in general, several weather parameters will influence the occurrence of any pest or disease in crop plants. Can we draw any correlation between GDD and disease incidence in crop plants?
Definitely, GDD reflect temp. at which pest and disease incidence depend. When cumulative GDD reach at specific temp. We can forecast that particular disease and pest will come. Also it helps in deciding harvesting time of crop.
Sadaiah its up to you how many driving/explanatory factors or indicators you want to include in your relation/model. A more detailed model and definitely more reliable one should also include factors other than GDD as well.
GDD includes sunshine hours and temperature for a crop during its cycle. Yes, pest and disease incidence are dependent on it. Pest-disease incidence prediction is possible based on GDD as well as temp. Besides, GDD can give an idea for crop maturity, harvest and yields.