Black foot disease is a scourge of newly planted vineyards worldwide.
The disease is caused by several species of Cylindrocarpon, a fungus present in some soils. It is a major cause of death in young grapevines and currently there is no known control.
Because this disease kills young vines it has the potential to cause significant economic loss to the New Zealand wine industry as diseased vines and inoculum must be removed or a new site sought.
Carolyn Bleach, a postgraduate candidate from the Department of Ecology at Lincoln University, undertook research to investigate a range of chemical, physical and biological treatments for reducing levels of Cylindrocarpon infection in young nursery-grown grapevines in two wine growing areas of New Zealand. Her aim was to find a potentially effective treatment to control this disease.
Carolyn showed that biofumigation (where pests and diseases are suppressed by natural compounds present in plants) using mustard plants incorporated into the soil, before planting young rootstocks, was a promising treatment as infection in treated plants was reduced by more than a third compared to untreated plants.
Black foot symptoms include slowed growth and yellowing leaves; however, the disease is named from the dark brown and black dead cells in the roots of diseased vines – the ‘feet’ of the vine.
“It was exciting to find that the mustard treatment was an effective, economical and natural way to reduce black foot infection. This treatment also has the added benefit of improving the structure and organic matter in nursery soils where the rootstock grapevines are initially grown,” said Carolyn.
“These findings show that biofumigation using mustard may be highly effective for reducing soil-borne Cylindrocarpon inoculum and so the incidence of black foot disease,” she said.
The basis of the treatment is that when the cells of brassica species such as mustard are damaged, they release volatile compounds called isothiocyanates which have been shown to suppress pests and pathogens in a range of plants, but not in grapevines until now.
For her first biofumigation experiment Carolyn grew crops of mustard, rape and oats for five weeks in two vineyard sites previously infected with Cylindrocarpon spp. After flowering the plants were incorporated into the soil by rotary hoeing and then covered with polythene to stop the release of allelochemicals. Two weeks later callused cuttings of two different grapevine rootstocks were planted into the soil, grown for nine months and then assessed for infection (presence of fungal growth) by growing tissue samples on agar plates. The results showed that the mustard plants were the most effective of the three treatments.
In her second experiment, Carolyn tested mustard meal and repeat crops of mustard incorporated into the soil and found again that pathogen levels were reduced in vines planted into the biofumigated soil.