Mosaic Disease Control on Susceptible Cucurbits

 in the West Indies

 Omer S. Lloyd Thomas
 Virologist/Pathologist, Senior Agricultural Officer
 Ministry of Agriculture, Food and Consumer Affairs
 Barbados, West Indies


 Aphid-borne virus diseases are the most important diseases
of cucurbits in the West Indies that cause significant reduction
in yield. Surveys of cucurbit farms throughout the West Indies
revealed the presence of mosaic, existing in varying degrees of
occurrence and severity, as the most predominant disease. The
diseases were found to be caused by aphid-borne viruses,
either in complexes or individually. Experiments to control the
spread of these diseases with emulsion oils in Barbados reveal-
ed a six-fold reduction as compared with controls. The


oil was applied with CP-3 knapsack sprayer (high volume) us-
ing cone jets to zucchini squash in a scheduled spray cycle.
Droplet size emitted by the sprayer averaged 20 pm at 36 psi
pressure. Rates of application averaged 7.5 ml/l of H20.
Reaping time has been prolonged to more than seven weeks.
Fruit quality was improved and crop yield increased. There
were no significant differences between disease spread in in-
oculated and uninoculated plots (P = .05).


 The West Indies, with a population of approximately eight
million people, imports a sizeable amount of its vegetable re-
quirements (Thomas, 1982). However, with modern agricultural
technology being introduced, vegetable and food production has
increased considerably.
 Diseases and pests take a very heavy toll in crop loss, but im-
proved farming systems and judicious use of pesticides make
epiphytotics rare. However, some diseases still remain prob-
lematic because there is no known direct treatment for their con-
trol. As a result they sometimes occur in epiphytotic proportions,
especially virus diseases.
 Most of the virus diseases known to afflict vegetables in the
West Indies are aphid-borne, and the group of crops most
seriously affected is the cucurbits. Cucumber mosaic virus
(CMV), squash mosaic virus (SMV) and watermelon mosaic virus
(WMV), the most common viruses associated with diseases in
cucurbits (Thomas, 1981; Turner and Stace-Smith, 1979), exist
both in complexes and individually (Thomas, 1981). Their con-
trol still remains an enigma, and an instantaneous solution is not
forthcoming.
 In most of the islands of the West Indies squash of the zuc-
chini, crooked necked and butternut types, watermelon, pump-
kin, cantaloupe and cucumber are widely cultivated. In Montser-
rat,cucumber mosaic virus inflicted severe damage on squash and
watermelon sometimes causing complete loss of the crops
(Thomas, 1981). Similar situations are also frequent in Jamaica
and Barbados.
 Since cucumber mosaic, watermelon mosaic and squash mosaic
viruses are all aphid-borne (Smith, 1972), and the most common
aphids observed to be present in cultivations are Aphis gossypii,
Myzus persicae, and Macrosiphum sp. Control measures always
aim at excluding them. So, insecticide sprays have for a long time
been the standard recommended control measure.
 In Florida and Maine, USA, oil is used to control virus spread
 in peppers, tomato and squash (Zitter and Ozaki, 1978). The oil
 used in those cases is the JMS stylet oil which was developed in
 Florida. This oil has never been tested in the West Indies to
 measure its performance under our tropical conditions.

VOL. XX-PROCEEDINGS of the CARIBBEAN FOOD CROPS SOCIETY


Therefore, a series of experiments were set up in Barbados to
evaluate for the first time the efficacy ofJMS stylet oil in reducing
the occurrence of aphid-borne cucurbit virus diseases in the West
Indies.
 This paper reports on the results of the experiments.

MATERIALS AND METHODS
Surveys: During the growing seasons of 1979-1984, farms of
cucurbits (cucumber, squash, watermelon, cantaloupe and
pumpkin) in six West Indian islands (Barbados, Grenada, An-
tigua, Montserrat, St. Lucia and Jamaica) were surveyed for the
presence of virus diseases. Over 60% of the cucurbit farms in the
islands were examined on a random basis. Samples of plants car-
rying symptoms of virus diseases were prepared for diagnostic
assays.
Diagnosis: Crude extracts were prepared from the diseased
plants selected by mascerating the leaves in mortar with pestle.
The homogenate was squeezed through a bi-layer of cheese-
cloth. This was partially purified by differential high and low
speed centrifugation using the methods described by Franki
(1972).
Serology: The partially clarified material extracted from the
diseased plants were tested against antisera to the viruses which
cause diseases in cucurbits as reported by Smith (1972). The
following antisera provided by Dr. Gooding from North Carolina
University were used: cucumber mosaic virus, squash mosaic
virus, watermelon virus and beta virus 1. The Agar Gel double
diffusion technique was used to test each antiserum against the
clarified extract from each of squash, watermelon, cantaloupe,
pumpkin and cucumber.

Disease Control Program
Oil Spray: The oil spray used in these trials wasJMS stylet oil.
This is a mineral emulsion oil which has been developed in
Florida.
Equipment: The oil was applied with an ordinary knapsack
sprayer (high volume) CP-3 hand pumped type using 36 psi and


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