Botrytis and what to do about it

Notes from a talk by Rob Agnew of Plant and Food Research
at the Wither Hills Organic Focus Field Day
Feb 14, 2013

with thanks to Ben Burridge, Wither Hills for these notes

Botrytis and what to do about it

Substantial amount of botrytis in Pinot Gris Org Focus Vineyard last year (Central Otago).

Organic canopy management has to be more onto it. B. cinerea is everywhere in environment. Has 200 host species.

Limited by what we can use for botrytis as there is a demand for residue free wine.

Number of sources for infection.

Vineyard trash can give rise to up to 70% botrytis on vine at flowering and 28% at harvest. Trash feeds into early season infection.

High incidence of B. cinerea germinating from rachii (90%).

95% of spores coming from the ground travel less than one meter.

Multiple pathways to infection
• Pathway 1: Early season establishment in necrotic floral tissues
• Pathway 2: (Latents) Early season infection of green structural tissues (pedicels, laterals, rachii). Many latents don’t make it to vintage due to natural defence mechanisms i.e. cuticular waxes, cuticle thickness, proanthocyanins and phytoalexins.
Research being conducted into weather sticker spreaders reduce the effectiveness of berry waxes.
• Pathway 3: Cap scar infection at cap fall.
Spore infects necrotic ring of tissue at the berry base (cap scar)
• Pathway 4: Wind dispersed botrytis spores accumulate on vine material waiting for ideal conditions to germinate.
• Pathway 5: Spores infect bunch and canopy trash

The Challenge! Cost effective ways to interrupt these pathways.
Biological – if the biological agent grows it may be more effective than a chemical, but need enough of the biological to outcompete B. cinerea.

Botryzen – covers trash. Germinating spores of product covers potential infection sites (Bacillus uses decaying carbon as a food source).

No decent infection period from veraison to harvest in Marlborough for past decade. This season (2013) there has only been 51.6mm of rain between 14th October and 13th of January. Usually there is approximately 160mm. (Botrytis Decision Support System)
Uses Bacchus infection periods and accumulates them for an indication of botrytis risk. Also shows how management actions can reduce risk.

Canopy Management techniques to reduce botrytis risk:
• Vigour management – rootstock, root pruning, deficit irrigation, interrow cover crop, nitrogen management.
• Fruit zone aeration – Leaf and shoot removal. Changes fruit zone micro climate, increases UV exposure which increases skin thickness (up to 35% thicker), increases waxes on berry (up to 19%), leads to higher mortality of bunch rot pathogens.

Leaf Removal Trial in Marlborough
No leaf plucking resulted in 5.9% crop loss; leaf plucking led to 2.9% crop loss. Average reduction of botrytis crop loss by 61%.

Effective canopy management reduces botrytis up to 50% with no botryticide treatment.

Undervine practices – encourage decomposition of materials
• Chop up prunings fairly small to encourage decomposition
• Organic mulch elevates soil micro-organisms, accelerates breakdown of vine materials
• Organic vines with lower nitrogen likely to have lower canopy density and reduced susceptibility to botrytis
• Want optimum juice nitrogen for ferment but not excessive.

B. cinerea good necrotrophe, strong saprophyte! Doesn’t generally like monocots (grasses).

Water sensitive papers are hugely valuable for testing spray coverage. Greater than 80% coverage is desired. Leaf and shoot removal improves spray deposition. Leaf area acts as a wall, preventing good spray coverage. Ideally want 70-80% fruit exposure pre bunch closure.

BRAT (Botrytis Risk Assessment Trainer)
Tool for training staff at assessing Botrytis severity
Three free uses.

With careful management, you can avoid this (photo by Fruition Horticulture)

With careful management, you can avoid this (photo by Fruition Horticulture)