Managing Citrus Root Pests

Nematologist Larry Duncan discussed efforts to control the root pests sting nematode and Diaprepes root weevil in his presentation during the virtual April 6 Florida Citrus Growers’ Institute. Duncan works at the University of Florida Institute of Food and Agricultural Sciences’ (UF/IFAS) Citrus Research and Education Center.

The sting nematode and Diaprepes are especially concerning in the age of HLB, because both feed on citrus roots that are already heavily diminished by HLB.

Duncan said sting nematodes were first recognized as a widespread pest of Florida citrus during the freezes of the 1980s. The sting nematode feeds at the root tip, causing stubby root symptoms, he added.

There are six relatively new nematicides available for use on sting nematode, Duncan reported. Research indicates that five of those nematicides reduce nematode populations. As the sting nematode populations drop, trees have better growth, he said.

Duncan reported that perennial peanut used as a cover crop in row middles also significantly decreases sting nematode populations.

Prior to HLB’s discovery in Florida in 2005, many growers who had Diaprepes root weevils in their groves considered them to be their worst production problem. Duncan pointed out that Diaprepes is difficult to control in large part because it has life phases both above and below ground. He added that fabric barriers placed on the grove surface will reduce or eliminate Diaprepes recolonization. Entomopathogenic nematodes also can aid in Diaprepes control.

Duncan said individual protective covers (IPCs) may eventually help growers with both the sting nematode and Diaprepes root weevil pests. The covers could help with sting nematodes by reducing the incidence of HLB in young trees, which will leave the trees with healthier root systems. Regarding Diaprepes, one of Duncan’s presentation slides stated, “Protective tree covers that prevent psyllid feeding will also prevent weevil egg laying.”    

Many citrus growers have begun using IPCs in recent years. UF/IFAS research has shown that the covers do a good job of keeping trees free of HLB by excluding psyllids from the tree canopy.  

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