/ 0,0-
NFREC Research Report 94-14
Iarst' o! Science
9/ / 1 PEARL MILLET WEED MANAGEMENT SYSTEMS FOR
GEORGIA AND FLORIDA 0 199
Clyde C. Dowler, David L. Wright and I.D. Teare i 00frid
ABSTRACT
Pearl millet is a potentially-productive, high-quality grain being developed
for the Southeastern United States. Published research on weed management
systems for pearl millet is virtually nonexistent. During the past several
years, field and greenhouse experiments have been conducted by the University of
Florida and USDA-ARS to evaluate herbicide and cultural practices, which would
effectively and economically control weeds, specifically annual grasses, in pearl
millet. Atrazine applied as early post-emergence was the most effective single
herbicide controlling a broad spectrum of weeds in pearl millet. Combinations
of Atrazine with Prowl and Ramrod or Ramrod with 2,4-D generally controlled grass
and broadleaf weeds and did not seriously injure pearl millet. Dual caused
moderate to severe pearl millet injuries and reduced yield. Conventional, no-
till, or stale seedbed preparation generally did not affect level of weed control
or pearl millet production. Cultural practices such as plant population and row
spacing can increase effectiveness of weed control systems in pearl millet.
Presently, there are no federally registered herbicides treatments for pearl
millet grown as grain. Utilizing no-till or stale seedbed techniques that use
Gramoxone Extra to kill existing vegetation before pearl millet emerges is an
effective, economical, and legal procedure.
C.C. Dowler; USDA ARS, Coastal Plain Exp. Stn., Tifton, GA 31793: D.L. Wright and
I.D. Teare. North Fla. Res. and Educ. Ctr., Quincy, FL 32351.
INTRODUCTION
Pearl Millet [Pennisetum glaucum (L.)] is a potentially-productive, high-
quality grain or silage crop (Burton et al., 1986 and Kumar et al., 1983). It
can be grown under relatively low-input management conditions with reduced
fertilizer and water application.
With the development of pearl millet as a potential grain crop for the
Southeastern U.S. there is an urgent need to develop weed management systems that
will result in improved quality and quantity of the grain produced. Presently,
there are only two herbicides, Banvel and 2,4-D, that are registered for use on
millet. There is no federally approved registration for these herbicides on
pearl millet as a grain crop. Banvel is registered under a special, local needs
(24C) permit in several western states for use on millet. The labeling of 2,4-D
suggest its use for forage crops, which would include millet. Therefore, the
registered use of these herbicides on pearl millet as a grain crop is unclear.
Weed pressures and diversity in the southeastern U.S. require development of
effective and efficient weed management systems for pearl millet. In addition
to a wide range of broadleaf weeds, annual grasses such as Texas panicum,
crabgrass, and crowfootgrass present major production problems for pearl millet.
Published research data on use of herbicides on pearl millet for grain is
virtually non-existent. The herbicides imazethapyr and nicosulfuron reduced
pearl millet grain yield 60 and 100 percent, respectively, compared to an
untreated check (Wright et al., 1993). Specific effects of herbicide stress on
pearl millet have only been reported in relation to head length (Pudelko, et al.,
1993).
The potential narrow herbicide selectivity range between annual grass weeds
and pearl millet presents a major problem in developing weed management systems.
Research in Florida and Georgia, during the past few years, has emphasized
systems that will selectively control annual grasses in pearl millet. The
objectives of developing weed management systems are to: 1) selectively control
annual grasses and broadleaf weeds in pearl millet; 2) develop low cost weed
control programs; 3) prevent potential injury and yield reduction from weed
management systems; and 4) provide efficacy data for potential registration of
herbicides or herbicide combinations for use in pearl millet.
METHODS AND MATERIALS
Weed control experiments in pearl millet were conducted under both
greenhouse and field conditions from 1988-1994. Pearl millet hybrid seed
HGM100, developed by the pearl millet breeding program of the USDA-ARS, Coastal
Plain Experiment Station, was used in all experiments.
