Influence of Mowing and Spraying Dates on Herbicidal Control of Macartney Rose

Abstract

We compared foliage sprays of (2,4-dichlorophenoxy)acetic acid (2,4-D) and 4-amino-3,5,6-trichloropicolinic acid (picloram) for control of Macartney rose (Rosa bracteata Wendl.) applied with ground equipment and airplane. Picloram at 0.5 lb/A was more effective than 2,4-D at 2 lb/A at all dates of application on mowed roses; however, time of application was important. Picloram was most effective in late April and early May, but 2,4-D was most effective in late May and early June. Combinations of picloram and 2,4-D were effective from late April to late June. If mowing is followed by foliage treatment of 2,4-D, the interval between mowing and spraying should be at least 1 year if mowing is done in the spring. The interval between mowing and spraying was not critical when picloram was applied not later than early May. Mowing in the summer reduced the effectiveness of subsequent 2,4-D and picloram treatments applied the following year. Aerial applications of 2,4-D and picloram on undisturbed Macartney rose plants in the fall were not as effective as spring applications; however, two successive fall applications of picloram at 1 lb/A resulted in control equivalent to that obtained with a single 2 lb/A application in spring.