|
|
Insecticide
Trials for Onion Thrips (Thrips tabaci)
Control – 2004
Lynn Jensen
Malheur County Extension Service
Oregon State University
Ontario, OR
Introduction
During the past 4 years alternative
insecticides have demonstrated superior control of onion thrips when compared
to conventional insecticides. Alternative insecticides in this trial are
azadirachtin (Aza-Direct® and Ecozin®) an extract from
the neem tree (Azadirachia indica, A.
Juss.), and spinosad (Success®), a bacterial fermentation product. Conventional
insecticides are the currently registered products in the synthetic pyrethroid
(Warrior®, Mustang®), organo-phosphate (parathion,
malathion, Guthion®, Diazinon), and carbamate (Lannate®,
Vydate®) classes. Different rates and combinations of these
insecticides were tested for efficacy against onion thrips.
Materials and Methods
A 36.7-ft-wide by 500-ft long
block was planted to onion (cv. ‘Vaquero’, Nunhems, Parma, ID) on March 23,
2004. The onions were planted as 2 double rows on a 44-inch bed. The double
rows were spaced 2 inches apart. The seeding rate was 137,000 seeds/acre. Lorsban 15G® was applied in a
6-inch band over each double row at planting at a rate of 3.7 oz/1,000 ft of
row for onion maggot control. Water was applied by furrow irrigation. The plots
were 7.3 ft wide (2 beds) by 25 ft long and were replicated 4 times.
There were 14 treatments as
outlined in Table 1. Acephate is an older insecticide that is now manufactured
by several companies. It is not currently registered for use on onions.
Insecticide applications
were made with a CO2-pressurized plot sprayer with 4 nozzles spaced
19 inches apart. All treatments were made with water as a carrier at 38.9
gal/acre. Thrips counts were made weekly through the growing season by counting
the total number of thrips on 20 plants.
The onion bulbs were
harvested by hand on September 10 and graded on October 11. The plot area harvested was 20 ft of the
center 2 double rows.
Treatment differences were
compared using ANOVA and least significant differences at the 5 percent
probability level, LSD (0.05). Means
were also compared using Duncan’s multiple range test.
Results and Discussion
Thrips populations in June
were fairly high (Fig.1). The acephate treatments provided the best thrips
control. Table 2 contains yield and grade information. All of the yield classes
had significant differences except for medium-size onions. Acephate treatments had
the highest yield of supercolossal plus colossal bulbs at both the 8.0-oz and
16.0-oz rate, and the 6.0 oz rate had the highest yield of colossal bulbs. The
Aza Direct plus Success (10.0 oz) had the overall highest yield followed by
treatment 13, which was a combination of Penncap M plus MSR® and
Warrior plus MSR. Acephate at the 6.0-oz rate also produced high yields.
Aza-Direct by itself
produced the lowest yields, followed by the late June and mid-July applications
of Warrior plus MSR and Warrior plus Lannate (treatment 2). Compost tea by
itself was not better than the untreated check. Aza-Direct plus the 6.0-oz rate
of Success was not better than the untreated check, whether applied as a weekly
spray mix or alternated weekly.
The iris yellow spot virus
infected the plot area late in the season. The treatments were evaluated for
resistance to disease expression and the data are shown in Table 3. Generally,
the treatments with the highest yields had less incidence of the disease
although the correlation was not very strong.
Conclusions
Azadirect (20 oz) plus Success
applied at the 10.0-oz rate (treatment 14) and acephate at the 8.0-oz rate (treatment
12) were the best treatments. Neither Success or acephate is currently
registered for use on onions although a section 18 emergency registration for
Success was granted in 2004 and is anticipated again in 2005.
There were significant
differences between treatments in all onion size classes except mediums.
Table 1. Insecticides
evaluated for thrips control, Malheur Experiment Station, Oregon State
University, Ontario, OR, 2004.
