Origin and control of fern weeds in orchid production in greenhouses in Hawaii

Weeds of Nephrolepis exaltata (sword fern) are the most serious problem in the cultivation of orchids on the island of Hawaii. Spores of N. exaltata were found in rainwater from the catchments used for irrigation. Filtration of rainwater through a 130-μm stainless screen filter, through 50 and 1-μm polyester filters eliminated more than 99% of spores in water. When Phalaenopsis orchids in pots were irrigated with filtered water, 95% of them were free from infestation with N. exaltata sword ferns. The method is simple and inexpensive, and should be applicable to solving the fern weed problem in the cultivation of potted ornamental foliage plants and other flowering plants.