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 Introduction
 Sequential disease control program...
 Table 1: Habitats of organisms...
 Table 2: Foliar fungicides for...






Group Title: Extension plant pathology reports
Title: Disease control program for watermelon
CITATION PAGE IMAGE ZOOMABLE PAGE TEXT
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00066914/00001
 Material Information
Title: Disease control program for watermelon
Series Title: Extension Plant Pathology Report 15
Physical Description: Book
Language: English
Creator: Kucharek, Tom
Roberts, Pam
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: 2005
 Subjects
Spatial Coverage: North America -- United States of America -- Florida
 Notes
Funding: Florida Historical Agriculture and Rural Life
 Record Information
Bibliographic ID: UF00066914
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.

Table of Contents
    Introduction
        Page 1
        Page 2
    Sequential disease control program for watermelons
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
    Table 1: Habitats of organisms causing plant diseases in watermelon
        Page 10
        Page 11
    Table 2: Foliar fungicides for watermelon diseases
        Page 12
        Page 13
        Page 14
Full Text






~c~T~


Watermelons are grown on a commercial basis in many of Florida's 67 counties.
Moreover, the geographical distribution of watermelon plantings is such that plantings exist
from the Naples-Immokalee area all the way up the peninsula and west through the panhandle.
Because of the northward, continual succession of watermelon plantings in Florida plus
Florida's moist, warm climate, an ideal situation for plant disease development in watermelons
has been created. Moreover, because of natural climatic differences between southern
watermelon areas and our northern watermelon areas, differences in plant disease intensity
exist within the state. Differences exist in degree of vigor incorporated in the disease control
programs by growers in different areas within the state. Disease control efforts have also
interacted with market prices typical of an area. For example, southern growers normally get
higher prices because of early marketing but without these higher prices they could not afford
to practice the intensive disease control program necessary for that area. Northern growers, on
the other hand, usually get lower prices for melons because of market conditions but,
fortunately, they do not need as intensive of a spray program as do the growers in south
Florida.

Summer-planted watermelons that are harvested in the fall will require the best possible
disease control program.

Watermelon diseases reduce yields and monetary returns. They do so by retarding
desirable plant development and by detracting from buyer appeal or preference. Most
watermelon diseases are obvious but some, such as rind necrosis, may not be obvious until
buyer's begin to inspect fruit. Post harvest rots in transit can occur but in recent years losses of
this type presumably have been minor in relation to field diseases.

Watermelon diseases are caused by fungi, bacteria or viruses. Fungi cause most diseases
that occur in watermelons in Florida but diseases caused by viruses can cause equal
devastation.

FUNGI are organisms that have no true roots, leaves, stems or chlorophyll. Instead,
they have hyphae (microscopic threads) of various types which can grow in the soil or in a host
plant. These threads absorb food from the plant or organic material in the soil. Fungi can not
make certain necessary food materials, so they must live on food products manufactured by
other organisms. Fungi reproduce by various methods. They produce different types of spores
(microscopic seeds). Some spores are spread by air currents and others by contact or rain
splash. Fungi that cause leaf spots, downy mildew and gummy stem blight produce hundreds


1


EXTENSION PLANT PATHOLOGY REPORT NO. 15
GAINESVILLE, FLORIDA JANUARY, 2005
REVISION 20

DISEASE CONTROL PROGRAM FOR WATERMELON
by Tom Kucharek and Pam Roberts

Introduction









and even thousands of these spores in one spot on a leaf or stem.


Many of the fungi causing seedling blights, root rots, wilts and certain fruit rots produce
"heavy duty" spores (resting spores) that are able to survive in the soil for many years. Fusarium
spp. produce chlamydospores and Pythium spp. produce oospores. This situation plus the lack
of convenient and economical fungicides for use in the soil make it difficult to control this group
of soilborne fungi. Other fungi produce visible resting structures called sclerotia. Southern
stem rot, caused by Sclerotium rolfsii, produces mustard seed-sized sclerotia. Many diseases can
be controlled over a period of time by using crop rotation because even heavy duty spores and
sclerotia are diminished in number by other microorganisms and certain environmental
conditions in the soil over time.

