Whiteflies

Whiteflies are one of the most persistent and widespread garden pests on Pohnpei. Despite the name, these tiny winged insects are more closely related to aphids than flies. They are so small that they can easily pass through mosquito netting, screens, etc. Whiteflies hang out on the undersides of leaves, where they suck the sap of the plant. They are particularly attracted to tomatoes, peppers, and basil. They are generally not interested in cilantro, parsley, dill, sage, rosemary, oregano, fennel, or mint. While feeding, the whiteflies produce a substance called honeydew which attracts mold growth.

FIGHTING THEM

Whiteflies are almost impossible to eradicate, but a number of tactics can help keep them at a minimum and prevent serious harm to the plants.

INSECTICIDAL SOAP SPRAY

Special soap sprays are available in the garden section of the hardware store, but you have to spray every part of the plant carefully every few days to make an impact. The draw is that the soap can cause minor cellular damage of the plant's leaves, killing or weakening some of them. It also only kills the adult whiteflies, so the entire population is never really wiped out unless you're doing it every few days and getting the new adults as soon as they emerge from the pupa. Treat the plant in the evening to avoid burning the leaves.

STICKY TRAPS

Since whiteflies are attracted to the color yellow, plastic cards coated with a ultra-sticky substance are available. You hang them near the problem plants and at least some of the whiteflies will be ensnared. I haven't had a great deal of success with these, and I wonder if having them around might actually be attracting more whiteflies to the general area. I suppose sticky traps would work better in an enclosed setting like a greenhouse. The downside to sticky traps in other settings is that they will catch pollinating insects like wasps and bees, too, but that's not a problem here on Pohnpei since there aren't any bees or beneficial wasps. They also blow around in the wind and stick to things you don't want them to--like the plant itself.

DESTROY DEAD LEAVES

Snipping off dead or near-dead leaves and burning them helps prevent whitefly infestation, since weakened leaves are more attractive to the pests. It's a good practice anyway, since it keeps the plants' energy focused on their healthy parts.

NEEM OIL

Many gardeners swear by this natural tree oil, which you spray all over the infected plants. It also supposedly has anti-fungal and anti-mold properties. I haven't tried it yet, so I can't personally vouch for it, but it's on my list.

GARLIC SPRAY

Another remedy people always mention involves pulverized garlic in water. Supposedly spraying the plant with the garlic water will repel whiteflies. I haven't tested this, although I did spread pulverized garlic all over the soil around my tomato plants and the whiteflies were unaffected.

BIOLOGICAL CONTROL

Ladybugs (ladybirds), green lacewings, and types of wasps prey on whiteflies. According to an article in the Kaselehlie Press, 50,000 Encarsia formsa wasps were introduced to Pohnpei in February 2012. E. formosa wasps parasitize whitefly eggs and have been used in many other places as a bio-control. A species of beetle (Delphastus catalinae) was also introduced at the same time, though it is unclear from the article exactly how the beetle figures into things. From another source, I confirmed that D. catalinae is a whitefly predator. Bio-controls take time to establish themselves, so it might be years before an impact is made by the wasps and beetles. But at least there's hope. :)

MANUAL REMOVAL

Believe it or not, the most successful tactic I've found for fighting whiteflies is inspecting the plants carefully twice a day and killing any whiteflies sighted. I simply crush them with my thumb. You can destroy the pupas this way, too. Of course, it's not going to be very practical if you have 20 plants, but it's working pretty well with only 6.