Assessing sugarcane (Saccharum spp.) stalk growth helps to adequately manage the phenological stages of the crop. The aim of this study was to describe the height-growth curve of four sugarcane varieties (RB92579, RB93509, RB931530 and SP79-1011), in irrigated plant-cane and ratoon cane plantations, using the Logistic and Gompertz nonlinear models, while considering all deviations from assumptions. The model parameters were estimated based on the least squares method using the Gauss-Newton algorithm. To select the most suitable model, nonlinear measures, adjusted coefficient of determination (R2 adj), residual standard deviation (RSD), and corrected Akaike information criterion (AICc) were used. Based on the best models, stalk height growth rates and crop phenological stages were determined using critical points. All tests were performed in the free software environment for statistical computing and graphics, R. In general, the Logistic and Gompertz models without AR(1) better described the plant-cane and ratoon cane stalk height, respectively. All varieties showed early growth, and the RB92579 variety presented higher rates in both cycles.

Over the years, cultivated areas of sorghum have expanded considerably in Brazil. Chemical weed control has become an obstacle due to the scarcity of herbicides registered for the crop. The aim of this study was to evaluate the efficiency of weed control and selectivity of herbicides applied in pre and post emergence in the crop. Two experiments were conducted. In one of them, the hybrid BRS 310 was used while DKB 550 was used in the other. The experiments were performed in the field in randomized block design, evaluating seven treatments with four replications. The used treatments were: 1. Hand weeding, 2. S-metolachlor (1,440 g a.i. ha-1), 3. S-metolachlor (1,440 g a.i. ha-1) + atrazine (2,000 g a.i. ha-1), 4. atrazine (2,000 g a.i. ha-1), 5. atrazine (3,000 g a.i. ha-1), 6. atrazine (2,000 g a.i. ha-1) + mineral oil (0.25%), and 7. atrazine (2,000 g a.i. ha-1) + mineral oil (0.5%). It was verified that post-emergence atrazine was efficient in the weed control and selective to the sorghum crop, not affecting productivity, except in mixture with mineral oil (0.5%). S-metolachlor cannot be recommended in pre-emergence for the tested cultivars because it is not selective, reducing plants and productivity.

The sugarcane borer Diatraea saccharalis Fabr. (Lepidoptera: Crambidae) is one of the most important pests of sugarcane in the Americas. The purpose of this study was to assess multiple resistance traits in eight sugarcane genotypes against D. saccharalis, including five commercial cultivars and three exotic germplasm with potential to serve as resistance sources against this pest. The oviposition preference was assessed by using both free-choice and non-choice tests. The performance of both early stage larvae feeding on the leaves and late stages larvae feeding within the stalks were also assessed. There were differences among genotypes for number of both eggs and egg cluster in the free-choice test while no differences in non-choice test were observed. There were also differences in survival of early stage larvae feeding on the leaves, foliar injury rating and stalk damage. The genotype IM76-228 was the least preferred for oviposition and it seems that leaf width had some influence on adults' preference rather than greening of the leaves. IM76-228 and RB867515 causes higher mortality of early stage larvae feeding in the stalks while IM76-228 and RB985523 had lower damage in both leaves and stalks. The genotype IM76-228 was the most resistant to D. saccharalis and could serve as genes sources for resistance in sugarcane breeding programs.Index terms: Saccharum spp.; Diatraea saccharalis; host-plant resistance. RESUMOA broca da cana-de-açúcar Diatraea saccharalis Fabr. (Lepidoptera: Crambidae) é uma das mais importantes pragas da cana-de-açúcar nas Américas. Este estudo foi realizado para investigar múltiplos traços de resistência em oito genótipos de cana-de-açúcar contra D. saccharalis, incluindo cinco cultivares comerciais e três germoplasmas exóticos com potencial para servir de fontes de resistência contra esta praga. A preferência de oviposição foi avaliada por meio de testes de escolha livre e de não-escolha. O desempenho de larvas de estágio inicial que se alimentam das folhas e de larvas de estádio tardio alimentando-se com os colmos também foi avaliado. Houve diferenças entre os genótipos para o número de ovos e posturas no teste de livre escolha, enquanto não foram observadas diferenças no teste de não-escolha. Houve também diferenças na sobrevivência de larvas de estádios iniciais que se alimentam das folhas, índice de lesões e dano no colmo. O genótipo IM76-228 foi o menos preferido para a oviposição e parece que a largura da folha teve alguma influência sobre a preferência dos adultos em vez da intensidade de verde das folhas. IM76-228 e RB867515 provocaram uma mortalidade mais elevada de larvas de estádio inicial alimentando-se dos colmos, enquanto que IM76-228 e RB985523 apresentaram menor dano nas folhas e nos colmos. O genótipo IM76-228 foi o mais resistente a D. saccharalis e pode servir como fonte de genes para resistência em programas de melhoramento de cana-de-açúcar.Termos para indexação: Saccharum spp.; Diatraea saccharalis; resistência de plantas hospedeiras.

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The current recommendations for nitrogen (N) doses may not contemplate the complex dynamics of N in the soil, what may imply in insufficiency to the crop demand. This study aimed to evaluate the use of two portable chlorophyll meters (Minolta SPAD 502 and ClorofiLOG model CFL 1030), after defining the nitrogen sufficiency index (NSI), to estimate the nitrogen fertilization factor in modern bean genotypes. A block design was used, with four replications. Each experiment consisted of four treatments, with doses of 0, 5, 10 and 20 kg ha-1 of N for each 1 % considered below the NSI defined as adequate for each cultivar. At the end of the cycle, the production components and yield were evaluated. It was not possible to obtain precise adjustments in the methodology for the TAA Gol cultivar. The fertilization factor of 12.5 kg ha-1 of N for each 1 % below the NSI of 90 % proved to be efficient for the Pérola cultivar, when the SPAD-502 chlorophyll meter was used. In genotypes with size and cycle characteristics similar to those of the BRSMG Uai cultivar and the VR 20 strain, using a fertilization factor between 14 and 16 kg ha-1 of N, the NSI of 95 % must be reduced, in order to increase the efficiency of the nitrogen fertilization.