As you might expect, a longer interval, in years, between watermelon plantings on the same
land is more effective for disease control than a shorter interval.

When pathogenic fungi come into contact with a watermelon plant, they grow on it and
eventually enter the plant. Some penetrate directly, while others gain entrance only when an
opening or a wound is present. Plants have natural openings through which fungi can grow
into the plant.

BACTERIA are microscopic one-celled organisms which increase by division. Bacteria
enter plants only through wounds or natural plant openings. Currently, angular leaf spot,
bacterial fruit blotch, a foliar disease with a fruit rot phase, rind necrosis, and a soft rot of fruit,
are the watermelon diseases caused by bacteria in Florida. None of these bacterial diseases are
common in Florida, but bacterial fruit blotch was devastating in some fields from 1989 through
1996. In 2000, bacterial fruit blotch occurred in commercially produced cantaloupe in Florida.

Most VIRUSES are particles composed by a nucleic acid core and a protein coat. No cellular
structure is present and viruses reproduce in living cells only. Viruses are so small they can not
be seen with the best light microscopes; an electron microscope is necessary to visualize these
particles. At the present time, papaya ring spot virus type W (PRSV-W), watermelon mosaic
virus 2 (WMV 2), and zucchini yellow mosaic virus (ZYMV) occur in watermelon, cantaloupe,
and other cucurbits in Florida. PRSV-W, formerly known as watermelon mosaic virus one,
predominates in south Florida and is found in wild cucurbits such as the wild balsam apple and
creeping cucumber. WMV-2, which predominates in central and northern Florida, can occur in
160 different hosts (e.g. Hibiscus, lupine, showy crotalaria, alfalfa, citron, hairy indigo, clovers)
but none have been demonstrated to be associated with epidemics or occurrences of WMV-2 in
Florida. Zucchini yellow mosaic virus (ZYMV) also occurs in watermelon and squash in
Florida. Aphids are the main vectors for transmitting PRSV-W, WMV-2, and ZYMV. Tomato
spotted wilt virus was found in watermelon in one field in 1987. It is transmitted by thrips.

A SUMMARY OF WATERMELON DISEASE-CAUSING ORGANISMS AND THEIR
HABITATS ARE PRESENTED IN TABLE 1.

With the basic information at hand, it becomes understandable that no one control measure
will be totally effective in controlling all watermelon diseases. Instead, a coordinated sequential
program of several methods should be used.


2











SEQUENTIAL DISEASE CONTROL PROGRAM FOR WATERMELONS


Before Planting

STEP 1. CROP ROTATION.

The use of new land had been the backbone for production of watermelons in many areas of
Florida and it is effective in reducing plant diseases. However, land availability has become
critical in Florida because of urban sprawl and land use programs directed by governmental
programs. As a grower you must begin a rotation plan now. Crop rotation is more essential
now than ever before. An interval of no less than 4-5 years or more between watermelon crops
is best even if varieties resistant to Fusarium wilt are used. Moreover, crop rotation plans
should be incorporated in your farm plans as a routine and not as a result of necessity. Never
plant watermelons on the same land two years in a row. In general, it is best to rotate grass
crops such as corn, pasture grasses, etc. with watermelons. Root-infecting diseases, such as
Fusarium wilt and Phytophthora blight, are the general targets for crop rotation but crop
rotation will minimize exposure of a crop to inocula of leaf- and stem-infecting fungi causing
gummy stem blight, anthracnose, and leaf spots.

STEP 2. SITE SELECTION.

When preparing a rotation plan for your farm, consider planting watermelons as far away as
possible from fields of squash, cucumbers, and other cucurbits because these crops are
susceptible to some of the same diseases (Table 1). For example, the major viral diseases of
watermelon occur commonly in squash in Florida. Phytophthora blight occurs in other
cucurbits, tomatoes, peppers, and eggplant and thus, locating watermelon plantings away from
these other crops may aid in the minimization of exposure to inoculum from this pathogen.
Spores of Phytophthora capsici can be spread by water movement from one field to another or
wind-borne rain. Phytophthora blight has been an increasing problem in Florida and other
areas in the United States, particularly during seasons with above average rainfall or irrigation.
For these reasons, watermelons should be planted on well drained land that minimizes
standing water during intense periods.

