Henrique da Silva Silveira Duarte

Manejo da requeima do tomateiro industrial empregando sistema de previsão

Three experiments were carried out using an industrial tomato hybrid H 7155N crop, in 2003 and 2004 seasons to fit a modified prediction system, which allows the criterious use of fungicides for the control of late blight caused by Phytophthora infestans. Trials were conducted in a randomized complete block design with ten treatments and three replications. The formulated systemic fungicides were applied when the disease severity values (DSV) reached eight, ten or twelve points. On weeks where DSVs values were lower than eight, ten or twelve, metiram was applied. The traditional late blight control consisted of weekly application of fungicides after the first symptoms disease, and those defined by the prediction system were carried out based on the DSVs accumulated throughout the experiment. Late blight severity was assessed weekly by using a descriptive key and diagrammatic scale. The efficiency of the control treatments was compared by the area under the disease progress curve, disease progress rate (r) and tomato yield. The r values of the best treatment (dimethomorph + chlorothalonil, DSV = 10, alternated with metiram), weekly application calendar fungicides and the check treatment varied from 0.03 to 0.07, 0.05 to 0.09 and 0.24 to 0.39, respectively. Dimethomorph + chlorothalonil DSV = 10 alternated with metiram was the most efficient and yielded more than 15,7 ton of tomato in average, above the weekly spraying calendar fungicides. Dimethomorph or metalaxyl-M mixtured with chlorothalonil (DSV = 10) based on the prediction scheme without alternation with metiram differed from the weekly spraying calendar fungicide based on disease severity and tomato yield. The treatments pyraclostrobim + metiram (DSV = 8; DSV = 10) alternated with metiram; dimethomorph + mancozeb (DSV = 8; DSV = 10) alternated with metiram gave intermediate control of late blight and tomato yield. The prediction scheme that used dimethomorph + chlorothalonil alternated with metiram (DSV = 10) allowed the reduction in one spray in two trials of the mixture dimethomorph + chlorothalonil compared to the weekly spraying calendar fungicide without any yield loss.

Efeito do silicato de potássio isoladamente ou em mistura com fungicida no controle da requeima da batateira

Este trabalho teve como objetivo avaliar o efeito da aplicacao foliar de silicato de potassio, isoladamente ou em mistura com diferentes doses do fungicida, no controle da requeima, causada por Phytophthora infestans, da batateira. O experimento foi conduzido em condicoes de campo utilizando-se o delineamento em blocos casualizados com 8 tratamentos e 4 repeticoes. A cultivar de batata usada foi a Asterix. Foi utilizado o fungicida Cimoxanil + Mancozeb (60 + 700 g/Kg i.a.) e silicato de potassio na dose de 60 g/L (pH = 5,5). Os tratamentos (T) utilizados foram: T1 - Testemunha; T2 - Cimoxanil + Mancozeb (2,0 Kg/ha); T3 - Cimoxanil + Mancozeb (2,5 Kg/ha); T4 - Cimoxanil + Mancozeb (2,0 Kg/ha) + silicato de potassio; T5 - Cimoxanil + Mancozeb (2,5 Kg/ha) + silicato de potassio; T6 - Cimoxanil + Mancozeb (3,0 Kg/ha) + silicato de potassio; T7 - silicato de potassio e T8 - Cimoxanil + Mancozeb (3,0 Kg/ha). As pulverizacoes foram realizadas semanalmente. A severidade da requeima foi avaliada utilizando-se uma escala descritiva com notas de 0 a 100%. Os resultados da severidade foram utilizados para calcular a area abaixo da curva do progresso da requeima (AACPR). A AACPR foi de 72,5; 23,8; 18,3; 29,5; 19,7; 17,9; 68,3 e 16,3, respectivamente, nos tratamentos T1, T2, T3, T4, T5, T6, T7 e T8. Os tratamentos 3, 5, 6 e 8 foram os mais eficientes (menores AACPRs e maiores rendimentos) no controle da requeima. O silicato de potassio nao foi eficiente e nao apresentou nenhum efeito aditivo quando misturado ao fungicida no controle da requeima.

