The Silverleaf whitefly (SLWF) is proving to be a big problem for cotton producers in Alabama. First found in Alabama in 1997, SLWF feeds on cotton plants and has been active in the Southeast the last few years.
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.
SLWF feeds using sucking mouth parts and is similar to that of aphids. Their feeding stunts the plant’s growth and reduces plant vigor. More serious than the feeding is the fly’s secretion of honeydew, which causes a sooty mold to grow. This mold will reduce the quality of the lint once cotton begins to open.
Dr. Ron Smith, an Alabama Extension cotton entomologist, said that this honeydew can cause problems when cotton is sent to the mills.
“Honeydew causes the cotton to become sticky and makes it extremely difficult to spin at the mill,” said Smith. “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.”
Smith said while the preferred host is cotton, SLWF can be seen on other plants.
“You will most often see Silverleaf whitefly on cotton, but they can also be found on soybeans and peanuts,” said Smith. “They will found to a lesser degree on these plants than they are in cotton.”
Smith said that heavy infestations of SLWF can cause premature defoliation.
“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.
“Population increases will be observed about two weeks after the first presence of adults,” said Smith. “The Silverleaf whitefly adults deposit eggs underneath the leaves. These eggs hatch into a crawler stage which finds a place under the leaf to begin feeding. The immature stage is immobile until it develops into an adult. Depending on temperature, the life cycle is 15 to 18 days.”
Treatment and Control
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 that farmers should apply control methods when they find immature stages on half of the plants.
“Controls are recommended when 50% of the plants have immatures on the lower surface of this leaf. Immatures will appear oval, flattened, and yellowish in color,” said Smith. “They can be separated from aphids by their flattened shape and the absence of appendages and movement.”
Controlling SLWF in 2017 will be expensive and challenging due to the unavailability or short supply of most recommended controls.
“Achieve the most effective control with insecticides containing insect growth regulators, such as Knack or Courier,” said Smith. “These work on the immature stage of the SLWF.”
Smith said that because these products might be unavailable, there are other products that have activity on SLWF. Producers should contact their Alabama Extension regional crops agent for help in identifying the best control methods for their crops.
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