PREEMERGENCE WEED CONTROL IN TUBEROSE1

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1 Table 2. Distribution of cucumber mosaic virus (CMV) in Rhodochiton atrosanguineum 6 weeks after inoculation. Indirect ELISA stratification CMV Plant tissue Plant 1 Plant 2 HEALTHY Roots Roots Lower stem Inoculated leaf Vine A-leaf 1 -leaf 2 -leaf 3 Vine B-leaf 1 -leaf 2 -leaf 3 Shoot apex 1.228* : L L Figure 2. Leaf deformity, marginal chlorosis and mosaic caused by cucum ber mosaic virus in purple bell vine. 'Shaded data squares represent positive ELISA absorbance values that indi cate the presence of virus. opportunity for this species to act as a reservoir host for both these viruses in the landscape as well. Literature Cited Alfieri, S. A. Jr., K. R. Langdon, C. Wehlburg and J. W. Kimbrough In dex of plant diseases in Florida. Bulletin 11. Fla. Dept. of Agr. Consumer Services, Div. Plant Industry. Gainesville, FL. Farr, D. F., G. F. Bills, G. P. Chamures and A. Y. Rossman Fungi on plants and plant products in the United States. APS Press. St. Paul, MN. Huxley, A., M. Griffiths and M. Levy (eds.) The new Royal Horticultur al Society dictionary of gardening. Vol. 4. Macmillan Press Ltd. London, England. Thornberry, H. H Plant pests of importance to North American agri culture. Index of Plant Virus Diseases. HndBk U.S. Dept. of Agr., Washington, D.C. Proc. Fla. State Hort. Soc. 108: PREEMERGENCE WEED CONTROL IN TUBEROSE1 James P. Gilreath Gulf Coast Research and Education Center University of Florida, IFAS Bradenton, FL Additional index words. Herbicide, tuber, Polianthes tuberosa. Abstract. Thirteen preemergence herbicides were evaluated for crop response and weed control in tuberose (Polianthes tube rosa L.) grown in flatwoods soil. Each herbicide was applied twice during 1986 and four times in Plots were handweeded weekly during 1986 to evaluate herbicide effects, whereas herbicide treated plots were handweeded only prior to each application in 1987 to evaluate weed control as well as herbicide effects. and thiobencarb were injurious to tuberose when applied pre- or postemergence in 1986, whereas methazole and clomazone only damaged plants when applied postemergence. Tuberose plant vigor was not affected by herbicide treatment until after three applications of herbi cide in 1987 at which time only those plants treated with prodiamine or oryzalin were as vigorous as plants in handweeded Florida Agricultural Experiment Station Journal Series No. N Mention of a specific proprietary product does not constitute an endorse ment by the author or the University of Florida. Growers should consult the label before application of any herbicide. plots. Crabgrass (Digitaria ciliaris (Retz.) Koel.) control was generally excellent with all treatments, except methazole, oxy fluorfen, and thiobencarb. Control of eclipta {Eclipta alba L.) was good with all herbicides until after the third application when only napropamide, methazole, clomazone, and oryzalin controlled eclipta as well as handweeding. After four applica tions of herbicide treatments, napropamide no longer con trolled eclipta as well as handweeding; whereas, methazole, clomazone, and oryzalin continued to control eclipta as well as handweeding. Plots treated with cinmethylin, prodiamine, and oryzalin pro duced as many flowers and equivalent flower weight as handweeded plots. Foliage production was similar to spike production with the exception that less biomass was produced with cinmethylin than with handweeding. More tubers were produced in plots treated with cinmethylin,, clomazone, and oryzalin than with napropamide in 1986., diethatyl, and oryzalin were the only herbicides which produced more tubers than the nontreated control plots (weedy) in 1987., prodiamine, clomazone, and alachlor produced as many medium to large size tubers as handweeding. Tuberose, grown for both flowers and tubers, has never been a large acreage cut flower crop in Florida, in part due to production problems. Historically, weed control has been one of the predominant production problems. Although some weed control research has been conducted (W. Skroch, personal communication), no published reports have been Proc. Fla. State Hort. Soc. 108:

2 found. Tuberose growers usually produce other tuber or bulb crops and typically use the same preemergence herbicide for all crops. Since all of the tuberose planting receives the same herbi cide, growers have little knowledge of the actual effects of that herbicide on tuberose, except when obvious phytotoxicity oc curs. As a result, yields could be reduced by the chosen herbi cide without the grower's knowledge. Research was conducted in 1986 and 1987 to identify preemergence herbi cides which were non-phytotoxic to tuberose, provided good weed control and resulted in yields equal to season-long handweeding when applied several times in a season-long weed control program. Materials and Methods Experiment 1. Thirteen herbicides (Table 1) were