Ornamental, Garden & Landscape Section
Proc. Fla. State Hort. Soc. 129:243–245. 2016.
Postemergence Control of Pilea microphylla (Artillery Weed)
Chris Marble*, Annette Chandler1, and Debalina Saha1 Department of Environmental Horticulture, Mid-Florida Research and Education Center, University of Florida/IFAS, 2725 S. Binion Rd., Apopka, FL 32703
Additional index words. artillery fern, herbicide, preemergence, ornamentals, landscape Pilea microphylla, also known as artillery weed, artillery fern, or gunpowder plant is weed of increasing importance in Florida. It has also recently become a nuisance in nurseries, but little information is available on herbicide efficacy. The objective of this trial was to evaluate selected nursery herbicides for postemergence control of artillery weed and measure regrowth potential following application. Nursery media was overseeded with artillery weed seeds. Artillery weed was grown for two months—at which time all plants were approximately 3.5–4.5 inches in height and had flowered. The following herbicides were applied at generally their highest label rate: sulfosulfuron [0.05 lb. active ingredient per acre (lb/aia)], sulfentrazone (0.37 lb/aia), indaziflam (0.06 lb/aia), diquat (0.5 lb/aia), oxadiazon (granular) (4 lb/ aia), glyphosate (3 lb/aia), pelargonic acid (4.2 lb/aia), flumioxazin (0.38 lb/aia), and dimethenamid-p (1.68 1.5 lb/aia). A non-treated control was also included. Data collected included visual control ratings at 1, 2, and 4 weeks after treat- ment (WAT) and shoot fresh weights (FW) were taken at 4 WAT. Plants were then grown for an additional 8 weeks to monitor any regrowth following treatment. Regrowth data indicated that the best long-term results were achieved with flumioxazin (100% control), oxadiazon (100% control) and indaziflam (100%). Results from this trial suggest that several active ingredients already labeled for use in nursery crops and landscapes can be used for artillery weed management. Oxadiazon (granular) and dimethenamid-p are also labeled for over-the-top use and could be prove to be valuable tools for controlling artillery weed in container-grown ornamentals. Further testing is needed in order to develop recommendations.
Pilea microphylla (L.) Liebm, commonly known as artillery in greenhouse crops and also invades containers where it thrives weed, artillery fern, rockweed, and gunpowder plant, is a low- under daily irrigation in fertile substrates. In landscapes, it is a growing annual or short-lived perennial succulent herb in the common weed in planting beds, cracks in hardscapes, and in Urticaceae family. Common names are derived from the fact that shaded and thinning turf areas. this weed forcefully ejects pollen. Artillery weed can be identi- Growers and landscape contractors regularly report poor con- fied by its distinguishable small lime green and shiny leaves and trol of artillery weed with glyphosate, the most commonly used clumping growth habit. Artillery weed was once commonly planted postemergence herbicide in landscape plantings beds and non-crop as an ornamental groundcover and was prized for its shiny green areas of nurseries. Conover and Stamps (1997) conducted one of foliage and ability to tolerate a wide range of conditions (Gilman, the only studies to evaluate postemergence herbicide efficacy of 2014). Today it is still available in the nursery trade from a variety artillery weed. Herbicides evaluated included both preemergence of online distributors. Pilea microphylla variegata ‘Tricolor’ is a (PRE) and postemergence (POST) herbicides that were all applied popular cultivar with some gardeners due to its showy white and POST including prodiamine, isoxaben, imazaquin, fluometralin, pink foliage. While once a popular landscape groundcover, artillery oxadiazon, and glyphosate. Applications were made to plants weed is highly invasive. While few studies have investigated the growing in full sun and under a 60% shade cloth. Results showed reproductive ability of artillery weed, preliminary data shows that that in both environments, the only effective herbicide was oxa- well over 1000 seeds can be produced on a single plant in only a diazon, and to a lesser degree, glyphosate. While glyphosate had few months and seed have no dormancy requirement and a very some effect, plants had begun to regrow 6 weeks following the high viability rate. Artillery weed has begun causing management treatment, similar to current reports from nursery managers and issues in several states, most notably Florida and Hawaii where landscape applicators. While this study was very useful for the it thrives in a tropical climate. Most commonly found growing in industry, multiple herbicides have been labeled for use in nursery shaded areas, artillery weed can grow in full sun with adequate production and landscapes since this study was conducted. moisture. While control has become predominately an issue in Currently, artillery weed management consists of hand weed- Florida and Hawaii, it has been documented from South Carolina ing or applying glyphosate or a contact herbicide, such as diquat. west to Texas and as far north as Kentucky (USDA, 2016), but is Current management practices typically result in reinfestations strictly a warm season annual in more northern climates. Artillery of this weed within weeks. Therefore, research is needed to de- weed has become increasingly invasive in container plant nurser- termine the most effective herbicide for control of artillery weed ies. It is a common greenhouse weed found on floors, walls, and which will not result in immediate regrowth and subsequently increase the cost of management. The objective of this study was to determine efficacy of selective POST herbicides for control *Corresponding author; email: [email protected] of artillery weed.
