Plant Doctor Archive

Pesky whitefly — 1

Question I’VE grown cucumbers in my greenhouse this year and whitefly have been a real pest. I’ve tried various sprays, including neem and yellow sticky traps, but don’t seem to be able to get on top of them. Any tips?

Answer  ONCE you’ve got a whitefly problem you need to spray at least three times, at 5–7 day intervals, to kill successive generations as they mature. The yellow traps do catch a few adults, but they don’t give very good control and have no effect on the young whitefly (nymphs), which look like tiny scale insects and feed on the undersides of the leaves.

You can use a systemic spray such as Target, Confidor or Rogor 100 to knock down the adults and affect the sap-sucking nymphs. Or try the less toxic Nature’s Way Insect Spray, but you’ll need to make sure to get really good coverage of both adults — which tend to fly around when you spray them — and nymphs under the leaves. Be careful to follow label recommendations, especially regarding withholding periods before eating sprayed cucumbers.

Whiteflies are common on some garden weeds like sow thistle (puha) in warm parts of the country, even during winter. So check around. That may be where your problem is coming from.

Weekend Gardener, Issue 152, 2004, Page 26