Codling Moth Control with Guthion/Intrepid Demonstration – 2001

Diane G. Alston and Carin A. Miller

Department of Biology, Utah State University

Objective: To evaluate and demonstrate the use of the insect growth regulator, Intrepid (methoxyfenozide) in rotation with a conventional organophosphate insecticide, Guthion (azinphosmethyl) for codling moth control in an entire apple orchard in northern Utah.

Brief Background on the New Insecticides Tested: Intrepid is an insect growth regulator (IGR), that mimics the insect molting hormone ecdysone. It is a very selective insecticide, controlling only the larvae of lepidopteran pests. Intrepid is classified by the EPA as a Reduced Risk Pesticide, and is an alternative to organophosphate insecticides.

Methods: The demonstration was conducted in a 2.1 acre apple orchard of mixed cultivars (‘Gala’, ‘Mutzu’, ‘Prime Gold’, ‘Idared’, ‘Jonathan’, and three strains of ‘Red Delicious’: ‘Ultrastripe’, ‘Dixiered’, and ‘Supreme’) at the Utah State University research farm in Kaysville, UT. A delayed-dormant oil was applied to the entire orchard on 5 April 2001. Other pesticides were applied to all or part of this orchard in addition to the Intrepid/Guthion rotation. These included one application each of Carzol (23 April 2001), Sevin (16 May 2001), and NAA 800 (16 May 2001) and multiple applications of Rally for powdery mildew control.

The adult male codling moth population was monitored with one pheromone-baited trap (wing-style 1CP) to determine biofix (first consistent moth catch) and to follow seasonal flight patterns. Timing of treatments was determined using biofix and a degree-day (DD) model. Four treatments were applied with an air blast sprayer at a rate of 70-80 gallons of dilute spray per acre:

1. Guthion 50WP (Bayer) @ 2 lb/acre on 24 May (Timing based on DD model and biofix; 250 DD after biofix was 23 May; treatment one day late).

2. Intrepid 80WSP (Rohm and Haas) @ 6 oz/acre on 15 June (22 days after first cover spray; treatment one day late).

3. Guthion 50WP @ 2 lb/acre on 16 July (Timing based on DD model and biofix; 1260 DD after biofix was 13 July; treatment 3 days late).

4. Intrepid 80WSP @ 6 oz/acre on 10 August (25 days after 3rd cover spray; treatment 4 days late).

Apple fruits were sampled at harvest to determine codling moth injury levels. Earlier - maturing varieties, ‘Gala’, ‘Jonathan’, and ‘Prime Gold’ were sampled on 15 August, followed by later-maturing varieties ‘Mutzu’, ‘Idared’, ‘Dixiered’, ‘Ultrastripe’, and ‘Supreme’ on 6 September. Trees were selected randomly and 100 fruits were sampled per variety. The surface of each fruit was examined for "stings" and then cut open to determine the presence of larvae or injury. Damage was recorded as either a "sting" or larval entry.

 

 

Results: Overall, fruit injury was low, ranging from 0% injury (‘Idared’) to 4% (‘Gala’). See Table 1 for a summary of fruit injury by variety.

Table 1. Percent codling moth injury for 100 fruit sampled for each of eight apple varieties in Kaysville, UT, 2001.

Variety

% stings

% larval entry

% total injury

Dixiered

1.0

1.0

2.0

Gala*

3.0

1.0

4.0

Idared

0

0

0

Jonathan*

0

2.0

2.0

Mutzu

1.0

1.0

2.0

Prime Gold*

0.9

0

0.9

Supreme

1.0

0

1.0

Ultrastripe

1.0

1.0

2.0

* Varieties sampled on 15 August, all others sampled on 6 September

Codling moth pressure was measured by pheromone trap throughout the growing season. Pressure was low to moderate, with a peak at the end of May (Fig. 1). The entire orchard was treated with insecticide and we did not have access to an untreated orchard in the vicinity to measure the population without insecticide.

Figure 1. Pheromone trap captures of codling moth at Kaysville, UT, 2001.

 

Conclusions: The apples in this trial had more injury from codling moth than in past years under a 4-application Guthion program (0-0.2% injury). ‘Gala’ was more susceptible to codling moth injury (4%) than the other cultivars (0-2%). Some of the greater injury in 2001 may be due to the late timing (1-4 days) of treatments as compared to the optimal timing based on biofix and the DD model. The timing of the IGR Intrepid is less flexible than Guthion because of its mode of action. The primary mode of exposure to larvae is through ingestion of treated foliage, which then induces a premature and lethal larval molt. Very few larvae are killed by direct contact with Intrepid, while Guthion is effective by contact alone. It appears that precise application timing of Intrepid is critical to achieve zero to very low injury.

Although fruit injury of 1-4% is higher than many commercial growers would prefer, we are still generally pleased with the control provided by the Guthion-Intrepid rotation. Rotation with the IGR Intrepid resulted in a 50% reduction in organophosphate use. Intrepid is a reduced-risk pesticide and has a short 4-hour restricted-entry interval (REI) and a 14-day pre-harvest interval (PHI). Use of Intrepid for the 2nd cover spray spray can alleviate interval restrictions for re-entering orchards following Guthion applications for hand thinning (14 day REI) and other maintenance activities (e.g. mowing, irrigating, scouting) (48 hr. REI).

In conclusion, use of Intrepid in a rotation program such as demonstrated holds promise. Additional demonstrations with more precise timing, higher codling moth populations, and more locations are needed to develop confidence and experience with the use of Intrepid in Utah.