Purple blotch disease of garlic: Development of the disease in Chiangmai‐Lamphun valley, Northern Thailand, considered in relation to fungicide use and other farming practices

Abstract

Abstract The development of purple blotch of garlic in farmers’ fields was studied in conjunction with surveys of fungicide use and other practices in the Chiangmai‐Lamphun valley, Northern Thailand. Purple blotch was consistently more severe, and effective fungicide applications most needed, when garlic had been planted early by omitting the normally preceding rice crop. Fungicide use was found to be widespread with a great variety of products encountered, several of which were unsuitable or had not been tested against purple blotch. This reflects erratic marketing of fungicides and lack of consistent extension activities. Fungicide use was not always related to the need to control purple blotch. Furthermore, few farmers used fungicides effectively where needed, because they were hardly aware of the factors affecting efficacy of applications, such as timing of applications, rates and weather conditions.