Proc. Fla. State Hort. Soc. 129: 2016. 243 Materials and Methods protected least significance difference (LSD) test. In all cases, means were considered significant at P = ≤ 0.05. An experiment was conducted in 2015 at the Mid-Florida Research and Education Center to determine efficacy of POST Results applied herbicides for control of artillery weed. On 31 Oct. 2015, 3.5-inch diameter (0.18 gal) nursery containers were filled At 1 WAT, the highest control ratings were recorded for plants with SunGrow® 52 substrate mix (pine bark, peat, perlite, ver- treated with pelargonic acid (9.2) followed by diquat (8.2) and miculite, dolomitic limestone, wetting agent, and starter charge; dimethenamid-p (7.5). By 2 WAT, injury ratings increased in all SunGrow Horticulture, Agawam, MA) that had been amended with treatments with the exception of pelargonic acid. Highest control Osmocote® Plus 15–9–12 at a rate of 9.4 lb/yd3. Approximately ratings were achieved with diquat and flumioxazin followed by 100 artillery weed seeds were sown to the surface of each pot. Pots dimethenamid-p and pelargonic acid. A similar trend was noted were placed in a heated shade house (60% shade) and irrigated at 4 WAT except that at this time, plants treated with glyphosate 0.5 inches each day via overhead irrigation. On 31 Dec. 2015, had control ratings similar to those treated with flumioxazin. Per- (clear skies, air temperature 81 °F, winds 9 mph, 71% relative cent control ratings collected at 4 WAT showed dimethenamid-p, humidity) artillery weeds were treated with selected herbicides diquat, glyphosate, flumioxazin, pelargonic acid, and oxadiazon (Table 1). All herbicides selected are labeled for use in container, provided the most control. Indaziflam and sulfentrazone provided field, greenhouse, or landscape ornamentals. Pots were removed marginal control (61% and 65%, respectively) while sulfosulfu- from the shade house prior to treatment and then placed back ron had little effect on artillery weed growth. Fresh weight data inside immediately after treatment. At the time of treatment, all collected at 8 WAT measuring regrowth potential after treatment plants were 3.5–4.5 inches tall and had flowered. Diquat and showed the best long-term control was achieved with flumioaxazin, pelargonic acid herbicides included the addition of Capsil® oxadiazon, and indaziflam (all 100% control); glyphosate, diquat, (Aquatrols, Paulsboro, NJ) at 0.25% by volume. All herbicides and dimethenamid-p provided similar results but small portions were applied using a CO2 backpack sprayer calibrated to deliver of green stems and leaves remained in these pots. Sulfentrazone 20 gal/acre. Plant foliage was dry at the time of application and (82%) also provided good control but was not as effective as other plants were not irrigated until the following day after treatment. herbicides evaluated. At 8 WAT, pelargonic acid only provided Data collected included visual control ratings on a scale of only marginal control (69%) and plants were able to regrow 0–10 (0 = no control; 10 = complete control, dead plant) at 1, following treatment. Sulfosulfuron only marginally suppressed 2, and 4 weeks after treatment (WAT). At 4 WAT, shoot fresh regrowth (41%). weights (FW) were recorded by cutting any remaining foliage at the soil line and immediately weighing. Plants were kept inside Discussion the greenhouse and then allowed to regrow for an additional 4 weeks to measure any regrowth. At 8 WAT, regrowth from each pot Results from this study indicate that several POST herbicides was recorded using the method described above. All shoot fresh can be used for control of artillery weed in nurseries, greenhouses, weight data were converted to percentage of control by using the and landscapes. Considering regrowth at 8 WAT, flumioxazin, following formula: Percentage of control = [(1 – (fresh weight of indaziflam, and oxidazon provided 100% control and no green treated/fresh weight of nontreated) x 100]. This experiment was stems or leaves remained in the pots at the final evaluation. designed as completely randomized block designs with minor Oxadiazon was also found to be the most effective herbicide differences in plant size as the blocking factor and 10 single plant in trials by Conover and Stamps (1997); however, in the cur- replications per treatment. All data were subjected to ANOVA rent study the granular formulation was evaluated compared to using SAS® (SAS, Cary, NC) and means separated using Fisher’s spray applied formulations in the Conover and Stamps trials.
