Florida’s populations of Diaprepes abbreviatus root weevil have been uncharacteristically low so far in 2023, entomologist Lauren Diepenbrock reported recently. The adult pests are normally active in April–May and in the fall, the University of Florida Institute of Food and Agricultural Sciences assistant professor noted.
Prior to the discovery of HLB disease in Florida in 2005, growers who had extensive diaprepes outbreaks in their groves considered it the worst pest they could have. It remains the most economically damaging root weevil in Florida citrus, Diepenbrock said.
Diaprepes lay eggs between citrus leaves, juveniles hatch, enter the soil and feed on large quantities of tree roots. The damage to the roots provides entry points to pathogens, especially phytophthora. The combination of diaprepes and phytophthora, termed the diaprepes/phytophthora complex, can be lethal to Florida citrus.
“Diaprepescan cause immense amounts of damage on their own. Add in the pathogen, and there is a greater risk of root loss and tree mortality,” stated a slide in Diepenbrock’s presentation. The entomologist suggested that growers choose rootstocks that are tolerant of or resistant to phytophthora to reduce the impact of the disease complex.
CULTURAL MANAGEMENT
Avoidance of wet soil can aid in diaprepesmanagement. Diepenbrock said weevil abundance and damage are highest in wet soil, and that trees stressed by wet soil are less tolerant of weevil damage. Additionally, some weevil natural enemies are less abundant in wet soil.
Soil pH above 6.5 can also stress trees, and some natural diaprepesenemies are intolerant of high soil pH, Diepenbrock added.
Landscape fabric can prevent larvae from entering the soil and adults from exiting. Herbicide savings equaled the cost of the fabric, Diepenbrock stated. She added that individual protective covers, frequently used in recent years to prevent HLB-spreading psyllids from feeding on trees, can also prevent diaprepesegg laying.
BIOLOGICAL CONTROL
The entomopathogenic nematode (EPN) Steinernema riobrave is effective against diaprepes, but other EPNs may not be as effective, Diepenbrock said. She reported that EPNs are more effective on Florida’s Central Ridge than in flatwoods.
Another effort at biological control has not worked well. Diepenbrock reported that egg parasitoids of diaprepes were introduced to Florida from Caribbean countries. Some establishment of the parasitoids occurred, but it hasn’t led to effective control.
OTHER MANAGEMENT METHODS
Monitoring of diaprepes is useful for timing management actions, Diepenbrock said. She noted that egg laying begins seven to 10 days after adults emerge from the soil, so insecticides should be targeted for diaprepes life stages based on monitoring data. Ovicide can be targeted to when eggs are likely present. Insecticidal barriers can be applied to the soil surface to kill neonates as they drop to the soil in an effort to prevent access to tree roots.
The choice of insecticides should be integrated with the rotation of active ingredients used for other ongoing management programs, Diepenbrock said. She suggested that growers see the Florida Citrus Production Guide chapter on root weevil management for recommended chemistries.
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