Silverleaf whitefly is a concern for growers across the state of Florida. The pest transmits tomato yellow leaf curl virus.
“Some years, it’s very heavy early on and growers have to replant. But so far, the pests seem to be pretty well managed,” says Hugh Smith, associate professor of entomology and nematology at the University of Florida’s Gulf Coast Research and Education Center.
A certain percentage of whiteflies carry a virus that is particular to tomatoes. It’s called tomato yellow leaf curl because it does exactly that; it turns the leaves bright yellow. Plants are stunted if they get infected early. If a plant gets infected with a virus within the first few weeks after planting, that plant is probably not going to produce anything. Early infestation can reduce yields. If whiteflies don’t cause a problem until closer to harvest, then impacts on yields will be less. The virus doesn’t cause any visible symptoms in the actual tomato, but it weakens the plant and reduces the amount of tomatoes that it will produce.
So far, it has been a quiet year for the virus. Growers in Smith’s area have been planting since late August, so there are established fields. “It’s showing up, but I haven’t heard about severe cases yet where growers are looking at significant losses,” says Smith.
Whiteflies can also cause a tomato plant disorder called irregular ripening. This seems to primarily be associated with higher numbers of whitefly nymphs (immature stage of the pest). The nymphs look like scale insects on the undersides of the leaves.
“It (irregular ripening) is not very well understood. What happens is that when tomatoes have been harvested and they’re gassed for the ripening process, they don’t ripen properly,” explains Smith. “You get irregular, sort of green longitudinal sections on the tomato where it should all be consistently red. If you cut into the tomato, it will be white in tissue on the inside.”
Smith believes that the heavy rains this year have kept the whitefly populations down. “We’ve had good rains. Whiteflies have been bad in the past when it’s been really hot and really dry, but with the regular Florida rains it could be helping keep the whitefly populations under control,” he says.
Whiteflies are still active during rains, but when it’s dry they reproduce more quickly. Different types of fungi will attack and thrive on insect pests, including whiteflies, when the humidity is high. “This isn’t something that I’ve seen very often in nature, but we do see it if we have whiteflies in a greenhouse and they have very high humidity. Sometimes some of these fungal pathogens becoming established on the whiteflies, reducing the populations,” explains Smith.
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