PROPYLENE OXIDE, A SOIL STERILANT WITH POTENTIAL AS A REPLACEMENT FOR METHYL BROMIDE

Transcription

1 PROPYLENE OXIDE, A SOIL STERILANT WITH POTENTIAL AS A REPLACEMENT FOR METHYL BROMIDE Jack A. Norton, Ph.D., Manager, IR-4 Methyl Bromide Alternatives Program INTRODUCTION: Propylene oxide (PPO) has the potential of being the most versatile agricultural fumigants under development as an alternative to Methyl Bromide. It is EPA-registered for control of stored pests in spices, in-shell nuts, nutmeats, cocoa, and cocoa beans, and as will be shown below, propylene oxide has shown good potential when applied to the soil for control of soil borne diseases, nematodes, and weeds. This product is one of few products that would not rely upon chloropicrin for broad spectrum control of soil pests. Because of its chemical and physical characteristics buffer zones should be minimal if needed at all, a factor limiting the use of most registered soil applied fumigants. Propylene oxide is a product with an excellent safety profile as is supported by the fact that it has been used as a post-harvest fumigant for over 35 years and with no reported incidences of adverse effects to fumigators or others. It has been shown to convert to propylene glycol (GRAS status by FDA) in water making it quite safe as a soil applied product. Also, in the unlikely event PPO was consumed by man, it would rapidly convert to propylene glycol at the ph in man s stomach (1,2). Many field research trials have been run with PPO where it was evaluated in direct comparison to methyl bromide/chloropicrin (MB/PIC) in areas where growers have relied on MB/PIC as a crop production tool for several years. These trials used MB/PIC as the standard, generally applied by shank injection at lbs ai per treated acre. The tests compared the standard and the PPO treatments to an untreated control (UTC) in all tests. Most rating criteria were efficacy against the plant pest complexes comprised of one or more plant parasitic nematodes, phytopathoenic fungi, and both annual and perennial weed species. Most trials also provided full season commercial yield data. In some early tests with PPO where the product was unnecessarily applied in combination with metam sodium for weed control, or when it was shank-injected too shallow for effective residual control, the data from these trails are not included in this summary because of mixed and scientifically compounded results. These reports will be made available by ABERCO upon request.

2 -2- The purpose of this report is an attempt to compile the field research and laboratory data collected to date across all crops and based on the data compilations draw statistically supportable conclusions on the usefulness of PPO as an alternative to MB/PIC. The report summarizes the data by crop. Most of the available data are from trials run in strawberries and tomatoes but some trials were run in multiple mulched vegetable crops. A few were conducted in ornamental bulb crops and the perennial crop, walnuts ( Carpathian spp.) against some of the replant disorder causal agents, plant parasitic nematodes. Since the use of fumigants in the crops that have relied on MB/PIC is similar from crop to crop and in many cases the pests affecting the production of those crops are the same, the conclusions drawn on one crop can be used for other crops having similar cultural practices and pest spectra (e. g. tomato data should also support conclusions for peppers, eggplants, and other mulched vegetables). Likewise, pest control data from ornamental bulbs and from grapes should be useful for conclusions drawn for vegetables and strawberries if the use of the PPO and the MB/PIC in these tests is the same as for vegetables and strawberries and if the pests are the same. Below is a table which summarizes the crops, rates of application and methods of application studied with PPO over several years of field investigation. Following this table will be a test-bytest summary of each test showing the efficacy of PPO in direct comparison to MB/PIC and UTC. Refer to the individual report summaries for comments concerning pest pressures. For the tests summarized in this report, means are separated statistically using analysis of variance (ANOV) at the 0.05 level of probability. Means followed by common letters are statistically the same.

