Lettuce Grey Mould
B. cinerea infections are related to free moisture. a) In open field production leaf wetness is a good indicator for this. In green house production there is a problem to measure leaf wetness representative and therefore air temperature and dew point have to be used as an indicator of free moisture too.
FieldClimate is indicating the risk of Botrytis cinerea on base of leaf wetness periods and the temperature during this periods. An completed infection period is assumed after a leaf wetness period indicated by the graph beside. Such a leaf wetness period will increase the risk by 30%. 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 figure by 20% of the actual value.
The same model is used for calculation of Grey mould in strawberry cultures.
The graph indicates a leaf wetness period leading to B. cinerea risk of 30%. Dry days will reduce the risk again.
Botrytis risk in Open Field Production, determined by temperature and leaf wetness periodes.
Practical use of the Grey Mould Model: The model indicates periods with risk of Botrytis infection. As longer the risk period last and as higher the risk is as higher the propability and the number of infections. The risk which is acceptable is very much depending on the marketing. Growers selling to super markets will not take any risk at the beginning of the season, knowing that infected fruits in the self will cost them their market. Wheras direct marketers might take a higher risk through all the season.