It’s getting to be that time of year where whitefly populations are getting ready to explode. This fly which is really no fly at all seems to come out of nowhere and can fill the air around you every-time you shake a branch or bush.
In reality they’ve been building up for awhile but you wouldn’t notice them as nymphs. Whiteflies molt 4 times before becoming adults and it is in the earlier stages that the major damage is done to your plants. If left untreated your infected plant will become listless and yellow and in this weakened state it may die or be vulnerable to other diseases or pests.
There are many products that are used to kill the whiteflies but repeated applications are often necessary because they have shown to be resistant to some insecticides. Larger plants make it difficult to treat thoroughly and they tend to spread out to more than just one. Often whole hedges or rows of ornamentals are infected. To make matters more difficult you must treat the underside of the leaf because that is where the whitefly lives, eats and lays their eggs. This can be quite the chore!
The most effective and easiest way to treat for whiteflies is to use a systemic insecticide with the active ingredient imidacloprid. This formulation is applied around the roots and sucked up by the plant making it essentially ‘toxic’ to the fly and many other harmful bugs. This product does however have a down side. Beneficial insects such as bees also feed on plant juices (nectar) and the insecticide is an equal opportunity killer. While there is no conclusive proof to connect the world wide collapse of bee colonies and imidachloprid it is worth considering other alternatives at least if it is flowering plants that you are treating.
Not to be outdone, traditional insecticides also are non discriminate and often kill beneficial predators of the whitefly. Lady bugs, lace wings and parasitic wasps feed on the whiteflies, aphids and other harmful inhabitants and die off when they come in contact with the pesticide.
What to do?
Personally I have used imidachloprid on non flowering plants and eliminated a severe whitefly infestation very quickly. I tried the traditional route several times but didn’t even put a dent in them and it was getting to be too much insecticide. Keep in mind I have the professional equipment and best products needed for a thorough job but got nowhere. Using the systemic route I solved the problem with far less product in about 20 minutes.
I love beneficial bugs and especially bees so I do not use this method on any flowering plants. (I also don’t have large numbers of flowers so it makes it easier) For those plants I used pyrethrum contact aerosols so there would be no residual but my results were not nearly as good. I also trimmed the most infested parts away and tried soaps and even seaweed spray. I lost a good bit of those plants but the following year the whiteflies were all but gone which I assume was more to the systemic side of things.
I’m not an alarmist nor have I hugged any Sycamores lately but responsible pest control is something you should expect from someone who’s been doing this for 26 years. Just because a chemical can kill large infestations of a certain bug sometimes the unseen consequences are just a bit to much.
My advice is for you to tread carefully with whiteflies and if you decide on the systemic approach use it only on non flowering plants. On the other hand traditional insecticide use is great but don’t keep piling it on just to get results that most times won’t be there. If you can knock it down enough to a low roar than the natural predators will move in and take care of the rest no harm no foul. The links above should give you all the info you need on what to use, I just wanted to impart a little wisdom on ‘what to do.’