I don’t live in a snow-prone area, but when I go outside to take a look at my hibiscus plants you’d think I did given the white infestation that seems to cover the plant.
The culprit that is making my plant look like it has a grey beard is a little-known terror known as the Giant Whitefly or White Ash Fly. It’s annoying, unsightly and a pain in the you-know-where to get rid of, but here are some tips on what you can do.
I first noticed the fly’s arrival about five years ago. At first I thought it was some dust or debris floating about from a nearby construction project. But it soon became apparent that it was something else and it wasn’t going to take kindly to attempts to get rid of it.
Credit: ucr.eduThe fly, known by its scientific name of Aleurodicus Dugesii, is very small – about 4 millimeters in length – but they arrive in hordes and they pack quite a wallop for their small size. In some cases you might not even readily see the infestation because they tend to do their damage to the underside of hibiscus and other plants. But, left untreated you can have a hibiscus plant that is enveloped like a cocoon. It’s definitely not what you want your hibiscus to look like.
Origins in Mexico
The fly looks like a tiny, white moth. Its origins are in Mexico and they floated up to the Southern California area in the 1990s. From there it has spread to other states and as far as Hawaii. Hibiscus plants seem to provide its most ideal residence, but they can and do enjoy other plants and shrubs as well. The adults of the species love to lay their eggs on the underside of leaves – and they lay a lot of eggs. As they enjoy their new home they excrete a waxy substance – also white – that forms layers of material until you have a thick, gooey and ugly scene that appears to be a blizzard covering your plant. They are also adept at sucking out the plant sap and killing leaves, although it’s rare that they’ll destroy the plant (at least a hibiscus plant – other plants may not be so fortunate).Credit: uc davis
My hibiscus was no match for the critters. My early attempts to get rid of them proved amateurish. I pulled out infested leaves only to find more and more of the flies and their droppings covering the underside of what appeared to be very healthy, green leaves. Of course the damage to plants and crops throughout the State of California and elsewhere is a serious business now and state officials consider it to be one of the most serious pests affecting agriculture and ornamental horticulture.
For my first effort I decided to cut the plant back to the ground thinking the plant needed a trim anyway and eliminating the source of the flies’ meals and spawning ground would do the bugs in. That worked for a short while. But hibiscuses are hardy plants and they grew back as expected. Unfortunately, within a few months the ash fly found its way back as well.
Having exhausted my own attempts to combat the fly, I turned to professionals. At my local nursery I was told there are several methods I could try. I wish I could say they worked to perfection, but I can’t. Combating the white ash fly is a marathon not a sprint. Just the same, here are some methods I was told to try. They may help you as well.
My nursery manager suggested ladybugs as a counter-force to the ash fly. I purchased a quantity of them, but I can’t say they were very successful. Obviously the ladybugs are going to go wherever they want once they are released and my hibiscus didn’t seem to be the home of choice for them.
However, there is a lot to be said for biologically controlling the pests. Some other species, such as lacewings, lady beetles and wasps are said to be effective, but again they are hard to control in terms of keeping them on or around your own garden.
If you are like me, the last alternative is spraying chemicals on your plants, around your home, pets, etc. But, sometimes it is the method of last resort. That being said, there really aren’t any sure fire chemicals that seem to work on ash flies, and I’ve tried many. Some insecticidal soaps or oils are said to be somewhat effective but they are very hard to apply and invariably need reapplication.
One of the most effective methods of control is to spray water on the pests regularly. Researchers at the University of California, Davis swear by the method. They say a strong stream of water directed weekly at the underside of the infected plant leaves will do the trick. As it works you can cut back your spraying to every two or three weeks.
Credit: UC RiversideIt’s not something officials are talking a lot about, but one lone nursery manager I spoke with suggested using earthworm castings to control the ash fly. A 10-pound bag of worm castings can usually be found in your nursery and it is typically used for plant beds and plant nutrients. They are known for their high level of nutrients and organic origins.
At first I was dubious about worm castings as a way to fight off ash flies. But the nursery manager told me to try it and so I did. I carefully cleared away debris from the base of my hibiscus and trenched around the plant to a depth of about six inches. I then filled the trough with the worm castings, filled the trench with water and lightly covered the area with soil.
I wish I could tell you that this worked perfectly, but although it seemed to do better than any other method I tried, eventually the flies returned. The earthworm castings do seem to have some effect, but the key is reapplication every few months and that takes a lot of effort.
So, I am still battling the ash fly. It appears that until a sure fire control agent or method can be found homeowners and plant lovers will either have to suffer while the battle goes on or decide to choose plants or shrubs that are less prone to the ash fly attacks. For now I’m still in the fight.
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