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Title: Rhizoctonia seedling blights of vegetables and field crops
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Permanent Link: http://ufdc.ufl.edu/UF00066850/00001
 Material Information
Title: Rhizoctonia seedling blights of vegetables and field crops
Series Title: Plant Pathology Fact Sheet PP-1
Physical Description: Book
Language: English
Creator: Kucharek, Tom
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: 1978
 Subjects
Spatial Coverage: North America -- United States of America -- Florida
 Record Information
Bibliographic ID: UF00066850
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 - 51334468

Table of Contents
    Introduction
        Page 1
    Figures
        Page 2
Full Text



Plant Pathology Fact Sheet


Rhizoctonia Seedling Blights of Vegetables

and Field Crops
Tom Kucharek, Professor, Extension Plant Pathologist, Plant Pathology Dept.
1978, Revised Nov. 2000
Florida Cooperative Extension Service/ Institute of Food and Agricultural Sciences/ University of Florida/ Christine Waddill, Dean


Introduction

Rhizoctonia spp. are soil inhabiting fungi that
commonly infect numerous plant species. Beans (veg-
etable types and soybeans) and peas (english, southern,
blackeyed, etc.) are commonly infected by Rhizocto-
nia spp., but seedlings of many other plant species are
also susceptible to these fungi. Infection of seedlings re-
sults in a disease called seedling blight. If infection oc-
curs prior to the emergence of the seedling, the resulting
disease is called preemergence seedling blight and it is
often lethal. Preemergence seedling blight may occur as
a result of infection by Rhizoctonia spp. alone or in com-
bination with Pythium spp., another group of soilborne
fungi (Figure 2). Rhizoctonia spp. may infect a seedling
prior to emergence or after emergence and cause vari-
ous kinds of stem lesions (Figures 1, 3, 4). Usually, in-
fections of stems occur near the soil surface and result in
some shade of brown, red or orange discoloration. Older
lesions will appear sunken with less red color and may
eventually rot the entire outer portion of the stem, thus
causing the plant to fall over.

Rhizoctonia spp. are capable of causing plant
diseases over a broad range of soil temperatures, soil
pH, soil types, fertilizer levels, and soil moistures. The
versatile nature of Rhizoctonia spp. results from their
broad genetic potential. Individual isolates of Rhizocto-
nia spp. can cause plant disease in numerous plant spe-
cies and under varied environmental conditions. Further,
the number of "strains" that exist can increase with each
new scientist added to the roster and the time spent on
strain identification..

Control

Control of seedling blight caused by Rhizocto-


nia spp. is achieved on commercial crops, such as to-
matoes, peppers, strawberries, celery transplant beds
and tobacco transplant beds, by preplant fumigation with
methyl bromide + chloropicrin or liquid fumigants such
as Vapam. Even though soil fumigation is highly effective
against Rhizoctonia spp., recontamination of fumigated
areas should be avoided. Any method that reduces
movement of soil from nonfumigated areas into fumi-
gated areas will achieve this goal. For example, mini-
mize stepping in fumigated areas from nonfumigated ar-
eas. Avoid soil wash due to rain or irrigation from
nonfumigated to fumigated areas by slightly elevating the
fumigated area.

Control ofRhizoctonia-induced diseases in situ-
ations not mentioned above is more difficult and erratic.
Because of the versatility ofRhizoctonia spp., we must
utilize several control measures, often in a sequence, to
attain maximum control if soil fumigation is not used. The
following control measures used collectively will reduce
seedling blights caused by Rhizoctonia and other fungi.
The major objective with this group of control mea-
sures is control on seedlings and stems of young
plants by establishing a fast growing seedling which
essentially reduces the "hazard time" as young
tender plants are more susceptible than older
plants.

1) Use only healthy disease-free seed, seedpieces or
transplants. AlthoughRhizoctonia is not notorious for
being seed-transmitted, poor quality seed will germi-
nate slowly, if at all, which offers a distinct advantage to
Rhizoctonia spp. 2) Avoid deep seeding, if moisture
permits, as deep planting is advantageous for infection.
Likewise, deep setting of transplants should be avoided.
3) Especially in fields where fumigation was not used,
plant when the soil temperature is suitablefor rapid


PP-1







germination. Okra, for example, is a warm season plant
which germinates slowly during March in the Gainesville
area, whereas a June planting will be conducive for rapid
germination thereby minimizing the "hazard period" for
infection. 4) Seed should be treated iith a fungicide
for protection against infection from Rhizoctonia spp.
in the soil. Seed treatment fungicides such as captain
and thiram are nonsystemic in the plant, but they are
labelled for use on numerous plant species. Chloroneb
(Demosan) is an effective systemic seed treatment fun-
gicide which offers further protection of stems or young
emerged seedlings. It is labelled for use on beans, south-
ern peas, soybeans, and cotton. 5) Use crop rotation.
6) Prepare land so that a minimum amount of old
plant debris is on the soil surface in the seeding zone.
Where minimum tillage is used, a debris-free strip should
be available in the zone used for seeding. 7) When
double cropping, after bottom plowing the old crop,
allow green matter to decompose for 30 days.
Undecomposed green matter has been a major source
of inoculum of Rhizoctonia spp. on green beans and
soybeans in Florida. 8) Control soil insects andnema-
todes. These organisms weaken the plant, thereby pre-
disposing the plant to infection. 9) Avoid high seeding
rates and close transplanting as Rhizoctonia spp. can
grow from an infected plant to adjacent healthy plants.
10) When cultivating, avoid moving the soil onto stems.


Figure 2. Preemergence seedling blight on
soybeans.


& 1 A4m


q .


Figure 3. Rhizoctonia seedling blight on
watermelon.


Figure 1. Rhizoctonia seedling blight on
soybean.


Figure 4. Rhizoctonia seedling blight on
green beans.




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