A number of tolerances for bromine in vegetables and fruits grown in soil fumigated 
with EDB have been set by the Food and Drug Administration, These range from 5 parts 
per million of inorganic bromide calculated as bromine in lima beans and strawberries 
to 75 p.p.m. in potatoes, melons, parsnips, and carrots, 
Information on residues from DBCP is not available, but it is apparent that some 
bromine remains in the soil. This fact is shown by bromine toxicity symptoms on plants 
especially sensitive to bromine, such as onion seedlings grown in treated soil (O'Bannon, 
1958). 
Dichloropropenes and D-D mixture hydrolyze and form hydrochloric acid in the 
soil (Shaw, 1948), but other breakdown products or residues in soil or plants under 
normal conditions of use have not been reported. However, it is quite certain that 
plants can take up something derived from these materials since toxicity symptoms 
appear if various kinds of plants are planted too soon after application, There are 
also reports of flavor tainting of vegetable grown in soil treated with excessive amounts. 
Technical dichloropropenes have been approved for preplanting fumigation of soil 
to be used for 20 kinds of vegetables and 7 kinds of fruits on a nonresidue basis. 
In addition to the materials already mentioned, 5 nematocides are used mostly on 
seedbeds, nurseries, greenhouses, or other small plots of valuable soil. These include 
methyl bromide, chloropicrin, sodium methyldithiocarbamate (SMDC), 0,2-dichlorophenyl 
0,0-diethyl phosphorothioate (VC-13), and 3,5-dimethyl tetrahydro-1,3,5,2H-thiadiazine -2 - 
thione (DMTT). All these materials combine nematode control with other features, such 
as control of soil insects, soil fungi, and weed seeds. For convenience, these are called 
seedbed nematocides to differentiate them from the field nematocides discussed previously. 
Of the seedbed nematocides, methyl bromide is most widely used, particularly on 
tobacco seedbeds. Since it is an odorless gas at temperatures above 38° F., itis usually 
formulated with 2 percent chloropicrin, which serves as a warning agent. Other formula- 
tions contain xylene as a solvent and can be handled as liquids at ordinary temperatures, 
Mixtures of methyl bromide and other chemicals are being tested experimentally. Methyl 
bromide is regularly used at rates of 1 to 21bs. per 100 square feet and is applied 
under a plastic cover, which is left in place 24 to 48 hours. Soil fumigated with methyl 
bromide has a residue containing bromine, This is sometimes troublesome with plants 
easily injured by bromine. However, most crop plants can be planted without injury in 
methyl bromide treated soil 72 hours after the cover has been removed. Methyl bromide 
is registered on a nonresidue basis for preplant soil treatment at 2 lbs. per 100 square 
feet with an aeration period of 72 hours, 
Chloropicrin is mostly used in greenhouses and on seedbeds at application rates 
ranging from 200 to 1,000 lbs. per acre, Application is by injection into the soil at 10- 
or 12-inch intervals. In the soil chloropicrin is adsorbed in amounts directly correlated 
with the percentage of clay. Organic matter adsorbs little chloropicrin (Stark, 1948). 
Aside from the well-known fact that chloropicrin is highly toxic to plants, both in 
soil and air, very little is known about its uptake by plants or the occurrence of residues 
derived from it in plants. It is registered on a non-residue basis for use on soil to be 
planted to strawberries or for vegetable seedbeds. Application of 482 lbs. per acre is 
permitted 2 weeks before planting. For use on celery seedbeds it is registered on a non- 
residue basis for use at 958 lbs. per acre 2 weeks before planting. 
Sodium methyl dithiocarbamate (SMDC) is applied in water solution at rates of 1/2 
to 1 lb. per 100 square feet and is washed down into the soil by liberal applications of 
water. It decomposes in the soil and some of the decomposition products have a fumigant 
IVIL 
