By Penny Ossowski
Over September and October I’d been having a problem with silverleaf whiteflies. A couple of years before when my neighbours yard was overgrown and full of weeds, I had silverleaf whiteflies on my cucumbers but after a good dose of Soap Spray I had no more problems until 2009. When I found them on my kale I sprayed with Soap Spray and they disappeared for a day or two, a follow up spray did not seem very effective. A close inspection and I found silverleaf whitefly not only on my kale but also on the lettuce, beans, pumpkin, cucumber, zucchini, tomatoes, egg plant, carrots, yacon and comfrey. I thought the showery humid weather may have caused the population explosion and also prevented the Soap Spray working as well (with the dry weather this year I don’t think the weather is relevant). I decided to try Eco Oil next and after 2 repeat sprayings the silverleaf whitefly has gone for now. There were a few predatory insects feeding on them but then the lizards seemed to be eating those insects, which led me to believe I had to spray. I really should have removed my Kale a couple of months ago when the weather got hot, but I have found it to be a very useful plant for cooking. (other plants I see them on at the moment include, carrots, parsley, lettuce, beans, rocket, marigolds, feverfew, some tomatoes but there are many other plants they will gather on) Here is a little about the silverleaf whitefly.
Whiteflies suck sap from the plant, resulting in a yellow mottling on the surface of the leaf, as well as leaf loss, wilting and stunting. Not only do they feed on plants, but they also produce honeydew, which spoils the plants' appearance, attracts ants and black sooty mould. Whiteflies can also transmit plant viruses.
The silverleaf whitefly is not really a fly, it is more like a tiny moth and is closely related to the aphid. It was detected for the first time in Australia in 1994 and has since spread to most states.
From the DPI Queensland “Adult silverleaf whitefly are small 0.8 to 1.2 mm long (smaller than greenhouse whitefly), sap sucking, flying insects. Adults hold their wings vertically tilted, like a peaked roof. They have white wings and yellow bodies, and congregate on the undersides of leaves, very high populations, can develop within three to four weeks.” Each female silverleaf whitefly lays between 50 and 400 eggs on the underside of a leaf. After eggs hatch and go through their nymphal stages, as per the diagram, the adults emerge and it takes about four hours before the adults can fly and up to 20 hours before the females can mate.
Small birds, spiders, lacewings, hoverflies, ground beetles, some ladybirds, myriad bugs and damsel bugs are the natural enemies of the silverleaf whitefly.
There are a couple of ways to check if you have silverleaf whitefly. Firstly gently shake the leaves to see if a cloud of tiny insects fly up and then quickly settle back on the leaves or look under the leaves for white dandruff like specks. There are also available sticky yellow traps available from various outlets which can be hung above plants in the garden to detect whitefly and other insect activity.
Charlie suggested a soil deficiency may cause some problems. I researched this and found it could possibly be a magnesium and/or a phosphorous deficiency.
Magnesium deficiency can be treated with epsom salts 113.4grams to 5.54 litres water and soak soil around infested plants.
Phosphorous deficiencies can be improved by applications of Blood and Bone, Rock Dust, Fish Emulsion, Fish Meal.
Jocelyn covers the soil under her tomatoes with aluminum foil which reflects light under the leaves to repel pests.
Spraying leaves with seaweed solution may make the leaves unsuitable for the silverleaf whitefly to breed on (it will also feed the plant)
You could also try garlic spray, chilli spray or neem oil (I am hesitant to use neem as it seems to harm a lot of other pests but give it a go)
Some useful websites to look at include