Table 1. Postemergence control of Pilea microphylla (Artillery weed) with selected herbicides. Visual Control Rating (0–10)z % Controlw % Control Herbicide Trade Name Rate (lbs. aia)y 1 WATx 2 WAT 4 WAT (4 WAT) (8 WAT) Dimethenamid-p Tower® 1.50 7.5 bv 8.6 b 8.6 b 92 a 93 ab Diquat Reward® 0.50 8.2 b 10.0 a 10.0 a 100 a 94 ab Glyphosate RoundUp Pro® 3.00 2.5 d 5.6 c 9.7 a 98 a 99 a Flumioxazin SureGuard® 0.38 5.3 c 10.0 a 10.0 a 100 a 100 a Indaziflam Marengo® 0.06 0.0 f 0.6 e 2.7 e 61 b 100 a Oxadiazon Ronstar® G 4.00 1.6 e 4.9 c 7.1 c 79 ab 100 a Pelargonic acid Scythe® 4.20 9.2 a 8.7 b 7.1 c 100 a 69 c Sulfentrazone Dismiss® 0.37 1.6 e 1.6 d 2.6 d 65 b 82 bc Sulfosulfuron Certainty® 0.05 0.7 fv 0.9 de 0.0 e 10 c 41 d Non-treated -- -- 0.0 0.0 0.0 0.0 0.0 zPhytotoxicity ratings were recorded on a scale of 0–10, where 0 = no injury, 10 = dead plant. yAll rates are shown in pounds of active ingredient per acre. xWAT = weeks after treatment. All treatments were applied on 31 Dec. 2015. wPercentage of control = [(1 – (fresh weight of treated/fresh weight of non-treated) x 100]. Fresh weights of control plants were 13.8 and 4.4 g at 4 and 8 weeks after treatment, respectively. vMeans followed by the same letter are not significantly different based upon Fisher's Protected LSD test (0.05) (n = 10)
244 Proc. Fla. State Hort. Soc. 129: 2016. The granular formulation is primarily used as a PRE herbicide be needed for effective control. All of these herbicides are labeled that can be applied over the top of selected ornamental plants. for use in either landscapes, nurseries, or greenhouses and could Previous research has shown oxadiazon can be root absorbed to provide growers and landscape applicators more effective options a small degree (Bingham et al., 1980) but further investigation for managing this weed in a variety of production scenarios. would be needed to determine how oxadiazon placement would Dimethenamid-p and the granular formulation of oxadiazon are affect control of artillery weed. Indaziflam, another PRE herbicide, labeled for use over the top of selected ornamentals and could also provided 100% control. Indaziflam is only labeled for use provide a valuable tool for container plant producers. Further in ornamentals as a directed application (Anonymous, 2014) due evaluation is needed to determine efficacy of herbicides such to severe injury that can occur if foliage is contacted during ap- as glufosinate, and also evaluate multiple rates of each product. plication. Research has shown that indaziflam can provide early It should be noted that limited experimental data are available postemergence control of several weeds including Oxalis stricta concerning efficacy of herbicides for control of artillery weed. (Marble et al., 2013) and Poa annua (Brosnan et al., 2012). The These trials will need to be repeated under a variety of conditions results of this trial indicate that indaziflam can provide control before recommendations can be made. Preemergence trials are also of fully mature artillery weed; however results would be slower needed for control in and around container-grown ornamentals than could be expected using other herbicides. Flumioxazin has in order for growers to develop herbicide rotation schedules for a similar mode of action to oxadiazon and provided excellent artillery weed. control throughout the trial. It is a common PRE herbicide that is often tank-mixed with glyphosate or other POST and provides Literature Cited a quick “burndown” effect while also provided PRE control. Dimethenamid-p, another PRE herbicide that has shown some Bingham, S.W., R.L. Shaver, and C.L. Guyton. 1980. Peanut uptake and activity on small Chamaesyce maculata (Marble et al., 2011) metabolism of 14C oxadiazon from soil. J. Agr. Food Chem. 28:735–740. also provided effective control of artillery weed; likely due to Brosnan, J.T., G.K. Breedon, P.E. McCullough, and G.M. Henry. 2012. the emulsifiable concentrate (EC) formulation which can injure Pre and post control of annual bluegrass (Poa annua) with indaziflam. sensitive plants under certain environmental conditions. It was Weed Tech. 26:48–53. Conover, C.A. and R.H. Stamps. 1997. Controlling artillery plant (Pilea expected that diquat would provide good results initially as it is a microphylla) with herbicides. Central Florida Res. Bul. RH-94-7. contact action herbicide, but at 8 WAT artillery weed had little to Accessed 3 Apr. 2016.
Proc. Fla. State Hort. Soc. 129: 2016. 245