Title: Melanose and phomopsis stem-end rot of citrus
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00066890/00001
 Material Information
Title: Melanose and phomopsis stem-end rot of citrus
Series Title: Plant Pathology Fact Sheet PP-26
Physical Description: Book
Language: English
Creator: Kucharek, Tom
Whiteside, Jack
Brown, Eldon
Affiliation: University of Florida -- Florida Cooperative Extension Service -- Department of Plant Pathology -- Institute of Food and Agricultural Sciences
Publisher: Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida
Publication Date: 1983
Spatial Coverage: North America -- United States of America -- Florida
 Record Information
Bibliographic ID: UF00066890
Volume ID: VID00001
Source Institution: Marston Science Library, George A. Smathers Libraries, University of Florida
Holding Location: Florida Agricultural Experiment Station, Florida Cooperative Extension Service, Florida Department of Agriculture and Consumer Services, and the Engineering and Industrial Experiment Station; Institute for Food and Agricultural Services (IFAS), University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 51340701

Table of Contents
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Full Text

Plant Pathology Fact Sheet

Melanose and Phomopsis Stem-End Rot of

Tom Kucharek, Jack Whiteside, and Eldon Brown, Professor and Extension Plant
Pathologist, Plant Pathology Department; Professor Emeritus and Plant Patholo-
gist, Citrus REC Lake Alfred; and Adjunct Professor (Retired), Citrus REC -
Lake Alfred; respectively, University of Florida. 1983. Revised January 2000.
Florida Cooperative Extension Service/ Institute of Food and Agricultural Sciences/ University of Florida/ Christine Waddill, Dean


The fungus Diaporthe citri causes
melanose and stem-end rot. The superficial
blemish on fruit associated with melanose cre-
ates a cosmetic problem on fruit intended for
the fresh market. Juice quality and quantity are
not affected. Stem-end rot of fruit occurs 10-20
days after harvest during storage or transit most
commonly in the latter part of the harvest sea-
son (Jan. -June). Because fruit intended for pro-
cessing are usually not held for more than one
week, stem-end rot is of little consequence on
fruit for processing. Melanose and stem-end rot
are of consequence only for fresh market cit-

The fungus Diaporthe citri produces
spores called ascospores (sexually produced)
and pycnidiospores asexuallyy produced). This
latter spore type is the part of the life cycle that
provides most of the inoculum for disease and
often is referred to as Phomopsis citri. Ascospores
are formed within a vesicle-like structure on
decaying wood on the soil or on dead branches
remaining on the tree or in brush sites. These
spores are produced in relatively small num-
bers and contribute slightly to disease poten-
tial within a grove. Their main contribution to
disease development relates to spread of the
fungus over long distances because ascospores
are windborne.

Pycnidiospores, on the other hand, are
produced abundantly on dead branches within
a flask-shaped structure (pycnidium). Because
they are released within a mucilage, they pro-
vide for short distance spread within a tree or
from one tree to an adjacent tree by rain or irri-
gation splash. Even more restricted movement
of these spores can occur by rain or irrigation
water washing over infected branches and drip-
ping onto leaves, fruits and twigs below, carry-
ing the spores in a passive fashion. Nursery
trees could be infected with the melanose fun-
gus and carry inoculum to the new site. Spores
of this fungus are produced on dead wood only,
not on melanose pustules found on leaves, fruit,
or live branch tissue. Therefore, freeze-dam-
aged citrus trees, older groves, and poorly
maintained groves with much dead wood
should be considered high melanose incidence
areas. All types of citrus are susceptible. Other
hosts for this fungus have not been identified.

Leaves become resistant to infection
once they are fully expanded. Fruit rind be-
comes resistant about 12 weeks after petal fall,
but the later infection occurs during that 12
week period the smaller will be the resulting
pustules. Thus, even though suitable weather
conditions exist for infection after late June,
melanose will not infect the fruit rind after that
time except in years when the bloom is later
than normal.

Temperature and moisture conditions during


periods of leaf expansion and during the first
12 weeks after petal fall regulate disease sever-
ity. After a spore lands on susceptible tissue, a
period of 10-12 hours of moisture is required
for infection at 77F (250C) while at 590F (150C),
18 to 24 hours of wetness are necessary for in-
fection. Thus, extended wet periods resulting
from afternoon rain showers plus dew periods
in May and June coupled with warmer tempera-
tures during these months create favorable
weather for infection. In contrast, rainfall prior
to May in central and south Florida is associ-
ated with fast-moving cold fronts that are
quickly followed by temperatures less favor-
able (too cool) for infection. Also, winds behind
the front quickly dry surface moisture on plant
tissue. At temperatures between 75-82F (24-
280C) initial symptoms can occur 4 to 7 days
after infection.

When temperature and moisture are
considered in relation to rind susceptibility,
May and June are normally high-hazard months
for melanose infection. Occasionally, March or
April can support favorable weather for
melanose infection. The shoots of the spring
growth flush usually emerge in March during
unfavorable weather for infection. Should a late
bloom occur, fruit remain susceptible into July,
a month that can be expected to be a highhazard
period because of favorable weather.