evaluat ed for crop phytotoxicity and yield effects in tuberose during The EauGallie fine sand soil (ph 6.4, 0.8% organic mat ter) was formed into 6-inch tall, 30-inch wide beds, spaced 4.5 ft apart. s were assigned to 8-ft long, single row plots arranged in a randomized complete block design with three replications. Five tuberose tubers (1-inch diameter) were planted 3 inches deep and 1 ft apart in each plot. The crop was grown using seepage irrigation and 180 lb of N per acre were supplied from a 6N-2.6P-5K (6-6-6) fertilizer with applications preplant and during the growing season. Plots were maintained weed-free for the crop season by manually removing weeds weekly; thus limiting crop response to herbi cide alone, not herbicide and weed effects. Herbicides were applied twice during the season, preemergence 1 day after planting (27 June 1986) and postemergence (18 Aug. 1986) when the plants were 18 to 24 inches tall. Applications were made with a CO2 powered, backpack sprayer equipped with a two nozzle boom, delivering 23.0 gal/acre. Phytotoxicity was evaluated on a 0 to 100 percentage scale, where 0 indicated no damage and 100 represented plant death 10 days after each herbicide application. Crop plant vigor was evaluated on a percentage scale 30 days after the second application of herbicide. Tuberose tubers were Table 1. Phytotoxicity of one and two applications of preemergence herbi cides to tuberose and effect of two applications on plant vigor in Experi ment 1 (1986). Herbicide 0 Phytotoxicity (%) 1 applic. 2 applic. * 20c 37b 13cd 60a led led 13cd 70a 7d 5 42bc 23cd l 5b - Plant vigor <%) 7 8b 68b b b dug 22 Dec. 1986, air dried, and graded by size, counted, and weighed on 16Jan Experiment 2. The same 13 herbicide treatments were eval uated for weed control and crop response in EauGallie fine sand soil (ph 7.2, 0.7% organic matter) was formed into raised beds as in the first experiment. Fertility and irrigation were the same as in the first experiment. s were as signed to 15-ft long, single row plots arranged in a random ized complete block design with five replications. Ten tubers ( to inch diameter) were planted 3 inches deep and 1 ft apart in each plot on 29 May plots were manually weeded every 2 weeks during the season and all plots were handweeded prior to each application of herbi cide. Herbicides were applied four times during the season: 3 June, 22 July, 6 Oct., and 10 Nov All applications were made with a CO2 powered, backpack sprayer equipped with a two nozzle boom, delivering 25.0 gal/acre. Crop plant vigor was evaluated on a percentage scale, where 0 indicated dead plants and 100 represented optimum plant growth, 40, 13, and 34 days after the first, second, and third applications, respectively. Phytotoxicity was evaluated on the previously employed percentage scale 13 days after the second application of herbicides. Weed control was evaluated by species, using a visual percentage scale, 40 days after the first two applications and 30 days after the third application. Tuberose flowers were harvested nine times, beginning 26 Aug. and ending 31 Dec Tubers were dug and foliage was removed and weighed 8 Jan Tubers were air dried for 1 month, and were graded by size, counted, and weighed 8 and 9 Feb Data from both experiments were subject ed to analysis of variance and treatment means were ranked by Duncan's new multiple range test at the 5% level of signif icance. Results and Discussion Experiment 1, One preemergence application of, ox yfluorfen, thiobencarb, diethatyl, or clomazone was injurious to tuberose plants (Table 1). When a second application was made directly to the crop foliage and soil, considerable phy totoxicity was observed with oxyfluorfen, thiobencarb, meth azole, and clomazone. After two applications of herbicide treatments, plants which received thiobencarb were less vigor ous than those which were treated with cinmethylin, napropa mide, or oryzalin. No other differences were evident for plant vigor. Few differences existed among treatments for the pro duction of number one size tubers (Table 2). None of the herbicides reduced the number of number one size tubers when compared to the nontreated control; however, fewer of these tubers were produced in plots treated with napropam ide as compared to and methazole. Production of the larger number two tubers was reduced by application of napropamide, oxyfluorfen, prodiamine, and diethatyl, whereas more number three size tubers were produced with oxyfluorfen and diethatyl when compared to the nontreated control. -treated plants produced more number three tubers than, metolachlor, thiobencarb, and met hazole. Production of number four size tubers was not affect ed by herbicide treatment. None of the herbicides reduced total tuber production compared to the nontreated control, but differences did exist among herbicide treatments. Cinm ethylin,, clomazone, and oryzalin produced more tu- 54 Proc. Fla. State Hort. Soc. 108: 1995.

