SNA RESEARCH CONFERENCE - VOL. 50 - 2005 Weed Control James Altland Section Editor and Moderator 431 SNA RESEARCH CONFERENCE - VOL. 50 - 2005 Preemergence Control of Winter Weeds in Overwintering Ornamental Crops Caren A. Judge, Joseph C. Neal and Robert E. Wooten Dept. of Horticultural Science, NC State University, Raleigh, NC 27695-7609 Index Words: annual bluegrass, birdseye pearlwort, common chickweed, common groundsel, hairy bittercress, spiny sowthistle, and yellow woodsorrel Signifi cance to Industry: BroadStar, OH2, and Snapshot TG were compared for control of winter weeds in overwintering nursery crop production. BroadStar, OH2, and Snapshot TG controlled common chickweed, common groundsel, hairy bittercress, and spiny sowthistle. OH2 and Snapshot TG controlled yellow woodsorrel better than Broadstar, although control was greater than 86% with all treatments. Annual bluegrass and birdseye pearlwort were controlled with Snapshot TG; BroadStar and OH2 were less effective on these species. If annual bluegrass or birdseye pearlwort are expected in overwintering structures, Snapshot TG should be used before covering or a dinitroaniline herbicide may need to be included with BroadStar to improve the spectrum of weed control. Nature of Work: The container nursery industry relies upon broad-spectrum preemergence herbicides and supplemental hand weeding for weed management (1). In the southeastern United States, weed management in container nursery crop production is a year-round endeavor due to the relatively mild winters and overwintering protection of crops. Overwintering structures moderate the temperatures and provide conditions favorable for germination and establishment of winter annual weeds. Weed management options are limited in overwintering structures because no preemergence herbicides are labeled for application within covered structures (3). Preemergence herbicides must be applied several weeks before plants are covered in late autumn. Weeds emerging in containers over the winter must be hand weeded, which is usually feasible only after the overwintering covers are removed in the spring. Few studies have investigated effi cacy of herbicides on weeds in container nursery crops in covered overwintering structures. Effective control of hairy bittercress (Cardamine hirsuta L.) and yellow woodsorrel (Oxalis stricta L.) was obtained from October and February applications of Regal O-O (oxyfl uorfen + oxadiazon) or Gallery (isoxaben) plus Ronstar (oxadiazon) (2). Yet, this trial was conducted outdoors, in large containers, not in a covered overwintering structure. For a more comprehensive evaluation of winter weed control in overwintering ornamental crops, experiments were conducted in 2002 and 2003 to evaluate the effi cacy of commonly used preemergence herbicides on several common winter nursery weeds in overwintering structures. Broadstar 0.25G (fl umioxazin) at 0.42 kg ai/ha (0.38 lbs ai/A), Scott’s Ornamental Herbicide II 3G (OH 2, oxyfl uorfen + pendimethalin) at 3.4 kg ai/ha (3.0 lbs ai/A), and Snapshot 2.5TG (isoxaben + trifl uralin) at 5.6 kg ai/ha (5.0 lbs ai/A) were applied to 4-L (1 gal) containers using a handheld shaker jar November 7, 2002 and November 25, 2003. All herbicide treatments were compared to nontreated plants. A pine bark plus sand substrate (7:1 v/v) was used and containers were 432 Weed Control Section SNA RESEARCH CONFERENCE - VOL. 50 - 2005 absent of ornamental plants, containing only the weed species. Containers were arranged in a randomized complete block design with fi ve one-container replications of each species in 2002 and eight one-container replications of each species in 2003. About one month after treatments, containers were placed in temporary overwintering structures. Structures were about 2.4 m (8 ft) wide, 10.7 m (35 ft) long, 1.2 m (4 ft) tall (at the center peak), and covered with 6 mil white plastic. The plastic was removed periodically to water plants and evaluate herbicide effi cacy. In 2002, the weed species evaluated were annual bluegrass (Poa annua L.), common chickweed (Stellaria media L.), common groundsel (Senecio vulgaris L.), hairy bittercress, and yellow woodsorrel. In 2003, the weed species evaluated were annual bluegrass, birdseye pearlwort (Sagina procumbens L.), common chickweed, common groundsel, hairy bittercress, spiny sowthistle (Sonchus asper L.), and yellow woodsorrel. Weed control was visually evaluated compared to nontreated plants through the winter and spring. Final evaluations were recorded approximately fi ve months after herbicide application. Data were subjected to analysis of variance and means were separated using Fisher’s protected LSD at the 5% signifi cance level (4). Because weed control was evaluated relative to nontreated plants, data from nontreated plants were not included in the analysis. Results and Discussion: In 2002, each herbicide controlled annual bluegrass, common chickweed, common groundsel, hairy bittercress, and yellow woodsorrel for the fi ve month evaluation period (Table 1). In 2003, for the fi ve