The experiments were conducted on a Norfolk sandy loam or Tifton loamy sand
(fine, loamy, siliceous, thermic Typic Kandiudults) located at the North Florida
Research and Education Center, Quincy, Florida, and the Coastal Plain Experiment
Station, Tifton, Georgia, respectively.
Weed species varied from year to year, but included Texas panicum,
crabgrass, crowfootgrass, smallflower morningglory, morningglory spp., Palmer
amaranth, cocklebur, carpetweed, purple nutsedge, and yellow nutsedge. Crop
injury and weed control efficacy was determined by visual observation of each
plot with 0 = no effect and 100 = complete kill. Bird damage was devastating to
experimental plots, but yield on some experiments were measured in two ways: 1)
predicting grain yield by regression analysis from head lengths as reported by
Pudelko, et al., 1993 or 2) bagging of 10 heads/plot after pollination, allowing
the grain to mature and dry, weighing the threshed grain, and then converting the
yield data to lb/A based on the number of heads/acre.
In Florida, the no-till systems were established on land that had been
fallowed for one year. The experimental area was mowed and treated with
Gramoxone Extra to kill existing vegetation before planting pearl millet. In
Georgia, stale seedbed systems were established by preparing a conventional
seedbed and then delaying planting of pearl millet 10-14 days. This allowed the
first flush of weeds to emerge, which were killed by applying Gramoxone Extra at
planting.
Pearl millet was planted 0.75 to 1.0 inch deep in either 18 or 36 inch rows.
Herbicides were applied with a conventional boom sprayer, applying 20 gal/A at
approximately 30 PSI. Where necessary, a nonionic surfactant or crop oil
concentrate was used with post-emergence herbicides.
The herbicides used in these experiments are listed in Table 1.
The experiments were either a split plot or randomized complete block design
with three or four replications. Results were subjected to analysis of variance
and means were separated using Fisher's Least Significant Difference Test, at the
0.05 level of probability.
RESULTS AND DISCUSSION
Florida
Weed control for individual herbicide treatments was similar in till and
no-till systems in 1993 and 1994 (Tables 2, 3, 4, and 5). In 1993, the level of
control of both grass and broadleaf weeds was good to excellent (83-100 percent).
Treatments that included Atrazine controlled 95-100 percent of all broadleaf
weeds. The addition of a crop oil concentrate increased the activity of Atrazine
on grasses when compared to Atrazine alone. Herbicide combinations of Dual,
Ramrod, and Prowl with 2,4-D or atrazine did not significantly improve weed
control over Atrazine applied alone in 1993. In 1994, herbicide combinations of
Ramrod and Prowl generally improved grass control compared to Atrazine applied
alone. However, the level of broadleaf weed control was not improved by
herbicide combinations compared to Atrazine alone.
Treatments that included Dual or Ramrod caused moderate to severe pearl
millet injury in 1993. The data in Tables 2 and 3 show that Dual injured pearl
millet more than Ramrod. Herbicide treatments that included Prowl also caused
moderate injury to pearl millet. The injury ratings were recorded approximately
two to three weeks after herbicide treatment. As the growing season progressed,
pearl millet recovered from this herbicide injury as reflected in yield data in
Tables 2 and 3. Severe herbicide injury, caused by Dual, resulted in reduced
pearl millet yield, but the early pearl millet injury recorded in excess of 95
percent did recover and produced some grain in both conventional and no-till
systems. These data would indicate that herbicides in the same chemical family
as Dual should not be considered for use in pearl millet. The silage yield data
in 1994, reflected the same general trend in yield response to herbicides as the
1993 grain yield. The herbicide treatments applied to pearl millet in 1994
caused slight to moderate injury to pearl millet shortly after treatment, but the
crop completely recovered later in the growing season (data not shown). When
compared to yield data for the handweeded check, Dual, Atrazine at 2 Ibs/A,
Ramrod + 2,4-D at 2.25 + 0.45 lbs/A, and Prowl + Atrazine at 0.75 + 1.0 lb/A
reduced pearl millet silage yield (Table 4). In the 1994 no-till system, most
of the herbicide treatments resulted in significant reduction in pearl millet
silage yield, as compared to the handweeded check (Table 5).
