Please check the following link.

https://www.researchgate.net/publication/266322141_Development_of_weather-based_prediction_models_for_leaf_rust_in_wheat_in_the_Indo-Gangetic_plains_of_India

Article Development of weather-based prediction models for leaf rust...

Please have a look at this link also.

http://link.springer.com/chapter/10.1007/978-3-319-19620-6_50

Thank you Dr.Arvind Singh for mentioning my work on leaf rust in your answer to the question asked by Ms.Priyanka.The paper will give some clue to your problem.

Coming to the question by Ms.Priyanka,no definite answer can be given.If we are developing statistical models,minimum number of years required depends on number of independent or predictor variables.General thumb rule says that number of data points or years should be more than number of variables+1.Statistics scientists say more the number of years more perfect the model.

Thank you Puppala Vijaya Kumar  sir

Thank you Arvind Singh sir I'll refer the paper mentioned by you.