Author: R. K. Gupta

Publisher:

Published: 1968

Total Pages: 0

ISBN-13:

In saline areas bordering Miquelon Lake, a water-fowl refuge, it was possible to maintain tall vegetative cover of Cirsium arvense L. Scop. (Canada thistle) and Sonchus arvensis L. (perennial sow thistle) while preventing their flowering and seed dispersal, by means of small dosages of 4-amino-3,5,6-trichloropicolinic acid (picloram) or of 2,4- dichlorophenoxyacetic acid (2,4-D) applied before the thistles flowered. Picloram sprays at a dosage as small as 0.25 oz/A prevented flowering of Canada thistle treated in early bud stage. For comparable results with perennial sow thistle which was somewhat more resistant to small dosages of picloram this treatment had to be applied just prior to the plants' early bud stage. Results comparable to those noted for picloram were achieved with 8 oz/A of 2,4-D. For complete prevention of flowering of both species of thistles treated at late bud stage, picloram at 1.5 oz/A or 2,4-D at 2 lb/A was necessary. However, these higher dosages also caused extensive damage to the vegetative top growth of the thistles. In other experiments with a dense stand of Canada thistle growing on cultivated fertile clay loam soil the objective was to study techniques of eradication of the thistles. Best results were obtained by mowing the weeds at their flowering stage and spraying their regrowth about a month later with 4 oz/A picloram, followed by a second treatment of regrowth with 2 oz/A picloram, after comparable mowing of the sur viving thistles during the following year. This practice was more effective than those where no mowing was included, involving either spraying thistles at flowering stage or spraying half dosage of herbicide at flowering stage and half in the fall. Both with regard to reduction in numbers of new shoots and of their total mass two years after the first treatment, effects of as little as 2 oz/A of picloram were greater than those resulting from use of 2 lb/A 2,4-D ester in any of the pro cedures noted. At Miquelon Lake where Hordeum jubatum L. (foxtail barley) was a dominant native component of the vegetation of the saline experimental areas, Canada thistle and perennial sow thistle top growth and regrowth were eliminated for at least two years duration of observations by single spray treatments with picloram at 4-6 oz/A. These resulted in an increase in cover of the native grass species associated with a decline or disappearance of some of the low-growing native dicotyledonous species present in some plots. 2-Methoxy-3,6-dichlorobenzoic acid (dicamba) applied at 6 to 24 oz/A and 2,4-D ethyl ester at 24 to 96 oz/A were incapable of complete supress- ion of regrowth from roots of treated thistles. Treatments with as little as 1 oz/A of picloram resulted in 907. reduction in stand of the thistles within a year in plots having foxtail barley and other grasses as com petitors able to fill in the cover. Ground sprayer applications of herbicide produced more uniform results than aerial spraying of narrow strips of this tie-infested land. From the agricultural standpoint complete eradication of the thistles would be the simplest procedure in this area where natural plant success ion is towards salt-tolerant grasses. From a wildlife management view point it is difficult to know, whether merely preventing flowering of thistles or removing them altogether would make any important difference insofar as strips of farmland shore line are concerned.