Georgia
Control of grasses such as Texas panicum was a major concern for developing
weed control systems in pearl millet. Preliminary experiments in greenhouse and
under field conditions were directed to controlling grasses in pearl millet.
Previous experience in grain sorghum and corn indicated an early post-emergence
applications of Atrazine and/or Prowl would control seedling (1-2 leaf) Texas
panicum. Greenhouse experiments confirm that Atrazine or Atrazine + Prowl would
control seedling grasses, but could also significantly injure pearl millet. At
rates and timing normally used in field corn or grain sorghum, Atrazine in excess
of 1 lb/A to 2-3 leaf pearl millet caused moderate to severe injury, but
suppressed Texas panicum emerging or in the 1-2 leaf stage. Application of
Atrazine at 1 lb/A to 4-leaf pearl millet did not cause significant injury, but
did not control Texas panicum beyond the 1-2 leaf stage. Several greenhouse
experiments involving rates and timing of application with Atrazine in various
combinations confirmed these results (data not shown). In 1991, two field
demonstration plots treated early postemergence with Atrazine at 1 lb/A confirmed
greenhouse experiments (Table 6).
The growth habit of pearl millet dictated that cultural aspects of weed
management needed to be evaluated. This include plant population, row spacing,
and the concept of stale seedbed preparation. Preliminary greenhouse experiments
indicated that delaying pearl millet planting 10-14 days after seedbed
preparation and killing the existing vegetation at planting would be feasible.
In 1992, a field demonstration plot of pearl millet was planted in 18 and
36 inch row spacing and then treated with paraquat at 0.5 lb/A within 48 hours
of planting. Weed control observations, 14-21 days after planting, showed
overall weed control at 95%, which included weeds such as Texas panicum,
crabgrass, Smallflower morningglory, and Palmer amaranth.
At approximately 21 days after planting, canopy closure (overlapping the row
middles) of pearl millet planted in 18 inch rows occurred and provided shade and
competition for weeds for the remainder of the growing season. Pearl millet
planted in 36 inch rows required about 4 weeks after planting for canopy closure,
which provided an opportunity for some weeds to emerge and grow in the row
middles. The use of stale seedbed techniques utilizing Gramoxone Extra was very
effective and economical as a weed management program in pearl millet. A second
demonstration plot, in 1992, indicated that pearl millet planted in a stale
seedbed and treated with Gramoxone Extra at 0.25 lb/A at planting, followed by
Atrazine at 0.75 lb/A as an early post-emergence treatment was also very
effective in controlling a broad spectrum of annual weeds and that 18 inch row
spacing provided more shade and competition to weeds than 36 inch row spacing.
In 1993 and 1994, experiments evaluated selected post-emergence herbicide
treatments on pearl millet grown in conventional and stale seedbed (Tables 7, 8,
9 and 10). In 1993, the control of all weeds generally ranged from good to
excellent. Some treatments caused slight to moderate injury to pearl millet, but
pearl millet recovered by maturity. A direct comparison between conventional and
stale seedbed results could not be made because these were separate experiments,
but the data in Tables 7 and 8 indicate very little difference in the level of
weed control between seedbed preparation and specific herbicide treatments.
Yield data were not collected in 1993 because of severe bird damage.
In 1994, data in Tables 9 and 10 indicate a much higher level of weed
control in stale seedbed than in the conventional seedbed. Again, statistical
comparison could not be made because these are separate experiments. But, the
control of Smallflower morningglory and Palmer amaranth was much higher and more
consistent in the stale seedbed experiment. The type of seedbed preparation did
not appear to affect pearl millet yield (Tables 9 and 10). There was a general
trend for better weed control for pearl millet planted in 18 inch rows as
compared to pearl millet planted in 36 inch rows. Pearl millet canopy planted
in 18 inch rows closed (overlapped the row middles) about 7-10 days earlier than
pearl millet planted in 36 inch rows, which would provide greater competition to
the weeds present.
It was also observed in border areas outside the experimental plots that
weed control in the stale seedbed experiment was much higher than in the
conventional seedbed experiment.
