Vol. 15—1961 - NorthEastern Weed Science Society

2$1.
The standard date of application was March 22, 1960.
Additional treatments With calcium arsenate, chlordane,
dacthal, L-13489, and Zytron were applied in ~arly April
and early May to determine the importance of ,timing.
Crabgrass control and turfgrass injury were d~termined
by averaging estimatesot three ±ndividuals. The
following scale was used forturfgrass inJury: O-none>
I-slight, 2-moderate, 3-severe, and 4-very severe - complete
kill.
Results
,
and Discussion
- .
The best performances of the eight pre-emergence herbicides
gave 'crabgrass control ratings that ranged frgm,
29 to 9~ (table I).' Calcium arsenate, dacthal, and L­
31864 effected 96% control with :80 and 84% control" obtained
tor zytron and 'chlordane, ,respectively.
The arsenical complex and the calcium arsenate
treatment rated a slight and moderate injury, re~pectively.
The injUry ratings tor the other treatments were 'lower
and can be considerenegligible.
'
The highest crabgrass control ratinga were obtained
with the early sprin~ treatments (March) ot chlordane'.
and dacthal (table 2). Calcium arsenate gave equall'Y
good control ratings with the March and Avril treatments
Which were tar more efficient than May':treatment. ',Als0 1
injUry ratings with this chemical increased with the delay
of treatment. Treatment With L-13489 and zytron in May
appeared no less effective than earlier treatments.
Summary and Conclusions
Pre-emergence treatments for crabgrass control Wer~
made With calcium arsenate} chlordane, dacthal, L-13489 1
L-31864, lead arsenate, an arsenical complex (Pax), and
zytron on a predominately KentuckY bluegrass turf.
Crabgrass started slowly and very little turfgrass failedduring
the season.
Estimates of crabgrass control made in September by
three independent observers showed ratings of 96% obtained
With calcium arsenate, dacthal, and L-31864. Zytron and
chlordane produced 89 and 84%control, respectiVely.
Ratings for turfgrass injury showed slight to moderate
injury for the arsenical complex and calcium arsenate.