Maple petiole borer and carpenter bees

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By Dennis Morgeson

Are numerous leaves dropping from your maple trees?

The culprit this time of year is probably the maple petiole borer.  

There are several other reasons why leaves will fall from maples like squirrels, drought, and heavy aphid or scale infestations, however the characteristics of the maple petiole borer is obvious.  

When petiole borers attack a leaf it looks generally healthy when it detaches from the tree.  

The petiole or leaf stalk will have a limp spot in it and will dangle in the breeze.  It will then fall from the tree.  

One half of the petiole will remain on the tree and one half attached to the leaf itself.

The maple petiole borers are small sawflies, which is a type of non-stinging wasp.  

After over wintering as pupae in the soil, they emerge as adults in the spring.  They lay eggs in the petioles or stems of leaves of the maple trees, mostly sugar maple.

When the eggs hatch they tunnel into the petiole where they feed on tissue.  They are about 1/3 inch long at maturity and are cream colored with brown heads.  

As the borers tunnel into the petioles they disrupt the connective tissue and cause the leaves to fall off prematurely and suddenly.  

The larvae remain in the portion of the petiole that remains on the tree.  

A few days later, the remaining petiole piece falls to the ground and the borer then burrows into the soil to complete its life cycle.  

There is generally only one generation per year.

The idea of your maple leaves falling to the ground just as they begin to grow may worry you; however it causes very little damage to your tree.  

Maples as well as other trees can lose a large number of their leaves without any ill effects.  

The maple petiole borer is simply a nuisance that doesn’t warrant control.  

The leaves will stop falling in a few weeks and the maple tree will continue growing like nothing happened.

Bees of all kinds were out and about last week.  

Carpenter bees have been the biggest pest, however.  

These large black bees resemble bumble bees without the usual yellow stripe across their back.  In the spring carpenter bees are active flying about looking for mates, especially the males.  

These large black bees will hover in front of a person or pet who gets too close to their nest.  

The interesting thing about carpenter bees is that many “old-timers” believe they won’t sting or didn’t have a stinger at all, well they were partially right.  

Male carpenter bees do not have stingers and therefore can’t sting, however the female does have a stinger and can inflict a painful wallop, although they won’t generally sting unless seriously provoked or handled.

Carpenter bees or wood bees as some people like to call them burrow into wood such as eaves, window trim, decks, and fascia boards which is different from bumble bees who nest in the ground.  

They can cause serious damage to any wood surface if allowed to continue year after year.   

The best control of carpenter bees is to deter them in the first place by keeping all wood surfaces painted or covered with a stain or preservative.  

Carpenter bees prefer wood that is left bare, weathered and easily accessible.

An exterminator may be required to completely rid you of carpenter bees however if you plan to try controlling them yourself it is best to go in at night when the bees aren’t active.  

Females will sting if threatened.  Wear protective clothing to keep the insecticide off of you skin and to protect against stings.  

Chemicals that are effective against carpenter bees are Sevin, Dursban, Permithrin and Cyfluthrin.  

These chemicals should be sprayed in tunnels and around holes where bees are active.  If the tunnels are particulary deep you can use a dust and squirt it into the holes.  

Wait a few days to allow the bees to distribute the chemical throughout the nest then plug the holes to deter future infestation.  It may take several chemical applications to control these pesky but beneficial bees.  

Happy Gardening!