REFERENCES
Burton, G. W., A. T. Primo, and R. S. Lowrey. 1986. Effect of clipping
frequency and maturity on the yield and quality of four pearl millets.
Crop Sci. 26:79-81.
Hanna, W. W. 1991. Pearl millet A potentially new crop for the U.S. In
Abstr. of Tech. Papers, No. 18, Southern Branch ASA, 2-6 Feb 1991, Ft.
Worth, TX.
Kumar, K. A., S. C. Gupta, and D. J. Andrews. 1983. Relationship between
nutritional quality characters and grain yield in pearl millet. Crop Sci.
23:232-234.
Pudelko, J. A., D. L. Wright, and I. D. Teare. 1993. A method for salvaging
bird damaged pearl millet research. Fla. Agric. Exp. Stn. Res. Rep. No.
NF 93-12:1-11.
Wright, D. L., I. D. Teare, F. M. Rhoads, and R. K. Sprenkel. 1993. Pearl
millet production in a no-tillage system. p. 152-159. In P. Bollich
(Ed.) 1993 Southern Cons. Tillage Conf. for Sustainable Agric.
June 15-17, Monroe, LA. SB 93-1.
TABLE 1. Herbicides evaluated on pearl millet in Florida and Georgia
Common Name Trade Name
atrazine Atrazine
bromoxynil Buctril
metolachlor Dual
paraquat Gramoxone Extra
pendimathalin Prowl
propachlor Ramrod
2,4-D Weedar-64
TA 2. Activity of selected herbicide treatments or arl millet and weeds in conventional seedbed.
Quincy, 1993
Percent Control
Treatment
Atrazinel
Atrazine
Atrazine"
Atrazine'
Dual + 2,4-D
Dual + 2,4-D
Dual + 2,4-D
Ramrod + 2,4-D
Ramrod + 2,4-D
Prowl + 2,4-D
Prowl + 2,4-D
Dual + Atrazine'
Dual + Atrazine*
Ramrod + Atrazine*
Ramrod + Atrazine*
Prowl + Atrazine'
Prowl + Atrazine"
Hand weed check
Non-treated
Non-treated
Ramrod
Prowl + Atrazine*
Prowl
Prowl + Atrazine*
LSD (0.05)
'Crop oil concentrate at 1 qt/A.
Rate
lb/A
1.5
2.0
1.5
2.0
1.0 + 0.5
1.5 + 0.5
2.0 + 0.5
3.0 + 0.5
4.5 + 0.5
0.5 + 0.5
0.75 + 0.5
1.0 + 1.0
1.5 + 1.0
3.0 + 1.0
4.5 + 1.0
0.5 + 1.0
0.75 + 1.0
Grass
83
88
94
95
88
99
100
94
90
100
95
100
100
99
99
95
93
100
0
0
94
99
Broadleaf
98
98
98
98
88
85
88
85
95
98
95
100
100
100
99
100
98
100
0
0
100
100
5
Percent
injury
9
15
25
20
81
95
96
33
43
21
16
95
100
64
59
13
25
0
0
0
0
0
8
Yield
lb/A
3016
2954
2675
2405
2435
1553
1506
3128
3202
3073
2806
1353
1612
2901
2544
2970
2877
2575
2754
2563
2909
2561
311
4.5
0.5 + 1.0'
0.5
0.5 + 0.5'
Al treatments of Atrazine applied postemergence.
TA 3. Activity of selected herbicide treatments on earl millet and weeds in a no-till system.
