Ambrosia beetles could mean bad year for local trees
Well I be dad-gum, if the drought and heat from this year didn’t do enough damage, now we have to contend with an insect that can surely wreak havoc on our stressed trees and shrubs.
The insect in question, the Ambrosia Beetle, is an early season threat to our trees and shrubs. Asian ambrosia beetles are tiny wood-boring insects (less than 1/8 inch long) that attack the trunks of young and weakened trees and shrubs.
Ambrosia beetles tunnel into stems and construct galleries where they raise their young. Beetles carry on their bodies a fungus that grows in these galleries producing ambrosia which feeds both adults and larvae. Ambrosia beetles can also carry the spores of disease pathogens that infect the tree. The growth of these fungi leads to weakening or death of the tree. Like I said ... dad-gum.
As beetles tunnel, they push sawdust out through their entry hole. This sawdust can cling together forming short ‘toothpicks’ sticking from the infested stem. These toothpicks make it easy to identify ambrosia beetle attacks. Wind and/or rain may destroy these toothpicks leaving just the small holes and scattered sawdust from the beetle. Since the entry holes are only about the size of a #2-pencil lead, close inspection is necessary to detect these attacks in time to treat.
Ambrosia beetles attack many types of trees and shrubs including crape myrtles, cherries, oaks, sweet gums, pecans, peaches and many others.
The ambrosia beetle’s first flight occurs with mild weather typically in late February to early March. Cold weather will put them off for a while, but we usually see a big emergence of the granulate ambrosia beetle in March or April for our area in north Georgia. The Georgia Gardener Walter Reeves has received reports of recent attacks in the Atlanta area,
Young trees in the landscapes (less than three years old) are vulnerable to attack even if they are not obviously stressed. This is especially true during the green-up period. Prompt action can save these trees if the number of attacks (“toothpicks”) is less than 4 - 5 per tree.
Trunk sprays containing a pyrethroid insecticide applied now will provide some protection. If applied in time, insecticides such as bifenthrin, cyfluthrin, or permethrin can repel the beetles even after plants are attacked. You should apply the insecticide now and repeat it every 10 - 14 days until the plants are completely leafed out.
Spray affected trees making sure to cover the trunk completely. Monitor the trees for signs of wilting of the new leaves, a sign that a pathogen has been introduced. Once the wilting starts, the tree will probably die. However, do not assume the attack will be fatal, trees may recover. Also watch treated trees to see if new toothpicks develop – a sign that the ambrosia beetles are still active.
If you see toothpicks on larger trees, the tree is probably severely stressed. If attacks are confined to one limb, pruning is an option. If the attacks are on the main stem, prepare to remove the tree if it dies.