If aerial applications of chemicals are to be used, it is best to select fields that are void of
power lines and trees. Aerially sprayed fields should be away from residential dwellings and
areas where people gather. Aerial applicators will not deposit spray on watermelons next to
hazards for the pilots. Fungicides perform best when spore numbers are minimized throughout
the vicinity.

The incidence of watermelon mosaic virus 2 has tended to be less in large fields when
compared to small fields.


3








STEP 3. DEEP PLOWING.


Deep plowing refers to the use of bottom plows and not discs. Burial of plant debris is an
effective disease control measure and within a geographical area, the more farmers that use this
practice the more effective it becomes for every one. Primary inoculum (early season) for
gummy stem blight survives on debris of previously infected crops. Ascospores are ejected into
wind currents which can carry them from one field to another. If plant debris with inoculum is
buried, primary inoculum is reduced.

Deep plowing is effective in reducing other diseases such as southern blight and leaf spots
because burial of these organisms, as opposed to leaving them on the surface, places them in
competition with soil organisms and mechanically inhibits their movement.

STEP 4. WEED CONTROL.

Two phases of weed control should be considered in relation to plant disease control for
watermelons. First, eliminate weeds such as citron, balsam apple, creeping cucumber and
volunteer cucurbits near watermelon fields because they harbor organisms that cause
watermelon diseases (Table 1). This is especially important for reducing papaya ring spot in
southern Florida, where wild balsam apple and creeping cucumber are the known wild hosts
this virus. Citron is a host plant for the bacterial fruit blotch bacterium. Solanaceous weeds
such as nightshades are likely hosts for Phythopthora capsici, the causal agent of Phytophthora
blight. It is understood that elimination of these weeds may be impossible but attempts in this
direction will reduce disease problems.

The second phase is overall control of weeds within the field themselves. Besides weeds
causing direct losses in yield, their presence aids in moisture retention on leaves and stems
which gives fungi a distinct advantage because moisture is necessary for spore germination.
Also, the presence of weeds interferes with deposition of fungicides on watermelon leaves and
stems.

STEP 5. USE DISEASE RESISTANT VARIETIES.

Fusarium wilt is a major limiting factor for watermelon production in Florida. As a result,
you should use a variety resistant to this disease. Up to recent years, nearly all contemporary
varieties have had some degree of resistance to Fusarium wilt and anthracnose. However,
many of the contemporary seedless varieties do not appear to have an adequate level of
resistance to Fusarium wilt. More Fusarium wilt has occurred in Florida with the advent of
intense plantings of seedless varieties.

It should be understood that resistance to these diseases is not complete; some plants within
a population are susceptible. Crimson sweet has had the least amount of Fusarium wilt
compared to other varieties when planted on the same Fusarium wilt-infested land after four or
more years of continuous cropping. Commercially usable resistance to downy mildew, gummy
stem blight, Phytophthora blight, or the viral diseases is not available. Crimson sweet has been
quite susceptible to rind necrosis (internal rind discoloration). Dark-skinned watermelons and
dark tissues in striped melons are less susceptible to bacterial fruit blotch than lighter-skinned
types.


4









STEP 6. PURCHASE SEEDS THAT HAVE BEEN INDEXED FREE OF INOCULUM FOR
BACTERIAL FRUIT BLOTCH.

The bacterium, Acidovorax avenae subsp. citrulli that causes bacterial fruit blotch can be
seedborne. However, most seed companies are indexing seed with either seedling grow outs or
PCR (polymerase chain reaction) techniques.

STEP 7. SEED AND SEEDLING PROTECTION.

Use of transplants minimizes seedling blight in the field.

For direct seeding, seed treatment increases the original stand by partially protecting seeds
and young seedlings from decay caused by fungi. Most seed treatment materials used on
watermelon are not systemic and their period of protection should not be expected to extend
beyond emergence. Ridomil Gold EC may be applied as a 7 to 12" band along the row center at
seeding. Use a rate of 1-2 pints/treated acre, respectively. This treatment will reduce Pythium
seedling blight.

