Plant Doctor Archive

Thrips a curse

I HAVE two problems. I have tried spraying thrips on a bay tree and rhododendron with Target as well as keeping the soil moist. Neither has worked. Also, my pony tail palm (3-4 years old) has sent up a circle of shoots on the top of the bulb. Are these shoots used for propagation and if so at what time of the year? Or should they be removed? I don't want a bushy plant.

THRIPS can be difficult to control, particularly on large shrubs in hot summer weather. They are tiny black-brown insects that rasp away at the undersides of leaves and feed on the leaf sap. Badly infested leaves often turn silvery then brown and eventually drop off.

Systemic sprays such as Confidor, Mavrik, Rogor 100 and Orthene should give good control on your rhododendrons if applied according to the label recommendations and at intervals through the growing season. You can also use Mavrik or Super Shield, but with these make sure to get good spray coverage under the leaves where the thrips are hiding.

Cross Hills Garden in Kimbolton has developed a Tree Health Band which, if applied to rhododendrons and other shrubs in early summer, helps control thrips as well as some other pests. For more information phone Cross Hills 0800 RHODOS (0800 746 367). If you intend to pick bay leaves for use in cooking I'd recommend not spraying or using the Tree Health Band, but to regularly cut out any infested shoots or leaves and throw them out with the rubbish. Fertilise to encourage new growth, which should be relatively free of thrips for some time.

It's probably best to take the shoots off your pony tail palm if you want it to remain a single stem. Cut them off carefully with a sharp knife, removing a little of the fleshy base. Leave the cut surfaces of the shoots in a warm spot for a few days to seal over, then plant them in some sand or coarse mix where they should eventually grow roots. Keep them in a warm, well-lit spot and make sure you don't overwater them.

Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.