How to control whiteflies

Hemiptera / Sternorrhyncha

What are Whiteflies?

Small white winged sap-sucking insects, that aren't actually flies at all. They resemble tiny white moths with a wingspan of 3mm. Whiteflies have become very prevalent in recent years and there are several different types which are major pests for home gardeners. The Greenhouse Whitefly (Trialeurodes vaporariorium) and the Sweet Potato Whitefly (Bemisia tabaci) are the most commonly encountered pests in NZ.

If the plant host is disturbed, a distinctive cloud of tiny insects fly out, but they soon settle back onto the same plant. Both the adult and juvenile (nymph) whiteflies suck the juices from the plant.

Favoured plants are hibiscus, poinsettia, gerberas, herbs such as sage and mint, vegetable seedlings such as squash, melon, eggplant, cabbage and bean, tomato and broccoli.

Whitefly has two life stages that are resistant to pesticides, which explains why a single spray often won't control it completely. A quick outline of the whitefly life cycle will be helpful to understand why.

The winged adults are usually found feeding on growing tips and new leaves. The females lay eggs on young leaves, close to where they are feeding. When the eggs hatch out, they go through four different larval stages, that look like tiny scale insects. The last larval stage stops feeding when fully grown and forms a pupa.

The challenge is that the egg and pupal stages are quite resistant to pesticides, while the adults and youngest nymphs are easily controlled by most pesticides. Because you can usually find all the different whitefly life stages on the same leaf, a single spray is often only partially effective.

Symptoms

Wilting and stunting of new shoots. Can cause silvering and yellowing of leaves, uneven ripening of tomatoes and sometimes plant death.

Sooty mould often accompanies large numbers of whiteflies, because they excrete honeydew when feeding on plant tissue.

How to Protect your plants

Whitefly is best controlled using alternating sprays, as the insects can build up chemical resistance very quickly. Alternating insecticides help to prevent this from happening.

We recommend using Yates Mavrik at 1-week intervals, and alternating with Yates Nature's Way Natrasoap Vegie Insect Spray to interrupt the life cycle and get complete control. Ensure you get complete spray coverage, including on the underside of leaves.

Spraying is best done in the early morning or late afternoon while the insects aren't as active.