Overwintering and epidemiology of Puccinia dracunculina, the causal agent of rust in open tarragon fields

Rust, caused by Puccinia dracunculina, is the main foliar disease of open-field tarragon ( Artemisia dracunculus )cropsinIsrael. As not much is known about the biology or epidemiolo gy of this pathogen, the long-term objective of the currentstudy was to accumulate the knowledge needed to develop an e ffective, environmentally friendly means of adequately man-aging the disease. Puccinia dracunculina is an autoecious brachy-form pathogen, but it is not known whether the life cycle iscompleted under field conditions in Israel. Field observations an d greenhouse studies revealed that although the telial stage isproduced, the pathogen overwinters in the uredinial stage. In vitro experiments were used to quantify the temperature andwetness requirements for urediniospore germination an d to calculate the daily duration of conducive weather ( DDCW);DDCW was defined as the number of hours during which temperature ranged between 15 and 25 C and RH was >90%.Cumulative DDCW values (CDDCW) were a good predictor of disease under na tural conditions in two growing seasons.Disease onset occurred when CDDCW values reached a level of 10 and the relationship between log CDDCW values andseason-long severity values (in logit) was highly significant, explaining 90 AE6% of the variation.Keywords: Artemisia dracunculus, epidemiology, herb, weather