Infestation of Whitefly

Answered by Harrod Horticultural Posted in Category Pest Control & Nature

Dear Martin

My infestation of white fly has been horrendous, so much so that almost all of the leaves of my tomato plants have been so covered with mildew that they have had to be removed. The white fly flourishes; as I have never had them do in all the 50 years I have grown tomatoes. They were well established by the time your “bugs” arrived. Was that too late for the little things, I wonder. Until a few years ago I was able to control them with smoke, which I have not been able to obtain locally. I wonder if that is due to brussels.

With regards
Tom Straton

Dear Tom

Many thanks for your recent message regarding the unfortunate infestation of whitefly you have experienced. In our experience, it is best to introduce the biological predator of these pests, encarsia formosa, the parasitic wasp, as early as possible after the whitefly appear. This enables the wasp to keep the infestation in check as in the height of summer, the whitefly life cycle can be completed in 3 weeks.

If you should experience a severe infestation again – and let’s hope this will not be the case – it is advisable to partially clear the adult population by introducing sticky traps or applying an organic pesticide such as the Natural Bug Killer or Derris, before introducing the encarsia formosa. We would not recommend using these sprays after introducing the predator. It is then possible to monitor the effectiveness of the predator by observing the number of black scales on the underside of the leaves; a white scale has not been parasitized by the wasp but a black one has and an adult wasp will eventually emerge. As with most biological control methods, the predator requires some population of the pest to be present for it to continue it’s life cycle, and this evidence is particularly helpful when planning future applications.  

The mildew that forms on the lower leaves is a by product of the whitefly; as they feed on the plant’s sap, the excess sugar is secreted and falls on these leaves which provides a perfect culture for the mould and mildew to flourish.   Unfortunately, it appears that the smoke cone previously supplied for the specific control of whitefly is no longer available in this country but Fumite do provide smoke controls containing permethrin; this however is designed for use on a commercial scale so we would advise careful research before considering this product, and as we are dedicated organic growers, we would not advocate this method of control.

Many thanks once again for your message and hopefully this information is of help; please feel free to contact us should you have any further questions or queries.

Martin