An Overview: Botrytis Cinerea || Gray Mould || Viticulture

The fungus that causes botrytis bunch rot and gray mould on grapevines is called botrytis cinerea. A decline in output and a decline in fruit quality in disease-prone years can result in significant economic loss. Due to the multiplicity of circumstances that can lead to infection and disease progression, managing botrytis can be difficult. It is necessary to be aware of these factors and ways to lessen their impact.

Factors influencing grapevine susceptibility:

A variety of environmental and managemental elements have an impact on a vine's vulnerability to botrytis infection.

• Weather: Botrytis cinerea is a pathogen that is influenced by the weather. High humidity or lengthy rain combined with cool or mild temperatures that leave berries with persistent wetness encourage the growth of illness and infection. A soggy spring followed by rain just before harvest is the worst-case seasonal scenario.
• Microclimate/Canopy architecture: Vines with closed, dense canopies retain moisture and create favourable circumstances for botrytis for a longer period of time. Closed vine canopies also hinder the effective application of pesticides and restrict spray penetration.
• Stage of grapevine development: Grapevine flowers, right after capfall, and berries following veraison are especially prone to botrytis infection. Green, hard berries can also contract the disease, though. The cap's abscission near the bottom leaves a wound that serves as a point of entry for the fungus. Berry swelling and softening start after veraison, as sugar levels increase and acids level out. Any fungus inside the berry left over from an earlier infection may be encouraged to flourish as sugar levels rise. Sugar leakage through the berry skin might support the growth of B. cinerea on the berry surface.
• Varietal susceptibility: Thin-skinned, densely packed bunches from vines are more likely to split and absorb moisture, which favours botrytis. Chardonnay, Chenin Blanc, Grenache, Muller Thurgau, Pinot Gris, Pinot Noir, Riesling, Sauvignon Blanc, Semillon, Traminer, and Sultana are the varieties most at risk. Botrytis can affect any kind.

Life-cycle of Botrytis Cinerea:

Fig. Life-cycle of Botrytis Cinerea

Infection: 

The first step in controlling the virus is to recognise it in all of its forms. Early-season symptoms suggest that the conditions have been favourable for disease development, and measures to limit future development should be made to lessen the severity of botrytis during harvest.

Both types of the fungus generate spores in moist or humid environments. These can sprout on harmed green tissue and are dispersed by the wind or water splashes. Damaged tissue is naturally found in flowers. A common infection location is where the bloom cap has come off and left a wound.

Fig. Botrytis infected Grape Leaves

Fig. Botrytis infected Grapes

Symptoms of Botrytis (Gray mould):

1. Young leaves have a distinctive V-shaped dead tissue region that spreads towards the major veins and have yellowing leaf edges.
2. Soft brown rotting spots appear on shoots that have sustained injury and are diseased.
3. At the moment where the caps abscise, it is typical for individual blooms to get an infection, yet there are no obvious symptoms.

Management of the disease Botrytis Cinerea/ Gray mould:

Botrytis control necessitates the fusion of cultural and chemical management techniques. Although even the finest attempts be aggravated by the weather circumstances are favourable to the development of illness near to harvest, there may be a chance of crop loss be decreased by taking measures early in the season.

Cultural practices:

Cultural practises that make flowers and bunches more accessible should be employed to boost spray effectiveness and to produce conditions that are unfriendly to the illness.
When planting in high-risk locations, choose types that are the least sensitive. These can be identified by the thicker-skinned berries and loose bunches they produce.
To lessen bunch zone congestion and limit bunches around trellis posts, use pruning and bunch thinning.
To hasten the decomposition of inoculum and the amount carried over from the previous season, cultivate prunings into the soil or manage the vineyard floor for elevated microbial activity.
Fruit can be collected deliberately and diseased fruit can be avoided for crops that are manually harvested. Pickers must be able to identify botrytis bunch rot and be aware of which rotten bunches need to be thrown to the ground.

Chemical control strategies:

A fungus called botrytis has the potential to seriously harm grape vines. The disease can be treated with a variety of medicines, and protectants work on the surface of the vine to stop spore germination. Spraying in advance of infection is advised to prevent fungicide resistance since it is more effective than spraying after illness. Eradicants, or curative chemicals, penetrate the vine to kill the fungus that is forming. When it's challenging to get a good spray coverage, translaminar fungicides, which can migrate within the leaf, provide protection. Botrytis's resistance to specific herbicides and the withholding periods imposed on grapes intended for export must be taken into account in any spray programme. In order to ensure that control alternatives are available at the conclusion of the season if necessary, chemicals must be utilised carefully.

Considerations for spraying at various growth stages:

To manage Botrytis infection, spraying grapevines should take into account conditions including early-season disease levels, early flowering, 80% capfall, pre-bunch closure, and veraison. If there are significant disease levels or vineyards are prone to leaf and shoot damage, fungicides can be used to protect young shoots and leaves. When the bloom caps come off, grapevine flowers are susceptible to Botrytis infection. If the weather is rainy and the flowering period is protracted, more spraying may be required. Translaminar sprays work best during the 80% capfall period because they target the wounds left by the fallen flower caps. The last chance to get chemicals within the bunch to safeguard more sensitive post-veraison berries as well as bunch and berry stems is during pre-bunch closure sprays. Spraying may be necessary during veraison to seven days prior to harvest, particularly at the first indications of berry damage or if a wet spell is predicted close to harvest. The selection of fungicides is constrained during this time due to market and winery constraints.

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