POTATO INVESTIGATIONS LABORATORY
Mimeo Report POL 64-5* October 1, 1963
CHEMICAL CONTROL OF WEEDS AND NUTGRASS IN POTATOES
E. N. McCubbin, Horticulturist
Studies on the control of weeds in potato fields with chemical herbicides have
been carried on at the Potato Investigations Laboratory for the last five years.
Control of Weeds Other than Crabgrass and Nutgrass: Best control of weeds in
potato fields has been obtained with DNBP (premerge). The treatment is made 2 to
3 weeks after potatoes are planted and before the potato plants emerge, with
3 pounds active ingredient, (one gallon) DNBP per acre. The herbicide is mixed in
80 to 100 gallons of water and sprayed over an acre of potato rows and alleys with
a sprayer. For best results the herbicide should be applied when the surface soil
is moist; immediately after a rain is a good time. The herbicidal treatment con-
trols broadleaf weeds in potato fields from planting until harvest. The few weeds
that grow in treated fields remain small and are of no consequence. Those growing
in nontreated fields develop to large size and are troublesome at harvest time.
Control of Nutgrass: Fields should be treated 3 times during the summer with
amine-type 2,4-D to obtain best.control of nutgrass. This material sprayed on the
nutgrass is absorbed and translocated into the nuts where it kills them. There are,
however, dormant nuts, those that are not growing, in most fields of nutgrass.
Hence, the necessity for 3 treatments. By disking the field at different times
during the summer, dormant nutgrass nutlets may be brought into growth so the 2,4-D
spray may be absorbed by the tops and moved into the nuts to kill them. Little or
no control will be had unless the full program of treatment is applied. The summer
cover crop will be lost, but control of nutgrass will compensate for this loss.
After the potatoes are harvested in the spring, wait until nutgrass plants are
4 to 6 inches tall and growing vigorously before treating. Spray each acre with 80
to 100 gallons of water, containing 5 pounds active ingredient, amine-type 2,4-D and
2 ounces of spreader-sticker, Triton B 1956. Five quarts of 2,4-D commercial
preparation containing 4 pounds of the active ingredient per gallon will be re-
quired. Treat roadways and water furrows also if these areas are infested with
nutgrass. Two or three weeks later disk the land and rebed it into low beds. Wait
for more nutgrass nutlets to grow.
After a period of 3 to 4 weeks, nutgrass will be growing again and will have
attained a height of 4 to 6 inches. It is time to make the second treatment. It is
made at the same rate and in the same way as was the first treatment. Two or three
weeks after the second treatment, disk the land and rebed it into low rows. Wait
for other nutgrass nutlets to grow.
The third treatment is made when the new nutgrass plants are 4 to 6 inches tall.
This treatment also is made at the same rate and in the same way as was the first
one. Two to three weeks later disk the land and rebed it into low beds.
*Reprint of Mimeo Rep':b t 62-7
This program of three 2,4-D treatments should be completed by the middle of
October or early November. The land may be left then until potato planting time
and prepared and planted to potatoes.
Read directions on herbicide labels and follow them. Avoid breathing
herbicidal sprays or getting wet with them.
After applying DNBP rinse the sprayer thoroughly with clean water and spray
some of the water through the sprayer.
After using 2,4-D in a sprayer clean it thoroughly before spraying other crops
;ith it as follows:
1. Fill spray tank with clean water and spray it through the sprayer
5 to 10 minutes. Drain the tank.
2. Fill sprayer tank nearly full of clean water. Add 1 gallon of
household ammonia per 100 gallons of water (a 500-gallon tank
would require 5 gallons of household ammonia). Finish filling
tank with water. Start engine and spray out solution for 3 to
5 minutes. Cut off sprayer and let the water and ammonia mixture
stay in the sprayer for 2 days. Then drain sprayer and fill it
with clean water. Spray some of the clean water through the sprayer
for 5 or 10 minutes and then drain the sprayer.
1. Burgis, D. S. Nutgrass control with 2,4-D in Florida. Fla. Agr. Exp. Sta. Cir.
2. McCubbin, E. N. Premerge controls weeds. Fla. Agr. Exp. Sta. Sunshine Res.
Rpt. 2: 4. 11. 1957.
3. Chemical control of weeds in potato fields. Proc. Fla. State
Hort. Soc. 72: 194-196. 1959.