Two insects threaten Louisiana citrus

Tobie Blanchard  |  9/9/2009 11:54:51 PM

News Release Distributed 09/09/09

The diaprepes root weevil comes in multiple colors, and it can cause problems for multiple plants according to LSU AgCenter entomologist Dr. Natalie Hummel.

The weevil “has a host range of about 270 different host plants including a number ornamental plants and trees as well,” Hummel said.

State agriculture experts are most concerned with the weevil and the Louisiana citrus crop. Growers were already on alert after the Asian citrus psyllid, an insect that transmits a disease that can kill citrus trees, was discovered last summer.

This latest insect is native to the Caribbean but has been in Florida since the 1960s, Hummel said. It was confirmed in a citrus orchard in lower Plaquemines Parish last fall.

Jerry Ragas noticed damage on his young trees, which were planted after Hurricane Katrina wiped out his orchard, but he blamed the damage on other factors.

“Hurricane Gustav came through here and shook these trees up plenty, and we had this huge influx of grasshoppers,” Ragas said. “But when the trees started dying back, I realized it was something more critical than the grasshoppers.”

Ragas has lost 20 trees, and he said around 50 more are dying.

A female diaprepes root weevil can lay up to 5,000 eggs in its lifetime – a tremendous amount according to Hummel. They lay the eggs on leaves, and the larvae feed on the leaves, then fall and burrow in the ground where they feed on plant roots. The adults also feed on the leaves.

“It’s important to have three lines of defense with this pest, which is unfortunate because it’s costly, but you need to control the egg stage, the adult stage and the larval stage,” Hummel said.

LSU AgCenter researchers have worked with state officials to recommend a treatment plan that includes a growth regulator that causes the females to lay sterile eggs, foliar sprays when adults are emerging and an insecticide barrier on top of the soil to kill the adults while they emerge.

Ragas’ 4-acre orchard is under quarantine, meaning plant material from the property can’t be moved.

“The state has decided not to take an eradication approach to this pest, but we are trying to come in and really proactively and aggressively treat this population with the hope that we can slow the spread throughout the state,” Hummel explained.

Hummel advises all citrus growers to be on the lookout for the pest, which potentially could be a problem for sweet potatoes and sugarcane. Growers also should keep an eye out for the psyllid.

In Plaquemines Parish, where the state’s citrus production is centered, officials are using helicopters to spray all the trees for the psyllid in a single day.

“We’ve managed to still maintain the population at a low level in Plaquemines Parish, and the parish is gearing up to do another area-wide management,” Hummel said.

The problem with the psyllid is greening disease. Areas can have the insect, but not have the disease.

“Since it was first found in Algiers, greening disease also has been found in Washington Parish,” Hummel said. “I think there were two or three trees that were found, and all those trees have been removed voluntarily and destroyed by the state.”

Growers in Plaquemines Parish are hoping to avoid getting the disease because its appearance would put restrictions on movement of plants from citrus nurseries in the area.

LSU AgCenter county agent Alan Vaughn stressed the importance for individuals not to bring in citrus plants from other states, citing that as a potential way for insects and diseases to spread.

Tobie Blanchard

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