When watermelon seed are planted in cool soils, you can expect a higher incidence of
seedling blight. Slow emerging seedlings are more likely to be infected by pathogenic fungi
(e.g. Rhizoctonia solani, Pythium, spp. etc.) than fast emerging seedlings.

CAUTION: DO NOT FEED TREATED SEED TO MAN OR BEAST UNDER ANY
CIRCUMSTANCES.

STEP 8. HEALTHY TRANSPLANTS.

If transplants are used, purchase or grow disease-free plants. Producers in Florida should
purchase plants from within Florida that are inspected by the Division of Plant Industry. Plant
production systems should not be near production fields. Avoid exposure of plants to
production fields (past or present) during transit by using covers on transport vehicles. See
Plant Protection Pointer No. 25 for details on producing healthy transplants. Also, avoid deep
setting of plants during the transplant operation. The transplants you purchase should be
inspected and issued a phytosanitary certificate before acceptance. Even though the transplants
you purchase or grow may have been inspected, you should examine each flat for defective
plants. Do not use plants in transplant trays that have infected or suspect plants. Transplants
are susceptible to ALL diseases mentioned in this publication and have been the source of
inoculum for Phytophthora blight, gummy stem blight, downy mildew, and others.

STEP 9. PROPER PLANTING DEPTH AND FIELD PLAN.

Planting excessively deep will offset benefits from seed treatments. The longer it takes for a
seedling to emerge, the longer the entire plant is exposed to soil-borne fungi. The
recommended planting depth is 1/2 to 2 inches depending upon soil surface moisture levels.

If a ground sprayer (airblast or hydraulic) is to be used, allow enough space in alleys to
accommodate tractor and spray equipment. Alleys will be of benefit during harvest operations.
Distance between alleys should be established based on the spray swath of either the airblast
distance or boom width.


5








After Planting

STEP 10. USE DRIP IRRIGATION

Drip irrigation will minimize spread of certain diseases compared to overhead irrigation.
Spread of bacterial fruit blotch and gummy stem blight are likely to be less severe with drip
irrigation compared to overhead irrigation. Also, minimization of leaf wetness with drip
irrigation, compared to overhead irrigation, will aid in suppressing Phytophthora blight and
other diseases during periods that have low to modest rainfall.


STEP 11. OBSERVATION.

Periodically walk through representative portions and low and wet areas of your fields looking
for disease. Don't wait until you can see diseased plants through a windshield. The county
agent can help you identify diseases. The best time to attempt diagnoses of bacterial fruit blotch
is on seedlings in the transplant house or in the field.

STEP 12. WORK IN FIELDS WHEN THEY ARE DRY.

Working in wet fields is likely to spread certain plant pathogens (e.g. gummy stem blight,
bacterial fruit blotch, Phytophthora blight). Also, teach workers about sanitation and how it can
minimize movement of pathogens from one field to another or one area of a field to another.

STEP 13. DELAYED THINNING.

Delay thinning in direct-seeded fields to the extent possible so that you cull more of the
plants susceptible to Fusarium wilt.

STEP 14. FOLIAR APPLICATIONS OF FUNGICIDES.

Materials.

This control measure is directed at downy mildew, gummy stem blight, anthracnose,
Cercospora leaf spot, Alternaria leaf spot, Phytophthora blight, and bacterial fruit blotch.
Fungicides and rates for controlling these diseases are listed in Table 2. All foliar fungicides
used on watermelons need constant agitation in the tank to keep them in suspension. Bacterial
leaf spots, if they appear, can be controlled by using a copper fungicide (e.g. Champ,
Champion, Basicop, Kocide 101). Copper fungicides can stunt or burn watermelon foliage;
thus, use a copper fungicide only when needed. Bacterial fruit blotch can be reduced by use of
copper sprays. If a spray program for bacterial fruit blotch is needed, it should begin at first
flower or earlier and continue till fruit have a thick, waxy cuticle. Use copper fungicides at the
highest labeled rate on a biweekly interval or at one half the highest rate on a weekly interval
(see Table 2). Bacterial fruit blotch has not been a problem in Florida in the past few years. It
occurred sporadically from 1989 till 1996.

Initiation of spray program for fungal diseases.

