Combating Citrus Greening with Fungus

By Breanna Kendrick

Researchers are using a fungus to kill Asian citrus psyllids. (USDA/ARS Photo by David Hall)

The University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) is testing an insect-killing fungus to combat the Asian citrus psyllid (ACP).

Pasco Avery, biological scientist at the UF/IFAS Indian River Research and Education Center in Fort Pierce, is researching the use of fungus-oil sprays and assessing the effects on ACP, the insect that transmits the bacterium associated with citrus greening disease, huanglongbing (HLB).

The fungus is called Isaria fumosorosea. In approximately 48 to 72 hours, it kills the ACP by penetrating its cuticle and then growing inside the insect’s body. The fungus naturally occurs in the environment, especially in Florida.

Once a spore lands on the insect cuticle, it germinates and forms a structure called an appressorium, which forms a penetration peg. Hyphae continue to penetrate through the body of the insect until they reach the hemocoel, where the blood is located. The hyphae then break off into little pieces called hyphal bodies or blastospores and travel throughout the entire body of the insect, eventually joining together and forming mycelia. Under high humidity, the hyphae in a mass of mycelia eventually puncture back through the cuticle and produce spores on the outside of the insect body. These spores become airborne in breezy conditions.

Avery’s goal in studying the fungus is to find out if infective spores would be able to persist on citrus leaf surfaces, and be as effective in the field compared to a conventional chemical insecticide, such as a spinetoram product, which is commonly being sprayed in citrus groves for ACP management.

The fungal biopesticide product that contains I. fumosorosea is commercially available and can be used by growers for management of citrus pests, including ACP. “Growers can certainly use the fungal product in the grove, and it is compatible with beneficial organisms such as lady beetles and the parasitic wasp Tamarixia radiata,” explains Avery. “One of the unique things about this product is that it can be used in conjunction with beneficial organisms, whether they are released or are natural residents in the grove.” Avery highly recommends that growers apply this product using a cold ultra-low volume sprayer or cold-fogger type machine.

The study is based on the use of an air blast sprayer in a citrus grove. “At first, we sprayed one side of the row because we were trying to spray through the foliage. Because of HLB, the foliage is less dense,” explains Avery. “We sprayed on one side of the row to determine if we could push the fungal product through the foliage, but what we found is that, on the underside of the leaves, the application coverage wasn’t as much as it was on the top side of the leaves. In September, we are going to redo this experiment and spray on both sides of the trees, which should increase the efficacy as well as persistence of the fungus for management of the psyllid populations.”