| Material Information
||Controlling brown leaf spot of Yucca
||ARC-A research report
||2 p. : ; 28 cm.
||Chase, A. R ( Ann Renee )
Agricultural Research Center (Apopka, Fla.)
||University of Florida, IFAS, Agricultural Research Center-Apopka
||Place of Publication:
||Leaf spots -- Control -- Florida ( lcsh )
Yucca -- Diseases and pests -- Control -- Florida ( lcsh )
||government publication (state, provincial, terriorial, dependent) ( marcgt )
non-fiction ( marcgt )
||Statement of Responsibility:
||Florida Historical Agriculture and Rural Life
The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
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site maintained by the Florida
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Copyright 2005, Board of Trustees, University
CONTROLLING BROWN LEAF SPOT OF YUCCA
A. R. Chase
IFAS, University of Florida
Agricultural Research Center Apopka
ARC-A Research Report, RH-1983-24
Brown leaf spot of thornless yucca (Yucca aloifolia L.) is one of
the most common diseases found on this plant in Florida. The disease is
caused by Coniothyrium concentricum (Desm.) Sacc. and is characterized by
1 to 2 mm long elliptical sunken black lesions primarily on lower leaves.
Lesions first appear however on leaves of medium age and are tiny ellip-
tical sunken spots with a yellow area surrounding them. The spots are
white at first and resemble a phytotoxic response in some cases. With
age, the spots turn the characteristic black and become increasingly sunken.
Spots form on the upper leaf surface, but can be seen on the lower leaf
surface as they enlarge. Lesions which are over six months old begin to
turn tan in the centers and the fruiting bodies (pycnidia or perithecia)
are easily seen at this stage. Another stage of this pathogen, the perfect
form, (Leptosphaeria obtusispora Speg.), is sometimes isolated from these
Control of Yucca leaf spot has been difficult at times since plants
are either grown in the open or under shade structures exposed to rainfall
and overhead irrigation. Spores spread easily under these conditions.
This report gives the results of a test performed at the ARC-Apopka using
naturally infected Yucca and several fungicides available for disease
control. The fungicides were applied weekly for four months (except for
two treatments). Plants were grown in a shadehouse and watered from over-
head to encourage disease development. Treatments are described in the
After four months, the number of new lesions on each of 12 plants per
treatment was rated (1 = no disease, 2 = slight disease, 3 = moderate disease,
4 = high disease, and 5 = severe disease) and analyzed for significant dif-
ferences. Daconil 75 WP used either once or twice a week provided excellent
control of brown leaf spot of Yucca. In the twice a week treatment, there
were no new lesions found on any plant (Table). Zineb 75 WP and Dithane M-45
also provided excellent control with slightly more lesions per plant than the
Daconil treatments. Benlate 50 WP also provided good control, although each
plant did have new lesions initiated during the four months of the trial.
Kocide 101 when applied either once or twice a week provided little, if any,
control of Coniothyrium sp. on Yucca. Of the fungicides tested, Daconil 75
WP was clearly the best for control of this disease.
Table. The effect of fungicide applications on severity of brown leaf spot
of thornless Yucca.
Lbs/ Applications/ Disease severity
Treatment 100 gal. week rating
Daconil 75 WP 1.5 1 0.2 a
Daconil 75 WP 1.5 2 0.0 a
Kocide 101 1.0 1 3.9 c
Kocide 101 1.0 2 2.9 bc
Zineb 75 WP 1.5 1 0.4 a
Dithane M-45 1.5 1 0.4 a
Benlate 50 WP 0.5 1 1.2 a
Water 2 4.3 c
Means were separated by Duncan's New Multiple Range Test ate the 5% level.
This report is not meant as an endorsement
of the products named by either the author
or the University of Florida.