Fungicides act as protectants primarily; that is, they protect the plant from infection. Except
for Ridomil/Bravo 81W and Ridomil MZ which are effective for downy mildew control,
fungicides are not highly therapeutic. If fungicide sprays are delayed until disease severity is


6








visible through a windshield of a car or pickup truck, it is difficult to minimize diseases such as
Phytophthora blight, downy mildew or gummy stem blight. These diseases will begin as just a
few spots on the leaves or stems but after a period of time their severity increases rapidly. If
your spray program begins after the appearance of disease with a non-therapeutic fungicide,
you can expect an increase of visible disease up to 7-10 days later because of infections already
present.

Because of the differences in climate and disease severity within the state of Florida, no one
spray schedule or plant can be suggested. Rather it may be more practical to divide the state
into areas and offer suggestions based on data and experiences from those areas. Four areas are
designated:

Area I Immokalee Naples

Area II Leesburg Wildwood Ocala

Area III Levy, Alachua and Gilchrist Counties

Area IV North Florida (Including the Panhandle)

Generally, disease intensity is greatest in Area I and least in Area IV, with areas II and III
being intermediate.

In Area I, downy mildew and other diseases can occur throughout the year on crops,
weeds and volunteer plants in the field and ditch banks. If a freeze does not destroy these
plants, inocula (spores) are present all year. Gummy stem blight also produces, inocula on old
vines when allowed to remain on the soil surface. Area I, then, should be on a continual alert
from emergence through harvest every year. It may become necessary to spray twice each
week to maintain spray on new foliage. When temperatures drop below 60 F and dew periods
are reduced, weekly spray schedules may be adequate because the rate of disease progress
decreases and plant growth is reduced. Generally, downy mildew and gummy stem blight
appear to be most intense from February to harvest in this area but control is difficult while
either disease is ravaging a crop. Rather, control is most effective when the level of disease is
maintained at a low level with a full-season spray program.

In Area II, downy mildew and gummy stem blight are potentially devastating every year,
but some years they may not be a problem. For example, between 1931 and 1959 either gummy
stem blight or downy mildew occurred in epidemic proportions in 16 out of the 29 years within
Area II. The following factors are known to be conducive of gummy stem blight and downy
mildew:
1. Mild or "warm" winters;
2. Above average rainfall from February to June;
3. Short or no crop rotation plans;
4. Failure to bury old vine debris and volunteers
after harvest (even in other fields);
5. Use of infected transplants;
6. Starting spray program late.

In Area II, growers should monitor their fields closely after emergence for symptoms of
disease. Proper identifications should be made promptly and if downy mildew or gummy stem
blight appears, spray programs should be started immediately. If downy mildew occurs in


7








your area, even if in someone elses field, start spraying immediately. Downy mildew
increases fast and knows no boundaries. Spraying watermelons with non-therapeutic
fungicides or therapeutic fungicides (eg. Ridomil/Bravo 81W or Ridomil MZ prior to the first
appearance of downy mildew in your field will be most effective.

In Area III, growers should keep in touch with county Extension personnel about the
occurrence of these diseases in their area. The same guidelines are true for Area III as well as
Area II. Generally, downy mildew will not be a problem in Area III if it is not a problem in
Area II that same year as this pathogen moves up the peninsula. For example, downy mildew
has been significant in 2 out of 6 watermelon seasons (1970-1975) in this area. Sometimes,
downy mildew is introduced into Areas II and III early in the season with infected transplants.
In such situations, earlier and extremely intense spray programs are required to minimize
disease progress. Gummy stem blight can occur in any area every year. Powdery mildew has
recently become a major problem in this area on watermelons.

In Area IV, the need for spraying is reduced if proper rotations and debris burial are
carried out. Within Area IV downy mildew has been epidemic in one of six seasons; (e.g. 1970-
1975) but gummy stem blight has occurred within this area in most seasons. Like Area III,
powdery mildew has become a major problem in recent years. Growers in Area IV should
maintain constant contact with county extension staff about the occurrence of watermelon
diseases in their area as well as Area III. Suspicious-looking disorders in watermelon plants
should be properly and promptly identified. Profit margins in this area are the least of all areas
and thus spraying should be done only when needed.