3 Table 2. Effect of two applications of herbicide treatments on tuberose tuber production in Experiment 1 (1986). Herbicide Non treated #1 4b> 48ab 60a 23b 51ab 36ab 41ab 42ab 56a 4b 40ab 39ab 48ab 5b Number of tubers per size grade' #2 70ab 59abc 7 47c 5bc 47c 49bc 61abc 56abc 46c 5c 49c c c #3 16c 26abc 18bc 2bc 30a 22abc 1 18bc 21abc 2bc 2 22abc 21abc #4 6a 2a Total 13bc a 99c 12bc 115bc 11c 12bc 13bc 115bc 12bc 118bc 138ab 142ab 'Size grade codes are based on diameter as follows: #1 = less than inches, #2 = to inches, #3 = to inches, #4 = to inches, #5 = to 2.5 inches. >Means within columns followed by the same letter are not significantly dif bers than napropamide; whereas, tuber production was greater with than with napropamide, oxyfluorfen, alachlor, prodiamine, and diethatyl. Experiment 2. When applications were made to emerged tuberose foliage in the second experiment, oxyfluorfen, thiobencarb, methazole, clomazone, and oryzalin produced considerable damage to foliage, with methazole causing the most injury (Table 3). One preemergence application of her bicides did not affect tuberose plant vigor. Although signifi cant injury was observed with several herbicides after the second application (first foliar application), plant vigor was not affected when evaluated later in the season. It should be noted, though, that considerable variability in vigor among Table 3. Phytotoxicity of one foliar application (evaluated 13 days after the second application) of preemergence herbicides to tuberose foliage and effect of herbicide treatment on vigor of tuberose plants 40, 13, and 34 days after the first, second, and third application respectively in Experi ment 2 (1987). replicates of the more phytotoxic treatments was observed at this time; a factor which possibly affected the results of analy sis of variance. After the third application of herbicides, tuberose plant vigor was reduced by all herbicide treatments, except prodi amine and oryzalin, when compared to handweeding. It was not until this time that plants in nontreated plots were less vig orous than those in handweeded plots, suggesting that weed competition was not a significant factor until this time. The least vigorous plants were those which had received thioben carb or methazole. These plants were no more vigorous than those which were growing in plots where no form of weed control was being practiced. Plants treated with many of the other herbicides were not different from plants in the nontreated (weedy) plots. Although numerous weed species were present during the experiment, crabgrass (Digitaria ciliaris) and eclipta (Eclipta alba) were present consistently and constituted the larger proportion of the overall weed population. Rorippa (Rorippa teres (Michx.) Stuckey), a winter annual, was not observed un til after the fourth application of herbicides; however, it was a major weed during that time interval, so data for it are pre sented. Crabgrass infested plots early and constituted the majority of the weed population for the time interval of the first two applications of herbicides. Germination and emergence of crabgrass were so rapid initially, when there were few other weeds present, that weekly handweeding did not provide ac ceptable control (Table 4). One application of all herbicides provided better crabgrass control than no herbicide and no handweeding (nontreated control)., napropam ide, oxyfluorfen, alachlor, prodiamine, and clomazone con trolled crabgrass better than handweeding at this time. Once weeds were removed manually and a second appli cation of herbicide treatments was made, all treatments pro vided equally good crabgrass control (Table 4). Crabgrass control in the nontreated plots was higher than one would ex pect because the existing crabgrass had senesced and the can opy was limiting germination and emergence of additional plants. Five days before a fourth application, crabgrass had re- Table 4. Effect of four applications of preemergence herbicides on crabgrass {Digitaria ciliaris) control in tuberose in Experiment 2 (1987). Vigor (%) Phytotoxicity- Applic. 1 Applic. 2 Applic. 3 Applic. 1 Control (%) Applic. 2 Applic. 3 Applic. 4 15bcd d 4d 31b 1d 32b 6 8cd 9cd 33b 25bc ' a a 76a 72a 82a 7 61a 9 39ef 56cdef 4ef 64bc 63bcd 50cdef 58bcde 37e 36e 7b 53cdef 68bc 62bcd 26c 48bc 8 7b 82a 7b 8 8 b 88a 70ab 71 ab 6 9 b 6c 8 24c 58b Proc. Fla. State Hort. Soc. 108:

