effect of different growth stages and dew period length on disease development of alternaria alternata as a biological control agent for convolvulus arvensis

abstract field bindweed is an important perinial weed of agricultural crops word-wide. there are plant pathogen fungus which could cause necrotic spots on the leaves and stems of convolvulus arvensis under natural coditions. in order to evaluate the effects of weed growth stage and length of dew period on disease development causes by aletrnaria alternata and fusarium sp. two expriments were performed in the greenhouse based on a completely randomized design in factorial arrangement with four replications during 2006-2007. spore concentration for both experiments was 107 spores per ml of distilled water. in the first experiment, treatments were different growth stages of field bindweed (cotyledon, 4-leaf, 6-leaf, 9-11-leaf stages). results showed that disease development in the fungus of a. alternata was higher than fusarium sp. the most susceptable growth stage of field bindweed plants to a. alternata was 2-4-leave stage. the second expriment was performed in order to study the effect of dew period length (6, 12, 24 and 48 hour dew periods) on disease development at 4-leaf growth stage of field bindweed. the maximum disease development and minimum weed dry weight were observed with application of the fungus of a. alternata at dew periods of 24 and 48 hour, however, plant damage was also observed with a length of 6 hours dew period.