It is imperative that watermelon diseases are diagnosed early in all areas. Identification
of watermelon diseases can be made by:
1. Local County Extension staff
2. Agricultural Research Centers
3. Plant Disease Clinics.
4. Some consulting organizations.

Spray intervals.

Once a spray program has been initiated, subsequent applications should be no longer
than 7 days apart. The addition of a spreader-sticker will aid in holding some wettable powder
fungicides on the leaves and stems during rains, but they are not recommended for liquid
formulations.

Application of fungicides.

Fungicide sprays may be applied by ground equipment or by aircraft. Ground
equipment includes boom sprayers (hydraulic sprayers) or air assist sprayers.

With respect to equipment, little data, if any, has been developed to prove one type being
definitely better than another. All methods have been effective and each method has
advantages and disadvantages depending on various considerations.

Advantages of ground equipment:

1. Coverage of foliage is good when adequate gallonage and proper nozzle
arrangements are used.


8









2. Small fields and fields bordered by trees and power lines are most accessible by
ground equipment.
3. Especially with boom equipment, there is less drift of the spray away from the
target.









Advantages of aerial application:

1. No soil compaction or plant damage by equipment occurs.
2. Applications can be made over the entire acreage when needed, even if the field is
too wet for ground equipment.
3. Growers have less handling tasks.
4. Fewer hours of labor are required by the grower's enterprise to operate and
maintain equipment.

The cost of using aerial application versus ground equipment is dependent upon the
acreage involved, cost of maintaining equipment, labor costs (if any) and life expectancy of
equipment. The grower should consider all these factors in relation to his own enterprise.

When using boom equipment, align the nozzles so that the spray pattern of each nozzle
slightly overlaps the adjacent pattern at the top of the foliage canopy. Complete coverage
along a band 4' wide, along the row center, is imperative for best control of gummy stem
blight. Penetration of foliage and leaf coverage is best with this type of spray pattern. Consult
with an equipment dealer on what sizes of nozzles are needed for various gallonage-pressure
combinations at a given tractor speed. Direct nozzles of boom sprayers to cover the foliage not
the soil.

When using airblast sprayers, don't try to stretch the distance between swaths. Adjust
nozzles to deliver an even distribution across the canopy. Consult the equipment manual for
determining the capability of your machine. Remember to do this before planting so alley
distances can be established prior to planting.

Minimum days to harvest after fungicide use.
Fungicides vary as to the time interval after their use on watermelonbefore harvests are
allowed. Intervals vary from 0-7 days; therefore, check each label for this information.

STEP 15. PLOW DOWN OLD DEBRIS AFTER HARVEST.

Debris allowed to remain on the soil surface will serve as a source of inoculum for
gummy stem blight for next years crop even for surrounding fields. Therefore, bury old debris
after harvest as soon as possible. This may seem to be an uncomfortable and an unnecessary
step but the fact remains that it does reduce primary inocula for gummy stem blight and other
watermelon diseases for the following crops.


9






Table 1. Habitats of organisms causing plant diseases in watermelon.


MOVED
PATHOGEN CARRIED IN SURVIVES IN SURVIVES TRANSMITTED MOVED SOME OTHER
ORGANISM DISEASES BY WIND
ORGANISM DISEASES TYPE OR ON SEED SOIL IN WEEDS BY INSECTS HOST PLANTS
OR RAIN

Pythium spp. Seedling blight, Fungus 1 ++ + +/- Most other crops
fruit rot

Rhizoctonia spp. Seedling blight Fungus ++ + +/- Most other crops

Fusarium oxysporum f sp Fusaumwil Fungus Citron, balsam
Fusarium wilt Fungus ++ + ? s
niveum apple, squash

Cantaloupe,
Squash, pumpkin,
Didymella bryoniae G stem Fungus + ++ + + + citron, cucumber,
t chayote, balsam
apple

Cantaloupe,
Psuedoperonospora Cantaloupe,
cubensis2 Downy mildew Fungus + + cucumber, squash,
pumpkin, citron2

Colletotrichum lagenarium Anthracnose Fungus ++ ++ + + + S
mildew

Alternaria leaf Cantaloupe,
Alternaria cucumerina Alternaria leaf Fungus ++ ++ ++ + Cantaloupe,
spot squash, cucumber

