-glufosinate. Podendo-se inclusive utilizar pyrithiobac-sodium na primeira aplicacao em pos-emergencia.