Title: Florida plant disease management guide
ALL VOLUMES CITATION PDF VIEWER THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00053871/00023
 Material Information
Title: Florida plant disease management guide
Alternate Title: Ornamentals and turf
Fruit and vegetables
General plant pathology, field crops and pasture grasses, fungicides, adjuvants and application techniques
Physical Description: v. : ; 28 cm.
Language: English
Creator: University of Florida -- Dept. of Plant Pathology
Florida Cooperative Extension Service
Publisher: The Extension
Place of Publication: Gainesville Fla
Frequency: annual
regular
 Subjects
Subject: Plant diseases -- Periodicals -- Florida   ( lcsh )
Pesticides -- Periodicals   ( lcsh )
 Notes
Statement of Responsibility: Plant Pathology Dept., University of Florida and Institute of Food and Agricultural Sciences, Florida Cooperative Extension, University of Florida.
Numbering Peculiarities: Issued in three volumes: v. 1, General plant pathology, field crops and pasture grasses, fungicides, adjuvants and application techniques; v. 2, Ornamentals and turf; v. 3, Fruit and vegetables.
General Note: Description based on: 1999-2000.
General Note: "SP-52"
 Record Information
Bibliographic ID: UF00053871
Volume ID: VID00023
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 44549741
lccn - 00229071
 Related Items
Preceded by: Florida plant disease control guide

Downloads

This item has the following downloads:

PG05700 ( PDF )


Full Text




PDMG-V3-51
UF UNIVERSITY of
UFFLORIDA
IFAS Extension



2006 Florida Plant Disease Management Guide: Sweet

Corn1


Richard Raid and Tom Kucharek2


Specific Common Diseases

Bacterial Leaf Blight (Pseudomonas avenae)

Symptoms: Incited by a bacterium, bacterial leaf
blight is characterized by sharply delineated dead
spots and stripes on the leaf. These may measure
about 1/16 inch wide and up to several inches long.
The spots initially appear water-soaked, turn brown,
and then white to gray. Newly-formed lesions
typically occur on leaves as they emerge from the
whorl, with little elongation once the leaf is fully
expanded. Bacterial blight rarely advances once the
corn has tasseled.

Cultural Controls: Since severe bacterial blight
has been observed to follow heavy budworm
infestations, good insect control may aid in lessening
the disease. Additionally, since the bacterium may
survive on grassy weeds, particularly Vasey grass,
control of such weed hosts, particularly along ditch
banks, is often beneficial. The disease is favored by
warm, wet conditions. Some varieties are more
resistant to bacterial blight than others and these
should be considered in disease prone areas.


Bacterial Stripe (Pseudomonas
andropogonis)

Symptoms: Primary lesions are typically amber-
to olive-colored, with parallel sides. Lesions usually
elongate, giving a stripe appearance, and may
coalesce. Unlike bacterial leaf blight, bacterial stripe
symptoms appear first on the lower leaves and
spreads upwards. Leaves superior to the ear are
seldom affected and therefore bacterial stripe is
seldom of economic importance.

Cultural Controls: Bacterial stripe, like bacterial
blight, is most severe under warm wet conditions. It
also survives on weed hosts such as Johnsongrass and
Sudangrass. Resistant varieties and proper weed
control will reduce disease incidence.

Common Rust (Puccinia sorghi)

Symptoms: Common rust is a fungal disease
characterized by small, circular to elongate, reddish
brown to dark brown pustules on the leaf surface.
Common rust pustules are frequently erumpent on
both the upper and lower leaf surface. Pustules give
rise to tens of thousands of cinnamon brown spores


1. This document is PDMG-V3-51, part of the 2006 Florida Plant Disease Management Guide, one of a series of the Department of Plant Pathology, Florida
Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Date Reviewed: January 2006. Please visit the EDIS
Web site at http://edis.ifas.ufl.edu.
2. R.N. Raid, professor, Plant Pathology Department, Everglades Research and Education Center--Belle Glade, FL; T.A. Kucharek, professor, Plant
Pathology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611.

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. U.S. Department of Agriculture, Cooperative Extension Service,
University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry
Arrington, Dean






2006 Florida Plant Disease Management Guide: Sweet Corn 2


which are easily dislodged during periods of reduced
humidity. When severe, common rust may cause
extensive yellowing and premature desiccation of
cor foliage, resulting in leaf necrosis. In extreme
cases, heavy rust infestations may result in stunting,
incomplete ear tip fill, and pustules on ear husks,
reducing marketability.

