Malheur Experiment Station Information for Sustainable Agriculture

INSECTICIDE EFFICACY TRIAL FOR THRIPS CONTROL IN

DRY BULB ONIONS - 2008

Lynn Jensen

Malheur CountyExtension Service

Oregon State University

Ontario, OR

Introduction

Controlling thrips (onion and western flower) is becoming increasingly difficult for commercial onion growers in the Treasure Valley. One of the problems is resistance to some of the commonly used insecticides. The objective of this trial was to screen registered and non-registered insecticides to find those with have potential for use in thrips control programs. Not all insecticides referred to in this report are registered for use on onions. Always obtain and read the insecticide label to ensure that the product is registered for the crop for which it is intended.

Materials and Methods

A 1-acre field, soil type Nyssa silt loam, was planted with the onion variety 'Vaquero' (Nunhems, Parma, ID) on March 24, 2008. The onions were planted as 2 double rows on a 40-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 row at planting at a rate of 3.7 oz/1,000 ft of row for onion maggot control. Water was applied by drip irrigation.

Treatments were made by CO₂-pressurized plot sprayer with four nozzles spaced 19 inches apart. It was set to apply 35 gal/acre, with water as the carrier. A silicone surfactant was added to all treatments, and Carzol^®, dimethoate and Lannate^® were buffered to pH 6.0. Treatments were applied on a weekly basis beginning on June 5. Thrips counts were also made on a weekly basis by visually counting the total number of thrips on 15 plants in each plot. Insecticides tested include Radiant™, Assail^®,

ARY- 0504-015, Battallion^®, Movento^®, Trilogy^® and Dimethoate. These products were compared to an untreated check and a grower standard. The grower standard consisted of three consecutive applications of Success^® plus Aza-Direct^®, then two consecutive Lannate applications, a Carzol treatment, then two more consecutive Lannate applications applied on a weekly interval. Radiant is a new insecticide from Dow AgriScience that is closely related to Success. Assail is a neonicotinoid insecticide marketed by United Phosphorus. ARY-0504-015 is a numbered compound that was thought to have enough insecticidal properties to enhance the activity of other insecticides. Battallion is the synthetic pyrethroid deltamethrin. Movento is a new, systemic insecticide being introduced by Bayer. Trilogy is a neem product sold by Certis. Thrips injury ratings were also taken as a subjective measurement of foliage damage caused by thrips feeding. A scale of 0-5 (0 = no injury, 5 = complete silvering of the leaves) was used; treatments are listed in Table 1.

Table 1. Insecticide treatments evaluated in the onion thrips efficacy trial,

Malheur Experiment Station, Oregon State University, Ontario, OR, 2008.

The application dates and environmental conditions are listed in Table 2. The onions were harvested September 22-24, 2008, and graded October 9-13, 2008.

Table 2. Application information, onion thrips efficacy trial, Malheur Experiment Station, Oregon State University, Ontario, OR, 2008.

Results and Discussion

Thrips counts were to be made by counting the total number of thrips on each of 15 plants in each plot, but through miscommunication, only adult thrips were counted until midway through the season. The thrips count mix-up rendered the data useless, so two evaluations of thrips damage to the onion foliage were taken on July 22 and July 31. The foliage evaluations are shown in Table 3.

Table 3. Onion foliage damage caused by thrips feeding, Malheur Experiment Station, Oregon State University, Ontario, OR, 2008.

^a0 = no feeding damage, 5 = complete silvering of foliage.

^bMSO = methylated seed oil.

More foliage was damaged with the synthetic pyrethroid, Batallion than in the untreated check. This phenomenon has been observed over the past few seasons and is likely related to thrips resistance to this class of insecticides, plus the harmful broad-spectrum effect on predators.

Ratings for the neonicotinoid insecticide, Assail, were similar to the untreated control. This is typical of thrips response to this class of insecticides from previous trials at the Malheur Experiment Station.

Trilogy and Dimethoate had reduced foliage damage compared to the untreated check, but were not nearly as effective as some of the other treatments. These treatments had significantly higher thrips feeding damage ratings than the grower standard treatment.

Radiant and Movento had the lowest thrips injury ratings. The addition of ARY-0504-015, Trilogy, or methylated seed oil (MSO) to Radiant significantly reduced thrips injury compared to the addition of Aza-Direct. The 10-oz application of Radiant had slightly lower thrips injury ratings than the 6-oz rate. Lannate performed well in the trial, but the addition of ARY-0504-015 did not improve thrips damage ratings.

Success plus Aza-Direct also performed well in this trial. The yield and grade results are listed in Table 4.

Table 4. Yield and grade response to insecticide treatments, Malheur Experiment Station, Oregon State University, Ontario, OR, 2008.

^aMethylated seed oil.

^bSuccess + Aza-Direct (3 applications), Lannate (4 applications), Carzol (1 application).

The highest yielding treatments also had the highest yield of colossal plus supercolossal bulbs. The Movento, Radiant plus ARY-0504-015 and Radiant (10 oz) plus MSO treatments were the highest in total yield, and also had significantly higher yield of colossal plus supercolossal bulbs than any other treatment.

All of the Assail and Batallion treatments had significantly lower yield than the untreated check, indicating a negative impact from their application. The addition of ARY-0504-015 to Lannate, Assail, or Batallion gave no added effect.

Lannate, Radiant plus Aza-Direct, Trilogy, and dimethoate all yielded better than the untreated check, but the yields were substantially below the best three treatments.

There was a strong correlation between total yield and onion foliage damage (Fig. 1). The treatments with the lowest damage rating had the highest yields. This is also observed in Figure 2 where foliage damage and colossal plus supercolossal yield were compared. When the average rating was above 1.0, yield of colossal plus supercolossal bulbs decreased dramatically.

Conclusions

Radiant at the 10-oz rate performed better than the 6-oz rate.

Movento and Radiant mixed with either MSO or ARY-0504-015 gave the highest total yield and significantly higher colossal plus supercolossal yields than any other treatment.

The synthetic pyrethroid (Batallion) and the neonicotinoid (Assail) had significantly lower yields compared to the untreated check.

Figure 1. A comparison of total onion yield and onion thrips feeding damage (rating scale of 0-5 with 0 = no injury and 5 = complete silvering of foliage). Malheur Experiment Station, Oregon State University, Ontario, OR, 2008.

Figure 2. A comparison of colossal plus supercolossal yields and onion thrips feeding damage ratings (rating scale of 0-5 with 0 = no injury and 5 = complete silvering of foliage). Malheur Experiment Station, Oregon State University, Ontario, OR, 2008.

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Last updated  Tuesday June 28, 2011.