The Effect of Selected Herbicides on Growth of Aucuba and Flowering of Scaevola

Liners of Aucuba japonica ‘Variegata’ and Scaevola aemula ‘Scala Blue’ were potted in 12 L and 4 L pots, respectively in June.  Within 7 days of potting, Aucuba plants were treated with 3 rates each of sulfentrazone (F6875), isoxaben (Gallery), dimethenamid-p (Tower), indaziflam, oxyfluorfen + prodiamine (Biathlon), pendimethalin + dimethenamid-p (Freehand), or trifluralin + isoxaben (Snapshot).  Also within 7 days of potting, Scaevola plants were treated with 3 rates each of Tower and Freehand.  An untreated control was included for both species.  Plants were grown under container nursery conditions using a randomized complete-block design with Aucuba under 30% saran and Scaevola under full sun.  Treatments were repeated 6 weeks after the first treatments were applied.  At 1, 2, and 4 weeks after each application, phytotoxicity was rated for each plant.  Stunting symptoms were noted on Aucuba plants, which were rated at 4 weeks after the first application and at 1, 2, and 4 weeks after the second application.  An effect on flowering was observed on Scaevola, which was rated at 1, 2, and 4 weeks after the second application.  Plant heights and widths were measured at the beginning of the study and at the end of the evaluation period so that changes in plant growth could be calculated.  For Aucuba, F6875 and Gallery treatment resulted in significantly more phytotoxicity and stunting than control plants after both applications.  With Gallery, phyto and stunting symptoms decrease over time after the first application.  Growth over the course of the experiment was less than the control for all rates of F6875, but this held only for height of plants treated with the highest rate of Gallery.  For Scaevola, there was no effect of any of the treatments on growth.  However, flowering was reduced by all treatments when compared to the control at 2 weeks after the second application.  By 4 weeks after the second application, flowering on treated plants had completely recovered.