3 -3- Table 1. Results comparable to or better than commercial standards, including Methyl Bromide in most trials Pages in Crop Dose Range (Gal/A) Primary Pests /Loc. Methods of Applic. Report Strawberry Root Nibbling Fungi -CA Drip Tapes 4-5 Tomato Root Knot Nematode -FL Drip Tapes 6-7 Tomato 45 Fusarium oxysporum-fl Shank Injection 8 Tomato 45 Ralstonia spp. -FL Shank Injection 8 Tomato 45 Belonolaimus spp. -FL Shank Injection 8-9 Tomato 45 Tylenchorhynchus spp, -FL Shank Injection 9-10 Tomato 60 Annual Weeds -NC Drip Tapes 11 Tomato 60 Annual Weeds -NC Shank Injection 11 Cantaloupes 60 Annual Weeds -NC Shank Injection 11 Gladiolus 30 Torpedograss -FL Shank Injection 12 Gladiolus 30 Evening Primrose -FL Shank Injection 12 Gladiolus 30 Pigweed -FL Shank Injection 12 Gladiolus 30 Dollar Weed -FL Shank Injection 12

4 -4- DATA SUMMARIES Strawberries Driscolls Strawberry Associates, Watsonville, CA , Dr. Mansun Kong PPO gal per treated acre---38,180a gm/plot total yields MB/PIC lbs ai per treated acre---38,630a gm/plot total yields UTC ,481bc gm/plot total yields Notes: Pest spectrum comprised of root nibbler fungal complex comprised mainly of Pythium spp., Rhizoctonia spp. and Cylindrocarpon spp. Conclusion: PPO applied by drip irrigation at 30 gal per treated acre in 1.5 acre inches of water controlled the fungal complex as well as the MB/PIC standard and provided strawberry yields statistically equal to the MB/PIC standard in this test. Driscolls Strawberry Associates, Watsonville, CA , Dr. Mansun Kong PPO gal per treated acre ,900bc gm/plot total yields PPO gal per treated acre ,665cd gm/plot total yields MB/PIC lbs ai per treated acre-- 37,415cd gm/plot total yields UTC ,625d gm/plot total yields Notes: Same pest spectrum as above for Conclusion: PPO applied by drip irrigation at 20 and 30 gal per treated acre in 1.5 acre inches of water controlled the indigenous fungal complex as well as the MB/PIC standard and both rates provided yields statistically equal to the standard MB/PIC treatment in this test.

5 -5- Driscolls Strawberry Associates, Watsonville, CA , Dr. Mansun Kong PPO gal per treated acre ,301a gm/plot total yields PPO gal per treated acre ,397a gm/plot total yields MB/PIC lbs ai per treated acre ,887a gm/plot total yields UTC ,276bc gm/plot total yields Note: Same pest spectrum as above for 2002 and Conclusion: PPO applied by drip irrigation at 35 and 45 gal per treated acre in 1.5 acre inches of water controlled the indigenous fungal complex as well as the MB/PIC standard and both rates provided yields statistically equal to the standard MB/PIC treatment in this test. Driscolls Strawberry Associates, Watsonville, CA , Dr. Mansun Kong PPO gal per acre ,134 a gm/plot total yield PPO gal per acre ,383 a gm/plot total yield MB/PIC Not included in 2005 UTC ,596 a gm/plot total yield Note: Same pest spectrum as above for Conclusion: A non-conclusive test. There were no statistical differences between the UTC and any of the fumigation treatments due to an unusually warm winter and under chilling of the strawberry plants. This caused sporadic yield responses across the field and as a consequence the differences between treatments could not be separated statistically.