4 j established itself in the nontreated plots and, oxyfluo rfen, thiobencarb, and methazole were not controlling it as well as handweeding or most of the other herbicides. After plots were handweeded and herbicides were applied for the fourth time, just prior to digging tubers, all herbicides, except methazole, and diethatyl, controlled crabgrass as well as handweeding. Although eclipta was an important weed in this experi ment, it was not until midseason that it became a weed of great concern. There were no differences in eclipta control after the first application, and was the only herbicide which provided less control than handweeding after two ap plications (Table 5). Just prior to the fourth application, eclipta had become a serious weed problem throughout the test area and only napropamide, methazole, clomazone, and oryzalin controlled it as well as handweeding. When evaluated Table 5. Effect of four applications of preemergence herbicides on eclipta {Eclipta alba) and rorippa (Rorippa terres) control in tuberose in Experi ment 2 (1987). after the fourth application of herbicide treatments, meth azole, clomazone, and oryzalin were the only herbicides which provided season-long control of eclipta. None of the other herbicide treatments provided acceptable control (>70% control) at the time of tuber harvest. As previously mentioned, rorippa was not present until the cooler temperatures of fall when it became one of the ma jor weeds in this experiment. Most of the herbicides provided rorippa control equal to handweeding, but, napropa mide, methazole, and clomazone did not (Table 5). The pre dominant impact of rorippa was interference with tuber harvest due to the lateness of its appearance. Flower production was recorded as well as tuber yields be cause both are marketable commodities., oxyfluorfen, thiobencarb, and methazole reduced the number and weight of flowers produced compared to hand weeding (Ta ble 6)., prodiamine, and oryzalin were the only herbicides which produced weights of flowers similar to hand- Control ( %) foliage weight after harvest in Experiment 2 (1987). - Appl. 1 Appl. 2 Eclipta Appl. 3 Appl. 4 Rorippa Appl. 4 Number Bloom spikes Weight (lb) - Foliage weight (lb) 66ab* 5 58ab 56ab 5b 72ab 66ab b 65b 9 62b 88a 89a 89a 91a 9 Oe cd Of 7c 14f 46de 62bcd 4f 9 64bcd 52cde 27ef 9 8b 57c c l 51c 43c b 53c 44c 20d 22d b 5cd 51cd c b c 9b 5cd 78abc 69abc 48cd 8ab* lla 8ab 5b 9ab 1.8bc 3.2a 2.1abc ] L ] L9bc ] L4bc ] L3bc ] L ] L2bc ().9c c >.b ] L.3bc ] L8bc ] L.c 2.2ab 0.41 bed 1.19a 0.65bcd 0.43bcd 0.48bcd 0.91abc 0.41cd 0.63bcd 0.35d 0.44bcd 0.b 0.63bcd 0.69bcd 0.61bcd 0.81 abed Table 7. Effect of four applications of preemergence herbicide treatments on production of tuberose tubers in Experiment 2 (1987). Number of tubers per size gradez per plot i\.d.lc No. 1 No. 2 No. 3 No. 4 No. 5 Total 156a' 171a 176a 1 159a 170a 152a 160a 161a a 169a 1 84e 15b lllcde 115bcde 13cd 13cd 11de 132abcd 12bcd 96de 13bcd 141abc 162a 132abcd 14c 21d 76a 44bcd 20d 33cd 36cd 32cd 41bcd 22d 18d 5c 29cd 40cd 50abcd 72ab c 1 c c 5c c 5c 9abc loab 8bc c ledef bcde 2bcdef 2bcdef ldef 2abcdef Of b bcd bc bcde 267cd 419a 340abcd 320abcd 338abcd 351abc 30cd 34bcd 31bcd 242d 3b 3c 3b 362abc 41 'Size grades are based on tuber diameter as follows: no.l = less than inches, no. 2 = tol.o inches, no. 3 = 1 to inches, no. 4 = to inches, and no. 5 = greater than 2 inches in diameter. >Means within columns followed by the same letter are not significantly dif signif icance. 56 Proc. Ha. State Hort. Soc. 108: 1995.

