tow wks

Issued By The

UNITED STATES GOLF ASSOCIATION GREEN SECTION

ROOM 307. BUILDING 4 
BUREAU OF PLANT INDUSTRY STATION 
BELTSVILLE, MB.

GROWTH-REGULATING SUBSTANCES GIVE PROMISING RESULTS AS TURF HERBICIDES: It has been 
recognized for numerous years that the turf grasses are not so sensitive to growth-regu­
lating substances as are many other plants. In the November, 1940, issue of TURF 
CULTURE an article was published summarizing the various attempts, on the part of the 
Green Section staff to stimulate turf grasses with growth-regulating substances of 
various sorts. Regardless of whether applications were made to established turf, to 
stolons, or to seed, no noticeable results could be observed as the result of applications 
of any of the several compounds tried. It was not, however, until August of this year 
that the possible advantage of this lack of sensitivity was recognized. The particular 
compound (2, 4-diehlorophenoxyacetic acid) with which the experiments to date have been 
concerned is only one of many such compounds. It, however, is one which is easily manu­
factured, is relatively inexpensive and to which many of our common weeds are decidedly 
sensitive. Moreover, fair stocks of it are already available in the hands of the manu­
facturers.

Wien weeds which are sensitive to 2, 4-dichlorophenoxyacetic acid are sprayed 

with 0.1$, and in some cases .05$, solutions of it the compound is absorbed by the weeds 
through their leaves and often within 48 hours the first modification of growth of the 
weeds is evident in growth curvatures. These are particularly conspicuous in plants 
such as narrow-leaf plantain or dandelion and less so in the small-leafed plants such as 
clover, heal-all and lawn pennywort. This curvature stage is followed by a yellowing 
of the leaves which, when the rate of application is sufficiently high, eventually turn 
brown and completely disintegrate. Applications made in late August and early Septem­
ber required from 1 to 3 weeks for death to take place, depending on the weed involved 
and also the growing conditions. Obviously, since ultimate death depends on a modifi­
cation of the growth of the plant, quickest results may be expected from applications 
made at a time of year when the weeds in question are growing most rapidly. Narrow­
leaf plantain treated after the middle of October has been much slower to react to the 
chemical than it was when treated early in September. It is conceivable in fact that 
many of the plants may not die until growth is resumed next year. As a matter of fact, 
experiments are under way at present to determine whether or not applications made in 
late fall and winter when labor is available (so long as the foliage of perennial weeds 
is still present to absorb the chemical) may be effective next spring when growth of 
the weeds is resumed.

As has been indicated, plants vary widely in their sensitivity to growth­

regulating substances in general and .to 2, 4-dichlorophenoxyacetic acid in particular. 
Kentucky bluegrass is the most resistant of any of the turf grasses so far treated, 
showing no injury even when cut at 1-inch height. There is some indication of slight 
sensitivity of fescues and more of creeping bent when cut at putting green height. 
Experiments have indicated that applications to putting green turf in early fall cannot 
be at a concentration greater than .05%. The number of applications and the frequency 
at which they can be made without serious injury to the bent have not as yet been de­
termined. Tests have not as yet been made on Bermuda grass turf cut either at fairway 
or putting green height.

Of the weedy grasses and weeds so far observed in treated turf crabgrass shows 

no sensitivity whatsoever; goose grass gives only a slight reaction; wild garlic has given 
no reaction; broad-leaf plantain, Ajuga reptans, and several species of Antennaria have 

November, 1944

given only very slight reactions; clover, knotweed, dandelion and narrow-leaf plantain 
have been very effectively controlled with single applications of the 0.1% solution at 
the rate of 5 gallons to 1,000 square feet; whereas heal-all, chickweed and lawn pennywort 
have been effectively controlled with the .05% solution applied at the rate of 5 gallons 
to 1,000 square feet.

