by Courtney Llewellyn
Farmers constantly have to be on the lookout for the next worst thing so they can still work toward raising successful crops. Cindy McKenzie, Ph.D., a research entomologist with the USDA-ARS, recently led an online session to talk about a growing threat throughout the U.S. – silverleaf whitefly.
As background, McKenzie described the pest (Latin name Bemisia tabaci), which all look identical. There are currently three biotypes of the whitefly: New World (type A), Asia Minor (type B) and Mediterranean (type Q). It was first discovered in America in 1897 on tobacco and sweet potato plants. Fast forward to 1985, and Biotype B was found on hibiscus. By 1989, it was causing tomato mottle. In 1993, it led to golden bean mosaic. By 1995, it was causing tomato yellow leaf curl. All these instances were found first in Florida, but they spread quickly.
McKenzie noted, “Whitefly attacks more than 600 species from 74 plant families. They love ornamentals. They are one of top 10 pests worldwide, and they vector over 100 plant viruses.” Whitefly is a phloem-feeder and inflicts damage by direct feeding and then secreting honeydew that triggers sooty mold as well. They typically feed and lay eggs on the undersides of leaves.
Whitefly Biotype Q is particularly ominous, as conventional insecticide control options are limited, according to McKenzie. When Biotype Q was first identified as problematic, it was flagged as a regulatory concern threatening cotton and vegetable production.
McKenzie said the pest is always found in protected commercial horticultural greenhouse plantings in all assortments of ornamental and herbaceous plants, but never in open field agriculture.
“The Mediterranean type is resistant to almost every chemical they tested on it,” McKenzie said. After having been discovered in Florida for the first time in 2005, it was then spotted in Arizona. The USDA-ARS had to figure out where it was and how to treat it. Today, 27 states have reported Biotype Q whitefly problems, including all of the eastern seaboard, the Midwest from Ohio out to Illinois and Wisconsin, and the Pacific Northwest.
There is a little good news: Most of the tested rotational insecticide programs managed total populations (although none dropped the population to completely zero). It was noted that dinotefuran resulted in 97.4% control, pyrifloquinazon 95.4% control and cyantraniliprole 93% – 97% control on salvia tests. Additionally, foliar applications performed better than drenches at low label rates.