redroot pigweed (Amaranthus retro- Tolerance of Hardy Ferns to Selected fl exus) and large crabgrass (Digitaria Preemergence Herbicides sanguinalis) reduced the dry weight of japanese holly (Ilex crenata) by 47% and 60%, respectively. Research on perennial 1 2 2 Glenn B. Fain , Charles H. Gilliam , and Gary J. Keever crops has shown signifi cant reductions in growth and or marketability of plants ADDITIONAL INDEX WORDS. Arachniodes simplicior ‘Variegata,’ Cyrtomium falcatum due to weed infestations (Gibson, 1985; ‘Rochfordianum,’ Dryopteris erythrosora, Dryopteris ludoviciana, isoxaben, oryza- Staats et al., 1998). lin, oxadiazon, oxyfl uorfen, pendimethalin, prodiamine, trifl uralin Some form of weed control is SUMMARY. Hardy ferns are widely grown for use in the landscape. The 1998 necessary with effectiveness, crop National Agricultural Statistics Services census of horticulture reported produc- tolerance, and cost primary consider- tion of hardy/garden ferns at 3,107,000 containers from over 1200 nurseries. ations in selecting control programs. There is little research on herbicide use in hardy ferns, and herbicides that are Nurseries reported spending as much labeled for container production are not labeled for use on hardy ferns. Stud- as $4000/acre per year to manually ies were conducted to evaluate the tolerance of variegated east indian holly fern remove weeds in containers (Mathers, (Arachniodes simplicior ‘Variegata’), tassel fern (Polystichum polyblepharum), autumn fern (Dryopteris erythrosora), rochford’s japanese holly fern (Cyrtomium 2003). In 1974, cost to hand weed 1 falcatum ‘Rochfordianum’), and southern wood fern (Dryopteris ludoviciana), acre of containers was reported to be to applications of selected preemergence applied herbicides. Herbicides evaluated $3600 (Weatherspoon and Currey, included selected granular or liquid applied preemergence herbicides. Spray-ap- 1975). In comparison, it was reported plied herbicides were pendimethalin at 3.0 or 6.0 lb/acre, prodiamine at 1.0 or in 1990 that total cost for three ap- 2.0 lb/acre, isoxaben at 1.0 or 2.0 lb/acre, and prodiamine + isoxaben at 1.0 plications of oxyfl uorfen + oryzalin + 1.0 lb/acre. Granular-applied herbicides were pendimethalin at 3.0 or 6.0 (Rout; Scotts-Sierra Crop Protection lb/acre, prodiamine at 1.0 or 2.0 lb/acre, oxadiazon + prodiamine at 1.0 + 0.2 Co., Marysville, Ohio), was about or 2.0 + 0.4 lb/acre, oxyfl uorfen + oryzalin at 2.0 + 1.0 or 4.0 + 2.0 lb/acre, $566/acre with labor for hand weed- trifl uralin + isoxaben at 2.0 + 0.5 or 4.0 + 1.0 lb/acre, oxadiazon at 4.0 or 8.0 ing of uncontrolled weeds adding lb/acre, and oxadiazon + pendimethalin at 2.0 + 1.25 or 4.0 + 2.5 lb/acre. The greatest reduction in growth of autumn fern was observed with the high rates another $256-$567/acre, resulting of oxadiazon, oxadiazon + pendimethalin, and oxadiazon + prodiamine. Reduc- in a total cost for weed control of tions in rochford’s japanese holly fern growth were most severe when plants were about $812–$1133/acre (Gilliam et treated with the high rate of trifl uralin + isoxaben resulting in a 66% and 72% al. 1990). In North Carolina, it was decrease in frond length and frond number, respectively. There were also reduc- reported that without herbicide appli- tions in frond length and number of fronds when treated with the high rate of cations it may cost as much as $1367 oxadiazon + pendimethalin. There were no reductions in frond numbers on tassel to hand weed 1000 3-qt containers fern with any herbicides tested. However, there were reductions in frond length over a 4-month period based on an from four of the 10 herbicides evaluated. The most sensitive fern to herbicides hourly wage of $14.75, an average evaluated in 2004 was variegated east indian holly fern with reductions in frond labor cost provided by local nurseries length and number of fronds with four of the 10 herbicides tested. Southern wood fern appeared to be quite tolerant of the herbicides tested with the excep- (Darden and Neal, 1999). In this study tion of the high rate of oxadiazon. Granular prodiamine proved to be a safe her- even marginally effective herbicides bicide for all species tested in both 2004 and 2005. In 2005 all plants from all reduced hand weeding time and costs treatments were considered marketable by the end of the study. The durations of while the most effective herbicides both studies were over 120 days giving adequate time for any visual injury to be reduced costs of hand weeding over masked by new growth. However, there was signifi cant visual injury observed on 95%. Herbicides are widely used in the rochford’s japanese holly fern treated with isoxaben at 60 and 90 days after nursery production primarily due to