Chemistry Reference
In-Depth Information
spacing of 22.9 cm (9”). Treatments consisted of three neonicotinoid insecticides, at full
labeled rates, and an untreated: imidacloprid (Admire PRO, 635.9 ml/ha [8.7 fl oz/acre],
BayerCropScience, Research Triangle Park, NC), thiamethoxam (Platinum 2SC, 584.2 ml/ha
[8.0 fl oz/acre], Syngenta, Greensboro, NC), dinotefuran (Venom 70SG, 525.5 g/ha [7.5
oz/acre], Valent BioSciences, Libertyville, IL), and an untreated water spray. The solubility
of the three neonicotinoids, from least to most soluble, are imidacloprid (solubility of 0.51
g/liter at 20
0
C, [20], thiamethoxam (solubility of 4.1 g/liter at 20
0
C, [12], and dinotefuran
(solubility of 40.0 g/liter at 20
0
C, [21]. To simulate a field application, treatments of
insecticides were applied over the top of the pot as a 10.2 cm (4”) band open-furrow
application on 23 Apr using a 3785 ml (1 gal) Agway (Southern States Cooperative,
Richmond, VA) water sprinkler calibrated to deliver 189.3 liter/0.405 ha (50 gpa). The seed
pieces were then covered by filling the pots with clean field soil. Because soil texture, clay
content and organic matter influence mobility, the same soil (Sassafrass sandy loam, 65%
sand, 23% silt, 12% clay, 1% organic matter) was used for all the laboratory pots and for the
field trials. A total of 32 pots were prepared (8 pots per treatment with the 4 treatments
described above) and were immediately moved to an environmentally-controlled plexiglass
greenhouse. Pots were evenly divided into 2 groups, with 4 pots (4 replications) of each
treatment in the low rainfall group and 4 pots of each treatment in the high rainfall group.
Thus main plots were amount of rainfall, and sub-plots were insecticide treatment. All 16
pots in either the low rainfall group or high rainfall group were placed on an 1.8 m (6 ft)
diameter round table. A mechanical rainfall simulator [see 22] consisting of a rotating boom
with a single TeeJet 8010 nozzle, operated by a 0.254 metric hp (¼ hp) electrical motor,
delivered a 20.3 cm (8”) band of water over the pots to simulate rainfall. Two rain gauges
were placed opposite each other on the table between the pots: once every Monday the low
rainfall group received 1.3 cm water (0.5”) as measured in the rainfall gauge, and every
Monday and Thursday the high rainfall group received 3.8 cm (1.5”) each time, for a total of
7.62 cm (3”) per week. Simulated rainfall commenced on 26 Apr, 3 days after planting, and
continued every week until 11 Jun (a period of 8 weeks for a total of 4” low rainfall regimen,
and 24” high rainfall regimen). Two leaves from the middle 1/3 foliage from each plant in
each pot were picked and placed in sterile 12.7 cm diameter (5”) Petri dishes on 30 May, 3,
15, 25 Jun and 2 Jul. Just after leaves were placed in the Petri dishes, CPB larvae were
collected from untreated nursery potato plots (“Superior” cv) in the field and five same-
instar larvae were placed in each Petri dish with the leaves and placed in the laboratory (2
nd
and 3
rd
instar larvae were tested May through early Jun, 3
rd
and 4
th
instar larvae were tested
mid- to late Jun, and adults were tested early Jul because no larvae were available). After 72
hr, the total percentage leaf-feeding, based on visual assessment of percentage leaf tissue
consumed by the CPB, and the number of live CPB in each Petri dish was recorded (3, 8, 21,
28 Jun and 5 Jul).
Field Trials.
“Superior” cv. white potatoes were planted on 10 Apr into a prepared (disked,
limed and fertilized) Sassafras sandy loam field. This soil was the same as used in the
laboratory trials previously described. Plots consisted of 3 rows of potatoes, each row 7.62 m
long (25 ft) and 0.9 m wide (3 ft), replicated 4 times in a split-plot design: whole plots were
