Pests and predators battle over native gumbo limbo

Pests and predators battle over native gumbo limbo

By Jeff Wasielewski

The sturdy and fast-growing native tree known as the gumbo limbo, Bursera simaruba, has succumbed to a tandem of pests that have combined to turn this once-beautiful tree into something belonging in a post-apocalyptic landscape.

The gumbo limbo was the first tree I ever wrote an entire article on and for as long as I have taught the class “South Florida’s Top 40 Plants,” the gumbo has sat proudly near the top of that list as a quick-growing, elegant native that could produce quick shade while beautifying one’s yard. When my daughter Samantha was born 11 years ago, I planted a tiny gumbo seedling in her honor. A gumbo that is now 35 feet tall and just as wide.

So you see, the gumbo limbo and I have a long history, and I can honestly say that looking at the state the gumbo is in across the suburban landscape of South Florida brings me great sorrow.

The gumbo’s troubles began about two years ago when the croton scale began feeding on the gumbo’s succulent stems and leaves. This pest did not do major damage to the tree, but as it fed, it dripped something called honeydew onto the leaves and branches below. A black fungus called sooty mold grows on this honeydew and it quickly covered not only the gumbo’s leaves, but its trunk as well. Sooty mold is not particular and will grow on other plants, cars, deck chairs and anything else that happens to have the unfortunate lot to reside under the feeding croton scale.

The croton scale did minor damage to my daughter’s tree and countless other gumbos across South Florida, but I fought any impulse to spray pesticides as I waited and held fast to my belief that natural predators would come and help in the fight against this messy pest.

My predator prayers were answered in the form of a voracious ladybug known as Azya orbigera. This natural predator feeds on croton scale when it is in the larvae stage. The larval stage looks like a tiny little dust mop and is often mistaken for a pest.

With the help of my newfound ladybug friend, the croton scale and the resulting sooty mold were under control and I felt the worst had passed.

I was wrong.

Soon a new pest blew into South Florida, and set its sights on not only my beloved gumbo limbo, but just about everything else. Enter the rugose whitefly. This new pest affects gumbo limbos, oaks, black olives, coconut palms and a host of other South Florida staples. It is rarely fatal, but does make a mess in the form of the aforementioned sooty mold.

The rugose whitefly is larger than most whiteflies and leaves a pattern of eggs on the underside of affected leaves. It likes gumbo limbos so much that its common name was originally the gumbo limbo spiraling whitefly.

Although the croton scale and the rugose whitefly are being held somewhat in check by predators, their combined effect on most gumbo limbos across town is devastating. Gumbos aren’t dying, but they do look horrible.

The gumbo is a widespread native tree in South Florida and is so durable that it has been planted in swales and parking lots as well as housing developments and backyards all across the tri-county area.

The combined visual effect of the sooty mold on the thousands of gumbos across South Florida is harsh: The trees appear to be burnt and blackened beyond recognition.

Has a once-proud native tree finally met its match?

Probably not, as there is a new and very small ladybug as well as a parasitic wasp that have begun to control the rugose whitefly. And don’t forget the croton scale is being fairly well controlled by the Azya orbigera ladybug.

Although the trees look terrible now, the fact that they are semi-deciduous means that they will soon put out new flushes of growth to replace the old leaves that continue to shed through spring.

What can you do if your tree is covered in sooty mold as a result of a pest? My advice is to try to create an environment that is attractive to predator insects that will help you control your pests.

This is accomplished by having a variety of plants in your yard and refraining from pesticide use. Pesticides, when used improperly, can end up making a pest situation worse as pesticides are often more efficient at killing the natural predators than the actual pest. Just think of it this way: A pest population will rebound from a toxic spray much quicker than a predator will simply because pests reproduce much more quickly than predators.

As for the state of gumbos across the South Florida landscape, the future should hold an upswing for this magnificent native, but for the present, please try to be patient as the natural predators slowly work their magic.

For more information about gardening in South Florida, visit www.fairchildgarden.org/gardening.

Jeff Wasielewski is the multimedia specialist at Fairchild, an expert in South Florida horticulture and a professor of horticulture at Miami Dade College.

Read more here: http://www.miamiherald.com/2012/04/08/2735577/pests-and-predators-battle-over.html#storylink=cpy

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