by Holly Davis, Ph.D. – Certis Biologicals Field Development Manager, Southwestern U.S.
Whiteflies have been a persistent problem this year for Texas growers. These insects can be especially difficult to control in organic production. There are numerous OMRI certified biologicals, or biopesticides, available to growers but, to get the best efficacy, it is important to understand a few things about them.
First, biopesticides need to be applied at the first sign of whitefly activity. Trying to clean up a situation where plants are heavily infested with all life-stages of whiteflies (or any insect or disease) is extremely difficult and there may be no escaping loss of quality and/or yield. The use of yellow sticky cards in greenhouses or around field margins can help detect whitefly activity early so that applications can begin in a timely manner.
Most biopesticides labelled for whitefly control are contact pesticides, meaning they must either be sprayed directly on the pest, or the pest must move across a treated surface while the biopesticide is still active. This can be tricky for insects like whiteflies which spend the majority of their time on the underside of leaves, sometimes deep within plant canopies. For that reason, it is important to use the correct amount of carrier, the right spray equipment, and nozzles, and to include a spreader sticker when appropriate to ensure product is distributed as evenly as possible and adheres to plant tissue.
Once applied, biopesticides may not persist in the environment for a long period of time. Many are degraded by sunlight and/or other environmental factors. Remember, most do not move through the plant (are not systemic) so any new plant growth after application will not be protected. For this reason, biopesticides need to be applied on a regular interval, often every 7-14 days, to ensure that whitefly populations do not build up between applications.
Finally, it is important to understand what to expect from different types of biopesticides. For example, while some products like Des-X®, an insecticidal soap concentrate, have the advantage of providing a quick knock-down of whitefly populations by breaking down the insect cuticle, there is no residual efficacy. Any insect that lands on a leaf after the treatment has dried will not be impacted. Other products such as the entomopathogenic fungi, Beauveria bassiana, found in BoteGHA®/BotaniGard®, may take several days to kill whiteflies by overwhelming them with fungal spores, but can persist in the environment and continue to infect immigrating or emerging insects. This typically happens when there is high relative humidity and/or a dense plant canopy.
This persistence can be recognized by mycosis, or the presence of emerging spores from a fungus-killed insect. However, lack of visible mycosis does not mean an entomopathogenic fungi is not working. In many cases, whiteflies may simply darken and desiccate.
No matter what biopesticide you chose, it is incredibly important to read the label and understand the product to get the best efficacy possible!
A big thanks to Dr. Davis for supplying such helpful information. For more information on Certis Biologicals, please visit https://www.certisbio.com/