Vol. 15—1961 - NorthEastern Weed Science Society

have very littla real II'+eaningas far as crabgrass control is concerned.
About all that can be concluded is that most of the treatments controlled
crabgrass, at least at the 5 per cent level of signific&lCe j but no real differences
were demonstrated between the degrees of control resulting from the
different treatments. Previously it seemed that making crabgrass control
applications on high quality turf had. particular value because of its
similarity to the usual turf to which such chemicals might be applied.
Apparently the practice of thinning heavy turf and seeding in crabgrass
deliberately has real merit as insurance against the possibility of climatic
conditions particularly unfavorable to crabgrass.
Turf injury
In reporting on our 1959 plots (1) we noted that there was no turf injury
from t,he crabgrass control chemicals except for Dacthal, which severely
injured red fescue.
our first opportunity to work with ~ron was in our spring 1959 plots.
In those trials we noted no turf injury from the use of granular 2'¥tron at
the rate of 20 pounds active ingredient per acr~. As noted in Tables 1 and
2, this same 20 pound (" standard") rate of granular ~ron caused some
temporary discoloration of both fescue and bent in the fall 1959 plots and
a little, but considerably' less, discoloration from the spring 1960 treatments.
The 40 pound rate of granular 7Qtron as well as the 20 and 40 pound
rates of ~ron emulsion caused severe turf injury in the fall treatments
and the 20 pound rate ( the only one included) in the spring treatments also
caused severe but somewhat less turf injury.
The Dacthal wettable powder was available for use in both our fall 1958
and spring 1959 treatments. While it produced excellent crabgrass control
at the rate of 12 pounds active ingredient per acre, it caused severe injUry
to red fescue in both fall and sl?ring (1). The same material applied at the
same rate in the fall of 1959 and the spring of 1960 caused rather conspicuous
temporary discoloraticn of red fescue and bent in the autumn plots
but very slight discoloration in a single replicate of the spring plots.
A new granular formulation of Dacthal, first available in the spring of
1960, caused no discoloration at tha.t time. Rid, the commercial formulation
of Dacthal, was available in the spring of 1960 only. At the recommended
rates of application, it caused no visible turf injury.
In the 1959 work Dacthal caused marked injury to red fescue. To investigate
the Dacthal injury further, unreplicated 48. sq. it. plots were
laid out on a predominantly red fescue turf. Dacthal wettable powder and
Rid, a granular commercial formulation of Dacthal, were applied at rates of
6, 10, 12, and 18 pounds active ingredient per acre on March 1 and May 2,
1960. The crabgrass counts appear in Table 3.
It is interesting to note that while crabgrass control was essentially
complete on all plots except where the 6 pound rate of Rid was used, there
was no visible· turf discoloration at any time. These observations are in
line with the performance of the same materials in the other spring 1960
applications reported in Table 2. The implication from the 1960 plots alone
is that Dacthal caused little or no turf injury. Yet the same material in the
spring of 1959 did cause severe injUry. Apparently the degree of fescue injury
from Dacthal is influenced by factors in addition to season of application.