Made available in DSpace on 2014-08-20T14:07:35Z (GMT). No. of bitstreams: 1 dissertacao_nixon_da_rosa_westendorff.pdf: 1164743 bytes, checksum: 0e98d540bb2c2b7a5450d35d0dfaf837 (MD5) Previous issue date: 2012-02-28 / Weeds are responsible for most part of the reduction in rice yield. The species Cyperus esculentus, a Cyperaceae plant, stands out by adaptation to the flooded environment. Little is known about the competitive ability of the specie rice and what is the extent of the economic loss caused. The economic thresholds (ET) has been an important tool to quantify weed damage to crops, in addition to supporting decision making of when the adoption of compensatory measure of control. The most obvious consequences of the use of ET in decision making are reduction of production costs, less use of herbicides and thereby benefitting the environment and man, and minimization of the selection pressure that select weeds resistant. The objectives of this research were to study the adaptive value, the competitive ability and the determination of ET for C. esculentus on flooded rice, using mathematical model for nonlinear regression derived from the rectangular hyperbolic, depending on the cycle of rice cultivars, irrigation timing and population of the weed. Studies were conducted for adaptation and competition in the field and greenhouse in the 2010/11 growing season. In general, the rice cultivars studied have superior adaptive value than C. esculentus. For rice, the intraspecific competition is more important, while for the weed interspecific competition is more pronounced. The hyperbolic model satisfactorily estimates the yield losses that C. esculentus causes in rice. The explanatory variable is the population of Cyperus esculentus that best fit the model. The reduction in the development cycle of rice cultivar and the anticipation of irrigation, increase the competitive potential of the culture and consequently increase the C. esculentus ET. / As plantas daninhas são responsáveis por grande parte da redução de produtividade das lavouras de arroz irrigado. A espécie Cyperus esculentus, pertencente à família Cyperaceae, destaca-se pela adaptação ao ambiente irrigado. Pouco se conhece sobre a habilidade competitiva da espécie com a cultura do arroz e qual é a dimensão do prejuízo econômico causado. O nível de dano econômico (NDE) tem sido importante ferramenta na quantificação de prejuízos às culturas, além de subsidiar a tomada de decisão de quando é compensatória a adoção de medida de controle. As vantagens mais evidentes do uso de NDE na tomada de decisão são diminuição dos custos de produção, menor uso de herbicidas e, com isso, menor contaminação do ambiente e do homem e minimização do processo de seleção que torna as plantas daninhas resistentes. Os objetivos dessa pesquisa foram o estudo do valor adaptativo, da habilidade competitiva e a determinação do NDE de C. esculentus na cultura do arroz irrigado, pelo uso do modelo matemático de regressão não linear derivado da hipérbole retangular, em função do ciclo das cultivares de arroz irrigado, época de irrigação e população da planta daninha. Para tal, foram conduzidos estudos de adaptação e competição a campo e em casa de vegetação no ano agrícola 2010/11. Em geral, as cultivares de arroz estudadas possuem valor adaptativo superior a C. esculentus. Para a cultura do arroz, a competição intraespecífica é mais importante, enquanto que para a planta daninha a competição interespecífica é a mais pronunciada. O modelo hiperbólico estima satisfatoriamente as perdas de produtividade que C. esculentus causa à cultura do arroz. A variável explicativa população de Cyperus esculentus é a que mais se ajustou ao modelo. A redução no ciclo de desenvolvimento da cultivar de arroz e a antecipação da irrigação incrementam o potencial competitivo da cultura e, consequentemente, aumentam os NDE de C. esculentus.

Methyl bromide (MBr) was widely used as a soil fumigant to manage soilborne pests in plasticulture vegetable production; however, it has been banned by the United Nations Environment Programme. Alternatives to MBr must be implemented to sustain fresh market tomato productivity. Possible MBr alternatives include new fumigant compounds, improved plastic mulch, and grafting. Methyl iodide (MeI) and dimethyl disulfide (DMDS) were tested as fumigant alternatives to MBr for the control of yellow nutsedge and soilborne pathogens of tomato. Virtually impermeable film (VIF) and totally impermeable film (TIF) were tested for fumigant retention and yellow nutsedge control in tomato. Grafting onto resistant rootstocks was tested for bacterial wilt and nematode management in tomato. In the absence of a soil fumigant, TIF suppressed yellow nutsedge better than VIF. TIF increased fumigant retention compared to VIF at similar application rates. Reduced fumigant application rates could be used in combination with TIF while maintaining fumigant concentrations, weed control, and crop yields comparable to greater use rates with VIF. Shank applied DMDS rates could be lowered to 281 L/ha under TIF from 468 L/ha under VIF; shank applied MeI application rates could be reduced to 56 L/ha under TIF compared to 93 L/ha under VIF and drip applied DMDS could be reduced from 561 L/ha under VIF film to 374 L/ha under TIF. Grafting susceptible commercial tomato cultivars onto resistant tomato hybrid rootstocks increased yields and plant survival in bacterial wilt infested fields. "Cheong Gang", "BHN 998", and "BHN 1054" were the best performing rootstocks for bacterial wilt resistance and tomato fruit yield in severely infested fields. Grafting increased tomato yield and decreased root galling from root-knot nematodes in an infested field. Hybrid rootstock "RST 106" resulted in the lowest root-knot nematode galling. In conclusion, TIF with reduced rates of DMDS or MeI is a viable MBr alternative for fresh market tomato production to retain effective doses of fumigant, manage yellow nutsedge and maintain yields. Grafting is an effective MBr alternative to manage bacterial wilt and root-knot nematode and maintain tomato yields. / Ph. D.