Colorado potato beetle management in potatoes

Field evaluations of registered and experimental insecticides for managing Colorado potato beetle on potatoes.

The Colorado potato beetle (Leptinotarsa decemlineata, Say, Coleoptera: Chrysomelidae) is the most widespread and destructive insect pest of potato crops in the eastern United States and Canada. Its ability to develop resistance makes it important to continue testing the efficacy of insecticides in the field. Such tests provide data on comparative effectiveness of products and data to help support future registrations and use recommendations.

Methods

Fifteen insecticide treatments and an untreated control (Table 1) were tested at the Michigan State University Montcalm Research Farm for control of Colorado potato beetles. ‘Atlantic’ potato seed pieces were planted 12 inches apart with 34-inch row spacing on May 28, 2014. Treatments were replicated four times in a randomized complete block design. Plots were 50 feet long and three rows wide with untreated guard rows bordering each plot.        

Treatment 1 was applied as a seed treatment, and Treatments 2-5 were sprayed in-furrow at planting (Table 1). Two treatments (6 and 7 in Table 1) were a mix of at-planting and foliar sprays. Foliar treatments were first applied at 80 percent Colorado potato beetle egg hatch on June 25, 2014. Based on the economic threshold of more than one large larva per plant, additional first generation foliar sprays were needed for Treatment 7 (July 10 and 17), Treatment 8 (July 10) and Treatments 10-15 (July 3); no subsequent applications were necessary for any of the other foliar treatments. All applications were made using a single-nozzle, hand-held boom with a flat tip nozzle (30 gallons per acre and 30 psi).

Post-spray counts of first generation Colorado potato beetle adults, small larvae (first and second instars) and large larvae (third and fourth instars) from five randomly selected plants from the middle row of each plot were made weekly, on July 1, 9 and 16. Plots were visually rated for defoliation weekly by estimating total defoliation per plot.

The numbers of small larvae, large larvae and adults were transformed log (x + 0.1) prior to analysis. Analysis of variance was used for data analysis and ad-hoc Tukey means separation was used to compare treatment means (P < 0.05).

Results

Except for Treatments 15 and 16, all treatments resulted in significantly fewer large larvae than the untreated control (Figure 1). The neonicotinoid, Platinum, at-planting application continues to perform well, providing excellent first generation beetle control. Similar in performance is the newly registered cyazypyr, Verimark, at the higher rate of 13.5 ounces per acre. The lower rate of Verimark at 6.75 ounces per acre was somewhat less effective, although not statistically significant from the high rate; it performed similarly to the Verimark seed treatment.

Among the combined at-planting and foliar applications, Treatment 6 provided excellent first generation beetle control, while Treatment 7 provided less protection, although the difference between the two treatments was not statistically significant. For the two foliar applications (Treatments 8 and 9), Blackhawk provided significantly weaker control, with two applications needed, than the newly registered Exirel, which with only one application was able to suppress larval numbers below threshold in the first generation. Bacillus thuringiensis (Bt) effectively suppressed large larvae below threshold with two foliar applications during the first generation.

The untreated plots had significantly greater defoliation compared to all other treatments except for Treatments 14 and 15. The seasonal defoliation average was 21.6 percent in the untreated plots, compared to less than 8 percent for all other treatments. Differences in defoliation among insecticide-treated plots ranged from 1 to 10 percent, except for Treatments 14 and 15 which were similar to the control.

In summary, some neonicotinoid insecticides, such as Platinum, are still providing sufficient Colorado potato beetle control during the first generation, but new chemistries like cyazypr (Verimark, Exirel) are proving to be effective alternatives to neonicotinoids.

Table 1. Insecticide treatments in the 2014 MSU potato trial, Montcalm Research Farm

#

Product name

Application rate

Mode of application

1

Verimark (66 pounds seed per 50-foot plot)

0.3 fluid ounces per plot = 8.87 milliliters per plot

At planting, on seed

2

Platinum

2.66 ounces per acre

At-plant in furrow

3

Verimark

6.75 ounces per acre (pH 4-6)

At-plant in furrow

4

Verimark

13.5 ounces per acre (pH 4-6)

At-plant in furrow

5

Admire Pro

7 ounces per acre

At-plant in furrow

6

Platinum

2.66 ounces per acre

At-plant in furrow

Gladiator + NIS

19 ounces per acre + 0.25% v/v

Foliar broadcast

7

Capture

25.5 ounces per acre

At-plant in furrow

Admire Pro

5.22 ounces per acre

At-plant in furrow

Gladiator + NIS

19 ounces per acre + 0.25% v/v/

Foliar broadcast

8

Blackhawk

2.5 ounces per acre

Foliar broadcast

9

Exirel

5 ounces per acre (pH 4-6)

Foliar broadcast

10

*Bt + NIS

 

Foliar broadcast

11

Peptide + Bt + NIS

1x

Foliar broadcast

12

Peptide + Bt + NIS

2x

Foliar broadcast

13

Peptide + Bt + NIS

4x

Foliar broadcast

14

Peptide + NIS

2x

Foliar broadcast

15

Peptide + NIS

24x

Foliar broadcast

16

untreated control

 

 

*Bt = Bacillus thuringiensis

Figure 1. Average number of large larvae across three weekly sampling dates during the first generation of Colorado potato beetles at the Montcalm Research Farm insecticide trial. Bars that share the same letters are not statistically different from each other. Treatment numbers correspond to numbers in the Table 1.

Larvae graph

Dr. Szendrei’s work is funded in part by MSU’s AgBioResearch.

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