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Publication #PP322

Phytophthora Management in Citrus Nurseries1

Megan M. Dewdney and Jamie D. Burrow2

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General Sanitation Practices

  • Do not enter greenhouses after visiting citrus groves.

  • Keep head house area and greenhouse walkways swept and free of debris.

  • Don’t use surface water as an irrigation water source.

  • It is recommended to have a disinfesting copper footbath at each house entry.

Tools

  • Shovels should be disinfested before and after each use and should NEVER touch the floor during storage.

  • Hose nozzles should never contact the ground.

  • Hose nozzles should remain on bench tops or hooks when stored.

  • If the hose nozzle contacts the ground, decontaminate immediately (see other side).

Buckets, Pots, and Tubs

  • Should only be filled with clean potting media.

  • If pots have sat on the floor, do not stack pots on top of one another.

  • Do not store pots directly on the ground or within a splash zone.

Potting Media

  • Where possible, source potting media from Phytophthora-free supplier.

  • Store potting media on a concrete pad and periodically disinfest the pad.

  • Storage areas should be protected from wind and rain.

  • Pile should be kept covered.

  • Restrict access to media storage area.

  • Station a copper footbath at entrance of storage area.

  • Footwear should be disinfested at each entry.

  • Tractor tires, scoops, and shovels used to move media should be disinfested as needed.

General Sanitation Management

  • Sanitizing should be at the start of each workday for personnel and tools, when moving among plants within or between benches, or when moving from one house to another within the nursery.

  • All equipment should be re-sanitized if dropped or if used in a non-clean area.

  • When hand watering, keep water splash to a minimum.

  • Nursery workers should not stand on or use tables or pots as a step.

Tables

Table 1. 

Common disinfestants and factors to consider in their selection for nursery use.

Disinfestant

Factors affecting efficacy

Corrosive to metals

Residual activity

Bleach (10%)

  • efficacy reduced by organic matter

  • degrades in sunlight, solutions need to be made fresh daily

  • water pH (optimal pH range for maximum efficacy is 6.5–7.5)

Yes

Low

Alcohol (70%)

  • ineffective in the presence of organic matter

  • alcohol will evaporate if not kept in a closed container, which will reduce efficacy

No

Low

Hydrogen Peroxide

  • efficacy reduced by organic matter

  • degrades in sunlight

Moderate

Low

Quaternary ammonium

  • hard water (>400 ppm Ca) reduces efficacy

No

Good

Table 2. 

Chemicals approved for use in citrus nurseries for Phytophthora*.

Fungicide1

Mode of Action

(MOA)

Restricted Entry Interval

(REI)

Postharvest Interval

(PHI)

Rate

Application Method

Resistance Management

Adorn

Group 43

6 days for thinning, pruning, and pinching

365 days

1-4 fl oz/100 gal

Foliar; drench

Tank mix with another registered fungicide with different mode of action; no more than 2 applications per cropping cycle; do not apply sequentially, alternate with another fungicide registered for citrus nurseries.

Oxiphos (O), Prophyt (P), Reveille (R)

Group 33

0 hours for non-spraying application in enclosed structures (O) 4 hours (P,R)

0 days

0.5-1.0 gal/100 gal (O); 2 gal/100 gal (P, R)

Drench (O,P,R);

drip irrigation (P,R)

Apply prior to appearance of disease or as disease is first observed. Initiate when environmental conditions are favorable for disease. Do not combine with other products.

Revus**

Group 40

4 hours

365 days

8-16 fl oz/100 gal

Drench

To be used preventively.

Maximum of four applications during one calendar season.

* Mefenoxam and metalaxyl do not have a label for nursery use and should never be used in nurseries.

**For use in container production in nurseries and prior to transplanting.

Table 3. 

Personal protective equipment (PPE) reference guide for citrus nursery fungicides (applicators and other handlers).

Fungicide1

Long-sleeved shirt and long pants

Chemical-resistant gloves

Shoes and socks

Comments

Adorn

Yes

Yes

Yes

Chemical-resistant gloves made of any waterproof material such as natural rubber > 14 mils.

Revus

Yes

N/R

Yes

For early entry, PPE requirements are coveralls, chemical-resistant gloves made of any waterproof material, and shoes plus socks.

Oxiphos, Prophyt, Reveille

Yes

Yes

Yes

For early entry, PPE requirements are coveralls, chemical-resistant gloves made of any waterproof material, and shoes plus socks.

1All listed pesticides are registered and trademarked products

Refer to label for additional information. This guide does not supersede the label. The label is the law!

Footnotes

1.

This document is PP322, one of a series of the Plant Pathology Department, UF/IFAS Extension. Original publication date January 2016. Visit the EDIS website at http://edis.ifas.ufl.edu.

2.

Megan M. Dewdney, associate professor, Plant Pathology; and Jamie D. Burrow, coordinator for canker, HLB, and Exotic Disease Extension Education, UF/IFAS Citrus Research and Education Center; Lake Alfred, FL 33850.


The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.