Cultural Controls: Common rust, because it is
favored by cool to moderate temperatures (60-73
C), is most prevalent during Floridas spring growing
season. It is seldom a problem during the fall in
Southern Florida when southern rust is the more
prevalent rust disease. During the late 1980s and
throughout the 1990s, common rust was the most
important disease of Florida sweet corn. New
varieties, specifically bred for rust resistance, have
proven to be very beneficial in the control of this
disease.

Chemical Control: Early detection is extremely
important in initiating a chemical control program for
rust. Since the fungus produces millions of spores
which are wind-disseminated over large areas, rust
may build up to high levels in a very short time. The
newer strobilurin and sterol-inhibiting fungicides,
which have some systemic properties, are more
effective in controlling rust than the broad spectrum
protectants. However, they should be used in a
program (either tank-mixed or alternated) with the
protectants to minimize the development of resistant
strains of the rust fungus and to maximize efficacy.
See PPP-6.

Damping-Off (Fusarium spp., Penicillium
spp., and Pythium spp., and Rhizoctonia
solani)

Symptoms: A number of soilbome fungi may
infect the seed or seedling, causing them to rot or to
die shortly after germination. Affected seed kernels
are soft, and deteriorate in the soil. Seedlings that do
emerge may show chlorosis or tip bum of the seed
leaf as well as the first true leaves. Many of these
will die, falling over at the soil surface. Root systems
of affected plants will show dark lesions on roots
and/or the coleoptile. See Plant Pathology Fact Sheet
PP-1.


Cultural Controls: Damping-off is most
prevalent when soils are cold and wet. Any condition
that delays emergence will enhance disease incidence
and severity. Plant in warm, well-drained but moist
soils when possible. Use quality seed of high
germination and avoid mechanical injury to the seed
when planting.

Chemical Controls: Seed-protectant fungicides,
including some of the standard protectants (i.e.
captain and thiram) and some of the newer systemics
can provide excellent control of damping off
Planting only seed which has been commercially
treated with combinations of these compounds
greatly enhances the opportunity for excellent stand
establishment, particularly during cool, moist soil
conditions.

Maize Dwarf Mosaic (Maize Dwarf Mosaic
Virus)

Symptoms: Although there are a number of viral
diseases of sweet corn, maize dwarf mosaic virus
(MDMV) is the most common in Florida. Symptoms
are highly variable. Leaves may have irregular, light
and dark green mottle or mosaic patterns. These may
develop as narrow, light green or yellow streaks
along the veins. Infected plants may become stunted
with a resulting reduction in ear size and
development.

Cultural Controls: MDMV is retained and
transmitted in a non-persistent manner (up to 6 hrs)
by over 20 species of aphids. There are also over 200
wild and cultivated grass hosts for this virus. It
causes an economic problem in Northern Florida.
Resistant varieties are currently under development.
Because Johnson grass is a major host for this virus,
Johnson grass must be eliminated around and in
fields used for production of sweet corn.

Northern Corn Leaf Blight (Exserohilum
turcicum)

Symptoms: Along with common rust, this is one
of the most important diseases of sweet corn in
Florida. This fungal disease is characterized by long,
spindle-shaped lesions which are at first pale green,
gradually turning gray-brown with age. Lesions may
eventually be up to 1/2 inch wide by 4-6 inches long.






2006 Florida Plant Disease Management Guide: Sweet Corn 3


Under favorable conditions, numerous lesions may
coalesce to kill large amounts of foliage. The disease
usually starts on the oldest leaves and works its way
up the plant. The causal agent produces tiny stalks
that emerge from the stomates located within the
lesion area to give rise to long, multi-celled spores.
These may be observed using a hand lens after
periods of high humidity.

Cultural Controls: Exserohilum turcicum is
favored by moderate temperatures (65-80 F) and
periods of prolonged leaf wetness. It is slowed by
periods of extended dryness. If the disease is well
established prior to silking, economic losses may
ensue. Lesions on ear husks also reduce marketability
of sweet corn intended for the fresh market. Resistant
hybrids are currently available to aid in the control of
northern blight and are highly recommended,
particularly for the spring growing season. Northern
blight is seldom a concern in the fall in southern
Florida, when southern corn leaf blight is more
prevalent.

