Vol. 16—1962 - NorthEastern Weed Science Society

More and more each year since the advent of truly selective weed chemicals
the publiC has come to rely on the herbicides as anessentail part of turf management.
I doubt if there are many who would argu& with this belief. Weeds
such as crabgrass, Veronica, mouse~ear chickweed, mwhlenbergia, dandelion,
plantain and, when out of place, bentgrass are seldom controlled by management
alone. There are other weeds in this category also. Mlny of our commonturfgrass
weeds are controlled readily with 2,4-D. I WOulddoubt, however, whether
there are many turf specialists who still don't have certain qualms, even after
manyyears of research and use, about recommendingthis widely used herbicide.
Injuries are reported every year, as are failures, even when the material is
used to the best of our knowledge. Because of the many interactions amongthe
wide range of variables governing the growth of a given piece of turf we still
cannot predict with accuracy the reiponse to herbicide treatment. A chemical
that is dependable in one area of our region may not be in another. Endothal
is recommendedfor the control of a Veronica species in one state in the Northeast
but cannot be made to work safely in another. Chlordane, for crabgrass
control, has given erratic reSUlts from one location to another and from one
season to another. One of the newer crabgrass herbicides, Diphenatrile, has
given excellent results in two years of testing within one state but has done
poorly in another state only 200 mil~S distant. Calcium and lead arsenates,
although exhibiting real possibilities, have not been promoted because of lack
of consistancy. They almost always give excellent control of crabgrass but
on occasion they are damaging to the turf.
The reasons for variable results with the many herbicides are numerous.
Most of the reasOns are not clear or fully established. Weknowthat soil
type or texture has a bearing on results with chemicals applied to the soil.
The base exchange capacity of the soil, influenced mostly by the clay and organic
matter content influences the actiVity of herbicides. Microbial populations
of the soil govern breakdown of certain herbicides. The persistence
of these herbicides in the soil, then, would depend on the size of the microbial
popUlation and the rate at which they can increase.
Time of application of herbicides - spring, summeror fall, is critical
and for various reasons. The growth rate of the turfgrasses and the weeds at
the time of herbicide application is most important. This has been documented
and reported, on many occasions. Factors governing the growth rate - soil
moisture, temperatures and fertility levels must always be adequate for the
optimumtiming of herbicide application.
A recent study by Rice (11) at the University o~ Rhode Island indicated
that the roots of certain putting green grasses reach their greatest depth and
maximumextensiveness during the spring months. Extensiveness and depth both
decrease during the summerand roots remain shallow even through the fall
months. This study is not complete but if the present indications shOUldbe
born out by further research or review then mid- to late-spring application of
herbicides to turf for selective control of biennial or perennial weeds should
prove considerably safer than late summeror fall applications. CurrentlY both
seasons are suggested with the fall season frequently being favored. Additional
studies of this more basic nature are badly needed in the turfgrass field. Regional
projects on turfgrasses, completely lacking in the northeastern region,
at the moment, could be most instrumental in conSOlidating and validating many
of the loose-ends and conceptions or mis-conceptions currentlv exis~ina_
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