Big Bend Tree Banes

As summer of 2020 progresses into its hottest months, the local growth of trees, and warm season plants and weeds is accelerating rapidly. Fortunately, the rain has been sufficient, its distribution wide, and the timing good (at least so far) to support the development.

Leaves, frons, and needles are producing green tones and shades which form the backdrop for north Florida’s summer. The thick seasonal foliage obscures or complements a wide variety of structures and objects which will be far more obvious during the reduced inventory of greenery in the winter.

Unfortunately, there are two native trees in rapid decline and facing possible extinction in north Florida. In both cases the cause for their elimination from the vegetative population are impossible to control.

Flowering dogwood trees (Cornus florida) and redbay trees (Persea borbonia) are dying at an alarming rate and will change the appearance of native areas. Healthy trees of both species were once a common site in the Big Bend region but now are a rarity.

Dogwoods are susceptible to anthracnose, a fungal disease which effects a variety of plants. Cool, wet spring weather promote the spread and establishment of this pathogen.

Early symptoms are small and abnormally pale green leaves in the spring. In the autumn leaves on effected branches will turn red before other leaves.

Initially, the signs of infection are localized, but will be systemic after a season or two. Drought and other stresses can add to the vulnerability of dogwood trees.

Some named dogwood cultivars have shown resistance potential, but environmental conditions are major contributing factor. Prevention recommendations include planting the tree in locations where it will dry off as quickly as possible.

One little non-native insect in the Xyleborini tribe of beetles is destroying bay trees and other species at a shocking rate. While native ambrosia beetles are known for attacking various woody plants, their damage is limited to limb and stem dieback with occasional plant death in extreme cases.

Unfortunately, some exotic ambrosia beetles, such as the Redbay Ambrosia Beetle attack healthy trees. Of additional importance, the fungus which causes laurel wilt accompanies this beetle and typically causes tree death.

Most ambrosia beetles have a symbiotic relationship with a fungus which the beetles carry the spores on their bodies. When the beetles bore into the sapwood of the host tree, the galleries formed from the beetle boring are inoculated with the fungal spores.

The adult female Redbay Ambrosia Beetle has a special pouch in its mouth which transports the fungal spores responsible for laurel wilt disease (Raffaelea lauricola). When these beetles bore into the wood, forming galleries, the spores transported in its mouth and on its body infect the tree.

As this pathogen germinates, it colonizes the sapwood of the host plant by using the tree’s circulatory system to spread the disease. Unfortunately, the tree is quickly doomed at this point.

The Redbay Ambrosia Beetle (Xyleborus glabratus) is very small; at about 2 millimeters in length, 15 could fit head to toe in an inch. They are a dark brown to black, cylinder-shaped beetle, similar to other ambrosia beetle species found in Florida.

This pest species is native to east Asia, but the origin of the destructive fungus accompanying the beetle is not known. The beetle is believed to have been inadvertently released into Georgia in 2002 through infested packing materials, such as wooden crates and pallets.

Several species of bay trees, sassafras and avocado trees area all potential hosts for this imported pest. At present there are no registered fungicides for avocado that will control laurel wilt.

The best control measures are to not bring in wooden pallets and other similar products which may carry the tiny beetles, their larvae and the fungus.  Firewood from distant sources is another potential carrier of this problem species.

Hopefully, some bay and dogwood trees have natural resistance to these conditions. If not, the panhandle’s landscape will be changed forever, and not for the better.