It should be remembered that these experiments have been conducted primarily 

during the month of September. It cannot now be predicted with certainty what may be 
the results' from applications made at other times of the year. Most of the turf 
applications have been made by means of a fine spray. It is important that the spray 
be uniformly distributed and a satisfactory coverage of the vegetation obtained. At 
the same time, until further experiments can be conducted, it is advisable not to wet 
the soil with the spray since very little is known to date concerning the effect which 
this material may have on the soil when applied at these rates. A sizable series of 
10x10-foot plots has been established, however, to determine what, if any, may be the re­
sults of applying the growth regulator dry either mixed with sand or fertilizer to weed- 
infested turf. The effect naturally has been much slower in becoming evident and no 
conclusions can be drawn from this test until next season.

When applied in spray to turf which is severely infested with one or more weeds 
the treatment should be accompanied by an application of fertilizer and seed. Tests have 
shown that the seed and fertilizer can be applied to the weed-infested turf and topdressed 
lightly to cover the seeds to some extent, immediately before the turf is sprayed with the 
2, 4-dichlorophenoxyacetic acid. In one series of experiments directed to clover con­
trol, a careful study of plugs of turf taken from the seeded portions of both the treated 
plots and the untreated checks showed a greater number of seedlings in the plots which 
were sprayed than in the ones which were not sprayed. This may well have been due to the 
fact that the seedlings could not become established in the already densely populated soil 
on the weed and clover-infested plots. When the undesirable vegetation was removed by 
the 2, 4-dichlorophenoxyacetic acid, however, the development of the germinating seedlings 
was not restricted by competition with established perennial plants.

As indicated elsewhere in this issue, to apply 2, 4-dichlorophenoxyacetic acid 

at the rate of 5 gallons of a 0.1% solution to 1,000 square feet requires 1-3/4 pounds of 
the growth regulator and 8 pounds of the Carbowax to be used as a carrier and spreader.

One of the manufacturers has indicated that "at the present time the price on 

2, 4-dichlorophenoxyacetic acid ranges from $.85 to $1.10 per pound.” Figuring on the 
basis of a cost of $2.00 a pound for the 2, 4-dichlorophenoxyacetic acid in order to allow 
amply for the cost of handling, freight, etc., before the material reaches the consumer, 
the cost for one application at the heaviest recommended rate would be.$3.50 per acre. 
The cost of the Carbowax 1500 when purchased in 510-pound lots (55-gallon drums) is at 
present 300 a pound, f.o.b., South Charleston, W. Va. Allowing for the added cost of 
freight, it is estimated that the cost of Carbowax may be on the average about $2.75 an 
acre, bringing the total cost per acre of materials to $6.25. Lists are being compiled 
at present of the various manufacturers which are in a position to manufacture 2, 4-dich­
lorophenoxyacetic acid.

LAWN PENNYWORT CONTROL: Lawn pennywort (Hydrocotyle rotund i folia) has been found to be an 
extremely difficult weed to control with the customary herbicides. With 2, 4-dichloro­
phenoxyacetic acid, however, it is relatively easy to kill. Applications of 2, 4-dichlorc- 
phenoxyacetic acid at the rate of 5 gallons of .05% solution to 1,000 square feet killed 
all of the established lawn pennywort in turf in which it was present to the extent of 80% 
of the entire plant population. However, since lawn pennywort seeds prolifinally subse­
quent Treatment will be necessary to kill the seedling plants as soon as the seedling 
leaves are sufficiently large to absorb the chemical. Equally satisfactory results were 
obtained with 2g gallons of 0.1% solution as with the 5 gallons of .05% solution as long as 
uniform coverage was secured. When the lawn pennywort has succeeded in crowding out the 
turf grasses to the extent that it had on the areas under test, applications of seed and 
fertilizer must accompany the eradication program in order to establish a satisfactory 
turf as soon as possible and thereby insure against subsequent invasion of other weeds.

November, 1944 

T.T.T. 2

Sheet No. 3 exhausted

CLOVER CONTROL IN TURF: Clover is frequently considered to be a desirable component of 
turf on private lawns, parks, cemeteries, etc. On golf courses, however, it is a turf 
weed of the first magnitude. Moreover, wartime curtailments in maintenance programs 
in general have served to encourage rather than discourage the development of clover, 
with the result that its control is rapidly becoming one of the leading maintenance 
problems on both greens and fairways.

