Quantification of Airborne Inoculum as an Aid in the Management of Leaf Blight of Onion Caused by Botrytis squamosa

Abstract

Botrytis leaf blight, caused by Botrytis squamosa, is a common and frequently damaging disease of onion crops, but the severity of epidemics varies widely from year to year. The disease is initiated and spread by airborne conidia. The relationship between airborne conidium concentration (ACC) and lesion development was studied in the field. A linear relationship was found between ACC and number of lesions per leaf: ACC values of 10 to 15 and 25 to 35 conidia m-3 were associated with 1 and 2.5 lesions per leaf, respectively. In 2000 and 2001, at three sites, four different criteria were used to start a fungicide spray program and their effect on epidemic development was compared with that of a grower's conventional schedule. The criteria were: at the fourth-true-leaf growth stage; according to an inoculum production index; when the ACC reached 10 to 15 conidia m-3; and when the ACC reached 25 to 35 conidia m-3. A nonsprayed control plot was included in the trial. Fungicide programs started when the ACC reached 10 to 15 conidia m-3 were as effective as the conventional program, but used fewer sprays. A fungicide spray program based on measurements of ACC and disease severity was evaluated in 2002 and 2003 in five and three commercial onion fields, respectively. At each site, half of the field was sprayed according to the grower's schedule and, in the other half, fungicide sprays were initiated when a threshold of 10 to 15 conidia m-3 or five lesions on the lower leaf (whichever came first) was reached. Overall, the number of fungicide applications was reduced by 75 and 56% in 2002 and 2003, respectively, without causing significant yield reduction. In both years, the reduction in number of fungicide applications was due mainly to the delay in initiation of the fungicide program.

Development of detection systems for the sporangia of Peronospora destructor

“…Control of plant pathogens could be improved if inoculum could be detected quickly in the field directly by the grower. Airborne inoculum plays a vital role in the development of epidemics caused by Botrytis leaf blight on onion crops (Carisse et al 2003(Carisse et al , 2005. In this work, a linear relationship was found between number of lesions on plants and airborne Botrytis conidial concentrations.…”

“…The environmental requirements for infection and sporulation by P. destructor have been reported (Yarwood 1937(Yarwood , 1943Hildebrand and Sutton 1982). Mathematical models describing climatic effects on sporulation and infection have been described (Gilles et al 2004;Battilani et al New approaches in forecasting diseases of onion crops based on estimation of spore numbers in air samples have been reported (Carisse et al 2005;Berger 1970). Detection and quantification of airborne spore numbers can be used to predict disease accurately before it is visible in the crop.…”

Botrytis squamosa: The Pathogen of Market Disease of Garlic Sprouts

“…Allium crops, such as onion [15][16][17][18][19][20] , garlic and chives 21) . There are many reports about this pathogen infecting garlic sprouts in storage periods 1,2,5) , but fewer about the disease symptoms and damage in markets.…”

Detection of Fungal Pathogens in the Environment

“…Fungicide application was recommended when the ACC reached 10-15 conidia/m 3 . By following this procedure fungicide application was reduced by 75% and 56% in 2002 and 2003 respectively, resulting in saving of fungicide cost considerably (Carisse et al 2005).…”