Leaf symptoms begin as tiny
watersoaked specks that become depressed in
the center with a surrounding translucent, yel-
low area that is not depressed (Fig 1). Later, the
leaf cuticle ruptures and a gummy substance
is exuded which turns brown and hardens (Fig.
2). The yellowish margin disappears and the
hardened gummed areas will have a sandpa-
per-like feel. Infected areas on the leaf may be
scattered, aggregated or in streaks, depending
on where water transported the spores prior to
infection. Heavily infected leaves become pale
green to yellow, can be distorted in shape (Fig.

3), and may fall from the tree. Melanose is sel-
dom severe on the spring growth flush. When
it does occur on this flush, the pustules are usu-
ally few in number and little or no leaf drop
occurs. On the summer growth flushes,
melanose can be severe enough to cause seri-
ous defoliation, particularly in years following
freeze-induced twig dieback.

Fruit symptoms are of two types. The
melanose symptom occurs in the field.
Melanose symptoms on fruit are similar to
those found on leaves, but there is a greater ten-
dency for the diseased areas to be streaked from
the top to the bottom of the fruit with regards
to fruit orientation on the tree (Figs. 4 & 5). Fruit
infected when young may remain small and
abscise prematurely. Late infection produces
small pustules (Fig. 6). If the severity is such
that solid patches of blemish are produced, the
fruit surface can crack producing a roughened
condition sometimes called mudcake melanose
(Fig. 7). Mudcake melanose occurs if infection
takes place soon after petal fall (usually early
April). Melanose on fruit can be distinguished
from rust mite injury by the presence of a rough-
ened surface with melanose and a smooth rind
blemish with rust mite injury. Color is not a
reliable characteristic for distinguishing
melanose from rust mite blemish.

Stem-end rot is the second fruit symp-
tom associated with this disease and it occurs
as a postharvest decay in the fresh market trade
where long-term handling, storing and trans-
porting are involved. Hyphae (growth fila-
ments) of this fungus can be present in necrotic
tissue of the calyx; then, after harvest, penetra-
tion can occur through the abscission area dur-
ing periods of suitable temperatures and mois-
ture. Symptoms usually begin to appear after
10 days. The infected area is soft, tan or brown
(Fig. 8). The internal core of the fruit becomes
infected and turns dark. Later season fruit are
more apt to have stem-end rot than early sea-
son fruit.


Control of melanose and stem-end rot is
necessary for fruit intended for the fresh mar-
ket only. Melanose is best controlled by using
a combination of techniques. Pruning and burn-
ing dead wood will reduce inoculum (spore
supply). Regardless of how conscientiously the
prune and burn technique is carried out, fungi-
cide spraying will still be necessary to produce
blemish-free fruit. Fungicides could be applied
prior to the initiation of spring growth, which
generally occurs in late February. Because no
susceptible tissue (leaf or fruit) is present at this
time, a fungicide applied while trees are dor-
mant must be able to either inhibit spore pro-
duction or inactivate spores that are produced
on dead wood. The fungicide applied during
dormancy must remain stable over time and be
redistributable. These two characteristics will
be beneficial in allowing the fungicide to re-
main toxic to the spores over time and move in
water with the spores. For example, Difolatan
had these characteristics when used at high but
costly rates. Copper fungicides effectively pro-
tect fruit rind tissue from infection as postbloom
sprays but are ineffective as a dormant spray
because they do not reduce spore numbers and
they are not redistributed sufficiently. Benlate
reduces spore reduction to some extent but it
does not redistribute effectively. Also it does
not function as well as a protectant fungicide
against melanose. Resistance to Benlate now
exists in this fungus and thus its effectiveness
of any degree has been lost. Therefore, Benlate
is not adequate for melanose control. For cur-

rent fungicide recommendations obtain a copy
of the Florida Citrus Pest Management Guide

Stem-end rot is reduced by utilizing nu-
merous control measures in the field during
production and during harvest and postharvest
handling periods. Because the calyx of imma-
ture fruit on the tree is also infected during pe-
riods of melanose infection, fungicide sprays
and removal of dead wood (source of spores)
for melanose control will contribute to
Phomopsis stem-end rot control. Such benefi-
cial effects may not show up until the fruit is
harvested (possibly months later) and stored
at cooler temperatures. Warm temperatures
associated with ethylene degreening after har-
vest are more favorable for development of
Diplodia natalensis, the other stem-end rot fun-
gus, than for growth of Phomopsis. Phomopsis
becomes more prevalent than Diplodia later in
the season from January to June when naturally
colored fruit do not require degreening. Also,
the incidence of Phomopsis stem end rot will
increase in fruit grown on older trees where
more inoculum is likely to be present.

In the packinghouse the use of fungi-
cides in a postharvest application are necessary
regardless of prior control measures. Applica-
tion of fungicides with water is superior to the
incorporation of fungicides in the wax.
Throughout harvest and postharvest periods,
fruit should not be handled in a rough fashion.

Figure 1. Early leaf spots of melanose. Figure 2. Pustules of melanose in leaf.

Figure 3. Melanose in grapefruit leaves
associated with source of spores on dead
branches above leaves.

Figure 4. Streaked melanose on grapefruit
caused by spores moving in water down the

Figure 5. Generalized distribution of
melanose on grapefruit when infection
occurs in May or June.

Figure 6. Smaller melanose pustules associ-
ated with infection occurring while fruit rind
is becoming less susceptible.

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Figure 8. Stem-end rotsymptom.

Figure 7. Mudcake melanose.

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