Unfortunately many of the accepted turf herbicides are not so effective 

against clover as they are against some of the other troublesome turf weeds such as 
crabgrass, chickweed, etc. It is extremely difficult to apply these materials at 
rates sufficiently high to burn the clover seriously without also injuring the permanent 
grasses at least temporarily. The principle on which these herbicides operate is that 
of plant starvation, accomplished by judicially burning the foliage at short timely in­
tervals. If this starvation of the clover plants is accompanied by a fertilization 
and seeding program designed to encourage the grass to crowd out the gradually starving 
clover plants a reasonable control can eventually be effected. For many years sulfate 
of ammonia has been the accepted remedy for removing clover since, in addition to burn­
ing the clover leaves, it supplies a readily available source of nitrogen to the grass 
plants, thus enabling them to compete more successfully with the clover. Also it makes 
the soil more acid and this in itself discourages the clover.

The Green Section is particularly happy at this time to report recent tests 

which have been made here in Washington in collaboration with Drs. Joon V.h Mitchell and 
Paul C. Marth, of the Bureau of Plant Industry, Soils and Agricultural Engineering, 
which demonstrate the effectiveness of a plant growth regulator known chemically as 
2, 4-dichlorophenoxyacetis acid, in the selective control of clover in fairway turf. 
This material operates on an entirely different principle from previously used herbicides. 
Instead of depending on a simple burning of the tops of the plant, the growth regulator 
when applied to turf is absorbed by the clover plant, and the acid, or a derivative of it, 
greatly reduces the general growth of the plant and hastens the death processes. Thus the 
killing effect is a physiological and systemic one rather than the physical and superficial 
burning which is the basis of the herbicidal effects of the arsenicals and other mate­
rials commonly used for the killing of turf weeds.

Applications in the late summer and early fall of the 2, 4-dichlorophenoxy­
acetic acid at the rate of 5 gallons of a 0.1/? solution to 1,000 square feet have re­
duced clover stands from as much as To/o to less than 1% without any apparent injury to 
the Kentucky bluegrass in the plots. A careful examination of the surface inch of the 
treated turf showed many of the stolons completely disintegrated and the majority of the 
remaining ones brown and flaccid with no signs of life. The few stolons which were still 
apparently alive had almost all lost their leaves and in most cases had not produced 
many new leaves. Experience has shown that weakened plants which go into 'winter in a de­
foliated condition are readily winterkilled and it is entirely possible that the injured 
clover in this instance will not survive until spring.

Although it has not yet been-possible to* test the herbicidal activity of this 

chemical on clover or any of the other turf pests throughout the year, since these ex­
periments were not initiated until August of this year, it is reasonable to presume that, 
so far as clover is concerned, late summer or fall may be the best time of year for ef­
fective application. Applications made then may make it possible for winter weather to 
complete the job that the application of 2, 4-dichlorophenoxyacetic acid initiates. A 
repeated application may be necessary in late spring if any significant amount of clover 
survives. Because of the relatively low concentration of 2, 4-dichlorophenoxyacetic 
acid which is required as compared with herbicides as they are customarily used, it is 
easier to consider rates in terms of 5,000 rather than the usual 1,000 square feet. 
3J ounces of this chemical made up in 25 gallons of solution will treat 5,000 square 
feet, or for larger areas the rate may be expressed as 1 3/4 pounds in 200 gallons of 
solution per acre. This is the rate recommended for fairway or lavm purposes.

In the short time in which these tests have been under way it has not been pos­

sible to work out the rates which can be used safely and effectively on putting green turf 
for the control of clover. It has been determined that creeping bent turf cut at putting 
green height will tolerate c gallons to 1,000 square feet of a solution of half the above 

November, 1944

T.T.T. 4

concentration without any conspicuous discoloration. Therefore it appears at present to 
'oe possible, by reducing the amount of 2, 4-dichlorophenoxyacetic acid applied, to control 
the clover on putting greens by repeated applications. It is to be hoped that current ex­
periments may form the basis for recommendations for the use of this material on putting 
greens next season.

