Effects of weed management on the prevalence of pink pineapple mealybugs in Ghana

Abstract

An on-farm experiment was conducted in August 2010 to evaluate the efficacy of various weed management methods used in pineapple cultivation in Ghana in limiting the prevalence of the pineapple mealybugs and their tending ants. The experiment was a 5X5 Latin Square design with 5 replications. The weed management methods (the treatments) imposed was weedy check (no weed control), manual weeding by hoeing, synthetic herbicide application, plastic mulch + manual weeding and plastic mulch + synthetic herbicide application. The field was ploughed and harrowed and plots each measuring 2m by 2.7m were marked out. Suckers obtained from a nearby commercial farm were planted at the spacing of 90 x 60 x 25 cm. Fertilizer was applied at the recommended rate and pests were controlled by spraying with both fungicide and an insecticide. Data taken from the inner 20 plants of each plot were: time taken for weeds to re-emerge, weed species that emerged, weed population and weight and presence of mealybugs on the fruits and in the root zone. The result showed that, time of weed re-emergence was longest in the plastic mulch + herbicide treatment, whilst re-emergence was fastest in the manual weed control treatment. Guinea grass (Panicum maximum) belonging to the Poaceae family re-emerged on all treatment plots. The plastic mulch + herbicide treatment was able to control all broadleaved weeds, whilst most broadleaved and grass species re-emerged from the manual weeding treatment throughout the period. Weed population, weed dry weight and number of weed species re-emerged, were all significantly lower in the plastic mulch + herbicide treatment than in all other treatments but were greatest in the manual weed treatment. The results indicated that weed control efficiency of 90.6, 80.2, 73.4 and 69.2% in the plastic mulch + herbicide, plastic mulch + manual control, herbicide alone and the manual control over the weedy check, respectively. However, mealybug populations were not affected by the weed management methods employed, although all treatment effects were significantly greater than weedy check. The ability of the treatments to reduce mealybug populations on both the fruits and the root zone might be that during weed control, the mealybugs were exposed to predators that feed on them or that weed control dislodges their tending ants which subsequently limit their spread. This study affirms that proper weed control would reduce mealybug population and minimize the damage to fruits.

Keywords: pineapple, mealy bug, weed control efficiency, plastic mulch, guinea grass