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Publication #PP-145

2014 Florida Citrus Pest Management Guide: Melanose1

M.M. Dewdney and L.W. Timmer2

Control of melanose, caused by the fungus Diaporthe citri, is often necessary in mature groves where fruit is intended for the fresh market, particularly if recently killed twigs and wood are present as a result of freezes or other causes. It is not usually needed in groves less than 10 years old or those where fruit is intended for processing. Grapefruit is very susceptible to melanose but all citrus may be damaged by the disease.

Spores produced by the asexual stage, Phomopsis citri, are the inoculum of this fungus. Diaporthe citri is the sexual stage and is relatively unimportant for the disease. The asexual spores are produced in flask-shaped structures embedded in dead twigs in the tree canopy, especially those twigs that have died within the last several months. In addition to producing spores on melanose-affected twigs after they die, P citri is able to colonize dead twigs that were originally healthy and produce inoculum on those twigs as well. Spores are produced during wet periods and dispersed to young, susceptible leaves and fruit by rain splash. No spores are produced on symptomatic leaves, fruit, or living twigs. At 75–80°F, 10–12 hours of leaf wetness are required for infection and at lower temperatures up to 18–24 hours may be needed.

Grapefruit is susceptible to melanose infection from fruit set until it reaches 2.5–3 inches in diameter, normally in late June or early July. Fungicides are effective for only short periods when applied to rapidly expanding fruit or leaves. Since April is usually a low rainfall month and fruit is small and growing rapidly, the first spray for melanose control is not usually applied until mid- to late April. One or two applications are sufficient for control on oranges and most tangerines, unless the trees have abundant dead wood like in a year after a freeze. For fresh market grapefruit, the first application should be made when the fruit reaches a diameter of 1/4 to 1/2 inch (about mid- to late April depending on local conditions). With average quality copper products, usually about 2 lb./acre of metallic copper are needed for each three-week period. Rates can be decreased if applications are made more frequently or increased if applications are made less often. Additional applications should be made at three-week intervals until the fruit becomes resistant. For melanose control on large trees, no more than 8–12 lb. metallic copper are needed per year even if copper is also used for the control of scab, canker, and/or greasy spot.

Copper residues are reduced with fruit expansion and as a result of rainfall. A model, http://www.agroclimate.org/tools/cudecay/, is available to determine whether residues remaining on fruit are sufficient to control the disease. It is based on fruit growth models, the rate and time of the last application, and rainfall since the last spray. It has proven helpful for timing of sprays for melanose control. Further information about the model is available in EDIS PP289 "A Web-based tool for timing copper applications in Florida citrus."

An early June spray of copper to control late melanose damage will serve as the first greasy-spot spray. However, applications of copper in hot, dry weather may cause fruit spotting or darken existing blemishes. If copper fungicides are applied from May to September, they should be applied when temperatures are moderate (< 94°F), at rates no more than 2 lb. of metallic copper per acre, without petroleum oil, and using spray volumes of at least 125 gal./acre.

The strobilurin-containing fungicides—Abound, Gem, Headline, Pristine or Quadris Top—are also effective for melanose control and can be used at any time for disease control. Copper fungicides are more economical and are most important for melanose control. However, since copper fungicides applied in hot weather can damage fruit, use of strobilurin-containing fungicides at that time will avoid this damage and control greasy spot as well as melanose. Strobilurins appear to have lower residual activity for melanose control than do copper fungicides. Thus, applications may have to be made at shorter intervals, especially when rainfall is high.

Fungi may develop resistance to strobilurin fungicides. These materials should never be used more than twice in a row, and no more than two strobilurin applications should be used for melanose control.

Recommended Chemical Controls

READ THE LABEL.

See Table 1.

Rates for pesticides are given as the maximum amount required to treat mature citrus trees unless otherwise noted. To treat smaller trees with commercial application equipment including handguns, mix the per acre rate for mature trees in 125 gallons of water. Calibrate and arrange nozzles to deliver thorough distribution and treat as many acres as this volume of spray allows.

Tables

Table 1. 

Recommended Chemical Controls for Melanose

Pesticide

FRAC

MOA2

Mature Trees

Rate/Acre1

copper fungicide

M1

Use label rate.

Abound3

11

12.0–15.5 fl. oz. Do not apply more than 92.3 fl. oz. (1.5 lb. a.i.)/acre/season for all uses.

Gem 500 SC3

11

1.9–3.8 fl. oz. Do not apply more than 15.2 fl. oz./acre/season for all uses. Do not apply within 7 days of harvest.

Headline SC3

11

12–15 fl. oz. Do not apply more than 54 fl. oz. (0.88 lb. a.i.)/acre/season for all uses.

Pristine3

11/7

16–18.5 oz. Do not apply more than 74 oz./acre/season for all uses.

Quadris Top3

11/3

15.4 fl. oz. Do not apply more than 61.5 fl. oz./acre/season for all uses. Do not apply more than 0.5 lb. a.i./acre/season difenoconazole. Do not apply more than 1.5 lb. a.i./acre/season azoxystrobin.

1Lower rates can be used on smaller trees. Do not use less than the minimum label rate.

2Mode of action class for citrus pesticides from the Fungicide Resistance Action Committee (FRAC) 2013. Refer to ENY624, Pesticide Resistance and Resistance Management, in the 2014 Florida Citrus Pest Management Guide for more details.

3Do not use more than 4 applications of strobilurin-containing fungicides/season. Do not make more than 2 sequential applications of strobilurin fungicides.

Footnotes

1.

This document is PP-145, one of a series of the Plant Pathology Department, UF/IFAS Extension. Original publication date December 1999. Revised January 2014. Visit the EDIS website at http://edis.ifas.ufl.edu.

2.

M.M. Dewdney, assistant professor; and L.W. Timmer, professor emeritus, Plant Pathology Department, Citrus REC, Lake Alfred, Florida; UF/IFAS Extension, University of Florida, Gainesville, FL 32611.

The use of trade names in this publication is solely for the purpose of providing specific information. It is not a guarantee or warranty of the products named, and does not signify that they are approved to the exclusion of others of suitable composition.


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.