6 /2002 IR-4 Strawberry Trial, Salinas, CA---Plant Sciences, Inc, Watsonville, CA PPO gal per treated acre--- 2,598 ac crates marketable yield per acre MB/PIC lbs ai per treated acre---- 2,524 ad crates marketable yield per acre UTC ,156 ef crates marketable yield per acre Note: Same pest spectrum as in the Driscolls tests. Conclusion: PPO shank injected into pre-formed beds at 30 gallons per treated acre (10-12 inches deep, 2 shanks per 26 inch bed) controlled the root nibbling fungal complex in this test and as a consequence provided marketable yields statistically comparable to the yields in plots treated with the MB/PIC standard 350 lbs ai per acre shank injected treatment. Tomatoes W. Ralph and G.T. Khair, Plant Quarantine Research Station, Canberra, A. C. T. This was a laboratory study that showed the importance of soil concentration and resident fumigation time on the activity of PPO against rootknot nematode (Meloidogyne hapla Chitwood). These researchers showed that when PPO was applied at rates of 0.5 and 3.5 ml/l of soil and exposure periods varied from 5 to 30 minutes that there was a gradual decrease in hatch of nematode eggs as exposure time increased, with complete inhibition of hatch at both rates after 30 minutes. Newly hatched rootknot nematode larvae were quickly killed when exposed to either rate of PPO. Galling of tomato indicator plants (tomato cv. Grosse Lisse) was not evident when a 2 day aeration period was observed at air concentrations above 0.28 ml/l.these researchers concluded that PPO has many attributes of a good soil fumigant: it has good penetration, a boiling point of ~ 35 C (which makes sealing of treated soil with plastic film important) and it is both fungicidal and strongly ovicidal and larvicidal against M. hapla. They commented that further study of PPO in field situations is warranted. PPO Conc. No. Larvae Galling of Tomatoes Galling of Tomatoes (ml/l air) Mean Count After 2 Days Aeration After 14 Days Aeration

7 -7- J. W. Noling, J. P. Gilreath, and E.R. Rosskopf, University of FL, Lake Alfred and Bradenton, FL, and USDA ARS, Ft. Pierce, FL, respectively. Alternatives to Methyl Bromide Field Research Efforts for Nematode Control in Florida. Fall 2000/Spring 2001 Drs. Noling, Gilreath and Rosskopf evaluated a number of potential MB/PIC alternatives for tomatoes in micro plot studies in FL in the fall of 2000 and the spring of The alternative fumigants, propargyl bromide ( lbs ai per acre), Telone II (12 gal / acre), Telone C17 (17 gal/acre), Telone C35 (26 gal / acre), Vapam (75 gal/acre), Basamid (400 lbs per acre), and PPO (50 and 75 gal / acre) were evaluated for control of the southern rootknot nematode (Meloidogyne incognita). Root gall severity at final tomato harvest was used as an indication of the effectiveness of the alternative fumigants for control of Meloidgyne incognita. In 2000 PPO at 50 gal/a was compared to Vapam at 75 gal/acre, Basamid at 400 lbs per acre, Propargyl Bromide at 100 lbs per acre, and two biological compounds Rezist and Messenger, both in repeated foliar applications. A Methyl Bromide standard treatment was not included in the 2000 study.root galling severity ratings on a subjective of 0-10 showed the low PPO rate to be equal to the Propargyl 100 lb per acre rate and superior to all other treatments. UTC a Vapam@75 gal per acre b Basamid@400 lb/acre b Propargyl Bromide@100 lbs/acre-----2c Rezist a Messenger a PPO@ 50 gal per acre c In 2001, the treatments compared PPO at 75 gallons per acre to a MB/PIC standard at treatment of 350 lbs ai per acre, Telone C35 at 26 gallons per acre, Propargyl Bromide at 120 lbs per acre, and the biological products Messenger foliar applications, and Armorex at 30 gallons per acre. Root galling severity ratings on the subjective 0-10 scale showed PPO to be equal to the best treatments in the test, including the MB/PIC standard. UTC a MB/PIC@ 350 lbs per acre b Telone gal per acre c Propargyl 120 lbs per acre c Messenger Foliar (Multiple Sprays) ab 30 gal per acre a 75 gal per acre bc

