Grey Mould Risk of Tomato
Grey mould (Botrytis cinerea) overwinters as sclerotia or as mycelium in plant debris and may be seedborne as spores or mycelium in a few crops. Other crops may also serve as sources of the pathogen and are likely to cross-infect. Conidia are airborne and may also be carried on the surface of splashing rain drops. High relative humidities are necessary for prolific spore production. In the field, spores landing on tomato plants germinate and produce an infection when free water from rain, dew, fog, or irrigation occurs on the plant surface.
Optimum temperatures for infection are between 18° and 24° C, and infection can occur within 5 hours. High temperatures, above 28° C, suppress growth and spore production. Dying flowers are a favorable site for infection, but infections can also result from direct contact with moist infested soil or plant debris. In the greenhouse, stem lesions develop either by direct colonization of wounds or through infected leaves. The presence of external nutrients, such as pollen grains in the infection droplet, can markedly increase infection. The type of wound is said to influence stem lesion development; breaking off leaves is reported to give a lower incidence of stem lesions than cutting off leaves with a knife, leaving a stub.
FieldClimate is indicating the risk of a Botrytis cinerea infection on base of leaf wetness periods and the temperature. The graph below shows the duration of wet leaves in dependence of the actual temperature needed for a Botrytis infection. If the risk is higher than 0 every leaf wetness period longer than 4 hours will increase the risk by the same relation. A day with a leaf wetness period shorter than 4 hours is assumed to be a dry day and will reduce the risk by 20% of the actual value.
The graph shows the correlation between duration of leaf wetness and temperature leading to a risk of 30% of a B.cinerea infection.
FieldClimate: Botrytis risk calculated from temperature and leaf wetness period, measured on the station.The FieldClimate Botrytis Risk Model results in a risk value of 0 to 100%. This value indicates the pressure of B. cinerea at the time. If we have a value of 100%it means that there has been several times a wetness period long enough to infect the susceptible tissue(we calculate so called "wet points" (array between leaf wetness, temperature with a maximum of initially 38400 points (beginning of season, which displays 30% risk). After this period each wet period with about 4000 wet points (array) increase the risk with 10% or on the other side each dry period reduce the risk by 1/5 of the former value. An application against B. cinerea is depending on the fruit and the production target.