New Zealand Journal of Crop and Horticultural Science abstracts

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Monitoring onion (Allium cepa) crops for onion thrips (Thrips tabaci) (Thysanoptera: Thripidae): testing a commercial protocol

N. A. Martin
P. J. Workman

Crop & Food Research
Private Bag 92 169
Auckland, New Zealand
email: martinn@crop.cri.nz

D. Hedderley

Crop & Food Research
Private Bag 11 600
Palmerston North, New Zealand

L. L. Fagan

Crop & Food Research
Private Bag 4704
Christchurch, New Zealand

Abstract Onion thrips (Thrips tabaci) is the main insect pest on New Zealand onions (Allium cepa). Insecticide applications are triggered by thrips numbers exceeding action thresholds. A new crop monitoring protocol that involves sampling a minimum of 100 plants (up to 4 ha) or 25 plants/ha, was tested in 10 young or mature onion crops. Two people independently sampled each crop by zigzagging up and down groups of onion beds defined by pairs of sprayer wheel tracks and selecting a plant at random at predetermined intervals along the crop beds. The number of thrips adults and larvae per plant was recorded. A strong relationship was found between total numbers of thrips and the percentage of plants infested. If the onion industry raised its spray action threshold from 0.1 thrips/plant to 2 or 3 thrips/plant (c. 50% plants infested), it could adopt presence-absence sampling that would be faster than counting all thrips. The time to monitor a crop was affected by field size, and only increased slightly with higher levels of infestation. The new guidelines could also be used for monitoring disease and weeds.

Keywords onion thrips; Thrips tabaci; crop monitoring; crop scout; threshold

New Zealand Journal of Crop and Horticultural Science, 2008, Vol. 36: 145–152
0014–0671/08/3602–0145 © The Royal Society of New Zealand 2008
H08042; Online publication date 24 June 2008
Received 22 April 2008; accepted 4 June 2008

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