Dan's Papers - August 29, 2008

You have probably never heard of Margery Daughtry or Dan Gilrein. Employed by Cornell Co-operative Extension, they are very well known and highly respected in the horticultural world. When I was in Chicago one year the owner of the largest privately held seed company in the world told me that Margery Daughtry's research was famous - used widely in countries throughout the globe. Daugherty and Gilrein are my favorite kind of people, nerds - I mean - scientists. Daughtry is a plant pathologist and Gilrein is an entomologist.

What they know is fascinating and the worlds they explore - bugs in Gilrein's case and diseases in Daughtry's - affect on our landscapes. Insects and diseases have an enormous impact on nursery production and landscape plantings. For example, citrus and certain jasmine plants from Florida are under a federal quarantine that was put in place to prevent the spread of disease. Sudden oak death shut down entire nurseries on the West Coast where that disease was found.

A recent local landscape dilemma brought these two scientists' passion for their pursuits together. A large, old, fern leaf beech had black ooze on the trunk. The arborist Ray Smith was called in to investigate. The 80' plus beech had a canker on the lower part of the trunk, which was caused by a strain of fungus called Phytophera. The wet weather may have contributed to the canker, which was treated by the arborists, but it was neither the beginning nor the end of this particular story.

A few months later a branch wilted and died. Smith was called in again for a close examination. This time, small worm-like projections were found coming out of the bark of the beech. Frass, or the debris left over from an insect tunneling its way into the tree, was being compacted and pushed out as the bug dug deeper into the wood of the trunk. Tiny holes in the bark the size of a pin indicated where other insects had been busy.

Cutting open a branch near the hole it was easy to find the path through the bark and into the wood of the beech. A bluish stain marked the edges of these tunnels - or galleries. Smith's team sent entomologist Gilrein some samples of miniscule beetles found deep in the galleries, along with pieces of the tree branches to identify the insect in question. After a brief look under the microscope, Gilrein quickly determined the culprit ("Beetles species are easy to identify," he noted). This was XY - a type of ambrosia beetle.

The ambrosia beetles tunnel into the tree to create galleries that extend into the wood of the tree. These are very secure, beetle-sized rooms - so to speak - where the bugs lay their eggs. It was not the one-millimeter size holes where they entered the tree bark that caused the worst damage. The beetle brings along a blue fungus as it burrows into the tree, which is what the darkening of the tunnel edges indicated. The fungus will eventually feed its young when they hatch, but one of the side effects of the fungus is that it shuts down the tree's circulatory system, the xylem and phloem that transport nutrients from the roots and sugars from the leaves, causing the branch to die.

So was it the canker or the beetle that caused the problem? Daughtry, the pathologist, suggests that the afflicted tree may have suffered from compaction around its roots, or struggled through a drought period - both of which would weaken its natural defenses. This made it susceptible to the primary phytophera canker. The tree then put out chemicals that signaled its distress, and the 3 mm long ambrosia beetle picked up those chemicals, sensing them like a pheromone that attracted them to the tree.

Throughout the botanical world this kind of complex relationship exists. And we have already experienced the longterm effects of these types of natural cycles here on Long Island. The turpentine beetle that bored much larger holes into Japanese black pines carried a similar fungus that did them in. Entire swaths of these trees along Dune Road were pampered by arborists to prevent their decline, but many succumbed. Dutch elm disease leveled the Dutch elm across the East End, but it was the elm bark beetle that infected the trees with the disease and lead to the transformation of East Hampton's Main Street.

So what to do now about a problem like this, and will it spread? Good sanitation as the best defense has long been a horticultural maxim, and Daughtry emphasizes those good horticultural practices like mulching and adequate feeding and watering give healthy trees some defense in shaking off these kinds of infestations. But according to Gilrein, any infected branches need to be eradicated and a minor infestation is not a death sentence, a return to good care can keep the tree alive.

Does that mean the problem is solved? Maybe not, another warning Daughtry cautions about is not cleaning pruning tools after use and tracking insects around on shoes. Chipping and composting may not kill off all the eggs of these insects - which is why the Dutch elms were not allowed to be used as fire wood for fear that the insects would still manage to survive in woodpiles.