Vol. 15—1961 - NorthEastern Weed Science Society

RELATIVEHERBICIDALEFFICr::NCYOF DACTHALY W'i!,;'l'l'ABLE
POWDER· AND~'JULAR FOKHULAT IONS
Faul H. Schuldt Y, L. E. Limpel Y, -A.· L. Galloway l/, and David Lamont ?J
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Abstract
The tre nd in the last few years toward the widespread use of granular
herbicides makes it necessary that new experimental materials like DACTHAL
(dimethyl ester of tetrachloroterephthalic acid) be examined as granular
preparations along with other more conventional formulations. It is necessary
to·detemine whether granulars increase or decrease herbicidal efficiency,
change the residual properties or alter crop tolerance. The physical
and chemical properties of a herbicidal candidate dictate or greatly influence
what type of formulation will be most successful. It has been demonstrated
that granular preparations of one chemical may decrease herbicidal action,
while in another, activity may be increased when compared to wettable powders
or emulsifiable concentrates. Compoundswith low vapor pressures, high melting
points, and very low solubility in water are likely to be less effective
when formulated as granulars.
The solubility of DACTHAL in water is less than 0.5 p.p.m. and it is
sparingly soluble in many organic solvents. It is a white crystalline compound
with a low vapor pressure and a melting point of 156 0 C. Thus, the
prospects for a successful granular preparation, particularly for crop use,
were not encouraging from either a performance or cost point of view. Therefore,
the primary purpose of studies over the last two years was to determine
whether a new type of granular formulation would perform satisfactorily compared
to a proven wettable powder formulation.
Based on the physical properties of DACTHAL an experimental granular composition
and a process were developed which allowed investigation of three variables,
i.e. active ingredient, mesh size, and rate of disintegration in water.
Active ingredient in the granular pr-eparatd.ons varied from 1.25 to 10 per cent
DACTHAL(0-1.25, G-l.5, 0-5, and 0-10). Three ranges in mesh size were tested:
20/40, 30/60, and 40/60. The rate of water disintegration ranged from fast (F)
through medium (M) to slow (S). A total of 12 different granular preparations
was studied in 15 pre-emergence field tests. In all tests various granular
formulations were compared for effectiveness with a 50 per cent wettable powder
(W-50). Tests were replicated at least four times in a randomized block design.
11DACTHAL is the trade-mark of the Diamond Alkali Companyproduct,
dimethyl ester of tetrachloroterephthalic acid.
?J Boyce Thompson Institute for Plant ResearCh, Inc., Yonkers, N. Y.
Diamond Alkali CompanyFellowship.
V DiamondAlkali Company, Roseareh Department, Painesville, Ohio.
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