Controlling Rhododendron spp. in the Turkish Black Sea Region

Rhododendrons (Rhododendron ponticum L. and Rhododendron luteumSweet) dominate the understories of the mesic forests of theBlack Sea Region (BSR) of Turkey. They dramatically reduce forestgrowth and regeneration and local plant diversity. This paperreports the results of a large rhododendron control experimentestablished on two different sites in the western and easternBSR of Turkey 5 years after treatments (YAT). The paper alsopresents the second-year results of a second experiment in whichthe foliar herbicides of the previous experiment were testedon rhododendron at much lower rates on a western BSR site. FiveYAT, grubbing and foliar spraying were still the best rhododendroncontrol methods in the first experiment. Cut-stump sprayingprovided an intermediate level of woody control. Hand-cuttingwas ineffective on R. ponticum and did not significantly differfrom the control treatment in rhododendron basal area 5 YAT.The performance ratings of foliar triclopyr ester and imazapyrfor woody control in both experiments were rate dependent. Athigh rates ranging between 2.6 and 5.8 kg ae ha^–1, foliarimazapyr controlled both rhododendron species significantlybetter than foliar triclopyr ester in the first experiment,suggesting enhanced imazapyr translocation to the roots. Someoff-target damage was observed in the beech overstory for imazapyrat high rates. The performance ratings of these foliar herbicideswere significantly reversed in the second experiment 2 YAT,where much lower rates were used (0.3–2.0 kg ae ha^–1)than in the first experiment. Insufficient imazapyr accumulationin rhododendron roots might account for the poor impact of thisherbicide. No beech damage was apparent from any of the herbicidesin the second experiment. The low-rate foliar triclopyr esteris recommended for effective and cost-efficient rhododendroncontrol.