Silverleaf whitefly (SLWF) is a sporadic and localized pest of cotton in Georgia. There are reasons for this localized infestation pattern and it is important we understand why this occurs. In Georgia SLWF infestations are most common in areas where both cotton and vegetable production occur. In these areas crops which serve as reproductive hosts are grown 12 months a year. SLWF infests brassica crops in the winter months, move to cucurbits in the spring, move to cotton in the summer, move to cucurbits in the fall, and back to brassica crops during the winter. This is a simplified view of movement and buildup of SLWF during the year. SLWF actually has many different hosts (both wild hosts and cultivated crops), but the crops mentioned are the drivers in SLWF population dynamics. What we do know is that it is important for all of agriculture to properly manage SLWF. Failure to properly manage SLWF in a crop will have negative consequences on the next crop SLWF infests. More information on SLWF and management can be found in the publication “Cross-Commodity Management of Silverleaf Whitefly in Georgia” (https://secure.caes.uga.edu/extension/publications/files/pdf/C%201141_1.PDF).
There are several risk factors influencing SLWF populations during the year. One important factor is winter weather. SLWF survive the winter months on both cultivated and wild host plants. Mild winters favor survival of SLWF. Although temperatures rarely are low enough in South Georgia to kill SLWF outright, freezing temperatures which kill host plants infested with immature SLWF effectively kills immature SLWF on those plants. Cold temperatures also slow development of SLWF. Higher survival and reproduction during winter months leads to higher populations in the spring and the opportunity for populations to rapidly build to damaging levels. To date we have only had 6 days in Tifton when the low temperature was below 32 degrees. When reviewing weather data for the last 15 years, this winter was tied for the fewest days below freezing. What does the lack of cold temperatures mean for cotton? The mild winter suggest our risk for SLWF in cotton is elevated. This does not mean we will have a SLWF problem in cotton, but we cannot ignore the lack of cold temperatures. Spring and summer weather will be the primary factor affecting SLWF populations from this point forward. Hot and dry conditions will favor SLWF population buildup. If you are in an area prone to have SLWF, NOW is the time to manage risk factors we can control.
Variety Selection: hairy leaf cottons are preferred by SLWF compared with smooth leaf cottons. There is a direct correlation of SLWF infestations in cotton based on the degree of leaf hairiness. Risk of SLWF is greatest on hairy varieties > light hairy > semi-smooth > smooth varieties. Smooth leaf varieties are the least preferred by SLWF. Plant Smooth Leaf Varieties
Planting Date: the risk of SLWF problems increases as planting dates are delayed. SLWF complete a generation in about 2 weeks during summer months and populations can increase rapidly. The impact of SLWF on yield is dependent on the growth stage of cotton when SLWF infest the crop. Potential yield loss is greater when infestations appear during squaring or early bloom compared with late bloom. The duration or time of control required to protect yield and quality from SLWF is also dependent upon
planting date. April and early May planted cotton is at lower risk for SLWF problems compared with late May and June planted cotton. Avoid Late Planting
Location (proximity of SLWF infested crops): crops produced in a given area can be viewed as sources and sinks for SLWF populations. Spring vegetable and melon crops are a source of SLWF infesting cotton. In the fall cotton is a source of SLWF infesting fall vegetables. The nearness of cotton to a SLWF infested field increases the risk of SLWF. Minimize Planting Cotton Next to SLWF Infested Crops. If planting cotton near SLWF infested crops, be sure to avoid late planting and use a smooth leaf variety. Destroy SLWF host crops immediately after harvest; this includes vegetable and melon crops in the spring and cotton (timely defoliation and harvest) and other crops in the fall.