It is obvious that when large stands of clover are killed there is not suffi­

cient grass left from which to develop a satisfactory turf even though it remains un­
injured. Therefore it is essential to accompany the application of 2, 4-dichlorophenoxy- 
acetic acid with a reseeding and fertilizing program when dense stands of clover are to be 
removed. When the clover has not crowded out the turf grasses to so serious an extent, 
a fertilizing program alone may be sufficient. Since fall is the best time of year for 
establishing new grass in most of the areas where clover is a problem, this is another 
point in favor of fall applications of 2, 4-dichlorophenoxyacetic acid to remove clover. 
Experiments have been performed which show that seed and fertilizer may be applied 
either immediately before or after the chemical application so that the grass can ger­
minate and become established as the clover dies. From 1 to 3 weeks may be necessary 
after treatment before the clover is killed since, as has been stated before, the effect 
is not one of immediate burning but rather one which results from modified growth 
processes throughout the entire plant.

It should be remembered that in a long-time maintenance program white clover can 

usually be controlled by proper fertilizing practices which should be initiated and followed 
conscientiously after the clover has been killed by the growth regulator or any other- 
treatment. Generally speaking, clover thrives much better in turf which has been limed 
than in turf which has been growing in acid soil. Excessive liming therefore should be 
avoided where clover is a problem. Also because of the nitrogen fixing bacteria in the 
root nodules, white clover grows well in soil which is low in nitrogen. Consequently on 
soils of low fertility it is able to compete more successfully with turf grasses (which 
must depend on the soluble nitrogen in the soil), than it can on fertile soils. Therefore, 
applications of high nitrogen fertilizers while encouraging the grass also discourage the 
clover.

PREPARATION OF CARBOWAX-GROWTH REGULATOR HERBICIDE SOLUTION: To prepare a solution of 
the growth regulator, 2, 4-dichlorophenoxyacetic acid, in water it is necessary to use a 
carrier or binder. For this purpose Carbowax 1500, which has been demonstrated to be 
harmless to even the most closely cut creeping bent turf when applied in quantities at 
least twice as great as those necessary for herbicidal purposes, has proved both satisfac­
tory and convenient.

The Carbowax-growth regulator solution may be prepared as follows. For each 

pound of Carbowax 1500 use 3.5 ounces of the 2, 4-dichlorophenoxyacetic acid. The 
Carbowax should be melted and while in that state the 2, 4-dichlorophenoxyacetic acid dis­
solved in it with stirring. This step in the procedure may be performed at any time since 
the growth regulator can be stored in the Carbowax very satisfactorily. As soon as the 
Carbowax cools to room temperature it hardens to its original consistency. For a 0.1% 
solution, which is the concentration necessary to kill dense stands of clover in. fairways 
in early fall, 1 pound and 3.5 ounces of this Carbowax-growth regulator mixture should be 
allowed to 25 gallons of water. For a .05% solution, which is sufficient to kill lawn 
pennywort,- heal-all and various other mat weeds, which are particularly sensitive to the 
growth regulator, 1 pound and 3.5 ounces of this mixture is sufficient for 50 gallons of 
water. At the time the spray solution is to be prepared the Carbowax-growth regulator 
mixture should again be melted and then mixed slowly with stirring with a gallon or two of 
warm water. The resulting soupy material can then be added slowly with stirring to the re­
mainder of the water, producing a clear solution. When warm water is available for the 
entire volume of solution this will be even more satisfactory since the melted Carbowax 
mixture can then be added directly to the required volume of water, provided some stirring 
device is available. 200 gallons of this spray mixture should be applied per acre. This 
is approximately the equivalent of 5 gallons to 1,000 square feet.

November, 1944

T.T.T. 5