Dealing with whiteflies can be very challenging, especially in greenhouses or in warmer climates like Florida. Here are some tips on how to get rid of them, without synthetic chemicals.
In New York State or similar temperate areas whiteflies are not usually a severe problem outdoors because they are kept in check by natural predators and cold winters. Occasionally, however, they get out of hand, often in a vegetable garden that was started in an infected greenhouse.
In Florida where the rugose spiraling whitefly used to be a problem, the fig whitefly is now destroying plants.
In this situation choosing plants that are not hosts, and eradicating weeds that are, is a great strategy, but not always possible. How do you know which weeds are hosts? See where the whiteflies are hanging out.
Over fertilization fuels whitefly growth. Don’t fertilize unless you have to.
Keep the plants healthy, good soil, the right amount of water, and preventing heat stress make the plants stronger and less susceptible.
Beyond that, a certified organic horticultural soap or certified organic oil such as neem oil can help. Because there are so many eggs on the bottom of plants, it is difficult to treat them all and repeated treatments are often necessary. Here are some references.
In greenhouses here is what you need to know.
Whiteflies don’t survive without plant material (including weeds). They don’t survive in soil. So getting rid of all of the plants and cleaning floors and benches will help.
Nip them in the bud! Get rid of them before there are too many. Yellow sticky cards will let you know early on that they are there.
Don’t over fertilize, keep your soil healthy, water correctly, and avoid heat stress.
In a greenhouse beneficials are effective.There are 2 tiny wasps that parasitize whitefly nymphs – Encarsia formosa (greenhouse whitefly) and Eretmocerus eremicus (sweetpotato whitefly). You either need to identify which whitefly you have (see article from KY) or get a mix of the wasps.
Certified organic horticultural soap and certified organic oil such as neem can be used, but again, difficult to get the whole plant and have to keep repeating. And of course, these kill the beneficials, too.
And here is a reference for greenhouses.
Many thanks to Dr. Elizabeth Lamb for this incredibly helpful information.
March 5, 2019