Tolerance of Containerized Ferns to Repeated Preemergence Herbicide Applications

Gary Bachman and Ted Whitwell

Department of Horticulture, Clemson University

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Introduction

Ferns are becoming popular landscape plants, however nursery productions techniques includmg weed management is not clearly identified. The tolerance of ferns to preemergence herbicides varies at different growth stages during the production cycle. Our previous work indicates that Gallery is the safest herbicide but application during February still injured certain species. Weeds emerge all year long and become major problems until ferns become fully mature and fill the pots. This study evaluated repeated applications of preemergence herbicides to several fern species. Efforts were made to evaluate phytotoxicity over the year long nursery production schedule to ascertain fern growth problems and bittercress control associated with repeated herbicide use.

Materials and Methods

Small liners of seven fern species were planted into 4" pots and treated on 9/8/94. Ferns were moved up to one gallon pots using the same media (50% peat and 50% perlite) on 12/20/94 and re-treated with the same herbicides on 12/31/94 and 4/10/95. A natural infestation of hairy bittercress developed during the study. Pots were hand weeded between herbicide applications. Visual evaluation of injury by species and bittercress control were made monthly on a scale of 0 to 100 % with 100 = plant death and 0 = no injury.

Results

Fern species varied in their response to herbicide application (Table 1). Minimum injury was observed after the first and second applications at the 10/17/94 and 2/10/95 evaluations. Polystichum polyblepharum was severely injured by Snapshot TG applications with the other treatments providing less than 20% damage. However, after the third application several species were injured from the herbicides and the injury was in the form of stunted growth. Pendulum and Snapshot TG caused < 20% injury to all species except Cyrtomium falcatum. Gallery and Factor were safer on the selected ferns at the rate evaluated with only two species having greater than 20% injury, however, Dryopteris marginalis was severely affected by all the herbicides including Factor. Bittercress control ranged from 67 to 93% control for the herbicides. Higher control (80 to 93%) was observed for Snapshot TG and Pendulum.

Significance to the industry: Ferns were sensitive to repeated applications of Pendulum and Snapshot TG at 4 and 5 lb. ai/A, respectively. Lower rates may be less phytotoxic. Gallery and Factor were less injurious to the species evaluated with the repeated applications.

Last Updated 2/1/97