5 weeding. When foliage was weighed at harvest, metolachlor, prodiamine, and oryzalin produced as much biomass as handweeding; whereas, the other herbicides did not. The effect of specific herbicides on tuber production was not consistent across all size grades and treatment differences were observed in size grades greater than number one (Table 7). Fewer number two size tubers were produced in plots treated with cinmethylin and methazole than in handweeded plots; whereas, the production of number three size tubers was reduced by all herbicides, except prodiamine, cloma zone, and oryzalin. Production of number four size tubers was equal to handweeding with four applications of prodiamine and oxadiazon, whereas an equivalent amount of the larger number five size tubers was produced with cinmethylin, alachlor, prodiamine, diethatyl, clomazone, and oryzalin. Production of tubers of all sizes combined was equal to handweeding with all herbicides, except oxyfluorfen and meth azole. Most of the tuber production was in the smaller number one to number two sizes with less than 2% of the tu bers having a diameter greater than inches (Table 8). Generally, use of herbicides shifted tuber production to the smaller sizes, while handweeding resulted in a greater percentage of tubers in the larger, more profitable, number three and four size grades., prodiamine, clomazone, and oryzalin resulted in production similar to handweeding for these larger tuber grades. Although the percentages with regard to size distribution were similar with these four herbi cides and handweeding, actual numbers of tubers produced were not similar, as alachlor resulted in fewer number three and four sizes than handweeding. Although produced some of the highest tuber yields in the first experiment, when weeds were not removed manua-ly, production declined as a result of poor weed con trol. Addition of weeds as a factor improved the performance of prodiamine by allowing the weed control provided to mask any reduction in flower, tuber, or foliage production due to the herbicide. performed consistently in both exper iments with no reduction in flower, tuber, or foliar biomass Table 8. Effect of four applications of herbicide treatments on number of tuberose tubers in each size grade expressed as a percentage of the total number of tubers in Experiment 2 (1987). pafp Jxd.LC Percentage of tubers in size ranges' No. 1 - No. 2 91afr 78d bc 89ab 8bcd b 91ab 83bcd 89ab bc 8bcd 80cd No. 3 - No. 4 9c 21a 13bc 8c lie 1bc 8c 9c 16abc lie 12bc 1bc 20ab No. 5 or > 0.3cdef 1.1a 0.1 ef 0.4bcdef 0.2def 0.cde O. O.Of l.oab O. 0.8abcd 0.9abc 'Size grades are based on tuber diameter as follows: no.l = less than inches, no. 2 = to inches, no. 3 = 1 to inches, no. 4 = to inches, and no. 5 = greater than 2 inches in diameter. ymeans within columns followed by the same letter are not significantly dif production. Although clomazone had little to no effect on tu ber production in both experiments, it did reduce weights of flowers and foliage in the second experiment. Since flower production is an important aspect of tuberose production and clomazone was observed to produce considerable foliar chlorosis, although ephemeral in this experiment, it is not be lieved to be suitable for use in tuberose production. Consid ering weed control and crop response, oryzalin appears to be the preferred preemergence herbicide; however, in certain situations prodiamine may be useful. Tuberose producers should consider current labeling and should evaluate these herbicides in small test blocks before selecting one product. Proc. Ha. State Hort. Soc. 108: