Weed Science. 1996. V61ume 44:7-1 I

Synthesis and Herbicidal Activity of Modified Structurally Similar to CinmethylinI

STEVEN F. VAUGHN and GAYLAND F. SPENCER2

Abstract. The preemergence herbicide cinmethylin is a benzyl use as herbicides. A group of natural products most successfully ether derivative of the l,4-cineole. Other oxy­ adapted for use have been (4, 5).. The soil-applied genated monoterpenes (carvone, , fenchone, gera­ preemergence herbicide cinmethylin is a benzyl ether derivative niol, and pulegone) were previously found to inhibit the ofthe monoterpene 1A-cineole (Figure 1). Cinmethylin is active germination and growth ofseveral weed species while exhib­ primarily against annual grass weeds and some small-seeded iting low phytotoxicity to soybean. Benzyl ether derivatives broadleaf weeds in several crops (9). Although a specific mode of these oxygenated monoterpenes were synthesized and ex­ of action for the compound has not been elucidated, the mecha­ amined for preemergence and postemergence activity to­ nism of action of cinmethylin appears to result from the inhibi­ wards corn, soybean, wheat, and velvetleaf. Benzyl pulegyl tion of mitosis in meristematic regions of susceptible plants (6, etherexhibited the most preemergence activity when applied 9). directly to the soil, completely inhibiting wheat and velvetleaf Monoterpenes containing several different functional groups emergence at 1.0 kg ha-1 while reducing soybean emergence were shown to inhibit the growth ofthe green alga ChIarella (8), 80%. Several of the benzyl ethers were more inhibitory to potato (Solanum tuberosum L.) tuber sprouting (15) and crop and velvetleaf radicle elongation relative to chmethylin but less weed seed germination (1, 2, 3, 7,10,11,14,16). We found that inhibitory to corn and wheat radicle elongation in petri dish several monoterpenes cpntaining oxygen functions were espe­ bioassays. Several of the benzyl ethers exhibited limited cially inhibitory to crop and weed species. These included postemergence activity when applied at 1.0 kg ha-1 to seed­ monoterpenes with ketone (carvone, fenchone, pulegone) and lings ofthe testspecies 10 d afteremergence. The benzyl ether alcohol (citronellol, ) functional groups (16; Figure 1). derivatives demonstrated altered selectivity and sensitivity The germination and growth ofseveral weed species were inhib­ as compared to the parent compounds and cinmethylin. ited by these monoterpenes, while soybean was not. However, Nomenclature. Cinmethylin, exo-l-methyl-4-(1-methyl­ these compounds are highly volatile and likely would be rapidly ethyl)-2-[(2-methylphenyl)methoxy]-7-oxabicyclo[2.2.l]­ lost unless immediately mixed into the soil by tillage or irriga­ heptane; carvone, 2-methyl-5-(1-methylethenyl)-2-cyclo­ tion. Because cinmethylin is a benzyl ether derivative of 1,4­ hexene-l-one; citronellol, 3,7-dimethyl-6-octen-l-ol; cineole and has a volatility several orders ofmagnitude less than fenchone, 1,3,3-trimethylbicyclo[2.2.l]heptan-2-one; gera­ its parent compound, the conversion of the parent monoterpenes niol, 3,7-dimethyl-2,6-octadien-l-ol; pulegone, 5-methyl-2­ to their respective benzyl ethers should decrease volatility. The (l-methylethylidene)cyclohexanone; benzyl carvyl ether, parent monoterpenes are readily available commercially by ex­ 1-(phenylmethoxy)-2-methyl-5(1-methylethenyl)-2-cyclo­ traction from plant sources or chemical synthesis, and generally hexene; benzyl citronellyl ether, 1-(phenylmethoxy)-3,7-di­ have low mammalian toxicities. To assess the potential of these methyl-6-octene; benzyl fenchyl ether, 2-(phenylmethoxy)­ 1,3,3-trimethylbicyclo[2.2.l]heptane; benzyl geranyl ether, l-(phenylmethoxy)-3,7-dimethyl-2,6-octadiene; benzyl pu­ legyl ether, 1-(phenylmethoxy)-5-methyl-2-(1-methyl­ ethylidene)cyclohexane; velvetIeaf, Ablltiloll theophrasti Medicus #3 ABUTH; corn, Zea mays L. 'Dekalb IL645-786'; 0 soybeans, Glycille max (L.) Merr. 'Williams'; wheat, Triticu11l aestivll11l L. 'Cardinal.' Additional index words. Terpenoids, growth inhibition. t:9: Geraniol Carvone Fenchone INTRODUCTION Plants produce a myriad ofchemicals that have only recently begun to be closely explored for use as pesticides, especially for

I Received for publication January 4. 1995, and in revised form May 30, 1995. 2Plant PhysioI. and former Res. Chern. (retired), respectively, Bioactive Constituents Res., USDA-ARS. Nat. Ctr. for Agric. Utilization Res., 1815 N. Cltronellol Pulegone University St., Peoria. IL 61604. Cinmethylln 3Letters following this symbol are a WSSA-approved computer code from Composite List of Weeds. Revised, 1989. Available from WSSA. 1508 West Figure I. Chemical structures ofcinmethylin and parent monoterpenes ofbenzyl University Ave., Champaign. IL 61801-3133. ethers. 7 VAUGHN AND SPENCER: \lODIFIED MONOTERPENES STRUCTURALLY SIMILAR TO CINMETHYLlN compounds as herbicides. we synthesized benzyl ether analogues 5890 gas chromatograph equipped with a flame ionization de­ of the compounds found to be most inhibitory in our previous tector and a 15 m DB-II column. temperature programmed from work (16). i.e.. carvone. citronella!. fenchone. geraniol. and 100 to 200 Cat 5°/min. I Hand I3C NMR spectra \vere measured pulegone. In this paper we describe their synthesis and report on in CDCh by a Brucker WM-300 spectrometer. Samples were their herbicidal activity. introduced through a Hewlett-Packard 5890 gas chromatograph and mass spectra \vere produced on a Hewlett-Packard 5971 Mass Selective Detector. MATERIALS AND METHODS Bioassays. Soybean. corn, wheat, and velvetleaf were used as Chemicals. Because our synthesis procedure required alcohols. bioassay species. To assess preemergence, soil-applied activity. the monoterpene ketones were converted to their corresponding five seeds of com and soybean or ten seeds of wheat and alcohols (i.e.• carvone/carveol: fenchonelfenchyl alcohol: pule­ velvetleaf were placed in 170 ml cups filled with 50 g of a gonelpulegyl alcohol). All compounds used were technical grade mixture of 20% coarse sand and 80% Redi-Earth"" (supple­ and were obtained from a commercial source-+ except for pulegyI mented with Osmocote"" and Micromax"")8 and watered to field alcohol, which was produced by the reduction of pulegone as capacity. The test compounds were added by thoroughly mixing follows: pulegone (50 g) was dissolved in 300 ml of MeOH. an additional 20 g of the soil mixture with 5 ml of solutions NaBH-+ (25 g) was added slowly to the mixture while stirring in containing the test compounds and 0.1 % (v/v) Tween-20 (neces­ an ice bath. The solution was allowed to come to room tempera­ sary as an emulsifying agent due to the low water of ture and stirring was continued overnight. The bath was re­ the ethers and cinmethylin) at rates equivalent to either 0.1 or 1.0 charged with ice and 6 N HCl was added very slowly to the kg ai ha-I (cinmethylin has recommended rates of 0.56-1.68 kg solution (this prevented the solution from overheating as the ai ha-I (17». This treated soil mixture was placed in the cups and reaction was highly exothermic) until it \vas acidic. Distilled 10 ml of water was added to activate the compounds. The cups water (500 ml) was then added to the solution. and the resultant were placed in a growth chamber with a 25/17 C (day/night) mixture containing pulegyl alcohol was extracted three times temperature regime with a 16-h day and 95% R.H. The high with ethyl ether (200 ml each). The ether extract was concen­ humidity prevented the soil mixture from drying. Emerged seed­ trated under N2 and purified by column chromatography over lings (~ I cm above the soil surface) were counted after 10 d and silica gel-+ (70 to 230 mesh) with hexane or hexane:ethyl acetate expressed as a percentage of