Quincy, FL 1993
Percent Control
Rate Percent Yield
Treatment lb/A Grass Broadleaf injury lb/A
Atrazine' 1.5 94 100 7 2720
Atrazine 2.0 90 100 11 2819
Atrazine* 1.5 95 99 17 2641
Atrazine* 2.0 94 100 25 3087
Dual + 2,4-D 1.0 + 0.5 98 93 83 1971
Dual + 2,4-D 1.5 + 0.5 89 96 96 1199
Dual + 2,4-D 2.0 + 0.5 98 90 97 509
Ramrod + 2,4-D 3.0 + 0.5 98 85 45 2173
Ramrod + 2,4-D 4.5 + 0.5 94 83 44 1823
Prowl + 2,4-D 0.5 + 0.5 95 97 16 3066
Prowl + 2,4-D 0.75 + 0.5 98 100 13 3382
Dual + Atrazine* 1.0 + 1.0 98 99 89 1892
Dual + Atrazine* 1.5 + 1.0 100 97 97 1001
Ramrod + Atrazine* 3.0 + 1.0 98 97 31 2103
Ramrod + Atrazine* 4.5 + 1.0 98 100 76 2319
Prowl + Atrazine* 0.5 + 1.0 99 97 10 2348
Prowl + Atrazine* 0.75 + 1.0 100 97 14 2678
Hand weed check 100 100 0 2807
Non-treated 0 0 0 2785
Non-treated 0 0 0 2799
LSD (0.05) 7 5 7 322
*Crop oil concentrate at 1 qt/A.
'All treatments of Atrazine applied postemergence.
TABLE 4. Activity of selected herbicide treatments on pearl millet and weeds in conventional seedbed.
Quincy, FL 1994
Percent Control
*Crop oil concentrate at 1 qt/A.
'All treatments of Atrazine applied postemergence.
2Silage consisted of 35% dry matter.
Treatment
Atrazine'
Atrazine
Atrazine'
Atrazine*
Ramrod + 2,4-D
Ramrod + 2,4-D
Prowl + 2,4-D
Prowl + 2,4-D
Ramrod + Atrazine*
Ramrod + Atrazine*
Prowl + Atrazine*
Prowl + Atrazine"
Dual
Hand weed check
Non-treated
LSD (0.05)
Rate
lb/A
1.5
2.0
1.0
1.5
1.5 + 0.5
2.25 + 0.5
0.5 + 0.5
0.75 + 0.5
1.5 + 1.0
2.25 + 1.0
0.5 + 1.0
0.75 + 1.0
1.0
Grass
59
30
47
42
70
43
67
85
69
43
79
46
27
100
0
32
Broadleaf
88
85
87
82
80
73
83
89
78
69
86
78
34
100
0
21
silage yield2
T/A
36
24
49
40
49
36
46
51
43
45
54
37
15
53
33
17
TABLE 5. Activity of selected herbicide treatments on pearl millet and weeds in a no-till system.
Quincy, FL 1994
Percent Weed Control
Rate Silage yield2
Treatment lb/A Grass Broadleaf T/A
Atrazine' 1.5 8 5 59
Atrazine 2.0 17 86 57
Atrazine* 1.0 57 87 41
Atrazine* 1.5 44 88 40
Ramrod + 2,4-D 1.5 + 0.5 73 81 60
Ramrod + 2,4-D 2.25 + 0.5 46 77 51
Prowl + 2,4-D 0.5 + 0.5 73 82 57
Prowl + 2,4-D 0.75 + 0.5 85 86 62
Ramrod + Atrazine' 1.5 + 1.0 85 89 52
Ramrod + Atrazine' 2.25 + 1.0 54 65 32
Prowl + Atrazine* 0.5 + 1.0 85 87 56
Prowl + Atrazine* 0.75 + 1.0 59 82 21
Dual 1.0 40 36 17
Hand weed check 100 100 77
Non-treated 0 0 52
LSD (0.05) 32 21 17
*Crop oil concentrate at 1 qt/A.
'All treatments of Atrazine applied postemergence.
2Silage consisted of 35% dry matter.
TABLE 6. Effect of atrazine on weed control and pearl millet yield. Tifton, GA 1991
Row Spacing
Spacing in Row Texas Crowfoot- Crab- Florida Florida Palmer Planting Date
(in.) (in.) panicum grass grass beggarweed pusley amaranth 5-24 6-14
------------------- % Control' --------------------- -- Yield, lb/A2 --
36 3 80 95 95 95 95 95 3,020 3,334 ab
36 6 2,943 2,889 b
18 3 90 95 100 100 100 100 2,942 2,975 b
18 6 2,745 3,636 a
NS
as determined by DMRT at
'Atrazine applied at 1 lb/A to 2-leaf pearl millet.
Data within column followed by the same letter are not significantly different
P = 0.05.
