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XI. Nitro- and Chloro-substituted Phenols

XI. Nitro- and Chloro-substituted Phenols

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and that pentachlorophenol and its salts could be used as direct substitutes for the dinitrocresols (Barrons, 1947; Crafts, 1945b, 1947b, 1948a,

b; Crafts and Reiber, 1945).

Because dinitrocresol proved more toxic than dinitropheno1, screening

tests were made on the ethyl, propyl, butyl, and amyl substituted phenols.

These proved that toxicity increased up to the butyl substitution, t,hat

the ortho compounds were more toxic than the meta or para compounds,

and that dinitro substitution was more effective than mononitro (Crafts,

1945b). With chloro substitutions on the phenol ring, toxicity increased

regularly to the penta compound.

At present the ammonium salt of dinitro secondary butyl phenol is

being used extensively as a selective herbicide (Dow Selective, Sinox W) .

Dinitro-secondary butyl phenol (Dow General) and amyl phenol (Sinox

General) are widely used to fortify oil sprays and to prepare fortified

oil emulsion sprays for general contact weed control, for potato top killing (Anonymous, 1947b) and as a selective spray in sugar cane (Crafts,

1948a, b; Crafts and Emanuelli, 1948; White and Mangual, 1948), corn,

milo, and similar crops (Crafts, 1948b) by selective placement of the

spray. Pentachlorophenol has recently been introduced as an oil fortifier

(Anonymous, 1948e; Crafts, 1947b, 1948a, b; Crafts and Emanuelli, 1948;

Crafts and Reiber, 1945, 1948; Hance, 1948a). Sodium pentachlorophenate is used in large quantities as a preemergence treatment and as a

selective soil sterilant in pineapples in Hawaii (Anonymous, 1948m).

There are still many opportunities for introduction of nitro-, chloro-,

and nitro-chloro substituted phenols as selective and general contact

herbicides as relatively few of such compounds have been tested as to

their special selectivities.

Combinations of nitro- and chlorophenol contact herbicides with 2,4-D

have proved very effective in certain situations where weeds susceptible

to both types of toxicants are present. Work on such combinations is

presented by White and Villafane (1946), Mangual (1948), White and

Mangual (1948), Crafts (1948a, b), Nolla (1948), and Hance (1948).


Petroleum fractions have long been used as weed killers. At first

waste products such as acid sludge, waste engine oil, and similar materials

were used; later smudge pot oil, Edeleanu extract, and diesel fuel were

adopted (Robbins et al., 1942). More recently stove oil has been used

as a selective weed killer in crops of the carrot family (Crafts, 1947a;

Crafts and Reiber, 1944, Grigsby, 1946; Lachman, 1945; Raynor, 1943;

Sweet, 1945; Sweet e t al., 1944, 1945; Warren, 1946; and Warren and

Hanning, 19461, and since actual research on the herbicidal properties



of oils has been (harried on (Crafts and Reiber, 1948) new weed oils have

been introduced. In the selective field Stoddard solvent or similar light

fractions have been used with eminent success (Crafts, 1947a; Lachman,

1945; Sweet, 1945; Warren, 1946). Standard Weedkiller #I, Shell Weedkiller #lo, and a number of cleaning solvents and paint thinners have

been placed on the market, and in California alone (Crafts, 1947a, b) well

over a million gallons per year are used. Recently a mixture of Stoddard

solvent and kerosene (Standard Weedkiller #11) has been successfully

used to kill wild oats and other grasses in flax (Crafts and Reiber, 1948;

Herbert, 1948).

Recent work in several eastern states has proved that seedlings of

coniferous trees tolerate oil fractions (Eliason, 1948) in the same way

as plants of the carrot family. Oil sprays are proving useful in handling

conifer nurseries and thousands of gallons of Stoddard Solvent and special

weed oils have been used during the past two seasons.

During the war much work was done in perfecting methods of weed

control in guayule using oils. Stove oil and diesel oil were used and

guayule proved highly resistant to them compared with weeds (Benedict,

1944). In fact, by the time the guayule work was abandoned, practically

all weeding operations were being carried on with oil. Oils have also

been suggested for use in onions (Crafts and Raynor, 1944; Crafts and

Reiber, 1948).

I n the field of general contact herbicides, a number of aromat.ic oils

have been introduced. The following list includes the weed oils registered for sale in California during the year 1947-48 (Anonymous, 19488).

Some of these are straight-run distillates; many are high in aromatics:

Avon Weed Killer, Chapman-Gilbert Weed Killer #5, Cox Hykil Weed

Oil, Cox Standard Weed Oil, Foothill Oil Weed Killer, General Weed

Exterminator, G & H Weed Oil, Harold Preston’s Weed Oil, Home Oil

Anaheim Weed Killer, Kem-Kill W, Richfield A, Shell Weedkiller #20,

Standard Weedkiller #2, Union 40-60 Distillate.

