Thrips

June 2004. In Vanuatu, the insecticide Attack is used for thrip control on cucumber, but some are still alive after treatments. Alternatives were requested.

Regent (fipronil) and Confidor (imidaclorprid) were suggested at alternatives. Success (spinosad) was also worth a try. Another method was to use a motorised sprayer with water only. Some of these insecticides are not effective against some species of thrips while being very efficacious against others.

If the problem is Thirps palmae, melon thrips, with a life cycle as short as 11 days in the tropics, using any kind of insecticide, will bring resistance in a very short time. In American Samoa, thrip are cyclic: usually they are a problem during prolonged dry spells, though not always. When it starts raining again, they “disappear”, moving off into other vegetation.

A field trial in American Samoa of trellised and non-trellised cucumbers grown side by side showed that the weeded, trellised, plants had high infestation of thrips. However, non-trellised cucumbers, not well weeded, had low levels of infestation.

Resurgence of thrips may also be due to reasons other than the failure of a pesticide.

• Neigbouring fields especially of the same crop can bring in new populations of thrips into well protected fields.
• Wind carries thrips great distances.

Some management practices suggested are:

• If the neigbouring farmer has the same crop and practices a different pesticide regime, a physical barrier would be helpful, e.g., two plots of green pepper can be separated by a thick row of maize or sorghum. Ideally a common regional policy on pesticide use will make life easier for everyone.
• Intercropping will be of great advantage in most situations.
• A permanent wind break across the path of the wind with quick growing tree species will also help in the long run. A rule of thumb is that a tree of 10 metre height will act as a wind barrier to a distance of about 150 metres.

The PAN-Germany’s new project Non-chemical pest management for the tropics (OISAT) is currently online at http://oisat.org/pests/insect_pests/very_small/thrips/curative_control.html and has many ‘oganic’ suggestions.