(E68)
POTATO: Solanum tuberosum L., ‘Russet Burbank’
GREEN PEACH APHID AND COLORADO POTATO BEETLE CONTROL WITH SEED
TREATMENT INSECTICIDES, 2000
Robert L. Stoltz and Nancy A. Matteson
University of Idaho
Twin Falls R & E Center
Twin Falls, ID 83301
Phone: (208) 736-3600
Green peach aphid (GPA): Myzus persicae (Sulzer)
Colorado potato beetle (CPB): Leptinotarsa decemlineata (Say)
Experimental plots were established on the UI Research and Extension Center, Kimberly, ID. Uncut G2,
‘Russet Burbank’ potato seed was obtained from the University of Idaho, Tetonia Research and Extension
Center. This seed was cut, weighed, and treated on the basis of grams formulation per weight of potato on
18 Apr. After cutting, seed was placed in heavyweight plastic bags, the dust treatment applied and then
loosely closed to prevent condensation and stored at 42o F until planted. Liquid seed treatment Genesis was
applied to cut seed that was spread in a single layer on 5-ml plastic sheeting. The appropriate amount of
chemical was mixed with enough water to bring spray volume to 30 ml. The mixture was sprayed onto the
potatoes using a small hand pump sprayer that produced a fine mist spray. Sprayed seed pieces were
allowed to dry before treating with fungicidal dusts as previously described. Potatoes were planted on 22
Apr and irrigated by solid set sprinkler. The soil type was Portneuf silt loam. Eight treatments and one
untreated check plot were replicated four times in an RCB design. Individual plots were 4 rows (36-inch
row spacing) wide by 25 ft long with 5-ft alleyways separating the plots. GPA (susceptible strain "Our")
were obtained from Dr. Tom Mowry, Parma R & E Center, and mass reared on greenhouse mustard plants
(‘Chinese Cabbage’) and bell pepper plants (‘California Wonder’) for release into individual plots. Aphid
releases were made into test plots on 1 Jun and 8 Jun. A total of two heavily infested leaves were placed in
each plot on each date. GPA counts were made weekly from nondestructively sampling 20 leaves at random
from the top, middle, and bottom sections of plants in the center two rows of each plot. The data collected
and presented are the total numbers of aphids per 20 leaves sampled. CPB counts were made weekly, from
nondestructively sampling five plants in the center two rows of each plot for a total of 10 plants per plot.
The total number of adults, large larvae (instar stages 3 and 4), small larvae (instar stages 1 and 2), and egg
masses were recorded. An estimation of percent defoliation was also made at this time. The data collected
and presented is the mean total number of beetle stages per 10 plants sampled and estimated mean percent
defoliation. Data were analyzed using ANOVA and Newman-Keuls multiple means comparison.
GPA numbers were significantly reduced relative to the untreated check by all treatments 74, 81, and 88
days after planting. GPA densities were low in all plots throughout the duration of the study. Density was
atypically low compared with GPA densities in Kimberly, Idaho potato test plots the previous 3 yr.
Large and small CPB larvae showed significant reductions in all treatment plots as compared with the
untreated check plot from 61 days after planting to 88 days after planting when larval numbers declined
naturally. Egg masses were significantly less than untreated check plots in all treatment plots at 67 and 96
days after planting when ovipositional activity was observed. Defoliation in the untreated check plot reached
a level of 30% between 88 and 96 days after planting. Defoliation levels never reached 1% in any of the
treatment plots and in most remained at zero percent defoliation until natural plant senescence occurred
prior to harvest. There were no significant differences in yield and grade among treatments and the
untreated check.