August 29, 2017
By Justin Miller
The silverleaf whitefly adults deposit eggs underneath cotton leaves. Photo by Joseph LaForest, University of Georgia, Bugwood.org
The silverleaf whitefly (SLWF) is proving to be a big problem for cotton producers in Alabama.
Feeding flies stunt the plant’s growth and reduce plant vigor, scientists say. More serious than the feeding is the fly’s secretion of honeydew, which causes a sooty mold to grow. This mold will reduce lint quality once cotton begins to open.
First found in Alabama in 1997, SLWF feeds on cotton plants and has been active in the Southeast the last few years.
“Honeydew causes the cotton to become sticky and makes it extremely difficult to spin at the mill,” said Dr. Ron Smith, an Alabama Extension cotton entomologist. “Most gins will not take this sticky cotton. That is why this insect is harmful to the cotton industry. It creates cotton that cannot be sold.”
In 2016, SLWF heavily infested cotton crops in several counties surrounding Tifton, Georgia. Now, SLWF has spread over much of the 1.3 million acres of cotton planted in Georgia. Recently, this infestation has spread into the Wiregrass area of southeastern Alabama.
Smith said while the preferred host is cotton, SLWF can be seen on other plants including soybeans and peanuts. Heavy infestations of SLWF can also cause premature defoliation, he said.
“Silverleaf whiteflies are not known to die off from a naturally occurring fungus like aphids do,” said Smith. “These populations increase until the leaves drop from SLWF feeding.”
The first sign producers can look for of a SLWF infestation is the presence of whiteflies clustering around the plant terminal or underneath the terminal leaves. Depending on temperature, the insects’ life cycle is 15 to 18 days.
To make SLWF treatment decisions, producers should examine the fifth main stem leaf below the terminal for the presence or absence of immature whiteflies, Smith said, adding that farmers should apply control methods when they find immature stages on half of the plants. He said controlling SLWF in 2017 will be expensive and challenging due to the unavailability or short supply of most recommended controls.
Producers should contact their Alabama Extension regional crops agent for help in identifying the best control methods for their crops.