The highly aromatic oils in this list are excellent weed oils, being

extremely toxic and effective against such grasses as Bermuda grass,

quack grass, Kikuyu grass, Johnson grass, and others. They are also

useful as oil bases in fortified oil emulsion herbicides (Crafts, 194713,

Crafts, 1948a, b; Crafts and Reiber, 1948; Hance, 1948a, b). Since the

use of such emulsions greatly extends the service of a given volume of

oil, they will probably become widely used as their properties become

known, and as oil becomes scarce. The use of straight oil for weed

hilling seems even now to be justified only where difficult-to-kill grasses

constitute a fair proportion of the weed population.






IPC (Isopropyl Phenylcarbamate)

Several new chemicals have been recently tested for herbicidal

Imperties. Probably the most widely known is I P C (O-isopropyl-Nphenyl carbamate), which was first reported as being toxic to cereals biit

iiot to certain broad-leaved plants by Templeman and Sexton (1945,

1946) in Great Britain. This work was verified a t Camp Detrick (Allard

et al., 1946). Many workers following these early leads tested the effectiveness of I P C on numerous grasses and broad-leaved plants (Anonymous, 1 9 4 7 ~ ) . In general, this chemical exhibits a selective toxicity

toward grasses, although there are notable exceptions. Because of its

low water solubility, i t has usually been applied dry with sand as a

carrier, or as a wettable powder. I P C appears to be noneffective when

applied as a foliage spray prior to elongation of the internodes (Ennis,

1947). Most of the experimental work has been concerned with applications to the soiI, either before or immediately after emergence of grass

seedlings. Early work on quack grass (Carlson, 1947b; Mitchell and

Kephart, 1947) indicated that IPC had definite possibilities but such

use has not yet proven satisfactory (Derscheid and Stahler, 1948,

Grigsby, 1948).

Although IPC has not complctely lived up to early expectations

(Freed, 1948), it is still an important herbicide. Probably its greatest

use will be in the control of weedy grasses in legumes such as alfalfa and

ladino clover (Tucker, 1948). The responses of fifty-two crop species

to this compound have been described by Ennis (1948). Much more

information is needed on formulation, application, and species tolerance

before I P C finds its proper place among modern herbicides.


2. T C A (Trichloracetic Acid)

The sodium and ammonium salts of trichloroacetic acid are presently

receiving wide attention as grass killers. There is less information currently available on these materials than on IPC. The early work indicates, however, that TCA is less selective as a grass killer than I P C

but is more toxic to certain species. Some success has attended its use

on Bermuda and Johnson grass and as a control for annual grasses which

appear after cotton is laid by (Evans, 1948). Both salts of the acid are

readily soluble in water and are usually applied as sprays. Action

through leaf absorption as well as through the soil has been noted with

somewhat less selectivity when applied to the tops. Again, more information is necessary before TCA finds its proper place in weed control.


31 I

3. PMAS (Phenyl Mercuric Acetate)

Recently phenyl mercuric acetate has received attention as a selective

crab grass killer (DeFrance, 1947). Most of the work reported to date

has been on lawns, turfs and golf greens, but successful development of

the material should be a boon in truck gardens and pastures. PMAS is

usually applied as a spray although its action, a t least in part, is through

the soil. I t s selective action on crabgrass may result from the rather

superficial root system of this species.

Developmental work is under way with two other chemicals (Evans,

1948) sodium isopropyl xanthate and ally1 chlorophenyl carbonate, but

little information is as yet available on them.


4. Cyanamid and Cyanate

Calcium cyanamid has long been used as a temporary soil sterilant

to rid soils of weed seeds preparatory to planting lawns (DeFrance, 1948),

tobacco seedbeds (Anonymous, 1948c), and various vegetable and field

crops (Wolf, 1948). Cyanamid dust lias been applied t o cereal crops

as a selective herbicide wherever dew is sufficient to provide moisture to

dissolve the chemical on the leaves of weeds.

More recently potassium cyanate sold under the name of Aero

Cyanate has proved effective as a selective spray in onion and other

bulb crops (Anonymous, 1948d; Evans, 1948). Upon breakdown in the

soil both of these materials leave residues that are high in nitrogen and

hence valuable as fertilizers.

5. CX2, DD, Prochlow

The Irerbicitlal properties of CS2 are well described by Hannesson

et al. (1945). DD (dichloropropane-dichloropropene mixture) proved

effective in the killing of deep-rooted perennial weeds but dosage was

many times that required for nematode control. Since the advent of

2,4-D this material has been limited to the latter use.

Prochlors (chlorinated propane-propene mixture) have been tested as

weed killers (Freed, 1947) but have not been widely used. They offer

some advantages over CS, but cost considerably more than 2,4-D in the

control of perennial weeds,

While generalization as to new chemicals in a field as fluid a s that

of herbicides is not without risk, nevertheless certain trends do appear.

Specific selectivities, undreamed of a few years ago, have aIready emerged

and become an integral part of the agricultural scene. More such selective chemicals are in the offing, bringing further advances in weed control. Also, new developments point to better grass killers both as

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