Vol. 15—1961 - NorthEastern Weed Science Society

253.
almost a week, with treatment occurring on May 13. At the time of herbicidal
application the trefoi I in 1959was showing approximately 2 inches of
new spring growth; in 1960the growth present when sprayed was at about 4-5
inches. In the 1957tri e l , pract i ca II y no new spr ing growth was showing
on the Empire plants at the time of spray application (May2).
Since the only appreciable differences between the 1959 and 1960
applications of dalapon on Mansfield birdsfoot trefoi I were in the stages
of growth existing at the time of application, it might be concluded that
this factor could be the reason for the results obtained. Schreiber
et al· (4) reported that a 5 pound application of delapon on Empire trefoi I
having 1.2 inches of new spring growth resulted in no appreciable injury
to the birdsfoot trefoi I. In this same stUdy 2.5 and 5 pound per acre
applications of dalapon to a 3-year-old Viking stand in the dormant
condition, and 17 days later when the trefoi I had 4-5 inches of new spring
growth, resulted in no noticeable injury. No seed yields were reported,
however, although the authors felt that spring applications at low rates
resulted in effective grass control.
Timing a spring application of dalapon for control of undesirable
grasses and other plant species, to coincide with insecticide application
for ~conomic reasons, can be an effective practice, from the standpoint
of both weed control and minimal detriment to the trefoil plants and seed
yield, apparently only if the trefoi I exhibits a minimumof new spring
growth. The studies on date of application of insecticides conducted at
this station and referred to above indicate that there is considerable
leeway in time of their application. Additional studies are needed to
determine an optimum date for herbicide application.
CONCLUSIONS
J. Early spring applications of low rates of dalspon to established
seed production· fieldS of birdsfoot trefoi t effectively control
undesirable grasses and certain broadleaf·plants.
2. T~e date for application can be timed to coincide with that of an
l nsect Ic lde application without detrlmental effects on plant growth
or seed yields.
3. The optimum time for dalapon application is possibly just after the
initiation. of new spring growth on the trefoi I.
REFERENCES CITED
I. Fertig, S. M., Meadows, M. W., and Bayer, G. The control of perennial
weeds in established birdsfoot trefoi I stands. Proc. Northeast Weed
Control Conf. 14:308-313. 1960.
2. Leonard, W. H., and Clar~ A. G.
ce., Minneapolis. 1939.
Field Plot Technique.
Burgess Publ.
3. MacCollom, G. B. Control of
production in Vermont. Jour.
insects affecting birds foot trefoil
Econ. Ent. 51: 492-494. 1958.
seed
4. Schreiber, M. M. Delapon residue in birdsfoot trefoi t. J. Agric.
Food Chern. 7:427-La9. 1959.