nontreated controls. (25: 1) as the eluting solvents, with approximately 80% yield The effect of the ethers on radicle elongation was studied (reduction of pulegone to pulegyl alcohol). Each monoterpene using a standard petri dish bioassay. Seeds were surface sterilized alcohol used for synthesis was analyzed at> 99% purity by gas with 0.5% NaOCI for 15 min, then rinsed twice with distilled chromatography-mass spectroscopy (GC-MS)5 and nuclear water. Seeds were wrapped in sterilized paper towels saturated magnetic resonance spectroscopy (NMR). with 10-4 M CaCI . After 24 (wheat) or 48 (velvetleaf, corn, Preparation of benzyl ethers. Benzyl ethers of monoterpene 2 soybean) h, five (com. soybean) or 10 (wheat, velvetleaf) seeds alcohols were prepared as follows: a monoterpene alcohol (50 g) were placed in 9 cm petri dishes containing a Whatman No. I and powdered KOH (100 g) were added to 200 ml of benzyl filter paper disk containing 2.0 ml of 0.1 % Tween-20 (controls) chloride and heated (70 C) with stirring for 3 h. Distilled water or solutions ofthe emulsified ethers (0.01 and 0.1 %, v/v) in 0.1 % (500 ml) was added, and the organic phase of the resulting (v/v) Tween-20. Plates were placed in darkness in a growth bipartite mixture was extracted three times in a separatory funnel chamber at 25 C for 4 d, at which time radicle lengths were with ethyl acetate (200 ml aliquots). The ethyl acetate fraction measured. was separated from the aqueous phase and concentrated by To examine postemergence activity, the four test species were rotoevaporation6, and the resultant ethers (> 80% of the total fraction) were purified (> 99%) by column chromatography on grown in the same growth medium as in the preemergence (a) Sephadex LH-20 eluted with methanol and then on (b) silica studies in a growth chamber with a 16-h photoperiod of 350 I-lE 2 gel (70 to 200 mesh) eluted with hexane:ethyl acetate (25: I). m- S-I PPFD. The temperature was held constant at 25 C with a Progress of the chromatography (i.e., isolation and purification relative humidity of 80%, with plants watered as needed. The of the ethers) was monitored by GC using a Hewlett-Packard ethers were dissolved in 0.1 % (v/v) Tween-20 and sprayed onto the foliage of the plants 10 d after emergence at a rate of 1.0 kg ha- I with a spray volume of421 L ha-I (controls contained 0.1 % (v/v) Tween-20 in water only). Plants were maintained under the "Aldrich Chem. Co.• Milwaukee. WI. Mention of a trademark. proprietary product. or vendor does not constitute a guarantee of the product by the USDA same environmental conditions for 10 d before evaluation of and does not imply its approval to the exclusion of other products that may be phytotoxicity. Above-ground plant heights were measured from suitable. the soil surface to the highest standing point of each plant, and 5Abbreviations: GC-MS. gas chromatography-mass spectrometry: NMR. nuclear magnetic resonance spectroscopy: EI-MS. electron ionization mass plants were harvested for fresh weight analysis. Heights and spectrometry: mJz. mass to charge ratio: s. singlet: d. doublet: m. multiplet: Abq. fresh weights were converted to a per plant basis and reported as AB quartet: J. coupling constant: OAT. days after treatment. a percentage of the controls. In all cases the experimental design 6Model 461. Buchi. FlawiI. Switzerland. 'J&\V Scientific. Folsom. CA. was completely randomized, each treatment was replicated five xGrace-Sierra Horticultural Products Co.. Milpitas. CA. times, and each experiment was repeated. Because initial analy-

