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'-} University of Flo.r
CENTRAL FLO ON CENTER
Research Report SAN 85-1 g 0 1984 July 1984
WEED CONT OL IN NO-TILLAGFEL CORN
r F.AS. Univ'.of
W. T. d N. Gallaher
Tropical field corn (Zea mays), because of its heat tolerance and disease
resistance, is adapted to summer planting in Central and South Florida. It
can be grown as a second crop following a spring planting of vegetables or
field corn and brought to maturity during the fall for either forage or
grain. Other early and full season types can only be grown in the spring to
give a satisfactory crop.
In order to evaluate weed control programs for no-tillage tropical corn,
the cultivar Pioneer 304C was planted on the Research Center farm on July 21,
1983. The soil, Immokalee fine sand, isan Arenic Haplaquod, with a shallow
hardpan at approximately 24 inches. The experiment was designed as a
factorial, with four contact post-emergent herbicide treatments to kill
existing growth, four pre-emergent herbicide treatments to inhibit further
weed development, and four replications. This comprised a total of 64 plots,
each with six rows 35 feet in length. Of the four replications, two were
on land with a heavy growth of annual weeds, primarily large crabgrass
* (Digitaria sanguinalis), narrowleaf signalgrass (Brachiaria piligera), and
goosegrass (Eleusine indica). The field had been used for vegetables during
the winter of 1982-83 followed by spring fallow. The other two replications
were planted on an adjacent field which had produced soybeans in 1981 followed
by fallow in 1982 and the spring of 1983. By the summer of 1983, it was
uniformly covered with a bermudagrass (Cynodon dactylon) sod with a few
large perennial weeds such as dogfennel (Eupatorium capillifolium) and
horseweed (Conyza canadensis).
The experiment was planted with a Buffalo Model 4570-2, 2-row All-Flex
Slot-Planter, supplied by Dr. R. N. Gallaher of the Agronomy Department,
courtesy of the Fleischer Manufacturing Co., Inc. of Columbus, Nebraska.
This planter has a front coulter, a slot-shoe opener, covering wheels, and
a rear tine incorporator. Using 30 inch row spacing, a 24-cell plate, and
sprockets to give a spacing in the row of'8.4 inches, 24,900 seed per acre
were planted. Although herbicide granule application equipment was attached,
the weed control chemicals were applied with a separate small plot sprayer
to permit uniform planting. The herbicides for each treatment were tank-
mixed and applied in water at 60 gallons per acre, with full broadcast coverage.
To kill existing broadleaved weeds and grasses, the treatments were
paraquat at two rates, 3/8 and 3/4 pound ai/acre, and glyphosate at two rates,
1 1/2 and 3 pounds. Ortho X-77 was added at 1/8% of the final volume to all
paraquat treatments. The preemergence herbicides were alachlor and
metolachlor, each used at both 2 pound and 3 pound rates, providing a total
* of 16 treatments. Additional broadleaf weed control was obtained with
atrazine at 1 pound ai/acre, tank-mixed with the other treatment chemicals
for all plots.
The crop was grown without any preparatory tillage or cultivation. One
insecticide application was made for budworm control and the crop was
irrigated twice, applying 1 inch of water each time by overhead sprinklers.
Weed control data were recorded on August 9. There was adequate control
in all plots of broadleaf weeds. Grass control was rated on a scale of 0 to
10, with 10 indicating complete grass elimination. Individual grass species
Vere not rated separately since there appeared to be little difference in
the composition of the species in the various plots, except in those
replications where bermudagrass predominated.
The ears were harvested on November 9. Yields are expressed as shelled
grain at 15.5% moisture.
Summary data on weed control and corn grain yields are given in Tables
1 through 4. Although paraquat gave a rapid burn-down of the weeds, regrowth
was evident within two weeks. Glyphosate was much more effective throughout
the whole crop growing season. This was also reflected in corn yields. There
was no significant effect of chemical rate with any of the herbicides.
Alachlor and metolachlor, in combination with atrazine, were equally
effective in controlling annual weed regrowth. A significant difference
in weed control and crop yield was evident between the two field areas.
Regrowth of the bermudagrass depressed corn yield to a lower level than was
obtained where annual weeds were present at planting time.
Table 1. Effect of paraquat and
of established grasses
glyphosate applied at planting on control
in no-till tropical corn.
Contact Chemical Weed Control
herbicide rate Rate mean Chemical mean
-lb ai/acre- -----------0-10 rating-------
Paraquat 3/8 6.6 6.9
Glyphosate 1 1/2 8.7 9.0
LSD (0.05) 1.0
Table 2. Effect of alachlor
growth of weeds in
and metolachlor applied at planting on subsequent
no-till tropical corn.
Weed Control Interaction with
Pre-emergence Chemical Rate Chemical contact herbicides
herbicide rate mean mean Paraquat Glyphosate
Ib ai/acre ---------- 0-10 rating-------------
Alachlor 2 7.9 7.8 6.7 9.0
Metalachlor 2 7.9 8.0 7.0 9.0
Significance N.S. N.S. N.S. N.S.
Table 3. Comparison of weed control in annual weed field with that observed
in bermudagrass sod planted to no-till tropical corn.
herbicide Annual weeds Bermudagrass sod Mean
------------------ 0-10 rating-----------------
Paraquat 6.5 7.2 6.9
Glyphosate 9.4 8.6 9.0
Mean 7.9 7.9
LSD (0.05) 1.0
Table 4. Mean yields of tropical corn observed in no-till trial,
comparing several experimental factors.
Comparison Kg/ha Bu/acre
Paraquat 5750 91.7
Glyphosate 6202 98.9