Chemistry Reference
In-Depth Information
amount of rainfall (a rainfall regimen of either 1.3 cm/week [½”] or 7.62 cm/week [3”), and
sub-plots were insecticide treatment (imidacloprid, thiamethoxam, dinotefuran, or
untreated). Insecticide treatments were the same as in the laboratory trials previously
described and were applied at the same rates to the furrow at planting using a hand-held 7.6
liter (2-gal) Agway sprinkler can calibrated to deliver 189.3 liter/0.405 ha (50 gpa) in a 10.2
cm (4-in) band, after which the furrows were immediately closed; one treatment consisted of
no insecticide. Whole plots were irrigated with an overhead irrigation system consisting of a
5.1 cm (2”) main water pipe connected to a Rainbird J-20 revolving irrigation head
delivering 0.5 cm water per 0.405 ha (0.2” per acre) per hour. Each whole plot had two rain
gauges at plant height, one located near the irrigation head and one at the furthest wet point
away from the irrigation head. Plots received overhead irrigation every Wednesday starting
23 Apr and continued each week through 27 Jun (either 1.3 cm [1/2”]or 7.62 cm [3”]) over a
total of 10 weeks. Plots that received a natural rainfall less then the treatment amount during
the week received additional irrigation only to bring the total to 1.3 cm or 7.62 cm, and plots
that received more natural rainfall than the treatment amount received no irrigation.
The total number of Colorado potato beetle larvae (small and large larvae) per 3 hills, and
percentage plant defoliation caused by CPB feeding were recorded on 1, 11, 17, and
defoliation ratings only on 25 Jun. Potato leafhopper damage ratings (0 = no damage, 5 =
severe damage) were recorded on 25 Jun and 3 Jul.
All data were recorded from the center row of each 3-row plot. Data were averaged to
obtain a plot mean for all recorded observation. Data for both the laboratory and field trial
were subjected to a split-plot analyses of variance (ANOVA) [23]. Means were separated
using Tukey's HSD Studentized range test [23] and were plotted on graphs with Microsoft
Excel (www.microsoft.com/en-US/excel365/). .
3. Results
3.1. Laboratory results
The results of the ANOVA to test the main effects (amount of simulated rainfall and
insecticide) and rainfall by insecticide interaction on CPB in laboratory trials are
summarized in Table 1. ANOVA demonstrated significant (P<0.05) insecticide effects for
both CPB mortality and percentage leaf feeding on all dates recorded. However, the main
effect of the amount of simulated rainfall was significant only on the first date for
percentage leaf tissue eaten by CPB larvae, and only on the first two dates for CPB larval
mortality (Table 1). Similarly, the rainfall by insecticide interaction for CPB mortality was
significant (P<0.01) only on the first observation date (Table 1, and significant (P<0.01) only
on the first two observation dates for percentage leaf tissue eaten..
When CPB larvae were placed on leaves treated with imidacloprid or thiamethoxam,
mortality was significantly (P<0.01) higher compared with larvae placed on leaves treated
with dinotefuran or the untreated for the low rainfall regimen until 17 Jun (Fig. 1
),
when
mortality of CPB on leaves treated with imidacloprid decreased; thiamethoxam remained