8 Volume 44. Issue I (January-March) 1996 WEED SCIENCE "j" indicated a lack of factor-by-experiment interactions. data (m, IH), 1.89 (m, IH), 2.02 (m, lH), 3.18 (d, J =1.8. lH), 4.67 were pooled and analyzed by ANOYA. Treatment means were (ABq, J = 12 Hz, 2H). 7.47 (m, 5H). I3C-NMR (75.47 MHz. separated using Duncan"s multiple range test. CDCI3): 20.1 (CH3), 20.8 (CH3), 26.0 (CH2), 26.2 (CHo), 31.7 (CH3), 39.5 (C),4j.4 (CH2), 48.8 (CH), 49.2 (C), 73.4 (CH), 92.4 RESULTS AND DISCUSSION (CH),127.1 (CH), 127.3 (CHx2), 128.0(CHx2),139.4(C). Benzylgeranylethel: EI-MS [m/z(7f;)]: 153 (4),136(7),123 (21), Chemical structures of benzyl ethers. The chemical structures 107 (8), 91 (100),69 (72). IH-NMR (300 MHz, CDCI 3): 1.69 (s, of the benzyl monoterpene ethers synthesized are shown in 3H), 1.72 (s, 3H), 1.77 (s, 3H), 2.16 (m, 2H), 2.20 (m, 2H), 4.10 Figure 2. Prominent diagnostic mass spectral ions and their (d, J = 6.5 Hz, 2H), 5.20 (m, lH), 5.50 (m, IH). 7.4 (m, 5H). relative intensities and 1H- and 13C-NMR spectra for the com­ 13C-NMR (75.47 MHz, CDCI ): 16.2 (CH ), 17.4 (CH ), 25.5 pounds are as follows: 3 3 3 (CH 3), 26.2 (CH2), 39.4 (CH2), 66.3 (CH2), 71.6 (CH2), 120.8 Benzyl canyl ethel: EI-MS [m/: (Ck)]: 151 (]3), 134 (l2). 119 (CH), 123.8 (CH), 127.2 (CH), 127.5 (CH x 2),128.0 (CH x 2), (6).109 (11).107 (11),97 (22). 91 (l00). IH-NMR (300 MHz. 131.2 (C), 138.4 (C), 139.9 (C). CDCI ): 1.60 (m, IH). 1.79 (s. 3H). 1.83 (s, 3H). 2.05 (m. 2H), 3 Benzylpulegyl ethel: EI-MS [m/z (Ck )]: 244 (2), 229 (4), 153 (45), 2.30 (m. 2H), 4.10 (m, IH), 4.63 (ABq. J = 11.7 Hz, 2H). 4.79 138 (55), 91 (100),69 (43). IH-NMR (300 MHz, CDCI ): 0.91 (s. 2H), 5.59 (m. IH). 7.38 (m. 5H). 13C-NMR (75.47 MHz. 3 (m, 1H), 1.17 (d, J = 6.5 Hz, 3H), 1.56 (m, 2H), 1.70, (s, 3H), CDCU: 19.4 (CH ). 20.3 (CH ), 31.0 (CH ), 34.0 (CH ), 40.7 3 3 2 2 1.77 (m, 2H), 2.26 (m, 2H), 4.38 (ABq, J = 12.0 Hz, 2H), 4.43 (CH). 70.2 (CH 2). 77.7 (CH). 109.0 (CH2). 124.5 (CH), 127.3 (m, lH), 7.33 (m, 5H). 13C-NMR (75.47 MHz, CDCI ): 19.9 (CH), 127.4 (CH x 2). 128.2 (CH x 2), 135.3 (C), 138.9 (C). 3 (CH ), 20.4 (CH ), 22.2 (CH ), 25.2 (CH ), 26.9 (CH), 36.0 148.9 (C). 3 3 3 2 (CH ), 41.3 (CH ), 68.5 (CH ), 73.0 (CH), 126.2 (C), 126.7 (CH Benzyl citlVnellyl ethel: EI-MS [//1/z (7f;)]: 161 (3). 138 (14).137 2 2 2 x2),128.9(CHx2), 130.7(C), 139.9 (C). All ofthe compounds (9).95 (33),91 (l00). 81 (62). IH-NMR (300 MHz, CDCI ): 3 were liquid at room temperature, were miscible with a large 0.98 (d, J =6.5 Hz. 3H). 1.26 (m, 1H). 1.43 (m, lH), 1.50 (m. range of organic solvents (e.g., acetone, dichloromethane, etha­ lH), 1.68 (s. 3H), 1.74 (m, 2H), 1.77 (s. 3H). 2.06 (m, 2H), 3.58 (m, 2H), 4.56 (s. 2H). 5.19 (m, 1H), 7.4 (m. 5H). 13C-NMR nol, ethyl ether), and displayed limited water (cin­ methy1in has a water solubility of 63 mg L-I at 20 C (9». (75.47 MHz, CDCI ): 17.5 (CH ). 19.5 (CH ), 25.4 (CH J ), 25.6 3 3 3 Although toxicological experiments concerning the ethers were (CH ). 29.5 (CH), 36.7 (CH ). 37.1 (CH ). 68.6 (CH;). 72.8 3 2 2 not conducted, high mammalian toxicities would not be ex­ (CH2), 124.7 (CH). 127.3 (CH), 127.4 (CH x 2), 128.2 (CH x 2), 130.8 (C), 138.6 (C). pected, as none of the parent compounds are considered highly Benzylfenclryl ethel: EI-MS [//1/z (Ye)]: 153 (39), 136 (64),109 toxic (their respective acute oral LD50 (rat) values range from 1300 mg kg-I for pulegone to 4400 mg kg-I for fenchone (12» (25),91 (86).81 (00). IH-NMR (300 MHz, CDCI3): 1.16 (s, 3H), 1.20 (s, 3H). 1.25 (m, 2H), 1.27 (s, 3H), 1.60 (m, 2H), 1.80 and cinmethylin has a low toxicity (acute oral LD50 (rat) =4500 mg kg-I (9». Preemergence activity of benzyl ethers. When benzyl ethers were applied preemergence directly to the soil mixture. there were striking differences between the responses of the four species (Table 1). At the lower (0.1 kg ha-I) rate soybean emer­ gence was inhibited only by benzyl citronellyl ether, although the inhibition was the same at the higher (1.0 kg ha- I ) rate.

