One of the oldest and widely used soil dis- 
infestants is a mixture of methyl bromide and 
chloropicrin (Dowfume MC 2), A relatively 
new formulation of methyl bromide in a 
petroleum solvent can be chisel injected into 
the soil with tractor-drawn equipment, Another 
useful, wide-range soil fumigant is a mixture 
of methyl bromide, chloropicrin, and pro- 
pargyl bromide (Trizone), A new and some- 
what cheaper soil sterilant mixture is 
composed of 1,3-dichloropropene and 1,2- 
dichloropropane and methyl isothiocyanate 
(Vorlex), A similar mixture of D-D and 
chloropicrin (Nemex) has been used success- 
fully in some areas of the Western States, 
Other available commercial soil sterilants in- 
clude sodium methyldithiocarbamate (Vapam) 
and 3,5-dimethyltetrahydro-1,3-5, 2H-thi- 
adiazinethione (Mylone), 
Most volatile soil fumigants control nema- 
todes primarily, though some may also con- 
trol certain insects, weeds, and soil fungi, 
Older chemicals of this type are ethylene 
dibromide (Dowfume W-85), a mixture of 
1,3-dichloropropene and 1,2-dichloropropane 
(D,D), and a related chemical composed of 
technical 1,3-dichloropropane (Telone), A 
highly effective mixture of ethylene dibromide 
and 1,3-dichloropropene (Dorlone) has proven 
useful for controlling a wide range of nema- 
tode types, Another chlorinated hydrocarbon 
nematocide, 1,2-dibromo-3-chloropropane 
(Nemagon), has won wide acceptance because 
it can be applied to tolerant crops as a pre- 
planting or postplanting treatment in irriga- 
tion water in the West and as a granular 
formulation mixed with fertilizer in other 
areas of the country. 
Within the last 2 years a new, relatively 
cheap, and low-volume nematocide has been 
recommended for treating some crops, This 
chemical, tetrachlorothiophene (Penphene), is 
particularly interesting because of its simi- 
larity to the toxic chemical that has been 
isolated from marigold roots, which make 
them resistant to nematode attack (23, 26), 
A new chemical, 2,4-dichlorophenyl meth- 
anesulfonate (SD-7727), entirely different in 
nematocidal structure from most proprietary 
nematocides, has very low volatility and is 
somewhat residual, with some indication of 
54 
systemic activity, It appears to be specific 
for controlling root-knot nematodes, but has 
little effect on other nematodes found in 
the soil (14), 
ORGANOPHOSPHATE 
NEMATOCIDES 
Many new nematocides currently being de- 
veloped by industry can be classed as either 
carbamates (e.g., Vapam) or organophos- 
phates, The organic phosphate group has a 
greater number of potential new nematocides 
than the carbamate group, The first organo- 
phosphate nematocide marketed (6) was 
O,2,4-dichlorophenyl, O,O-diethyl phos- 
phorothioate (V-C 13), The second organo- 
phosphate (13) of importance as a nematocide 
was O,O-diethyl O-2-pyrazinyl phosphoro- 
thioate (Cynem), A more recent experimental 
organophosphate is phenyl N,N-dimethyl phos- 
phorodiamidate (Nellite), which is effective 
only against root-knot nematodes, and may be 
applied at low dosage in irrigation and trans- 
plant water (25), Another experimental organic 
phosphate nematocide is O,O-diethyl O-p- 
(methylsulfinyl) phenyl phosphoroathioate 
(Bayer 25141), which appears to be effective 
in controlling nematodes in living roots, such 
as are found in infected nursery rootstock 
(2, 24), These compounds control many soil 
insects when applied to the soil at nematocidal 
dosages, which is usually two to four times 
higher than those required for economical 
insect control, 
Recent investigations (5, 10, 11, 19) have 
shown that the following organophosphate in- 
secticides will control nematodes under cer- 
tain conditions: O,O-diethyl O-p-nitrophenyl- 
thiophosphate (Parathion), O,O-diethyl S 
(and O)-2-(ethylthio)ethyl phosphorothioate 
(Systox), diethyl-S (ethyl thiomethyl) phos- 
phorothioate (Thimet), O,O-diethyl S-2- 
(ethylthio) ethyl phosphorodithioate 
(Di-Syston), O,O-diethyl O-(2-isopropyl-4- 
methyl-6-tyrimidinyl) phosphorothioate 
(Diazinon), and O,O0-dimethyl S-(methyl- 
carbamoylmethyl) phosphorodithioate 
(Dimethoate, Cygon), The herbicide Zytron 
(O-(2,4-dichlorophenyl)-O-m ethyl isopropyl 
