Table 1: Characteristics of major...

Group Title: Extension plant pathology reports
Title: Disease control for squash in Florida
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00066910/00001
 Material Information
Title: Disease control for squash in Florida
Series Title: Extension Plant Pathology Report 63
Physical Description: Book
Language: English
Creator: Roberts, Pam
Pernezny, Ken
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: 2001
Spatial Coverage: North America -- United States of America -- Florida
Funding: Florida Historical Agriculture and Rural Life
 Record Information
Bibliographic ID: UF00066910
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
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    Table 1: Characteristics of major squash diseases in Florida
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Full Text

Disease Control for Squash in Florida
Extension Plant Pathology Report Number 63
January 2001

Pam Roberts and Ken Pernezny

Summer and winter squash are grown commercially throughout the state of
Florida. In the middle of the winter, southern Florida is the primary supplier of fresh
squash for the produce departments of supermarkets all over the nation. In 1997-1998,
squash was harvested from 12,500 acres in the state with a total value of $54.5 million.

Several diseases must be controlled successfully if squash is to be grown
commercially in our subtropical environment. Even though many growers have been
combating these diseases for many years, substantial losses sometimes still occur. A
sequential disease control program is presented in this pointer as a guide for commercial
growers. If followed, disease losses should be minimized for the majority of plantings.

Characteristics of Pathogens that Cause of Squash

The great majority of plant health problems that we call diseases are caused by
microorganisms. These extremely tiny disease agents cause losses in squash in two basic
ways. Fruit may be attacked directly, rendering them unfit for consumption or reducing
their cosmetic appeal. The pathogens may attack plant parts other than the fruit. In these
cases, plant vigor and carbohydrate production may be reduced, with subsequent losses in

The pathogenic microorganisms attacking squash may be classified into three
major groups: fungi, bacteria, and viruses.

Fungi are microscopic organisms that we often call molds in everyday language. In the
past, they were commonly classified as plants. However, they are sufficiently different
from plants that most experts now classify fungi in a unique kingdom by themselves.
They have no true roots, stem, or leaves. Instead, they grow as hyphae (microscopic
threads of living matter) that absorb food and water directly into their cells. Although
fungi have cell walls, the chemical composition of the wall material is often drastically
different chemically from the cellulose wall material we find in higher plants. Fungi also
do not have chlorophyll; therefore, they must depend on outside sources of food,
including living plants.

Many of the fungi which attack squash reproduce by developing and releasing
large numbers of spores. Some spores (e.g., those of the powdery mildew fungus) are
readily spread by wind. Others require splashing rain or irrigation for dispersal. Some
fungi, particularly those that cause root and stem diseases, have specialized spores that
can push through and /or dissolve the cuticle and cell walls.

Bacteria are smaller than fungi and are not at all plant-like. All bacteria are just
one cell, and they lack chlorophyll. The ones that cause plant disease do not form spores.
The major type of reproduction for plant pathogenic bacteria is by simple cell division.
Bacteria never enter plants directly. They must have a wound or a natural opening to get
inside a potential host plant.

Viruses probably shouldn't be considered "organisms". They are nothing more
than very large molecules of nucleic acid (RNA or DNA) with a wrapping or "coat" of
protein. There are no cellular structures. New virus particles can only be reproduced
inside of living cells. They are much smaller than bacteria, and normally require
sophisticated techniques such as electron microscopes and polymerase chain reaction to
be studied. Viruses probably spread from infected weed hosts to squash. Aphids are
usually responsible for spread of virus particles on their feeding probe stylett). Healthy
plants then may become infected on subsequent feedings.

It must be remembered that the development of disease is dependent on the proper
combination of factors in the so-called disease triangle: a susceptible host, a virulent
strain of the pathogen, and weather conditions favorable for a given disease. If any of
these conditions is absent, plants will not become diseased.

Effective control of diseases of squash is based on a sound understanding of the
biology of both the host and the pathogen. It is essential that the disease is correctly
diagnosed. Selecting cultivars with minimal susceptibility to key diseases can reduce
dependence on other types of control. Knowing the weather conditions that enhance
development of certain diseases can lead to more informed control strategies. A brief
outline of the characteristics of the major diseases of squash in Florida given in Table 1.

With this important background information, we can proceed to a reasonable
sequential disease control program for squash grown commercially in Florida.


Squash is generally susceptible to a group of fungi in the soil that
cause damping off. Damping-off is a term to describe the death of plants before
or soon after emergence from the ground. Fungi in the soil, particularly Pythium
and Rhizoctonia, are responsible for damping-off. In order to minimize
damping-off damage, most commercial seed is treated with fungicide prior to
purchase. If the seed is not treated, a general-purpose seed treatment is desirable.


A. Mefenoxam

Mefenoxam treatments can be applied preplant for control of
Pythium, a soilbome fungus. This may be helpful in fields that have a

history of Pythium or Phytophthora damage. Historically, Pythium
has been most damaging during warm, rainy weather.
1. Ridomil Gold EC can be applied at the rate of 1-2 pt/treated
acre as a preplant incorporated application or as a soil surface
spray in a 7-inch band after planting. See the label and Plant
Protection Pointer No. 6 for details.


In some part of the state, particularly the Palm Beach
coastal area, squash is grown on raised, plastic-mulched beds that
have been fumigated prior to planting. These fumigants include
methyl bromide + chloropicrin and, more recently, Telone +
chloropicrin. They have a wide range of activity against many
soilbome pests including soil insects, nematodes, and weed seed.
When using fumigants, it is important that crop or weed residues
be worked thoroughly into the soil and allowed to decompose 4-6
weeks before application. The plastic mulch itself probably helps
reduce wet rot damage of fruit by serving as a barrier between fruit
and the soil.