8 -8- Conclusion: PPO effectively prevented root galling of tomatoes caused by the southern rootknot nematode (Meloidgyne incognita) as effectively or better than the registered alternatives Vapam, Telone II, and Telone C35. In 2001, the year where PPO was compared to the MB/PIC 350 lb per acre treatment for tomatoes, PPO was as good as the standard in preventing galling of tomatoes caused by the southern rootknot nematode. James. P. Gilreath, University of Florida, Bradenton, FL. Spring 2003 IR-4 Fresh Market Tomato Trail, Bradenton. This test compared the efficacy of potential Methyl Bromide Alternatives, both EPA-registered and experimental. Light to moderate nutsedge (Cyperus rotundus and Cyperus esculentus) pressure prevailed at this test location. The fungal pathogen, Fusarium oxysporum, and the soil bacterium Ralstonia solanacearum, and the plant parasitic nematode, Belonolaimus spp. were also present in numbers high enough for meaningful ratings. TREATMENTS Fusarium oxysporum Ralstonia spp. Belonolaimus Wilt Incidence Wilt Incidence Population Weeks After Treatment lbs ai per acre b 2.5b 3.8b 0b 0b 0b 5b 45 gal per acre b 8.8b 8.8b 0b 0b 0b 3b UTC a 35.0a 35.0a 3.8a 8.8a 8.8a 15a Tomato Vigor and Yields/Spring 2003 Vigor (100% optimum) Yield (t/ ha) 350 lbs ai per acre a 26a 45 gal per acre a 23.5a UTC b 15.1b Conclusion: PPO applied by shank injection at 45 gallons per treated acre controlled the soliborne diseases Fusarium wilt and Ralstonia wilt as effectively as the MB/PIC standard in this test. This was also true for the plant parasitic nematode, Belonolaimus spp. This degree of pest control, even in the presence of light to moderate nutsedge pressure produced tomato vigor and marketable yields from the PPO treatment statistically equal to that of the MB/PIC standard in this test.

9 -9- James P. Gilreath, University of Florida, Bradenton, FL. Fall 2003 IR-4 Fresh Market Tomato Trial, Bradenton. This test was similar to the one run in the spring of 2003 in terms of treatments but the pest populations were quite different. In this test Cyperus spp levels were moderate to high and the other economic pests were the two plant parasitic nematodes, Tylenchorhynchus spp. and Belonolaimus spp. Treatments Tylenchorhynchus Belonolaimus Cyperus Density Population Population (WAT) 11 WAT 11WAT lbs ai/a b 0 b 0.0 b 0.8 b 2.0 b 3.3b 45 gal/a b 0 b 2.6 a 17.5 a 29.2 a 29.6a UTC a 31 a 8.6 a 39.6 a 53.2 a 52.0a Tomato Vigor and Yields/Fall 2003 Vigor(100% optimum) Yield (t/ha) 350 lbs ai per acre a 39.6 a 45 gal per acre a 30.8 a UTC b 16.4 b Conclusions: The PPO treatment suppressed but failed to control a moderate population of Cyperus spp. as effectively as the MB/PIC standard in this test. Control of the two nematode species (Tylenchorhynchus spp. and Belonolaimus spp.)from PPO was excellent and statistically the same as that given by the MB/PIC standard. Tomato vigor and tomato yields in the PPO treatments were numerically less than in the MB/PIC treatment but statistically the same. This suppressant effect on the nutsedge instead of acceptable control probably affected the tomato vigor and yield. Subsequent studies have shown that the 45 gal per acre rate for PPO is not acceptable for optimal control of Cyperus spp. Rates of 45 gal per acre or less for PPO should be supplemented with a nutsedge herbicide that can be used selectively in the crop. Rates of 80 gallons or higher is needed for control of nutsedge according to results from follow up studies in FL (see below).

10 -10- James P. Gilreath, University of Florida, Bradenton, FL. Spring 2004 IR-4 Tomato Trial. Bradenton. This test compared the same treatments as in the spring and fall 2003 IR-4 trials but the pest spectrum and the pest pressures were different. Nutsedge (Cyperus esulentus and Cyperus rotondus) pressure was very heavy as was the incidence of Fusarium oxysporum wilt. The plant parasitic nematode, Tylenchorhynchus spp was present in numbers great enough for meaningful ratings but the pressure was relatively light. Treatments Fusarium oxysporum Tylenchorhynchus Cyperus spp. Wilt Incidence Population Density Weeks After Treatment lbs ai per acre b 11.0b 11.5b 3.0b 29.9 b 45 gal/a a 25.0a 39.0a 8.0b 79.8 a UTC a 40.0a 49.0a 18.0a a Tomato Vigor and Yield/ Spring 2004 Vigor (100 % Optimum) Yield (t/ha) 350 lbs ai per acre a 19.8 a 45 gal per acre b 8.6 b UTC b 1.7 b Conclusions: The results from this test bear out the importance of using an alternative herbicide that controls nutsedge if rates of 45 gal PPO or less are used under heavy nutsedge pressure, and in this test, under heavy Fusarium wilt pressure. Numerically, there was evidence of a suppressant effect on Cyperus spp. and on Fusarium oxysporum in this test but control was not statistically equal to the MB/PIC 350 lb per acre treatment. Lack of optimal control of nutsedge and Fusarium wilt from the PPO treatment resulted in tomato plant vigor and marketable tomato yields that were inferior to that obtained in the plots treated with MB/PIC.

