Pest and disease factsheet: Botrytis on ornamentals crops

Botrytis is a disease usually associated with cool, humid, still air conditions.

Botrytis symptoms - image: Dove Associates
Botrytis symptoms - image: Dove Associates

Its common name, grey mould, describes the easily visible brown/grey fluffy fungal growth that can form on soft, damaged plant growth on stems, leaves, flowers and fruit.

Fallen leaves, flowers and fruit are also susceptible to Botrytis. Many plant species are prone to this disease but tight cultural controls help to keep infection risk low.

How to recognise it

On most plants, under the microscope or with a hand lens, a fully developed infection shows as multiple conidiospores (long hyphae with branched tops) resembling a "forest" of brown/grey fungal growth. This can appear quite quickly in periods of high humidity. Sclerotia (black resting bodies) can survive for long periods in affected tissues, ready to reinfect vulnerable crops.

Biology

Botrytis has a wide temperature range for infection of 3-25 degsC. It is a weak pathogen and requires nutrients (leaking from a wound or dying tissue) before it can invade a plant. Using this food source, it spreads quickly and can even infect nearby healthy tissue. Spores can be spread on air currents and by water splash.

Symptoms

In low humidity, infections can show as patches of brown dieback, spotting on old flowers (especially roses), bulb or corm rotting or sunken areas on fruit. High humidity encourages grey fungal growth. Some infected plants may not show fungal growth even in high humidity. Wilting and dieback can be seen at the stem base on pot plants, especially with compact, tight foliage. Cuttings can show damage from the base and tip. The disease may also develop in transit on finished plants where airflow is poor.

Treatment: biological control

Bio-fungicides such as Prestop* and Serenade ASO* can protect plants from infection through competition for space on leaves, stems and flowers. Repeat applications of compost tea produce a similar effect.

Treatment: cultural control

- Keep growing beds as clean as possible and free from debris.

- Avoid damaging plants, especially crops with soft growth. Prune using sharp, clean equipment to avoid large surface areas of damage. Quickly remove damaged plant parts.

- Avoid potting too deep and space plants to allow adequate air flow.

- Avoid pruning immediately before or after overhead irrigation.

- Avoid over-feeding plants with high-nitrogen products during autumn and early spring.

- Reduce mist levels after cuttings have rooted.

- HDC fact sheets 23/02 and 25/02 detail relative humidity above 95 per cent for more than three hours at 10-20 degsC will initiate Botrytis.

- Heat and ventilate glasshouses and tunnels to avoid high humidity. Change the air in a structure at least once every 24 hours. Humidity will differ between the crop on the ground and the general atmosphere in a protected structure.

- Avoid sudden increases in air temperatures. Venting to within 1 degsC of the heating temperature will allow plants to warm up slowly and avoid condensation on lower leaves.

- The layout and size of protected structures along with the choice of irrigation and ventilation will influence whether Botrytis will be an issue during the growing season.

- Install side and roof vents to push the air around foliage, creating a chimney effect.

- Parallel or serial fan arrangements ensure no still air in a structure. Avoid a circular fan arrangement.

- Leave a 3m gap between growing structures to allow adequate airflow.

- Water early in the day during winter to ensure crop foliage is dry before nightfall. Foliage that lies wet all night can support Botrytis growth.

- Opening side doors can increase roof vent efficiency by 25 per cent.

- Use slatted rather than solid benches for better air movement.

- Anti-condensation films and polythenes that reduce ultraviolet levels such as SteriLite or Luminance will help to reduce infections.

- Some glasshouse computer systems have Botrytis-control programmes as an option.

Treatment: chemical control

Active ingredient Azoxystrobin

FRAC code 11

Formulations Various including Amistar* (Syngenta)

Action(s) Systemic, translaminar, protectant broad-spectrum fungicide - compatible with biological controls.

Active ingredient Bacillus subtilis strain QST713

FRAC code 44

Formulation Serenade ASO* (Bayer CropScience)

Action(s) Protectant bio-fungicide; compatible with biological controls.

Active ingredients Boscalid + pyraclostrobin

FRAC code 7 + 11

Formulation Signum* (BASF)

Action(s) Systemic, protectant and curative fungicide - compatible with some biological controls.

Active ingredient Captan

FRAC code M4

Formulation Alpha Captan 80WDG (Makhteshim)

Action(s) Protectant fungicide - compatible with biological controls.

Active ingredient Chlorothalonil

FRAC code M5

Formulations Bravo 500* (Syngenta)

Action(s) Protectant fungicide for selected outdoor crops - compatible with some biological controls.

Active ingredients Cyprodinil + fludioxinil

FRAC codes 9+12

Formulation Switch (Syngenta)

Action(s) Systemic, translaminar fungicide with long residual activity - incompatible with biological controls.

Active ingredient Gliocladium catenulatum strain J1446

Formulation Prestop* (Fargro)

Action(s) Bio-fungicide - compatible with biological controls (not on unrooted cuttings).

Active ingredient Iprodione

FRAC code 2

Formulation Rovral WG* (BASF)

Action(s) Protectant, contact fungicide - compatible with biological controls.

Active ingredient Prochloraz

FRAC code 3

Formulation Octave (Everris)

Action(s) Broad-spectrum protectant and eradicant fungicide - compatible with some biological controls.

Active ingredient Pyrimethanil

FRAC code 9

Formulation Scala* (BASF)

Action(s) Protectant fungicide - compatible with some biological controls.

Active ingredient Tebuconazole

FRAC code 3

Formulation Various including Folicur (Bayer CropScience)

Action(s) Systemic fungicide with protectant, curative action - compatible with biological controls.

Active ingredient Thiram

FRAC code M3

Formulations Triptam (Certis)

Action(s) Protectant, contact fungicide - compatible with some biological controls.

Fully updated by Dove Associates.

Use plant protection products safely. Always read the label and product information before use.

* Extension of Authorisation for Minor Use (EAMU) required for use in ornamental plant production outdoors and/or under protection.

Dove Associates shall in no event be liable for the loss or damage to any crops or biological control agents caused by the use of products mentioned.


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