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XI. Nitro- and Chloro-substituted Phenols
A. S. CRAFTS AND W. A. HARVEY
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;
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
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.
A. S. CRAFTS AND W. A. HARVEY
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,
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.
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