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Ministry of Agriculture, Food and Rural Affairs

Botrytis

Beginner

Scientific Name
            Botrytis cinerea

Identification
Leaves:

  • Infection begins as a dull green spot
  • Typically including the edge of the leaf blade, eventually becoming necrotic
  • When incubated under high humidity, produce greyish-tan spores

Rachis:

  • Infected areas dry out causing berries below the affected area to shrivel

Berries:

  • White cultivars become brown and shriveled
  • Red cultivars become reddish-brown
  • Covered with greyish-tan conidia frequently first seen in tufts or along splits in the berries
  • Skin is easily removed from the flesh (“slip skin”)
  • If dry weather follows infection, infected berries will shrivel and the infection will not progress (Noble rot)

Often Confused With
Downy mildew – infected tissues produce white spores on white branched structures; infected berries turn colour prematurely, remain hard and do not turn brown
  
Black rot – berries develop black pycnidia and mummify; no slip skins, no sporulation

Sour rot – berries are more pinkish-brown, the flesh degrades, no slip-skin, associated with odours of vinegar (acetic acid) and nail polish (ethyl acetate). Berries may be co-infected with botrytis and sour rot

Grape berry moth – berries turn brown and larvae are present inside or are hollowed out with only frass remaining. Cluster with GBM infestations are often also infected with botrytis, or sour rot, or both

Period of Activity
From onset of bloom and after veraison.  Physical injury to berries by hail or insects can also cause latent infections to sporulate between bloom and veraison.

Scouting Notes
Focus on tight-clustered, thin-skinned cultivars or blocks that have a history of grape berry moth problems. Monitor flower clusters after bloom for sporulation on shed caps.  Following severe weather with associated hail, examine clusters for sporulation.  After veraison, observe fruit for discolouration and sporulation.

To confirm Botrytis infection, enclose the tissue in a plastic bag containing a damp paper towel.  If botrytis is present, it will produce tannish-grey conidia in clumps on dark conidiophores.

Threshold
There is no threshold for initiating botryis control. Fungicides should be applied before infection occurs. 

Advanced

Scientific Name
            Botrytis cinerea

Identification
Leaves:

  • Infection begins as a dull green spot
  • Typically including the edge of the leaf blade, eventually becoming necrotic
  • When incubated under high humidity, produce greyish-tan spores

Rachis:

  • Infected areas dry out causing berries below the affected area to shrivel

Berries:

  • White cultivars become brown and shriveled
  • Red cultivars become reddish-brown
  • Covered with greyish-tan conidia frequently first seen in tufts or along splits in the berries
  • Skin is easily removed from the flesh (“slip skin”)
  • If dry weather follows infection, infected berries will shrivel and the infection will not progress (Noble rot)

Often Confused With
Downy mildew – infected tissues produce white spores on white branched structures; infected berries turn colour prematurely, remain hard and do not turn brown
  
Black rot – berries develop black pycnidia and mummify; no slip skins, no sporulation

Sour rot – berries are more pinkish-brown, the flesh degrades, no slip-skin, associated with odours of vinegar (acetic acid) and nail polish (ethyl acetate). Berries can be co-infected with botrytis and sour rot

Grape berry moth – berries turn brown and larvae are present inside or are hollowed out with only frass remaining. Cluster infested with GBM may also be infected by botrytis, sour rot or both

Biology
The causal fungus, Botrytis cinerea, overwinters as sclerotia or mycelium in infected plant debris.  Old cluster stems from the previous year appear to be a common source of inoculum. In spring, conidia form on overwintered tissues and are wind-dispersed to grape tissues. Infection is optimal at 15-20 º C when tissues remain wet for several continuous hours. Production of spores and subsequent infection are greatly favored by prolonged periods of wetness and high levels of humidity with little or no air movement.  New conidia produced on the infected tissues are dispersed by the wind. Several new cycles of sporulation and infection may occur throughout the growing season. Berries may be infected shortly after bloom through aging blossom parts but remain symptomless until veraison.  Berries become susceptible to direct infection by B. cinerea, (i.e. no wounds are required) at veraison and become increasingly susceptible as they mature. If the pre-harvest period is warm and wet there is a greater chance of a severe infection, resulting in reduced yield and quality.  Physical injury to the berries by grape berry moth, hail, previous powdery mildew infection or other agents provides wounds that allow the fungus to penetrate the berries. Infection can rapidly spread to adjacent healthy berries that are in contact with an infected berry.

Period of Activity
From onset of bloom and after veraison.  Physical injury to berries by hail or insects can also cause latent infections to sporulate between bloom and veraison.

Scouting Notes
Focus on tight-clustered, thin-skinned cultivars or blocks that have a history of grape berry moth problems. Monitor flower clusters after bloom for sporulation on shed caps.  Following severe weather with associated hail, examine clusters for sporulation.  After veraison, observe fruit for discolouration and sporulation.

To confirm Botrytis infection, enclose the tissue in a plastic bag containing a damp paper towel.  If botrytis is present, it will produce tannish-grey conidia in clumps on dark conidiophores.

Threshold
There is no threshold for initiating botryis control. Fungicides should be applied before infection occurs. 

Management Notes
Selection of a site with good air drainage,north-south orientation of the rows to maximize sun exposure, and practices that open the canopy so that air circulation and spray coverage are improved can help control of botrytis.

Pruning, training and leaf-removal to reduce shading and allow rapid air movement can reduce the frequency and duration of periods of high humidity which favour the disease.

Good weed control and proper soil drainage will reduce relative humidity and the amount of free moisture which may increase the spread of the fungus.

Thin-skinned, tight clustered cultivars tend to be more prone to Botrytis bunch rot.  See Table 6-5 Relative Susceptibility of Grape Cultivars to Diseases.

Prevent excessive vine growth by judicious use of water and fertilizer. Nitrogen fertilizers should not be applied after fruit set.

Control powdery mildew during the fruit susceptibility period.  Infections can cause splitting when the berries expand after veraison, providing entry sites for Botrytis.

Control grape berry moth and other insects that may injury berries.

Thin clusters so that they are not in close contact to reduce cluster-to-cluster spread.  If fruit is removed close to harvest for purposes of crop thinning or to eliminate infected clusters, take the clusters from the vineyard and bury them to prevent spread of the disease.
Management with fungicides – Fungicides are used to control Botrytis bunch rot in most commercial vineyards. See OMAFRA Publication 360, Guide to Fruit Production - Chapter 5 Grapes (PDF): Recommendations for Botrytis bunch rot at immediate post-bloom to early fruit set, berry touch and veraison.  If new Botrytis infections are observed after the veraison spray, another application may be required before harvest, but be aware of pre-harvest intervals of your processor.

Fungicides have different modes of action, and differ in their activity on grape diseases. See Table 5-6 Activity of fungicides on grape diseases.