Abstract
The most effective disease management method for yield reducing diseases affecting tomatoes is the use of fungicides. This study evaluated the efficacy of chemical control on three Phytophthora sp. isolates, pathogenic to tomatoes. The effect of fungicides on mycelial growth of Phytophthora sp. and on tomato wilt was evaluated in vitro and in vivo . Two tests were done in Petri plates, and one on seedlings, in completely randomized design as a 4x3 factorial, with 5 replications. In vitro tests were done in growth chamber, at 25°C. The experimental unit consisted of a 5-mm diameter fungal mycelial plug placed 30 mm away from a filter paper disk, of similar size, soaked in fungicide, over cornmeal agar. The first test evaluated four commercial products registered for the control of potato blight: clorotalonil+metalaxyl (Folio Gold ® 742.5 WP); propamocarb chloridrate (Infinito ® 687.5 CS), metalaxyl-m+mancozeb (Ridomil Gold ® 68 WP), cymoxanil + manconzeb (Curzate ® MZ 72 WG), at the recommended doses. The other assays evaluated three doses of Infinito (0.125%, 0.150% or 0.175%) and Ridomil. In vivo test was done in the greenhouse, and the experimental unit consisted of one pot, containing one tomato seedling, cultivar Alambra F1. Fungicide was drenched on the seedling soil one day prior to inoculation with 50,000 zoospores per pot. Data of mycelia growth inhibition by fungicide were submitted to analysis of variance and the averages compared by the Tukey test at 5% significance; efficacy was determined as a function of Ridomil®, the standard fungicide. In the first test, regardless of isolate, Infinito® presented performance similar to Ridomil ® with efficacy of 98.5%, while Folio Gold ® presented efficacy of 57.3% and Curzate ® had no fungicide effect. Growth of isolate PP3 was smaller in all fungicides. In the second in vitro test, all three doses of Infinito ® had efficacy above 82%. The best control was observed on isolates PP3 and PP4. In the third test, in vivo , no significant differences were observed in root matter among the standard fungicide and the doses of Infinito ® ; however, efficacy of Infinito ® at 0.175% was 14% greater than that obtained with Ridomil ® . It can be concluded that Infinito ® is one more option for the control of tomato wilt.
Highlights
Tomato (Solanum lycopersicum) has wide climate adaptation, and the most important factors for yield are temperature, soil and air moisture, and photoperiod (ALVARENGA, 2004)
No more than five of these may occur simultaneously, damage and losses may render the crop non viable in certain seasons of the year, when control becomes ineffective, or production costs increase in such a manner that there is no economic return from it (LOPES; ÁVILA, 2005)
Large scale tomato production is heavily dependent on fungicide use; its use depends on approval by the Ministério da Agricultura Pecuária e Abastecimento (MAPA) (LOPES; ÁVILA, 2005)
Summary
Tomato (Solanum lycopersicum) has wide climate adaptation, and the most important factors for yield are temperature, soil and air moisture, and photoperiod (ALVARENGA, 2004). No more than five of these may occur simultaneously, damage and losses may render the crop non viable in certain seasons of the year, when control becomes ineffective, or production costs increase in such a manner that there is no economic return from it (LOPES; ÁVILA, 2005) Control of these diseases does not consist in exterminating the pathogen after it becomes visible, but, it is permanent integrated control measures, preferably avoiding the entrance of the pathogen in the area or its establishment in it. Late blight is the most important tomato disease in Brazil, especially in the South and Southeast, where it is more aggressive; epidemics have been reported in the Northeast, when cold and moist nights might occur occasionally (LOPES; ÁVILA, 2005). This disease is caused by Phytophthora infestans, and can completely destroy tomato and potato fields in a very short period of time when environment conditions are adequate (REIS et al, 2001; KUROZAWA; PAVAN, 2005; LOPES; ÁVILA, 2005)
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