# Research on Plant Disease and Pest Diagnosis Model Based on Generalized Stochastic Petri Net
## 5 Case Study
### Verification of the Grape Downy Mildew Pest and Disease Early Warning System
The classification standards are as follows: mild infection is defined as when the lesion occupies less than 25% of the leaf area; moderate infection is when the lesion occupies between 25% and 75% of the leaf area; severe infection is when the lesion occupies more than 75% of the leaf area. The specific grading standards are shown in Table 11.  
Based on the GSPN model for the spread and evolution of grape downny mildew, the analysis of different combinations of disease occurrence probabilities enables the assessment of disease severity and the implementation of corresponding control strategies. Through comparative analysis of various infection stages, this study illustrates the spread of downny mildew in grape-growing areas of Kunming and demonstrates the effectiveness of the early warning mechanism. The specific descriptions of grape downny mildew severity are detailed in Table 12.  
According to the early warning activation rules, the early warning probability for grape downny mildew is determined to be \(\mathrm{P}(\mathrm{M}_{12})=0.018>0.015\), thereby triggering a red warning. Experimental data further show that on 30 April 2025, lesions almost completely \begin{table}
\begin{tabular}{c c c} \hline \hline
**Date** & **P(M12)** & **Detailed Disease Description** & **Warning Level** \\ \hline
10 April & 0.002 & Small, translucent spots appear on the front side of the leaves; under high humidity, mold is visible; lesion edges are unclear. & Blue Warning \\ \hline
11 April & 0.004 & Lesions begin to turn yellow and gradually take on a circular or irregular shape; a small amount of white mold appears on the leaf underside. & Blue Warning \\ \hline
18 April & 0.007 & Lesions expand; under high humidity, mold increases significantly; infected leaves begin to white, affecting grape photosynthesis. & Blue Warning \\ \hline
22 April & 0.012 & Lesions merge; mold spreads further with increased humidity; fruits begin to show signs of mold infection, affecting fruit development. & Yellow Warning \\ \hline
26 April & 0.014 & Lesions have extensively expanded; mold covers most leaves; some fruits show severe rot, impacting yield. & Yellow Warning \\ \hline
30 April & 0.018 & Lesions nearly cover all leaves; fruits rot; mold almost fully covers surfaces, causing severe damage to grapevine health. & Red Warning \\ \hline
3 May & 0.017 & Lesions decrease; some leaves recover, but mold persists; fruit conditions improve somewhat but full recovery has not yet occurred. & Yellow Warning \\ \hline
10 May & 0.013 & Most mold disappears; lesion area gradually reduces; grapevines begin to recover and resume growth; further management is still required. & Yellow Warning \\ \hline \hline \end{tabular}
\end{table} 
Table 11: Classification standard of downy mildew. \begin{table}
\begin{tabular}{c c} \hline \hline
**Severity Level** & **Description** \\ \hline Mild Infection & Lesions occupy less than 25\% of the leaf area \\ Moderate Infection & Lesions occupy 25\% to 75\% of the leaf area \\ Severe Infection & Lesions occupy more than 75\% of the leaf area \\ \hline \hline \end{tabular}
\end{table} 
Table 11: Classification standard of downy mildew. covered all leaves, fruits were rotting, and mold had nearly entirely spread across the plant surfaces, resulting in severe damage to grapevine health--consistent with the findings of this study. The disease progression trend of grape downy mildew is illustrated in Figure 11.