Benzyl Citronellyl Ether Several of the compounds suppressed soybean emergence at 1.0 kg ha-I , with benzyl pulegyl ether being the most inhibitory. Com emergence was suppressed by both rates ofcinmethylin, but only 1.0 kg ha-I benzyl fenchyl ether reduced emergence. The re­ sponses of wheat and velvetleaf were highly variable. Both rates of cinmethylin and 1.0 kg ha-I benzyl pulegyl ether treatment completely prevented wheat emergence, but of the other treat­ Benzyl Carvyl Ether Benzyl Geranyl Ether ments only the 1.0 kg ha-1 rate of benzyl carvyl and benzyl fenchyl ethers decreased emergence. Herbicidal activity of the compounds to velvetleafemergence was exhibited by the 1.0 kg ha-I benzyl citronellyl and benzyl fenchyl ether treatments and by both benzy1pulegyl ether treatments, with the 1.0 kg ha-I rate completely preventing emergence. Both rates of benzyl geranyl ether increased emergence. In these experiments, approximately ~ Benzyl Fenchyl Ether Benzyl Pulegyl Ether 60Ck of velvetleaf seeds germinated in nontreated controls, indi­ cating that at these levels the benzyl geranyl ether was stimula­ FiguTe 2. Chemical structures of benzyl monoterpene ethers. tory to velvetleaf germination and subsequent emergence.

