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IPI Model

The IPI model displays a negative prognosis, which has been developed by BUGIANI, CAVANNI, I. PONTI for the Emilia-Romagna region in Italy. It is used to estimate the date of the first spray against this disease in tomato.

Model Description:This model generates infection potential indexes (IPI) that predict the most probable inoculum increase of Phytophthora infestans in the environment. In Italy, IP indexes are used along with indicator plants plus spore traps to warn farmers about when to start spraying. The model does not give recommendations about subsequent fungicide applications. Negative prognosis can´t be used in areas with permanent cropping, areas with no winter.

Functionality:  To calculate daily IPI,relative indexes for average temperature and relative humidity and precipitation are calculated independently and combined by multiplying the temperature index by either the precipitation index or the relative humidity index. The cumulative daily IPI over a defined period is used by the model to evaluate late blight risk. The IPI-Model is used as a negative prognosis in Italy. At the time the IPI-Value comes over 15 they start to spray against Late Blight in tomato. As long as it stays below no spray is indicated.

Result: FieldClimate.com displays a steady increasing value for the IPI-Value. µLink displays a steady increasing line. At the time the IPI-Value reaches 18 a qualitative line is displayed in the bottom of the graph.

To calculate daily IPI, relative indexes for average temperature and relative humidity and precipitation are calculated independently and combined by multiplying the temperature index by either the precipitation index or the relative humidity index. The cumulative daily IPI over a defined period is used by the model to evaluate late blight risk. The IPI-Model is used as a negative prognosis in Italy. To calculate daily IPI,relative indexes for average temperature and relative humidity To calculate daily IPI,relative indexes for average temperature and relative humidity To calculate daily IPI,relative indexes for average temperature and relative humidity To calculate daily IPI,relative indexes for average temperature and relative humidity.

FieldClimate.com stops this calculation if temperature stays below 11°C for 96 hours. It starts the calculation again if temperature never falls below 6°C within 96 hours. The maximum value of this calculation is 40. To calculate daily IPI, relative indexes for average temperature and relative humidity and precipitation are calculated independently and combined by multiplying the temperature index by either the precipitation index or the relative humidity index. IPI only needs to be calculated when days have a minimum temperature higher than 7°C, an average temperature between 9 °C and 25°C and more than 0.2 mm of rain or an average relative humidity of more than 80%. Favourable weather conditions for Phytophthora infestans produce a positive IPI. Functions for index calculations are following the graphs beside.

The IPI model for Tomato Late Blight is a negative prognosis model. It is only helpful in areas where we have no permanent cropping of tomato. This means in areas with frost during winter. In such areas Phytophtora infestans inoculum potential is reduced during winter and has to build up in spring again. The IPI model indicates the build up of inoculum in field. If the IPI value reaches 15 the first spray is indicated in the area the model has been developed. If you use the area in another area please check if this value is valid for you.

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