Studies on the Contribution of Weeds and their Management to the Prevalence of Pineapple Mealybugs
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Date
2012-06-21
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Abstract
Weeds pose a serious problem to the production of pineapple causing losses of up to
83% on the farm. They compete for nutrients, water, light and other resources as well
as harbouring mealybugs and their tending ants which greatly affect production. This
research was thus conducted first to catalogue the prominent weeds found in three
major pineapple growing Districts in Ghana: Mfantsiman, Gomoa East and Akuapim
South Districts. It further sought to determine which of these weed species harboured
the pineapple mealybugs and their tending ants and to determine the effect of four
weed management methods on the prevalence of pineapple mealybugs and the
growth and yield of pineapples. The research was carried out in three phases: the first
phase consisted of a survey to identify and quantify the common weeds found on
pineapple farms in the three Districts. Cluster sampling method was employed to
determine the weed species with the aid of a 1m2 quadrat on 15 farms in the three
districts. The second phase involved the identification of the pineapple mealybugs
and their tending ants, interviews with pineapple farmers on various weed
management practices and alternative host of the mealybugs, and a scout for the
mealybugs on the weeds within and adjacent the 15 pineapple fields. The last phase
was a field experiment to evaluate the various methods of weed management
employed by pineapple farmers. The experiment was a Latin square design with 5
treatments and 5 replications. A total of 43 weed species from16 families were
recorded from the three districts with Mfantsiman recording the least number of
species (29), followed by Gomoa East (34), and Akuapim South (40). Only
Dysmicoccus brevipes (Homoptera: Pseudococcidae) was found to infest pineapples.
Four ant genera (Crematogaster, Camponotus Pheidole and Solenopsis) were found
to attend the mealybugs. No weed was identified as an alternative host to the D.
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brevipes. Six weed species were rather found to be positively associated with the
tending ants of the mealybugs. The Mfantsiman District recorded the highest
mealybug infestation with 78 ± 5.2 mealybugs per plant, and this was significantly
different from Akuapim South and the Gomoa East Districts. The populations of
tending ants and the density of grasses adjacent to field were found to be positively
correlated to the population of the pineapple mealybugs. Of the four weed
management methods evaluated, plastic mulch + synthetic herbicide was found to be
most efficient in weed control (90.6% over weedy check). This was followed by the
plastic mulch + manual weeding (80.2% over weedy check), synthetic herbicide only
(73.4 % over weedy check), then manual weeding only (69.2% over weedy check) in
that order. The same trend was observed in the ability of the weed management
method to promote growth and yield, with plastic mulch + synthetic herbicide
recording an average fruit weight of 1.95 kg, plastic mulch + manual weeding
recording 1.82 kg, synthetic herbicide only, 1.61 kg, manual weeding, 1.56 kg and
1.40 kg for the weedy check. The weed management methods significantly reduced
the populations of pineapple mealybugs on pineapple fruits but not on the roots.
Description
A thesis submitted to the School of Graduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirements for the award of the Degree of Master of Science, 2012