Volume 44. Issue I

Table 1. Preemergence activity of benzyl monoterpene ethers on soybean. com. wheat. and velvetleaf.

Emergence 10 OAT ('it of control)"

Compound Rate Soybean Com Wheat Velvetleaf

kg ha- I

Cinmethylin 0.1 79 abc 22 c Od 110 abc 1.0 67 be 30 c Od 110 abc Benzyl carvyl ether 0.1 83 abc 79 a 100 ab 110 abc 1.0 71 be 87 a 79 c 124ab Benzyl citronellyl ether 0.1 63 c 100 a 88 abc 124 ab 1.0 63 c 83 a 104 a SOc Benzyl fenchyl ether 0.1 92 abc 91 a 100 ab 110 abc 1.0 100 a 48 b 83 bc 70 bc Benzyl geranyl ether 0.1 96 ab 91 a 104 a 151 a 1.0 83 abc 91 a 104 a 160 a Benzyl pulegy1 ether 0.1 92 abc 96 a 104 a 70 be 1.0 21 d 87 a Od Od

"Mean values within a species followed by the same letter are not significantly different at the 5'it level using Duncan's multiple range test. Each value represents the average of ten replications.

Seedling radicle elongation. Data concerning the elongation of Postemergence activity. At the dose applied, there was not a seedling radicles exposed to benzyl ethers are shown in Table 2. great deal of activity exhibited by any of the compounds, al­ None ofthe tested compounds were highly inhibitory to soybean though the benzyl pulegyl ether decreased both plant heights and radicle elongation, with only the higher rate of cinmethylin fresh weights of all four species (Table 3). Benzyl carvyl ether having any negative effect. For com radicle elongation, both decreased com height and fresh weight but had no effect on the rates of benzyl carvyl ether and benzyl citronellyl ether had other species. Several of the treatments (benzyl citronellyl and similar levels of suppression, although in two cases (benzyl benzyl pulegyl ethers) caused a slight chlorotic mottling on the geranyl and benzyl pulegyl ethers) radicle elongation was sup­ leaves. even in cases where no differences in height and fresh pressed to a greater extent by the 0.01 % (v/v) rate than by the weight were observed. The lack of postemergence activity by 0.1 % (v/v) rate. This could possibly be due to the compounds these compounds was not unexpected, as cinmethylin has not coming out ofsolution at the higher rate and thus not being taken been reported to exhibit postemergence activity at recommended up by the seedlings. With wheat, while several ofthe compounds rates (9, 17). decreased elongation, none were as inhibitory as cinmethylin, Due to the small number of compounds tested, few conclu­ which was equally effective at both rates. In contrast, velvetleaf sions can be made about the relationship ofherbicidal activity to radicle elongation was unaffected by the cinmethylin treatments chemical structure. A recent study suggested that caution should but was depressed by both benzyl pulegyl ether treatments and be exercised when assessing bioassay results and predicting field the high rates of benzyl citronellyl and benzyl fenchyl ethers. activity from lab results (13). The difficulty in synthesizing and

Table 2. Effect of benzyl monoterpene ethers on seedling radicle elongation.

Radicle elongation ('it of control)"

Rate Soybean Com Wheat Velvetleaf

'it vlv

Cinmethylin 0.01 88 bcd 30 g 15 g III ab 0.10 76 d 41 fg 13 g 105 abc Benzyl carvyl ether 0.01 100 abc 68 de 94 b 93 c 0.10 110 a 72 de 80 cd 93 c Benzyl citronellyl ether 0.01 113 a 57 cf 90 bc 96 be 0.10 80cd 62 de 30 f 22 f Benzyl fenchyI ether 0.01 96 abcd 102 bc 96 ab 116 a 0.10 92 abcd 117 ab 97 ab 74d Benzyl geranyl ether 0.01 108 ab 82 cd 108 a 108 abc 0.10 104 ab 126 a 56 e 96 bc Benzyl pulegyI ether 0.01 113 a 69 de 70d 63 d 0.10 99 abc 115 ab 50 e 37 e

"Mean values within a species followed by the same letter are not significantly different at the 5% level using Duncan's multiple range test. Each value represents the average of ten replications.

