By Larry Hodgson
Question: I have a collection of African violets. I must have brought some thrips home by accident, as they’re now in the flowers of all my plants! No matter how much I treat with insecticidal soap, I can’t seem to get them all and they keep coming back. I know there are systemic insecticides, but I don’t want to use products that are harmful to the environment and myself. Are there natural systemic products? Or do you have other tips on controlling them?
Answer: First, just so other readers understand the situation, thrips are tiny insects that scrape the tissues of plants and thus cause distorted growth. They spread to other plants mostly by jumping, but also by flying, and are difficult to control.
The species that attacks the flowers of African violets (formerly Saintpaulia ionantha; now Streptocarpus ionanthus) is the western flower thrips* (Frankliniella occidentalis). It feeds on flower pollen and cuts holes into the yellow anthers in the center of African violet blooms, spreading pale pollen on nearby flower petals.
*Note that “thrips,” with an “s,” is both plural and singular.
The bad news is, no, there are no effective organic insecticides that are systemic. In fact, most systemic insecticides, that is, insecticides that are absorbed by plants and then circulate in their sap, making the whole plant poisonous, are synthetic (chemical) ones. And in many areas, you wouldn’t be able to buy them anyway, as synthetic systemic insecticides are considered dangerous to human health and their domestic use largely has been banned, although they may still be available to farmers or trained horticulturists. Examples of chemical systemic insecticides that are usually not available to home gardeners include Cygon and the various neonicotinoid insecticides.
Of course, there is neem oil, which is certainly organic, as it is made from a tropical tree (Azadirachta indica), which is said to have a certain systemic effect. However, in this specific case, it is not considered effective enough to eradicate flower thrips and thus the insects quickly return once the treatment is over.
African Violets Resistant to Flower Thrips
There is now a series of African violets that produces flowers without anthers and therefore without pollen. And since they have no pollen, western flower thrips have no reason to visit these plants. The series is called LooXo (pronounce it Looks So) and was introduced by Optimara, a major American producer of African violets.
A Pesticide-free Treatment
That said, there is a way to suppress flower thrips without using insecticides.
Since the western flower thrips necessarily spends part of its multistage life cycle in flowers or seed pods, if you remove all the flowers and flower buds, they’ll have nothing to feed on. That will, of course, prevent them from reproducing. However, you have carry this out for 3 full months, removing all flower buds as soon as you see them, if you want this method to be effective.
In addition, you can’t allow other plants to bloom either, as the western flower thrips visits many other types of blooms. So, you’ll have to remove the flowers from all your other plants over 3 months as well.
Even though you might find it disappointing to see no flowers for 3 months, imagine the profusion of bloom you’ll see afterwards, as your plants will store their energy and flower like never before when the treatment finally does end!
To learn more about thrips, read Thrips: The No-See-Sum Plant Pest.