treatment, which might reduce their early marketability. their effi cacy and cost effectiveness. Many studies have investigated the use ver the past decade there has control is always a top priority for grow- of preemergence herbicides on various been increasing popularity of ers due to potential growth reduction perennials with varying degrees of crop Oherbaceous perennials, includ- from weed competition for moisture, tolerance depending on herbicide and ing hardy ferns. This popularity has led nutrients, and light. Container nurser- plant species (Calkins et al., 1996; to an increasing number of producers ies provide an optimal environment for Derr, 1994; Porter, 1996; Skroch et and numbers of plants produced. The weed growth with frequent overhead al., 1990; Staats and Klett, 1993). National Agricultural Statistics Services irrigation and fertilizer applications. None of the herbicides in this 1998 census of horticulture reported Fretz (1972) reported that in 2.5-qt study are labeled for use on the fern spe- wholesales sales hardy/garden ferns at nursery containers, one plant each of cies tested. Furthermore, little research 3,107,000 containers (U.S. Depart- ment of Agriculture, 2001). Weed Units To convert U.S. to SI, To convert SI to U.S., 1USDA-ARS, Southern Horticultural Laboratory, P.O. multiply by U.S. unit SI unit multiply by Box 287, Poplarville, MS 39470. Mention of trade names or commercial products in this article is solely 0.4047 acre(s) ha 2.4711 for the purpose of providing specifi c information and 2.54 inch(es) cm 0.3937 does not imply recommendation or endorsement by 1.1209 lb/acre kg·ha–1 0.8922 the U.S. Department of Agriculture. 0.5933 lb/yard3 kg·m–3 1.6856 2Department of Horticulture, 101 Funchess Hall, 6.8948 psi kPa 0.1450 Auburn University, AL 36849. 0.9464 qt L 1.0567 ● October–December 2006 16(4) 605 OOct06HT.indbct06HT.indb 660505 99/22/06/22/06 11:47:03:47:03 PPMM RESEARCH REPORTS has been conducted on herbicide use liquid applied preemergence herbicides shaker while liquid formulations were in container-grown ferns. Lauderdale at the standard label rate and twice that applied using a CO2 backpack sprayer et al. (1993) evaluated the tolerance rate as well as a hand weeded control. calibrated to deliver 30 gal/acre at of container-grown rockford’s japanese Spray-applied herbicides were pen- 28 psi using an fl at fan nozzle (TeeJet holly fern and autumn fern to selected dimethalin (Pendulum 3.8 Aquacap; DG8003VS; Spraying Systems Co., granular and spray-applied herbicides. BASF Corp., Research Triangle Park, Wheaton, Ill.). Plants were arranged in Dithiopyr at 4.0 lb/acre caused sig- N.C.) at 3.0 or 6.0 lb/acre, prodiamine a completely randomized design within nifi cant injury to both autumn fern (Barricade 4L; Syngenta Crop Protec- species with six replications except for and rockford’s japanese holly fern tion, Inc. Greensboro, N.C.) at 1.0 or the southern wood fern which had fi ve while granular trifl uralin + isoxaben 2.0 lb/acre, isoxaben (Gallery 75DF; replications. at 4.0 + 1.0 lb/acre caused signifi cant Dow AgroSciences LLC, Indianapolis) Data collected were phytotoxicity injury to rochford’s japanese holly at 1.0 or 2.0 lb/acre, and prodiamine + ratings at 7, 15, 30, 60, and 90 d after fern but not to autumn fern. Previous isoxaben at 1.0 + 1.0 lb/acre. Granular- treatment (DAT). Ratings were based research identifi ed many herbicides applied herbicides were pendimethalin on a 0 -10 scale where 0 = no injury and that reduced yield or did not control (Pendulum 2G; BASF Corp.) at 3.0 or 10 = dead plant ratings of 3 or above weeds in ground beds of leatherleaf 6.0 lb/acre, prodiamine (RegalKade G; would be considered signifi cant enough fern (Rumohra adiantiformis) (Poole, Regal Chemical Co., Alpharetta, Ga.) to prevent marketability. On 15 Nov. 1979; Poole and Waters, 1974). Other at 1.0 or 2.0 lb/acre, oxadiazon + pro- 2004, the study was terminated with work in leatherleaf fern ground beds diamine (RegalStar G; Regal Chemical the recording of total number of fronds has shown that metolachlor or alachlor Co.) at 1.0 + 0.2 or 2.0 + 0.4 lb/acre, and length of the longest three fronds. applied every 2 months at 2.0, 4.0, oxyfl uorfen + oryzalin (Rout; The Herbicide effi cacy was not evaluated and 8.0 lb/acre or the same rate of Scotts Co.) at 2.0 + 1.0 or 4.0 + 2.0 and all containers were maintained oxadiazon applied every 4 months did lb/acre, trifl uralin + isoxaben (Snapshot weed free with periodic hand weed- not reduce the quality or quantity of 2.5 TG; Dow AgroSciences) at 2.0 + ing. For all data, herbicide treatments fern fronds over a 28-month period 0.5 or 4.0 + 1.0 lb/acre, oxadiazon were compared to the control using a (Stamps and Poole, 1987).