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Nicole Gauthier, Plant Pathology Extension Specialist          Kim Leonberger, Plant Pathology Extension Associate

Sara Long, Plant Disease Diagnostic Assistant                    Rachel Rudolph, Horticulture Extension Specialist

Introduction

In Kentucky, summer squash and zucchini are common cucurbit crops grown in open field production. Numerous plant pathogens can cause disease, resulting in plant damage and yield loss. Applications of fungicides and bactericides are often necessary to limit plant diseases. Fungicides and bactericides provide the greatest efficacy when applied preventively (prior to disease onset), rather than after observing disease symptoms. Growers can develop a spray schedule for each season to limit the impact of diseases on crop production. This document provides information on the timing of the most common summer squash and zucchini diseases, as well as an example spray schedule. Fungicides and bactericides recommended here include a few of the most common products. A complete list of registered fungicides can be found in the Vegetable Production Guide for Commercial Growers (ID-36) and the Southeast U.S. Vegetable Crop Handbook (SEVEW); generic products may also be available.

Timeline of common and important diseases occurring on summer squash and zucchini crops in field production.

1 Application necessary when diagnostic results confirm presence of disease or if field has a history of disease.

2 See SEVEW Table 3-53 Biopesticides for alternative products. (Note: This production guide is revised annually, and the location of this information can change with updates.)

3 Mancozeb is not effective for the management of powdery mildew.

Example field spray schedule for summer squash and zucchini

DM - downy mildew; LS - leaf spots; PM - powdery mildew

1 Chlorothalonil is effective against downy mildew; however Torino is not.

2 Refer to ipmpipe.org for risk and forecasting information.

Disclaimer

Fungicides listed here include a few of the most common products available and were selected to simplify information in this publication. No endorsement is intended nor is criticism implied of similar products that are not named.

Additional Resources

• Cucumber Beetles (EntFact-311)
• IPM Pipe Cucurbit Downy Mildew Forecasting Website (website)
• Plant Pathology Extension Publications (UK)
• Southeast U.S. Vegetable Crop Handbook (SEVEW)
• Vegetable Production Guide for Commercial Growers (ID-36)

April 2024

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Acknowledgments

The authors thank April Lamb, Plant Pathology Postdoctoral Scholar, University of Kentucky, and Henry Smith, Plant Pathology Graduate Student, University of Kentucky, for their reviews of this publication.

Editor: Cheryl Kaiser, Plant Pathology Extension Support

Photos: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org

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