Information for Sustainable Agriculture
Malheur Experiment Station
Evaluation of Neck Length and Insecticide Treatments for Thrips Control in Stored Onions
Oregon State University
Malheur County Extension Office
Ontario, OR, 2001
Controlling thrips in onions has become increasingly difficult over the
past decade. Consequently, the maturing crop has a higher population of
thrips than in prior years. Harvesting procedures have also changed for
processed onions; some onions are topped while the necks are immature,
cured for 1-2 days, and then brought into storage for heat curing. This
process has increased the problem of thrips damage in storage. Thrips continue
to feed near the neck region in stored bulbs, causing damage during the
storage period. Reports from New Zealand (Monty Spencer, personal communication)
indicate that longer neck length after topping helped lower thrips injury.
Materials and Methods
The treatment area was marked out of a commercial onion field. The treatments
were in a latin square design with five treatments and five replications.
The plot size was two beds wide by 15 ft in length. All treatments were
made on September 12, after which 20 bulbs from each plot were harvested
and placed into mesh bags made of "no-thrips insect screen". This material
has a mesh size of 81 x 81 with a hole opening size of 0.0059 x 0.0059
inches and a thread size of 0.15 mm. The treatments were:
After harvest the onions were placed into commercial onion storage at McCain
Foods. Storage conditions were the same as used for commercial onions.
The onions were removed from storage on March 28, warmed for 2 days, and
evaluated for thrips damage and decay on March 30.
1-inch neck left on onion
3-inch neck left on onion
3-inch neck plus Warrior insecticide treatment after topping
3-inch neck plus Lannate and MSR insecticide treatment after topping
5-inch neck left on onion
Results and Discussion
There were no observed thrips on any of the onions. There was scarring
around the neck region of the bulbs and this was scored on a scale of 0-10
with 0 meaning no damage and 10 being completely scarred. Black mold was
the principle decay organism present and it was evaluated for severity
with 0 equaling no disease present and 10 being completely decayed.
Table 1. Evaluation of stored Spanish onions for thrips damage and disease
severity. Ontario, OR. 2001.
||Black Mold Severity
|1-inch neck length
|3-inch neck length
|3-inch neck length + Warrior
|3-inch neck length + Lannate + MSR
|5-inch neck length
The insecticide treatments of Warrior or Lannate plus MSR resulted in
significantly less thrips damage than the other treatments. Neck length
did not influence thrips damage.
Although there was a trend towards less black mold with increasing neck
length, this was not statistically significant.
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additional information about the Malheur Agricultural Experiment
Station, please send an e-mail request to:
Dr. Clinton C. Shock
595 Onion Avenue
Ontario, OR 97914
Malheur Agricultural Experiment
FAX (541) 889-7831
January 17th, 2013.