Research Journal of Agricultural Science, 44 (2), 2012 131 STUDIES REGARDING THE INFLUENCE OF ACTIVE SUBSTANCES QUIZALOFOP-P-ETHYL AND – QUISALOFOP-P- TEFURIL IN SUPPRESSING SORGHUM HALEPENSE SPECIES IN WATERMELON CULTURE Ramona ŞTEF, Ioana GROZEA, A. CĂRĂBEŢ, Ana-Maria VﾎRTEIU, D. MANEA, Alexandra VESELIN, L. MOLNAR Banat’s University of Agricultural Sciences and Veterinary Medicine, Faculty of Agricultural Sciences, Timisoara, Aradului Street, no. 119, RO-300645, Romania E-mail: chirita_ramona@yahool.com Abstract: Research and field studies were conducted to determine the efficacy of substances quizalofop-p-ethyl and quisalofop-p-tefuril, applied post emergent in order to control the problem weed Sorghum halepense in watermelon culture. Watermelon variety used in the experiment was Crimson Sweet. The Field studies on reducing the population of the species Sorghum halepense L. were conducted in 2010 and 2011 on Didactical and Experimental Station at University of Agricultural Sciences and Veterinary Medicine of Banat Timişoara. The experimental plot was placed on cambic chernozem with 6 variants in three repetitions. Systemic postem herbicides used in experience were: Leopard 5 EC and Pantera 40 EC, applied in two doses. The herbicides were applied post emergent when Johnson grass plants had 10-15 cm height. After establishing the level of weed infestation through numerical quantitative method revealed that in the experimental variants were present Johnson grass plants, the number ranging from 48-152 plants/sqm. Unfavorable climatic conditions (2010) influenced the efficacy of herbicides applied postemergent. Obtained results regarding the efficacy of Substances quizalofop-p-ethyl and p-tefuril quisalofop against Johnson grass showed differences. After applying chemical treatments occurrence of phytotoxicity were not recorded. The administration of herbicide Leopard 5 EC using the recommended dose has led to the best effectiveness in reducing the number of individuals of Sorghum halepense in agroecosystems of watermelon. The results obtained in the four variants treated with herbicides showed very significant positive differences compared to untreated control, situation changed when these results were compared with the hoed control, which are very significant negative. Studies have shown that translocation of herbicides in plants of Johnson grass realized better when there is an excess of precipitation to the multiannual average. The results obtained in the variant treated with Leopard 5 EC 1.0 l / ha and 1.5 l / ha are very significantly positive compared the mean of experience. The most infested variant with Sorghum halepense was that treated with herbicide Panther 40 EC at 1.0 l / ha. Key words: control, efficacy, herbicides, watermelon, Johnson grass INTRODUCTION Watermelon is now cultivated on an area of 2,409,000 ha (STAN N. şi MUNTEANU N., 2001). Watermelons culture present special importance for the sandy soils and is one of the cultures that leverages high economic efficiency under specific environmental conditions In Romania from total area of 44 400 ha planted with watermelons, 51.5% were located on sandy soils in the counties Dolj, Galaţi, Brăila, Olt, Mehedinţi, Teleorman, Bihor and Satu Mare (http://hortitom.ro/tehnologii/pepeni-verzi-timpurii). Weeds cause substantial loses in agricultural production, so producers must manage the weed spectrum to optimize the quantity and quality of agricultural production (MOVAHEDPOUR F. şi col., 2010). The most damaging weeds in watermelon culture are Cynodon dactilon, Agropyron repens, Sorghum halepense.