month evaluation period, common chickweed, common groundsel, hairy bittercress, and spiny sowthistle were equally controlled by each herbicide (Table 1). Yellow woodsorrel control was slightly better with OH2 (98%) and Snapshot TG (100%) than BroadStar (86%). Snapshot TG was most effective on annual bluegrass providing 91% control. BroadStar and OH2 were less effective, providing 17% and 62% control, respectively. Trends for birdseye pearlwort control were similar to annual bluegrass; BroadStar provided 34% control, OH2 provided 72% control, and Snapshot TG provided 97% control. In general, Snapshot TG provided the best control for the winter weeds evaluated in these studies. Most weeds were equally controlled by BroadStar and OH2 with the exception of annual bluegrass, birdseye pearlwort, and yellow woodsorrel. If the presence of any of these weeds is expected in overwintering structures, Snapshot TG should be used before covering or a dinitroaniline herbicide may need to be included with BroadStar to improve the spectrum of weed control. Literature Cited: 1. Gilliam, C.H., W.J. Foster, J.L. Adrain, and R.L. Shumack. 1990. A survey of weed control costs and strategies in container production nurseries. J. Environ. Hort. 8:133-135. 2. Mickler, K.D. and J.M. Ruter. 2001. Evaluation of a year long weed control program for container grown ornamentals. Proc. Southern Nursery Assoc. Res. Conf. 46:454-456. Weed Control Section 433 SNA RESEARCH CONFERENCE - VOL. 50 - 2005 3. Neal, J.C. 1999. Weed control in greenhouses. Horticulture Information Leafl et No. 570. <http://www.ces.ncsu.edu/depts/hort/hil/pdf/hil-570.pdf> 4. [SAS] Statistical Analysis Systems. 1999. SAS/STAT User’s Guide. Version 8. Cary, NC: Statistical Analysis Systems Institute. 3884 p. Table 1. Percent control of winter weeds with BroadStar, OH2, and Snapshot TG. The 2002 experiment was evaluated April 14, 2003 and the 2003 experiment was evaluated April 1, 2004. BroadStar OH2 Snapshot TG 2002 Weed Species ------------------Percent Control------------------ Annual bluegrass 92 az 100 a 100 a Common chickweed 100 a 100 a 100 a Common groundsel 94 a 100 a 100 a Hairy bittercress 100 a 100 a 100 a Yellow woodsorrel 100 a 100 a 100 a 2003 Weed Species ------------------Percent Control------------------ Annual bluegrass 17 c 62 b 91 a Birdseye pearlwort 34 c 72 b 97 a Common chickweed 100 a 98 a 96 a Common groundsel 90 a 80 a 79 a Hairy bittercress 95 a 92 a 98 a Spiny sowthistle 90 a 96 a 100 a Yellow woodsorrel 86 b 98 a 100 a zMeans within a row followed by the same letter do no signifi cantly differ according to Fisher’s Protected LSD (P ≤ 0.05). Means cannot be compared within a column. 434 Weed Control Section SNA RESEARCH CONFERENCE - VOL. 50 - 2005 Doveweed, Florida Tasselfl ower and Eclipta Control Under Heavy Rainfall Conditions Using Granular Preemergence Herbicides Robert H. Stamps and Annette L. Chandler Univ. of Florida, Inst. of Food and Agr. Sci., Dept. of Environ. Hort., Mid- Florida Res. and Edu. Ctr., 2725 S. Binion Rd., Apopka, FL 32703-8504 [email protected]fl .edu Index words: fl umioxazin, oryzalin, oxyfl uorfen, pendimethalin, prodiamine, trifl uralin, BroadStar, OH2, RegalKade, Rout, Snapshot, Eclipta prostrata, Emilia fosbergii, Murdannia nudifl ora Signifi cance to Industry: This research shows that even under very heavy rainfall and irrigation conditions, there are several preemergence herbicides that can effectively control eclipta, Florida tasselfl ower and doveweed for at least eight weeks. Flumioxazin was particularly effective in controlling doveweed. Nature of Work: The introduction and spread of new weeds is a common occurrence in the nursery industry (3). In order to effectively manage these “new” weeds, it is necessary to determine the weed control effi cacy of preemergence herbicides. In addition, irrigation and rainfall amounts (2) and timing (1) can affect herbicide effi cacy. In this study, six commercial granular preemergence herbicides were evaluated for controlling three weeds of increasing signifi cance in ornamental plant production. The experiment was conducted outdoors at the Univ. of Florida/IFAS’ Mid- Florida Res. and Educ. Ctr. in Apopka, FL. On Aug. 5, 2004, 6-inch [15-cm] diameter plastic pots (Dillen Products) were fi lled with a soilless growing medium composed of 80% aged pine bark and 20% Canadian Sphagnum peat (Fafard). Initial medium pH and EC (dS/m) were 6.86 and 1.52, respectively. After the pots were fi lled, 15 seeds of one of the three weed species were sown in each one: Eclipta prostrata (eclipta), Emilia fosbergii (Florida tasselfl ower) or Murdannia nudifl ora (doveweed) Pots were then irrigated with 1.3 cm [½ in] of water. Each pot was reseeded with another 15 seeds of the same weed species on Sept. 16, six weeks after the initial sowing. Plots were irrigated daily using overhead sprinklers, except during periods of high rainfall or when there was no electrical power to operate the well pumps. During this three-month long experiment, rainfall + irrigation water totaled 149 cm [58.8 in].