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(F88)
SORGHUM (GRAIN): Sorghum bicolor (L.) Moench, ‘Pioneer 8282’, ‘Mycogen 1552’
SORGHUM MIDGE MANAGEMENT WITH SELECTED INSECTICIDE APPLICATION
TIMINGS
IN GRAIN SORGHUM, 2000
B. A. Castro, B. R. Leonard, and T. J. Riley
Department of Entomology
LSU Agricultural Center
Baton Rouge, LA 70803-1710
Phone: (225) 388-1634
Sorghum midge: Stenodiplosis sorghicola (Coquillett)
The efficacy of two insecticides applied at different sorghum reproductive stages was evaluated to suppress
sorghum midge damage in grain sorghum. Two commercial grain sorghum hybrids, ‘Mycogen 1552’ in
Tests I, II, and III and ‘Pioneer 8282’ in Test IV, were planted in a Gigger-Gilbert silt loam at the Macon
Ridge location of the Northeast Research Station near Winnsboro, LA. Tests I, II, and III were planted on
16 May and test IV was planted on 1 May in a conventional tillage. Plots consisted of 8 rows (40-inch
centers), 45 ft long in Tests I, II, and III and 50 ft long in Test IV. Treatments were arranged in an RCB
design with six replications in Tests I, II, and III and seven replications in Test IV. Karate-Z 2.09SC at
0.025 lb (AI)/acre (used in all tests) and Tracer 4F at 0.045 lb (AI)/acre (used in test I only) were applied at
selected target application intervals during reproductive stages of sorghum. Insecticides were applied with a
high-clearance sprayer equipped with a CO 2 charged system calibrated to deliver 4.8 gpa at 50 psi through
TX-8 cone nozzles (2/row). A panicle was considered to be emerged when it was completely out of the boot
with no open spikelets. A panicle was considered to be flowering when its upper 20% portion had open
spikelets with fresh yellow pollen. A panicle was considered to be post-flowering when 95% or more of its
spikelets were closed and anthers were reddish or brownish in color. Percent panicle emergence, panicle
flowering, and post-flowering per plot were estimated by recording the developmental stage of each of 50
randomly selected plants from the two center rows per plot and obtaining a percent value. Treated plots
received one insecticide application at each selected reproductive stage. Some treated plots received a
second insecticide application 5 d after the first application. Sorghum midge damage to seed heads was
evaluated in the field on 8 Aug Tests I, II, and III and 11 Aug Test IV. Sorghum midge injury was assessed
by visually estimating the percent blasted kernels on each of 10 randomly selected panicles per plot.
Sorghum midge damage data were transformed [arcsine (x/100)] prior to ANOVA and LSD.
Untransformed means are presented in tables. Sorghum seed yields were obtained on 22 Aug for Test IV
and 30 Aug for Tests I and II. No yield data were collected from Test III. Yields were obtained by
mechanically harvesting the four center rows in each plot and adjusting to 15.5% moisture.
No significant differences in sorghum midge injury nor in seed yields were observed in Test I between
Tracer, Karate-Z and the untreated checks (Table 1). Significant reduction in midge damage was observed
when sorghum was sprayed with Karate-Z during flowering stages compared with spraying during postflowering or when untreated. No differences in midge damage were observed when sorghum was treated
once or twice (Table 2 and 4). Sorghum midge damage was also reduced when Karate-Z applications were
performed during selected panicle emergence or panicle flowering compared with that in the untreated
check (Table 3). Significant differences in seed yields were observed only in Test II (Table 2). Sorghum
seed yields were significantly higher in all treated plots compared with that in the untreated check.