Chemical Control: Fungicides can be effective
in helping to control this disease. A forecasting
system based upon leaf wetness and temperature is
helpful in determining infection periods. While
sterol-inhibitor and strobilurin fungicides are more
effective than protectant fungicides in the control of
northern blight, these should be utilized in a program
with the broad-spectrum protectants to reduce the risk
posed by the development of fungicide insensitivity.
See PPP-6.

Smut (Ustilago maydis)

Symptoms: All plant parts above ground may be
infected, especially actively growing meristematic
tissue. The causal fungus produces spore-filled galls
which are initially greenish to silvery white. The
interior of the gall turns into a brown to black
powdery mass, as the spores mature. Galls may range
from 1/2 inch to 6 inches in diameter. Young plants
may die but this is infrequent. Leaf galls usually
remain small (1/4 to 1/2 inch in diam.) and become
hard, but seldom rupture.

Cultural Controls: Unlike most fungal diseases,
smut is favored by dry conditions. Favorable
temperatures range from 78 and 940 F. Since the


disease appears to be more severe when high nitrogen
fertility or heavy manure amendments are used,
maintain a balanced fertility program. Smut is also
favored by injuries due to hail, blowing sand, and
mechanical factors. Therefore, mechanical injuries
caused by cultivation and spraying should be
minimized. Where smut is a consistent problem,
choose varieties with generalized or polygenic
resistance to the causal fungus.

Southern Corn Leaf Blight (Bipolaris maydis)

Symptoms: Lesions caused by southern corn leaf
blight are much smaller (up to 1/2 inch wide and 1
inch long) than those incited by northern corn leaf
blight. Southern blight lesions are also lighter in
color (light tan to brown), and have parallel sides
rather than the tapering sides of lesions caused by E.
turcicum. When severe, lesions may become so
numerous that they coalesce and turn the entire leaf
necrotic. Southern blight, like northern blight, moves
from the lower canopy to the upper canopy. Fungal
sporulation may be observed with a simple hand lens
on foliar lesions following periods of high humidity.

Cultural Controls: Southern corn leaf blight is
most prevalent during the fall growing season in
south Florida, but may also appear at the end of the
spring growing season, particularly if unseasonably
warm. It is favored by warm to hot temperatures
(68-90 F) and periods of extended leaf wetness.
Resistant varieties are available and should be
considered, particularly for fall plantings.

Chemical Control: Fungicides can be effective
in helping to control this disease. These should be
applied early, particularly if the forecast is for warm,
humid weather. As with northern corn leaf blight, the
sterol inhibitors and strobilurin fungicides are most
efficacious. However, these should be utilized in
conjunction with a broad spectrum protectant to
minimize development of fungal insensitivity. See
PPP-6.

Southern Rust (Puccinia polysora)

Symptoms: Like common rust, southern rust is
characterized by pustules which erupt on through the
foliar epidermis. However, southern rust pustules are
more orange than brown, more circular than elongate,






2006 Florida Plant Disease Management Guide: Sweet Corn 4


and are more prevalent on the upper leaf surface than
on the lower leaf surface. Given favorable
conditions, southern rust may cause premature death
and dessication of corn leaves. In addition, plant
photosynthates intended for ear fill are diverted to the
pathogen for spore production, resulting in
incomplete ear tip fill. Most prevalent in fall sweet
corn in south Florida, southern rust is occasionally of
economic importance and warrants control.

Cultural and Chemical Controls: Southern rust,
in contrast to common rust, is favored by warm to hot
temperatures (80-90 F). It too likes high
humidities and long periods of leaf wetness. Hybrids
resistant to southern rust are not as numerous as those
resistant to common rust. Therefore, growers may
have to rely more on fungicides for control if
conditions are favorable. Growers should scout fields
and begin fungicide applications during early stages
of the disease. As with common rust, the newer
strobilurin and sterol-inhibiting fungicides, which
have some systemic properties, are more effective in
controlling rust than the broad spectrum protectants.
However, they should be used in a program (either
tank-mixed or alternated) with the protectants to
minimize the development of resistant strains of the
rust fungus and to maximize efficacy. See PPP-6.




University of Florida Home Page
© 2004 - 2010 University of Florida George A. Smathers Libraries.
All rights reserved.

Acceptable Use, Copyright, and Disclaimer Statement
Last updated October 10, 2010 - - mvs