Guava produces sweet-smelling fruits with an edible rind and creamy white, yellow or pink flesh. Guavas thrive in tropical areas, but their adaptability allows them to survive a few degrees of frost in Mediterranean climates. When ripe, guavas emit a pungent, musky odor that attracts fruit flies. Fruit flies lay their eggs beneath the fruit’s skin, and the maggots feed on the flesh. The damage causes guavas to rot.
Fruit fly infestations often spread quickly, but prompt treatment can get populations under control. Harvest guavas before they ripen fully. Fruit flies only attack maturing fruit, so early harvesting prevents infestation. Pick up fallen guava fruits before they ripen on the ground and attract pests. Monitor fruits for infestation. Apply a pesticide containing fenthion or dimethoate to infested trees. Mix the pesticide according to the directions on the container. Spray the foliage and fruit with 5 to 10 liters of the pesticide. Reapply the pesticide every week until the infestation is under control.