Field resistance of potato cultivars to foliar early blight and its relationship with foliage maturity and tuber skin types

Three field experiments were carried out to assess the level of resistance of several cultivars to early blight (EB) and to examine the association between host resistance and either foliage maturity or tuber skin types. A total of 26 cultivars were used in Exps. 1 and 2, and 24 in Exp. 3. Plants were inoculated with isolates of Alternaria grandis at 31 days after planting. EB severity was quantified in each plot every seven days. The approach to determine the resistance levels of potato cultivars was based on multivariate analysis techniques. The tested cultivars responded as either resistant, moderately resistant, moderately susceptible or susceptible to EB. Most of the cultivars were classified as susceptible or moderately susceptible to EB. Resistant cultivars were mid-season, mid-late or late maturity. None of the susceptible cultivars were later maturity (mid-late or late maturity). In most cases, susceptible cultivars were earlier maturity (early or mid-early maturity). Most resistant cultivars had rough, mid-rough or smooth skin. None of the susceptible cultivars had rough skin. In most cases, susceptible or moderately susceptible cultivars had smooth skin. Obtaining potato cultivars that are resistant to this destructive disease will help reduce production costs and the need for costly fungicides.

Controle da requeima em tomateiro industrial com fungicidas e silicato de potássio

The aim of this study was to test the effect of fungicides and potassium silicate sprays on the control of late blight (Phytophthora infestans) of industrial tomato. The fungicides were applied according to the Wallin forecast system (FS) and on the weekly calendar. The experiment was carried out in a completely randomized block design with six treatments and four replications. The treatments (T) were: T1 - control; T2 - dimethomorph + chlorothalonil (disease severity values - DSV = 10) + metiram; T3 - metalaxyl-M + chlorothalonil (DSV = 10) + metiram (metiram was sprayed weekly when the DSV did not reach the required value for the treatment); T4 - calendar: dimethomorph + chlorothalonil, mancozeb, metalaxyl-M + chlorothalonil and chlorothalonil, alternated weekly; T5 and T6 - potassium silicate (5 and 15 g/L), respectively. The severity of late blight was evaluated according to a scale from 0 to 100 %. The final disease severity was 100; 2.6; 12.3; 5.5; 97.6 and 96 %, respectively, on the treatments T1, T2, T3, T4, T5 and T6. Disease severity was 93 %, less on the treatments that received the application of fungicides compared to the control. The FS (treatment 2) showed better results than treatment 3. The treatment 2, based on the FS, showed efficiency comparable to the weekly calendar (treatment 4) with yield of 62.103,73 and 52.473,33 kg/ha, respectively. These yields were superior compared to the other treatments. The applications of potassium silicate did not differ from the control. This indicates the inefficiency of this product in the control of late blight.

Improving accuracy, precision and reliability of severity estimates of Glomerella leaf spot on apple leaves using a new standard area diagram set

Glomerella leaf spot (GLS) causes severe necrotic leaf symptoms on Gala, the most cultivated apple cultivar in Brazil. To evaluate this disease, the standard area diagram set (SADs) developed on the state of Paraná for a leaf severity level up to 30.93% has been used. However, in samples collected in the states of Santa Catarina and Rio Grande do Sul, disease symptoms reach 75% of severity. Therefore, the objective of this study was to develop and to validate new SADs that include higher GLS severity levels. The proposed SADs have 10 color images of diseased leaves with severity values ranging from 0.2 to 75%. These SADs were validated by 12 raters and have significantly improved the disease assessment. Therefore, it is believed that SADs developed in the present study will allow an adequate evaluation in regions or orchards where the disease is more severe.

First report of Pseudocercospora muntingiae on Muntingia calabura in Brazil

Pseudocercospora muntingiae is recorded as the cause of leaf spots on Muntingia calabura (Tiliaceae), for the first time from Brazil and also in South America.