Periodic application of foliar fungicides is important in an overall
program to control a number of foliar diseases in Florida. Failure to do so limits
the production of squash on a commercial scale. Aircraft or ground application is
used, but the latter is preferred because of superior coverage, especially of the
lower surfaces of leaves.

The method of application is as important as the choice of material if
adequate results are to be achieved. A typical planting of squash would be
sprayed with a tractor-mounted boom prayer at 50-250 psi and 30-100 gal
finished spray per acre. Equipment should be properly calibrated to a tractor
speed of 3 miles/hr or a speed desirable for calibration purposes. At 3 mph an
observer should be able to walk behind the tractor at a comfortable pace. When
these calibration guidelines are followed, most disease problems should be
adequately controlled on a 5-7 day spray schedule.

Thorough coverage is absolutely essential. Addition of drop nozzles will
enhance coverage of larger plants, especially the lower surfaces of leaves. The air
inside the squash canopy must be completely displaced by a fine mist of
fungicidal spray in order to prevent hard-to-detect disease outbreaks.

Fungicides are primarily preventative; that is, they must be applied before
pathogens penetrate plant surfaces in order to be effective. Timing of applications

is very important. If fungicides are applied after a disease is first found in a field,
it may be impossible to prevent serious losses from occurring.

Chlorothalonil (Ridomil Gold, Bravo, Bravo Weatherstik, etc.) will
control a number of foliar diseases of squash, including the serious disease downy
mildew. It also provides some control of powdery mildew. A number of
maneb/mancozeb compounds are also registered on squash for control of downy
mildew. Aliette is used for the downy mildew fungus and Phytophthora spp.

Powdery mildew control may require additional fungicide applications
aimed specifically at this disease. Flint, Benlate, Quadris, and Topsin are labeled
for Erysiphe but only the latter three are for use against Sp.hii ,ltthIcw.
Laboratory examination of the spores of the powdery mildew fungus is necessary
to confirm which of the two powdery mildew fungi exists in a field.

Phytophthora blight has rapidly become a limiting disease in squash
production in southern Florida. The disease causes substantial losses regardless
of control methods if environmental conditions are conducive to disease
development. Copper compounds are labeled for the foliar phase of this disease.
Water management and avoidance of previously infected field may help to
manage this disease.

Copper compounds may be needed if angular leaf spot is found. Quadris
and chlorothalonil are the registered compounds of choice when gummy stem
blight threatens (primarily a problem on winter squash).

Sprays of JMS Stylet Oil have been shown to be helpful in the
management of aphid-vectored viruses in squash if applied early enough.
Widespread and destructive outbreaks of papaya ringspot and other viruses have
occurred on squash in previous years. Applications of oil may reduce outbreaks;
however, very specific use directions must be followed for best results. The oil
must be applied with a ground rig at a pressure of 400 pounds per square inch.
TX5 SS nozzles must be used. These special requirements often dictate that a rig
or rigs be dedicated to oil applications.

Readers are urged to consult the Florida Plant Disease Control Guide or
their county extension agent for current, specific fungicide recommendations. In
addition, Plant Protection Pointer No. 6 presents an excellent summary of
fungicide recommendations for all commercial vegetables. This pointer is
available on request from your county extension office. The plant pathology fact
sheets listed in Appendix I can be used to aid in diagnosis of some of the diseases
discussed in this pointer.

1. Kucharek, T. Rhizoctonia seedling blights of vegetables and field crops. Plant Path.
Fact Sheet No. PP-1.

2. Kucharek, T. Downy mildew of cucurbits. Plant Path. Fact Sheet No. PP-2.

3. Kucharek, T. Alternaria leafspot of cucurbits. Plant Path. Fact Sheet No. PP-32.

4. Kucharek, T., and Simone, G. Wet rot of vegetable crops. Plant Path. Fact Sheet No.

5. Pohronezny, K., and Stall, W.M. Powdery mildew of vegetables. Plant Path. Fact
Sheet No. PP-14.

6. Kucharek, K., and Schenck, N. Gummy stem blight of cucurbits. Plant Path. Fact
Sheet No. PP-27.

7. Perenezny, K., and Simone, G.W. Target spot of severe vegetable crops. Plant Path.
Fact Sheet No. PP-39.

Table 1. Characteristics of major squash diseases in Florida.'
Type of Seed Soil Insect Favorable' Areas Most
Disease Pathogen(s) Organism Transmission Survival Transmission Conditions Likely to Occur

leaf spot



Wet rot

Gummy stem

syringae pv.





Didymella bryoniae




C, wet



W, wet







W, wet

W, wet





(winter squash,

crown rot


leaf spot
See Next Page

Pythium spp.

Phytophthora capsici








C, W, wet

W, wet



SF, All



Table 1. (Continued)'
Type of Seed Soil Insect Favorable' Areas Most
Disease Pathogen(s) Organism Transmission Survival Transmission Conditions Likely to Occur

Papaya ringspot PRSV-W virus ++ C SF
mosaic virus
race 1)

Watermelon WMV-2 virus ++ C CF, NF
mosaic virus
race 2

Zucchini ZYMV virus ++ C CF, NF
yellow mosaic

Target spot Corynespora fungus C, heavy dews All
cassiicola (primarily on

1+ = may occur occasionally, maybe of some importance.
++ = occurs often, important to know for proper disease control.
- = not known to occur or relatively unimportant.

2W = warm weather.
C = Cool weather.

3NF = North Florida.
CF = Central Florida.
SF = South Florida.

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