Granulate ambrosia beetle

About

A tiny, dark reddish-brown beetle from Asia, about 1/10 inch long, first found in the U.S. in peach trees near Charleston, South Carolina, in 1974. Unlike native ambrosia beetles, it attacks healthy trees as well as stressed ones, and it often kills young and newly planted trees.

Spotting it

Damage

Females bore into trunks and stems roughly 1 to 12 inches across and push out sawdust that hardens into little toothpicks sticking out of the bark. They carry in a fungus that blocks the tree's sap flow, causing wilting, branch dieback, late leaf-out, early leaf drop and cankers that can girdle and kill the tree.

How to find it early

In late winter and spring, check the trunks of young and newly planted trees for toothpick-like strands of sawdust and tiny holes about 2 millimeters (under 1/10 inch) wide. Traps baited with ethyl alcohol can show when beetles are flying.

When

Late winter through spring, with fewer attacks in summer and fall

Life cycle

Females tunnel into the sapwood, plant a fungus garden and lay eggs; both larvae and adults eat the fungus, not the wood. Eggs, larvae and pupae develop together inside the tree, and there are about two generations a year in the Southeast, with the most attacks in late winter and spring.

What to do, gentlest first

Start at the top. Sprays are a last step; always read and follow the product label.

1. Keep trees healthy and buy clean stock Prevent

   Water, drain and care for trees properly and avoid wounding the bark, since newly transplanted trees are the most at risk. Clemson says the less stressed a tree is, the more likely it is to avoid or survive attacks.

2. Remove badly infested plants By hand

   Cut out and destroy heavily attacked trees and shrubs so beetles can't breed in them and spread to nearby plants.

3. Preventive pyrethroid trunk spray Conventional spray

   On valuable young trees, a pyrethroid such as permethrin or bifenthrin sprayed on the trunk before beetles attack can keep them from boring in. Clemson says it must be put on before trees are attacked and repeated every few weeks, as the label allows.

   Once beetles are inside, sprays help little, and systemic products don't help because the beetles don't eat the wood. Pyrethroids are highly toxic to bees, so spray only when bees are not active. Read and follow the label and the pre-harvest interval on fruit trees.

Plants it goes after

Apple (backyard tree), Azalea, Crape myrtle, Eastern redbud, Fig, Peach, Persimmon (American and Asian), Plum

Pressure by region

It has spread to at least 29 states (Clemson): along the Southeast coastal plain to North Carolina, Florida, Louisiana and East Texas, and north to Virginia and Indiana (UF/IFAS), and it is present in Hawaii (UF/IFAS). UC IPM says it is not established in California, where it is sometimes caught at border stations, and that finds in Oregon and Washington appear to have been wiped out. It is still spreading, so report new finds to your state department of agriculture (in California, your county agricultural commissioner). Ratings outside the Southeast and south-central regions are estimates.

Ratings come from extension sources where available; some are estimates, as noted above.