Los bananos Musa spp del subgrupo Cavendish, procedente de la

COMPARISON OF SYSTEMIC FUNGICIDES FOR THE CONTROL
OF BLACK SIGATOKA IN COSTA RICA
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WASHINGTON, J.R. , QUESADA, R.
RESUMEN. Se evaluaron diecenueve tratamientos de fungicidas
sistémicos para su eficacia en reducir la necrosis causada por
Sigatoka negra, utilzando puebas de “Single Leaf” en varias zonas
de producción en Costa Rica. Los tratamientos evaluados incluyeron
los fungicidas triazoles, strobilurinas, tridemorph, fosfito de potasio, y
los nuevos fungicidas pyrimethanil y spiroxamine. Los tratamientos
evaluados tambien se incluyeron mezclas de los fungicidas
mencionados. Entre los fungicidas aplicados solos en emulsiones
de aceite en agua, difenoconazole fue lo mas efectivo. El fungicida
tridemorph significativamente mejoró la eficacia de todos los
fungicidas cuando fue combinado con ellos en mezcla de tanque.
Los fungicidas pyrimethanil y spiroxamine no demostraron ningun
efecto significativo sobre la enfermedad. Fosfito de potasio mejoró
significativamente la eficacia de difenoconazole cuando fue
combinado en mezcla de tanque. Las implicaciones para el manejo
de la enfermedad son discutidos.
CONCLUSIONS. Fungicide efficacy in Costa Rica is severely
compromised at the present. Only a few fungicide combinations remain
moderately effective in reducing disease severity as evidenced by single
leaf tests in banana production zones. Mixtures of fungicides from different
classes of chemistry appear to be the best alternative available to manage
the disease. Phosphorous acid or its salt potassium phosphite is an
economical alternative to conventional fungicides and is a valuable tank
mix partner with difenoconazole.
INTRODUCTION. Black Sigatoka has become extremely difficult to
manage in Costa Rica, where Mycosphaerella fijiensis resistance to
triazole and strobilurin fungicides has been reported (ref 1, 2) and is
known to be widespread. It is important to have a practical method to
routinely measure and compare the efficacy of fungicides in a given
location, in order to monitor their ability ro suppress the disease,
particularly in view of dynamic population genetics, fungicide resistance
status, and climatic variations. The current study summarizes the status
of comparitive fungicide efficacy in Costa Rica.
MATERIAL AND METHODS. Fungicides were mixed in oil-in-water
emulsions using 8 L/HA of spray oil unless otherwise stated, and
applied according to their full label rates. Treatments were applied to
one half of the youngest fully expanded leaf, on the upper side, in 2meter-tall plants established from meristem transplants of ‘Grand
Naine’. Spray application was made using a specially designed CO2
hand sprayer fitted with a Tee Jet TP800033 fine spray nozzle and
using a spray volume of 18 L/HA at 35 psi. Tests were performed in
banana production zones of Costa Rica, including Sarapiquí,
Pacuare, and Guápiles. The studies were conducted during 2005 and
2006.
Disease assessment was made beginning at 6 weeks
following treatment application and continued until disease
suppression was still evident in at least one treatment, generally up to
8-10 weeks. Statistical analysis was performed using ANOVA and
GraphPad Prism v. 3.0.
Figure 1. Leaves treated with Sico (0.4 L/HÁ) + Calixin (0.5 L/HÁ)
showing left side treated with fungicide vs right side untreated. The
photograph was taken eight weeks following a single treatment
application.
RESULTS AND DISCUSSION.
In comparisons of triazole and strobilurin fungicides applied alone,
difenoconazole was superior to bitertanol, tebuconazole, and to the
strobilurin fungicides trifloxystrobin, azoxystronin, and pyraclostrobin.
Tryfloxystrobin and pyraclostrobin were superior to azoxystroibin.
The fungicides pyrimethanil and spiroxamine showed no significant
activity compared to an oil-in-water emulsion applied alone. These
two fungicides appear to serve no useful purpose in suppression of
black Sigatoka in Costa Rica. Tridemorph significantly improved the
efficacy of the triazole and strobilurin fungicides, although less so with
azoxystrobin. Pyrimethanil and spiroxamine did not improve triazole
or strobilurin efficacy when used in mixtures. Potassium phosphite
significanly improved the effciacy of difenoconazole. Based on
results of these studies, tank mixtures with tridemorph are
recommended with the triazole and strobilurin fungicides. Potassium
phosphite appears to be a valuable partner in tank miztures with
difenoconazole and should be evaluated extensively in combinations
with other fungicides in disease management programs.
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Tropical Plant Technologies, Ciudad Colon, Costa Rica, AP 44-6100
Tropical Plant Technologies, Guapiles, Costa Rica,
tropplanttech@yahoo.com
REFERENCES.
1.
Amil, A.F. 2004. The dynamics of stobilurin (QoI) sensitivity
in Mycosphaerella fijiensis in Costa Rica. University of
Reading., Ph.D. thesis.
2.
FRAC working group, Banana, 2003.