|
Treatment no. |
Insecticide applied |
Formulated product |
Treatment date |
|||
|
|
|
Rate/acre |
6/7 |
6/28 |
7/16 |
7/29 |
|
1 |
Aza-Direct |
20.0 oz |
X |
X |
X |
X |
|
|
Warrior + MSR |
3.8 oz 2.0 pt |
|
X |
|
|
|
2 |
Warrior + Lannate |
3.8 oz 3.0 pt |
|
|
X |
|
|
3 |
Untreated check |
|
|
|
|
|
|
4 |
Aza-Direct |
20.0 oz |
X |
|
X |
|
|
|
Success |
6.0 oz |
|
X |
|
X |
|
5 |
Compost Tea |
4.0 gal |
X |
X |
X |
X |
|
6 |
Warrior |
3.8 oz |
X |
|
|
|
|
|
Warrior + Lannate |
3.8 oz 3.0 pt |
|
|
|
X |
|
7 |
Aza-Direct + Success |
20.0 oz 6.0 oz |
X |
X |
X |
X |
|
8 |
Acephate |
16.0 oz |
X |
X |
X |
X |
|
9 |
Success |
6.0 oz |
X |
|
X |
|
|
10 |
Success |
6.0 oz |
X |
X |
X |
X |
|
11 |
Warrior |
3.8 oz |
X |
|
|
|
|
|
Warrior + MSR |
3.8 oz 2.0 pt |
|
X |
|
|
|
|
Warrior + Lannate |
3.8 oz 3.0 pt |
|
|
X |
|
|
12 |
Acephate |
8.0 oz |
X |
X |
X |
X |
|
13 |
Penncap M + MSR |
2.0 pt 2.0 pt |
X |
X |
X |
|
|
|
Warrior + MSR |
3.8 oz 2.0 pt |
|
|
|
X |
|
14 |
Aza-Direct + Success |
20.0 oz 10.0 oz |
X |
X |
X |
X |
Table 2. Effects of different thrips treatments on
onion yield and grade, Malheur Experiment Station, Oregon State University,
Ontario, OR, 2004.
|
Treatment No. |
Medium |
Jumbo |
Colossal |
Super- colossal |
Colossal + S-Col. |
Jumbo + Col. + S-Col. |
Total Yield |
|
|
------------------------------------------cwt/acre---------------------------------------- |
||||||
|
1 |
18.2 |
464.2 |
220.2 |
10.7 |
230.9 |
695.1 |
713.3 |
|
2 |
13.2 |
394.0 |
278.9 |
39.4 |
318.3 |
712.3 |
725.5 |
|
3 |
11.5 |
475.3 |
241.9 |
44.2 |
286.1 |
761.4 |
773.0 |
|
4 |
12.4 |
399.8 |
322.1 |
43.7 |
365.8 |
765.6 |
778.0 |
|
5 |
9.9 |
501.5 |
263.3 |
36.4 |
299.7 |
801.2 |
811.1 |
|
6 |
13.0 |
432.0 |
318.9 |
50.7 |
369.6 |
801.6 |
814.6 |
|
7 |
7.4 |
351.0 |
351.1 |
107.3 |
458.5 |
809.5 |
816.9 |
|
8 |
7.7 |
296.5 |
379.3 |
160.0 |
539.2 |
835.7 |
843.4 |
|
9 |
13.3 |
435.8 |
346.2 |
87.2 |
433.3 |
869.1 |
882.4 |
|
10 |
13.2 |
388.8 |
398.9 |
89.6 |
488.4 |
877.2 |
890.3 |
|
11 |
11.0 |
398.0 |
411.4 |
85.9 |
497.2 |
895.2 |
906.3 |
|
12 |
6.2 |
260.0 |
489.2 |
165.2 |
654.4 |
914.4 |
920.6 |
|
13 |
14.1 |
486.3 |
382.3 |
42.4 |
424.7 |
911.1 |
925.2 |
|
14 |
13.3 |
431.4 |
392.5 |
105.6 |
498.1 |
929.6 |
942.9 |
|
LSD (0.05) |
ns |
133.6 |
110.8 |
65.7 |
142.0 |
133.6 |
132.1 |
Table 3. Evaluation of iris yellow spot virus disease
severity with different insecticide treatments for the thrips vector, Malheur
Experiment Station, Oregon State University, Ontario, OR, 2004.
|
Treatment Number |
Iris yellow spot virus severity |
|
|
0 = dead; 5 = no injury |
|
1 |
2.8 |
|
2 |
2.0 |
|
3 |
2.3 |
|
4 |
2.3 |
|
5 |
2.3 |
|
6 |
2.3 |
|
7 |
4.0 |
|
8 |
4.0 |
|
9 |
2.8 |
|
10 |
3.8 |
|
11 |
3.2 |
|
12 |
4.0 |
|
13 |
3.0 |
|
14 |
3.8 |
|
LSD
(0.05) |
0.6 |