Cantaloupe,
Cercospora citruina Cercospora leaf Fun ++ ++ + cucumber, squash,
Cercospora citrullina Fungus ++ ++ +
spot pumpkin, chayote,
balsam apple

Pepper, squash,
eggplant,
t r, l cucumber, tomato,
Fruit rot, leaf
Phytophthora capsiciit, st rot Fungus ? ++ + + papaya,
blight, stem rot cnl
cantaloupe,
marigold,
pumpkin, others

Sclerotium rolfsii Stem rot, fruit rot Fungus ++ + Many non-grass
plants

Sphaerotheca sp. continued Powdery mildew Fungus ? ? + Other cucurbits


10







MOVED
PATHOGEN CARRIED IN SURVIVES IN SURVIVES TRANSMITTED MOVED SOME OTHER
ORGANISM DISEASES BY WIND
ORGANISM DISEASES TYPE OR ON SEED SOIL IN WEEDS BY INSECTS W HOST PLANTS
OR RAIN

Pseudomonas lachrymans Cantaloupe,
Angular leaf spot, Bacterium ++ + squash, cucumber,
fruit rot citron, creeping
Table 1 continued cucumber


Citron, squash,
Fruit blotch, leaf Citron, squash,
Acidovorax avenue subsp. Fruit blotch, lf honeydews,
citrulli spot, seedling Bacterium ++ ++ +
citrulli blight cantaloupe, and
blight others
others

Erwinia spp. & others? Rind necrosis Bacterium ? ? ? ? ? ?

Cantaloupe,
cucumber,
Papaya ringspot virus type Leaf and fruit ++ pumpkin, creeping
W t,,i. tIlle ,., ,.,,,,..,, Virus ++
mosaic virus ) mosaics aphids cucumber, balsam
mosaic virus 1)
apple, citron,
squash

Cantaloupe,
pumpkin,
cucumber, citron,
n m v 2 Leaf and fruit ++ hibiscus, lupines,
Watermelon mosaic virus 2 Virus ++
mosaics aphids squash crotalaria,
hairy indigo,
clovers, alfalfa, &
others

Zucchini yellow mosaic Leaf and fruit ++ Cantaloupe,
rLeaf and fruit s++
virus Virus ?- ? squash, cucumber,
mosaics aphids pumpkin
pumpkin

Tomato spotted wilt virus4 Leaf mosaic Virus thrips Many crops &
Leafosaic Virusweeds.
++ weeds.


1 -= not known to occur; + = occurs; ++ = occurs commonly.
2 Often cucurbits other than watermelon will have downy mildew and watermelons will not.
cucurbits.
3 Includes survival on old watermelon debris or volunteers or both.
4 Seen only a couple of times in watermelon in Florida.


The strain of the fungus on watermelon appears to be different than those on other


11










Table 2. Foliar fungicides for watermelon diseases. Alternate fungicide types when possible to enhance resistance management.


Disease
MAXIMUM
RATE/ SEEDLING FUSARIUM DOWNY GUMMY ALTERNARIA CERCOSPORA POWDERY BACTERIAL
FUNGICIDE2 ACRE/ BLIGHT WILT MILDEW STEM BLIGHT ANTHRACNOSE LEAF SPOT LEAF SPOT MILDEW LEAF SPOTS
APPL


Aliette 80 WDG

Cuprofix Disperss 36.9 DF

Equus 720 or Echo 720, 6 FLs 5,
10

Bravo Ultrex 82.5 WDG5,15

Champ Formula 2 4.6 FL or
Kocide 4.5 LF

Dithane F45 or Manex II FLs6

Kocide 101, or Champion 77
WPs

ManKocide 61DF8

Penncozeb, Dithane M-45,
Manzate 80 WPs, or
Dithane, Manzate,
or Penncozeb 75 DFs7

Equus 82.5 or Echo 90 DFs


Ridomil-Bravo 81W4'5

Ridomil MZ WP 4

Topsin M 70WP3

Basicop 53 WP

Acrobat 50 WP17

Kocide 2000 53.8 DF

Champ 57.6 DP

Table 2 continued


5 lbs.

2.5 lbs.

