POTATO INVESTIGATIONS LABORATORY
Mimeo Report 60-2 September 25, 1959
CHEMICAL CONTROL OF WEEDS IN POTATOES
E. N. McCubbin
Preliminary treatments for control of weeds in potato fields with DNBP (pre-
merge) were made in fall- and spring-grown potatoes in 1956 and 1957. The herbicide
was used at 3 pounds active ingredient in 100 gallons of water per acre. It gave
excellent control of ragweed, rough pigweed, milkweed, chickweed and smartweed, but
it did not control crabgrass and nutgrass. Weeds in check plots at the end of the
growing season were numerous and almost large enough to hide the potato plants;
those in treated plots were small and of no consequence. Weed control with DNBP was
good whether the chemical was used on the soil before or after the weed seed had
germinated. It was necessary however, to apply the DNBP after the potatoes were
planted and before the plants came-up to keep from burning them off at the ground.
Work to find good herbicides for control of weeds in potato fields was enlarged
and expanded in 1958 and 1959. Emulsion concentrates of DNBP, CDEC (Vegadex), PCP
(pentachlorophenol) and granular CDEC were tested in four different replicated tests
in these two years. DNBP was applied at 1.5 and 3 pounds active ingredient per acre,
CDEC at 2 and 4 pounds per acre and PCP at 4 and 6 pounds per acre. Treatments were
applied at different numbers of days after the potatoes were planted, but before the
plants appeared above ground.
Best control of weeds was obtained with DNBP at 3 pounds per acre, CDEC at 4
pounds and PCP at 6 pounds. Almost as good weed kill, however, was obtained with
the lesser amounts of these herbicides.
Good control of weeds in potato fields, other than crabgrass and nutgrass, may
be obtained with 3 pounds of DNBP, 4 pounds of CDEC or 6 pounds of PCP. With fields
that are not so weedy, good control of weeds may be obtained with lesser amounts of
Apply these chemicals after planting potatoes and just before the plants emerge
from the soil. They should be applied to wet soil, or if the soil is dry when the
chemicals are applied, irrigate to wet the soil surface.
DNBP may be applied to a field either free of weeds or with the weeds growing
and 1 to 2 inches tall. CDEC will not kill young weeds. Cultivate to kill weeds
and then apply this herbicide.
1. Read directions on the herbicide labels and follow them. Avoid breathing or
getting wet with herbicidal sprays.
2. After using a sprayer to apply DNBP, CDEC and PCP rinse the sprayer thoroughly
with clean water and spray some through the machine.
3. Weed kill may be so thorough from these herbicides that a heavy rain near the
end of the growing season may wash the soil off the tubers and expose them to
sunlight. If this occurs cover the potatoes with soil as soon as possible o'L
References ( l
v 001 16
McCubbin, E. N. Premerge Controls Weeds. Fla. Agr. Exp. Sta. Sunshine Re
Rpt. 2: 4 p. 11. 1957.
-_. Chemical Control of Weeds in Potato Fields. Proc. Fla. Sta .
Hort. Soc. 72: 1959. (In Press) ';