10 Volume 44. Issue I (January-March) J996 WEED SCIENCE Table 3. Effect of po'!emergence treatments of 1.0 kg ha- I benzyl monoterpene tained an alcohol group (citronellol, geraniol) or a keto group ethers on plant height and fresh weight. (carvone, fenchone, pulegone) which was converted to an ether Plant Fresh linkage in producing the modified compounds, Perhaps these Compound height" weight groups are important to their activity, as cinmethylin has a second 0/< of control ether moiety directly on the monoterpene ring in addition to the benzyl-ether linkage. Synthesis of other benzyl ether analogues Soybean Benzyl canyl ether 98 a 100 a in which a second oxygen function remains attached to the Benzyl citronellyl ether 107 a 110 a monoterpene ring (such as cinmethylin) would indicate if this is Benzyl fenchyl ether 101 a 101 a essential for herbicidal activity, Benzyl geranyl ether 99 a 103 a Benzyl pulegyl ether 68 b 61b Corn Benzyl can'yl ether 88 b 82 bc ACKNOWLEDGEMENT Benzyl citronellyl ether 101 a 104 a Benzyl fenchyl ether 100 a 98 a The authors wish to thank Dr. David Weisleder for obtaining Benzyl geranyl ether 101 a 100 a NMR spectra, Benzyl pulegyl ether 78 c 71 c Wheat Benzyl carvyl ether 101 a 102 a Benzyl citronellyl ether 97 ab 103 a LITERATURE CITED Benzyl fenchyl ether 100 a 100 a I, Alsaadawi. I. S" M. B, Arif, and A. J Alrubeaa, 1985, Allelopathic effects Benzyl geranyl ether 93 b 96 b of Citrus aurantium L II. Isolation. characterization. and biological activi­ Benzyl pulegyl ether 93 bc 95 b ties of phytotoxins, J. Chem. EcoL 11 :1527-1534, Velvetleaf 2. Asakawa. Y. R, Matsuda, M, Tori. and T. Hashimoto. 1988, Preparation of Benzyl carvyl ether 109 a 107 a biologically active substances and animal and microbial metabolites from Benzyl citronellyl ether 104 a 99 ab menthols, cineoles and kauranes. Phytochemistry 27:3861-3869, Benzyl fenchyl ether 97 bc 97 b 3, Asplund. R. 0, 1968, Monoterpenes: Relationship between structure and Benzyl geranyl ether 91 c 97 b inhibition of germination, Phytochemistry 7: 1995-1997, Benzyl pulegyl ether 65 d 86 c 4. Duke, S. O. 1991. Plant terpenoids as pesticides. Pages 269-296 in R. "Mean values in a column within a species followed by the same letter are EKeeler and A. T, Tu. eds, VoL 6. Toxicology of Plant and Fungal Com­ not significantly different at the 50/< level using Duncan's multiple range test. pounds, Marcel Dekker, Inc., New York. Each value represents the mean of ten replications. 5, Elakovich. S. D, 1988. Terpenoids as models for new agrochemicals. Pages 250-261 ill H. G, Cutler. Ed, Biologically Active Natural products: Potential Use in Agriculture. Am. Chem. Soc" Washington. DC. 6. EI-Deek. M. H. and E D. Hess. 1986. Inhibited mitotic entry is the cause of growth inhibition by cinmethylin. Weed Sci. 34:684-688. purifying large quantities of the benzyI ethers prevented us from 7. Fischer. N. H. 1986. The function of mono and as plant examining more plant species orperforming field tests. Although germination and growth regulators. Pages 203-218 in The Science of the limited number of rates tested in this study make it difficult Allelopathy. John Wiley & Sons, New York. 8. Ikawa. M.• S. P. Mosley. and L J. Barbero. 1992. Inhibitory effects ofterpene to discern clearly differences between the benzyl ethers, it ap­ alcohols and aldehydes on growth of green alga Chlorella pyrenoidosa. J pears that some changes in both herbicidal activity and selectiv­ Chern. EcoL 18:1755-1759. ' ity occurred relative to the parent monoterpenes. We had 9. May.J w..J. R. Goss.J. M. Moncorge,andM. W. Murphy. 1985. SD95481 previously found that there was a strong correlation between the a versatile new herbicide with wide spectrum crop use. Proc. Br. Crop Protect. ConL 12:265-270. presence of an oxygen function (i.e., an alcohol, aldehyde, ether 10. Muller. C. H.. W. H. Muller. and B. L Haines. 1964. Volatile growth or ketone group) and activity (16), which is supported by evi­ inhibitors produced by aromatic shrubs. Science 143:471-473. dence from other studies (2, 3, 14). While small-seeded species 11. Muller. W. H. and C. H. Muller. 1964. Volatile growth inhibitors produced were generally more sensitive to monoterpenes than large­ by Salvia species. BulL Torrey Bot. Club 91 :327-330. 12. National Institute for Occupational Safety and Health. 1978. Registry of seeded species, obvious differences between the responses of Toxic Effects of Chemical Substances. R. J. Lewis. ed. United States grasses (monocots) and broadleaved (dicots) plants were not Government Printing Office. Washington, D.C. 1363 pp. evident (16), From the limited number ofbioassay species tested 13. Northam. E E. and R. H. Callihan. 1994. Interpreting germination results against the benzyl ethers, it does appear that their selectivity is based on differing embryonic emergence criteria. Weed Sci. 42:474-481. 14. Reynolds. T. 1987. Comparative effects of alicyclic compounds and qui­ more closely associated with seed size rather than whether it is nones on inhibition of lettuce fruit geITtJination. Ann. Bot. 60:215-223. a grass or broadleaf. The benzyl pulegyl ether was particularly 15. Vaughn. S. E and G. E Spencer. 1991. Volatile monoterpenes inhibit potato inhibitory when applied preemergence to the small-seeded spe­ tuber sprouting. Am. Potato J. 68:821-831. cies (wheat, velvetleaf), although it had little or no effect on the 16. Vaughn. S. E and G. E Spencer. 1993. Volatile monoterpenes as potential parent structures for new herbicides. Weed Sci. 41: 114-119. large-seeded species (corn, soybean), All of the parent monoter­ 17. Weed Science Society of America. 1989. Pages 62-63 in Herbicide Hand­ penes used for chemical modification in this study either con- book of the Weed Science Society of America. WSSA. Champaign. IL

Volume 44. Issue 1 (January-March) 1996 11