Conventional Fungicide Recommendations for Cucurbit Powdery Mildew – Vegetable Crops Hotline

Conventional Fungicide Recommendations for Cucurbit Powdery Mildew

The following article was written by a colleague located on Long Island in New York. She is an expert on cucurbit powdery mildew.  The fungicides which are effective against cucurbit powdery mildew changes frequently as fungi become resistant to certain fungicides. While the situation Dr. McGrath describes may not match your field exactly, it makes sense to make most fungicide applications using the top choices given below and avoid those products which are described as non effective. Note that some products may be used in a limited amount of applications. As always, alternate FRAC codes. 

Margaret Tuttle McGrath
Plant Pathology and Plant-Microbe Biology Section, SIPS, Cornell University
Long Island Horticultural Research and Extension Center (LIHREC)
3059 Sound Avenue, Riverhead, NY 11901; mtm3@cornell.edu

Cucurbit powdery mildew control can be achieved with targeted fungicides applied starting at the action threshold of one of 50 older leaves with symptoms. It is important to look at the lower surface of older leaves as symptoms often appear there first. This disease typically starts to develop around start of fruit development so first flowers is when to start looking or when to start a preventive spray program. This pathogen has proven adept at developing resistance to fungicides, thereby rendering them ineffective. Fungicide recommendations are based on fungicide evaluations and resistance monitoring work conducted at LIHREC. Alternating among fungicides that are chemically different (in different FRAC groups) is recommended to manage resistance and to comply with label restrictions on number of consecutive applications, which is two for most targeted fungicides.

Top choices to include in a fungicide program:

– DMI fungicides (FRAC 3).  Proline® is highly effective, seasonal limit for a crop is 2 applications.  Procure®, Luna Experience®, and Aprovia Top® are also good choices. Multiple DMI fungicides can be used in a program.

– Vivando (50). Seasonal limit is 3 applications. Prolivo®, another FRAC 50, does not appear to be as effective as Vivando®.

– SDHI fungicides (7). Aprovia Top® and Luna Experience® have two active ingredients, SDHI as well as DMI.

Fungicides that could be included:

– Gatten® (U13) has exhibited variable efficacy; it was moderately effective in a fungicide evaluation in PA in 2021.

– Quintec® (13) or Torino® (U8). One application of either of these might contribute to control. Pathogen isolates resistant to both fungicides were found commonly in commercial crops treated twice with Quintec® in a program. Multi-fungicide resistance is common. Most of the Quintec®-resistant isolates in the 2021 collection and all in the 2020 collection were also resistant to Torino® and Endura® although these fungicides were not used in almost all locations, and these fungicides are not cross resistant.

Fungicides not recommended because of resistance:

Topsin M® (1) and QoI fungicides (Cabrio®, Flint®, Quadris®, etc.) (11) are not expected to provide any control because almost all pathogen isolates tested have been found to be resistant. Endura®, Pristine®, and Merivon® are not recommended because isolates with full resistance (insensitive to highest label rate) are common and there are other SDHI fungicides (Aprovia Top®, Luna Experience®) that bind enough differently that they are not fully cross resistant.

Example recommended targeted fungicide programs (there are other good combinations) (including a contact, protectant fungicide with each application is recommended):

Proline®, Vivando®, Proline®, Vivando®, Luna Experience†®, Vivando® (6 applications total)*.

Proline®, Vivando®, Proline®, Vivando®, Procure®, Vivando®, Procure® (7 applications total)*.

Proline®, Vivando®, Proline®, Vivando®, Aprovia Top®, Vivando® (7 applications total)*.

Proline®, Vivando®, Aprovia Top®, Proline®, Vivando®, Luna Experience†®, Procure®, Vivando® (8)*.

*program has maximum number of applications of Proline® and Vivando® permitted to a crop.

†Aprovia Top® could be used instead of Luna Experience®

Additional information about this disease and its management are at the Cucurbit Powdery Mildew website.

original posting was on the web at https://www.vegetables.cornell.edu/pest-management/disease-factsheets/cucurbit-powdery-mildew/

Updated: June 2022

 

 

 

 

 

Share This Article
It is the policy of the Purdue University that all persons have equal opportunity and access to its educational programs, services, activities, and facilities without regard to race, religion, color, sex, age, national origin or ancestry, marital status, parental status, sexual orientation, disability or status as a veteran. Purdue is an Affirmative Action Institution. This material may be available in alternative formats. 1-888-EXT-INFO Disclaimer: Reference to products in this publication is not intended to be an endorsement to the exclusion of others which may have similar uses. Any person using products listed in this publication assumes full responsibility for their use in accordance with current directions of the manufacturer.
Vegetable Crops Hotline - Horticulture & Landscape Architecture, 625 Agriculture Mall, West Lafayette, IN 47907

© 2022 Purdue University | An equal access/equal opportunity university | Copyright Complaints | Maintained by Vegetable Crops Hotline

If you have trouble accessing this page because of a disability, please contact Vegetable Crops Hotline at guan40@purdue.edu | Accessibility Resources