The role of seed-borne inoculum in the epidemiology of net blotch of barley in New Zealand

Abstract

The replacement of mercury-based seed treatments by captan in the early 1970s resulted in the build-up of net blotch — caused by Drechslera teres (Sacc.) Shoem., the conidial state of Pyrenophora teres Drechs. — to an epiphytotic in the 1975–76 and 1976–77 seasons. The replacement of captan seed treatments by carboxin + thiram or carbendazim + mancozeb produced a dramatic reduction in seed-borne inoculum, number of infected crops, and amount of infected tissue in Manawatu and Wairarapa crops in the 1977–78 season, and in other districts in the 1978–79 season, to the extent that net blotch is no longer regarded as a serious threat to grain production. The importance of seed-borne infection as a source of primary inoculum in New Zealand barley crops was therefore demonstrated, in that where efficient seed treatment is applied, the disease is of little consequence.

Keywords:

• Drechslera teres
• Hordeum vulgare
• seed-borne inoculum
• net blotch
• seed treatment
• carboxin + thiram
• carbendazim + mancozeb
• primary inoculum source