Pruning wound protection of rootstock mother vines
ARC Infruitec-Nietvoorbij Plant Protection Division, Viticulture Division
Objectives and Rationale
The aim of the study was to select and evaluate various chemical and biological control agents in order to formulate a protocol for local grapevine nurseries, rootstock mother block owners and the Plant Improvement Scheme on effective pruning wound protection of rootstock mother vines in order to manage pruning wound infections and to minimise the risks of spreading trunk pathogens through infected propagation material.
(1) To select chemical and biological control agents suitable for pruning wound experiments;
(2) To determine the duration of pruning wound susceptibility (field trials);
(3) To evaluate selected chemical and biological control agents as wound protectants in rootstock mother vines (field trials)
In vitro fungicide efficacy trials were conducted against Phaeomoniella chlamydospora (Petri disease). In field trials, each conducted in two rootstock mother blocks over two seasons, the duration of wound susceptibility and efficacy of selected fungicides and biological control agents to prevent P. chlamydospora artificial inoculations were evaluated.
Wounds remained susceptible to Pa. chlamydospora infection 42 days after pruning. Wounds were most susceptible directly after pruning and declined significantly thereafter. USMT1 + carbendazim and USMT1 + thiophanate-methyl most consistent, reduced Pa chlamydospora incidences by 56% and 53% (wounds challenged after 1 day) and 25% and 31% (challenged after 7 days), respectively. Eco77 and UST1 also showed potential, reducing Pa chlamydospora incidences by 28% and 36% (wounds challenged after 7 days), respectively.
Key Conclusion of Discussion
The fact that several treatments provided significant reduction in Pa. chlamydospora incidence despite a high spore load highlights the potential of these formulations to be used in field conditions when exposed to natural infection. Furthermore, the potential of biological control agents based on Trichoderma species, to provide environmentally friendly protection of pruning wounds over a long susceptibility period is of cardinal importance to the grapevine industry.
It is highly recommended that the current study be followed up by a study investigating the efficacy of the identified treatments against a broader range of grapevine trunk disease pathogens, i.e. Phaeoacremonium spp., Cadophora spp., Pleurostoma richardsiae (Petri disease) and members of the Botryosphaeriaceae (Bot canker and dieback) and Diaporthaceae (Phomopsis dieback) families. These pathogens are all found as latent infections in rootstock propagation material and many of them (i.e. Petri disease pathogens) are not completely inhibited by treatments currently employed in grapevine nurseries. For example several Phaeoacremonium spp. and Ca. luteo-olivacea are able to survive HWT of 50°C for 45min and Pl. richardsiae was even able to grow at 60°C. Effective pruning wound protection of rootstock mother vines is therefore a critical step in an integrated approach to manage grapevine trunk diseases. More rootstocks must also be included in such a study because it is known that the current range of rootstocks used in South Africa differ in their sensitivity towards grapevine trunk disease pathogens.
Take Home Message for Industry
Given the overwhelming evidence for the need to protect rootstock mother vine pruning wounds against grapevine trunk pathogen infections it is highly recommended that pruning wound protection is made mandatory in rootstock mother blocks.