Hot water treatment to reduce incidence of black foot pathogens in young grapevines grown in cool climates

Abstract

Black foot disease causes death of infected grapevines but management of this soil-borne disease by preventative measures such as pre-planting fungicide dips has not been totally effective. Hot water treatment (HWT; 50°C for 30 min) of young dormant grapevine plants has been shown to significantly reduce infection. However, it has been reported to cause unacceptable damage to young vines in cooler climate countries like New Zealand, so this study examined the effects of different HWT protocols on the New Zealand black foot isolates. In vitro testing of different HWT protocols was conducted on conidia, mycelium and detached, inoculated grapevine canes using three isolates each of the species I. liriodendri (“C”. liriodendri) and the complexes, I. radicicola (“C”. destructans) and I. macrodidyma (“C”. macrodidymum). Heat treatments greater than 40°C for 5 min killed all conidia (P<0.001), and treatments greater than 47°C for 30 min inhibited (P≤0.003) further growth of treated mycelium plugs for all but one isolate. Within cane pieces, infection by Ilyonectria (“Cylindrocarpon”) isolates was significantly reduced (P<0.001) by 30 min at 48.5 and 50°C. Additionally, these studies showed different responses to the different treatments for the three isolates of each species complex and differences between species. In field trials, HWT of 48.5 and 50°C for 30 min significantly reduced disease incidence in dormant plants to 0% (P≤0.001). This study confirmed that HWT of 48.5°C for 30 min could be used to eliminate black foot disease in dormant nursery grapevines grown in New Zealand prior to their use for establishing new vineyards.