The citrus root borer (Diaprepes abbreviatus) is a new invasive insect pest of specialty crops in Leon County. The first samples of the insect were collected from satsuma mandarin trees at the FAMU Viticulture and Small Fruit Research Center during the summer.
Common host plants for citrus rootworm include citrus, grape, papaya, sweet potato, sugar cane, cotton, peanut, corn, and other plant species. The pest is known to feed on more than 270 plant species from 59 different families.
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Although the pest is native to the Caribbean, it was introduced to Florida in 1964 in a shipment of ornamental plants from Puerto Rico.
Since then, the pest has spread over a large area of central and southern Florida, and current climate vulnerability to production systems is causing wheat to invade new geographic areas and potential crops.
Recently, it has been recorded in North Florida in Leon County, where it feeds and breeds on citrus and other host plants.
It damages crops as soon as it spreads
The pest can reach South Georgia at any time, where it can cause problems for many commercial food crops. Preliminary economic estimates indicate that the pest causes approximately $70 million in damage annually in Florida alone and infests more than 100,000 acres of citrus.
Both larval and adult stages of the pest can cause serious damage to host plants. In citrus fruits, the larvae feed on the roots. After infestation, plant roots become more susceptible to Phytophthora fungi. In citrus fruits, even a few larvae can cause serious damage while feeding, and adult grubs can cut leaves and tender shoots.
Although most mature plants can withstand this damage, one larva can kill a young citrus plant. Citrus root adults emerge from the soil from late May to early July, and the second peak occurs from late August to late October.
A mature citrus root is less than two centimeters long, with a dark black body covered with small white, orange and/or yellow circular scales. Scales are often rubbed on ridges in old weeds, and dark brown-black streaks appear.
Wild citrus eggs are very small, oblong-oval in shape and laid in clusters of 30 to 265. They can be found enclosed in leaves folded and glued together by the female.
The economic impact is increasing
The economic impact of damage to nursery crops and field production is increasing. There is no pheromone to control pest density, and monitoring and sampling larvae is difficult because larvae feed on roots below ground.
Annual seasonal abundance of weeds in citrus orchards can be monitored by using traps to capture young adults.
To collect the adult bugs, hold a white paper plate under the branch and shake or tap the branch to dislodge the insects. Using regular insect sweep nets for collection is also useful. Due to their size, mature wild plants can also be hand-picked from host plants.
The presence of adults feeding on citrus can alert growers to control this serious pest, but there are very few pesticides registered to control young larvae. Over the past 10 years, heavy use of pesticides to control citrus psyllids has reduced their ability to provide adequate pest control.
Few natural enemies of the citrus root weevil are known, including two egg parasitoids and some general predators such as the predatory stink bug, the king jumping spider, and several species of ants. Some nematode species that occur naturally in Florida soil may also provide some control.
It is important for anyone growing citrus or other citrus root weeds to be aware of this emerging pest and monitor their crops for its presence.
Dr. Muhammad Haseeb is an Associate Professor of Entomology at Florida A&M University’s College of Agriculture and Food Sciences, Center for Biological Surveillance, and a volunteer writer for UF/IFAS Extension Leon County, an Equal Opportunity Institute. For gardening questions, email AskAMasterGardener@ifas.ufl.edu.
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