3 pts


2.7 lbs.

1 1/3 pts.


2.4 qts

3.0 lbs.


2.66 lbs.





3 lbs.

2.5 lbs



3 lbs.

2.5 lbs.

2 lbs.

2 lbs

6.4 ozs..

1.5 lbs.

1 1/3 lbs..


01

0

0


0

0


0

0


0





0

0



0

0

0

0

0

0

0


0

0

0


0

0


0

0


0





0

0


+-

+-

++


++

+


++










-H-
++


++





++

++


0 ++


0

0

0

0

0

0


++

0

+

++

+

+


12


0

+-

++


++

+


+

+


+





+

++


+

+

++3

+

0

+

+


0

+

+


+

+


+

+


+





+

+


+

+

+

+

0

+

+


0

+

+


+

+


+

+


+





+

+


+

+

0

+

0

+

+


0

+-

++


++

+


+

+


+





+

++


++

+

+

+

0

+

+


0

0

++


++

0


+

0










-H-
+
+

++


+

+

0

0

0

0

0


0

+

0


0

+


0

+


+





0

0


0

0

0

+

0

+

+











Disease
MAXIMUM
RATE/ SEEDLING FUSARIUM DOWNY GUMMY ALTERNARIA CERCOSPORA POWDERY BACTERIAL
FUNGICIDE2 ACRE/ BLIGHT WILT MILDEW STEM BLIGHT ANTHRACNOSE LEAF SPOT LEAF SPOT MILDEW LEAF SPOTS
APPL

Table 2 continued
Nova 40 W12 5.0 ozs. 0 0 0 0 0 0 0 ++ 0

Pristine 38 WG20 18.5 ozs. 0 0 ++ + + + + 0
+-

Bravo Weatherstiks 1 1/2 -3 pts. 0 0 ++ ++ + + ++ ++ 0
Gavel 75 DF 21bs 0 0 + 0 0 + 0 0 0

Amistar 80 DF 5 oz + 0 ++ ++3 ++ ++ ++ ++ 0
Quadris 2.09 FL 3.2 pts 0 0 + ++3 ++ ++ ++ ++ 0

Cabrio 2.09 FL1 16 fl oz 0 0 ++ ++3 ++ ++ ++ ++ 0

Flint 50 WDG4'9 4 oz 0 0 +/0 0 ? ? ? ++ 0

Maneb 75 DF11 2 lbs. 0 0 + + + + + + 0

Manex 4F13 1.6 qts. 0 0 + + + + + + 0

Tanos 50 DF4'21 8 ozs. 0 0 ++ ? ? ? ? ? ?
Topsin 4.5 FL 10 fl
ozs. 0 0 0 ++ + 0 + 0 0
Footnotes for Table 2 are on next page.


13









Table 2 continued with footnotes


++ = highly effective, + = may be effective; 0 = not effective.

2Minimum days to harvest from last use varies among different fungicides (e.g. coppers-1 day; Amistar-1 day; EBDC types 5
days; chlorothalonil 12 hrs to 7days depending on availability of eyewash equipment; Flint, Pristine, & Nova-0 days). Read the
label.

Not for routine disease control because numerous isolates of the gummy stem blight pathogen are resistant to this type of
active ingredient.

Limit is 4 appl./crop.

Avoid applications during cloudless days, particularly after fruit have set.

Limit is 19.2 qts./acre/crop.

Limit is 24 lb./acre/crop (limit is 25.6 lbs./acre/crop for Dithane Rainshield DF).

Limit is 128 lbs/acre/crop.

9Limit is 20 ozs./acre/crop

10 Limit is 21 pts./acre/crop.

11 Limit is 17.1 lbs/acre/crop.

12 Limit is 1.5 lbs./acre/crop

13 Limit is 12.8 qts/acre/crop

14Limit is 64 fl oz/crop

15 Limit is 19.1 lbs/acre/crop

16 Limit is 17.5 lbs/acre/crop

17 Limit is 32 ozs.acre/crop

18 Limit is 35 lbs/acre/crop

19 Limit is 8 ozs./acre/crop

20 Limit is 74 ozs./acre/crop

21 Limit is 32 oz/acre/crop


14




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