TABLE 7. Effect of postemergence herbicide treatments to weeds in pearl millet on conventional seedbed.
Tifton, GA 1993
---- Treatment --- --------------- % Weed Control-----------------
Rate Row Spacing Weed Crowfoot- Texas Palmer Wild
Herbicide lb/A (in.) control grass panicum amaranth radish
Atrazine 0.75 36 98 97 100 100 100
Atrazine 0.75 18 100 100 100 100 100
Buctril 0.38 36 94 93 97 95 100
Buctril 0.38 18 98 100 100 97 100
Buctril 0.38 36 98 97 100 98 100
Atrazine 0.75
Buctril 0.38 18 100 100 100 100 100
Atrazine 0.75
2,4-D 0.5 36 95 90 97 98 100
2,4-D 0.5 18 98 93 99 99 100
'Weed control data collected two weeks after application.
TABLE 8. Effect of postemergence herbicide treatments to weeds in pearl millet on stale seedbed'.
Tifton, GA 1993
----- Treatment ------ --------------- % Weed Control -----------------
Rate Row Spacing Weed Crowfoot- Texas Palmer Wild Injury
Herbicide lb/A (in.) control grass panicum amaranth radish %
Atrazine 0.75 36 96 93 100 100 100 5
Atrazine 1.0 18 97 95 97 100 100 7
Buctril 0.38 36 95 93 100 87 100 6
Buctril 0.38 18 97 95 100 100 100 0
Buctril 0.38 36 97 97 97 100 100 13
Atrazine 0.75
Buctril 0.38 18 97 95 100 100 100 27
Atrazine 0.75
2,4-D 0.5 36 96 95 95 100 100 0
2,4-D 0.5 18 90 70 93 100 100 7
'All plots treated with paraquat at 0.5 lb/A
2Weed control data collected two weeks after
after planting.
application.
TABLE 9. Effect of postemergence herbicide treatments to weeds in pearl millet on conventional seedbed.
Tifton, GA 1994
---- Treatment --- ------------ % Weed Control-----------------
Rate Row Spacing Crowfoot- carpet- Smallflower Palmer Yield
Herbicide Ib/A (in.) grass weed morningglory amaranth Nutsedge Ib/A
Atrazine 0.75 18 0 100 17 47 97 2,174
Atrazine 0.75 36 0 100 30 40 100 1,829
Atrazine 1.0 18 10 100 27 60 100 2,702
Atrazine 1.0 36 0 100 17 47 100 2,183
Buctril 0.38 18 0 100 10 57 100 2,350
Buctril 0.38 36 0 100 17 7 100 2,033
Buctril 0.38 18 3 100 67 80 100 2,486
Atrazine 0.75
Buctril 0.38 36 3 100 20 73 100 2,102
Atrazine 0.75
2,4-D 0.5 18 3 100 17 40 100 2,111
2,4-D 0.5 36 0 100 0 27 100 2,079
NS
TABLE 10. Effect of postemergence herbicide treatments to weeds in pearl millet on stale seedbed'.
Tifton, GA 1994
----- Treatment ----- % Weed Control-----------------------
Rate Row Spacing Crowfoot- Crab- Carpet- Smallflower Palmer Yield
Herbicide Ib/A (in.) grass grass weed morningglory amaranth Nutsedge lb/A
Atrazine 0.75 36 3 78 83 93 100 100 2,340
Atrazine 0.75 18 7 73 100 90 100 100 2,491
Atrazine 1.0 36 7 93 100 93 100 100 2,266
Atrazine 1.0 18 3 77 100 100 100 100 2,412
Buctril 0.38 36 3 63 100 80 100 100 1,970
Buctril 0.38 18 0 40 100 75 100 100 1,985
Buctril 0.38 36 5 85 100 90 100 100 2,334
Atrazine 0.75
Buctril 0.38 18 10 87 100 83 100 100 2,777
Atrazine 0.75
2,4-D 0.5 36 0 27 90 57 100 100 2,757
2,4-D 0.5 18 0 43 93 83 100 100 2,372
NS
'All plots treated with paraquat at 0.5 lb/A after planting.
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