Latest research data on impact of fungicide spray programs on watermelon powdery mildew in Florida
Prepared by: Mathews Paret, Susannah Da Silva, and Bob Hochmuth
University of Florida, North Florida Research and Education Center
Watermelon powdery mildew is an emerging disease in Florida. The disease in North Florida is typically seen late in the spring season but has the potential to cause yield losses if routine scouting and timely effective fungicide application is not practiced (Fig. 1).
Fig. 1. A section in a watermelon field in North Florida with an early-stage powdery mildew infection (left), and a close-up of an infected leaf from another section of the field. Images Ó Dr. Mathews L. Paret, University of Florida
A study in 2021 funded by USDA-AMS-FDACS-SCBGP program asked the question on how different fungicide programs tailored to powdery mildew (PM Standard), downy mildew (DM Standard), gummy stem blight (GSB Standard) or a Conventional Standard approach could perform under powdery mildew pressure. We also asked the question if using Environmental Favorability Index (EFI) in which fungicides spray programs that are only triggered when local weather conditions meet a threshold number for disease occurrence and spread could be a valuable tool in decision making including potentially reduced number of sprays (EFI +30, EFI +35, EFI +40). Another question we asked is whether incorporating some newer materials (Theia and Esendo - EPA pending review; and Howler) into an IPM program could have benefits. We used plots sprayed with water as a control for the experiment. The findings are shown in Fig. 2 and the details of each of the programs are given in Table 1 in the reference information section.
Fig. 2. Weekly fungicide programs and impact on watermelon powdery mildew disease severity as indicated by Area Under Disease Progress Curve (AUDPC) in a study conducted during spring 2021 at NFREC-Suwannee Valley, Live Oak, FL. The error bars indicate standard error of mean. Different letters above the bars indicate significant differences based on Tukey’s HSD p<0.05. PM = powdery mildew. DM = downy mildew, GSB = gummy stem blight, EFI = Environmental Favorability Index is a program in which fungicides spray programs are only triggered when local weather conditions meet a threshold number as indicated by +30, +35 or +40.
What can be summarized from the study?
- There is more likelihood of a powdery mildew tailored program (PM standard), gummy stem blight tailored program (GSB standard) or conventional standard to perform better in disease management in a year with powdery mildew as the main issue in comparison to a downy mildew tailored program (DM standard). Even though statistically there are no difference between these treatments, the trend of downy mildew program having higher disease severity is relevant. This observation is not surprising as some of the fungicides used for downy mildew are very specific to the pathogen causing downy mildew. A question is whether this response of programs could vary in a year with more downy mildew? Absolutely, we should expect that in general, downy mildew program should perform better under those conditions. However, the time of infection in a crop production stage, environmental conditions and the disease pressure will be relevant factors in field performance of the programs. Routine field scouting and modifying programs based on diagnostic confirmations of diseases can play a huge role in effective management.
- We found that environmental favorability index could help in reducing fungicide applications without significant increase in disease severity. While this is an exciting result, we need to investigate this further with repeating experiments in North Florida in 2022.
- Some of the new tested materials have shown utility in an IPM rotation program and should be tested further to evaluate consistency in performance.
The authors would like to acknowledge USDA-AMS-FDACS Specialty Crops Block Grant Program Award 026708 for funding this project, and the Florida Watermelon Association for support of this research. We also like to acknowledge farm crew at UF-NFREC-Live Oak and Quincy and the fungicide companies who donated chemicals and supported this study. The authors would like to also acknowledge Dr. Pam Roberts, and Dr. Bill Turecheck for collaborative efforts.
Table 1: Fungicide program details. Read top to down in each column to see the weekly fungicide applications for that specific program. PM = powdery mildew. DM = downy mildew, GSB = Gummy stem blight, EFI = Environmental Favorability Index is a program in which fungicides spray programs are only triggered when local weather conditions meet a threshold number as indicated by +30, +35 or +40.