11 -11- James P. Gilreath, University of Florida, Bradenton, FL, Spring 2004, Effects of Propozone on Nutsedge Densities and Marketable Tomato Yields. Treatments Nutsedge Plants per 70 sq. ft. Total Marketable Yield (Kg/ 15 plants) UTC 542 a 17.1 c PPO 20 gal/a 568 a 40.4 b PPO 40 gal/a 477 a 45.9 b PPO 60 gal/a 430 a 46.2 b PPO 80 gal/a 117 b 69.6 a PPO 100 gal/a 35 b 58.9 ab PPO was shank injected in this test at multiple rates and compared to an untreated check to assess nutsedge control (mixed population of Cyperus rotundus and Cyperus esculentus) and harvestable tomato yields. Conclusions: Nutsedge was severe in this test and as evidenced by the high numbers of plants in the UTC. PPO failed to reduce nutsedge numbers significantly until 80 or 100 gallons of product per acre were applied. The highest tomato yields were obtained in plots treated at either 80 or 100 gallons per acre which reflects the reduced competition from nutsedge given by these high rates of PPO. Of interest was the significant yield increases given by the lower rates of PPO (20, 40 and 60 gal/a) compared to the UTC, indicating that even though nutsedge control was not good at these rates, PPO had a beneficial effect against some other pest not evaluated in this trial. Based on these results, PPO would need to be partnered with an acceptable nutsedge herbicide if used under heavy nutsedge pressure in tomatoes at rates less than 80 gal/a. Frank Louws, North Carolina State University, Raleigh, NC. Efficacy of Methyl Bromide Alternatives for Verticillium and Weed Management in Tomatoes and Cantaloupes, Note: With the exception of weed control ratings in tomatoes, differences between treatments for all other rating parameters were not statistically separated between treatments in the tests that included PPO. This included root galling ratings in cantaloupe and the incidence of Verticillium in tomatoes (MB/PIC, UTC, and PPO all statistically the same). As a consequence, the only data reported for PPO in this report are the weed control ratings made at three intervals following application ( PPO applied by shank injection at 60 gal per treated acre on June 1; Weed counts made on July 16, July 29, and August 19). Weeds were comprised of annual species, primarily various pig weed species (Amaranthus spp.)

12 -12- Treatments Weed Counts/ Plot July 16 July 29 August lbs ai per acre a 0.5 a 0.0 a 60 gal per acre (shank-applied) a 11.0 a 2.5 a 60 gal per acre (drip-applied) a 0.3 a 0.0 a UTC b 37.8 b 25.0 b Conclusions: PPO applied either by shank injection or in drip irrigation water at 60 gallons per treated acre provided full season control of annual weeds, primarily Amaranthus spp., equal to the MB/PIC shank-injected 400 lb ai per acre standard treatment. Gladiolus Cormels James P. Gilreath, University of Florida, Bradenton, FL. Methyl Bromide Alternatives for Gladiolus Cormels, Bradenton, FL, Note: The most value from this test was from the weed control data and on some weed species. It was of limited value because the weed populations were sporadic across the test area and this resulted in an inability to separate the results from the MB/PIC standard from the results in the UTC and other treatments. Treatments Weed Numbers Per Plot ~ 5 Weeks After Treatment Nutsedge Torpedograss Evening Primrose Pigweed Dollar Weed 350 lbs ai/a b 0.2 b 0.0 b 0.0 b 0.0 b 15 gal/a a 7.5 a 6.8 a 1.9 a 2.0 a 30 gal /A b 0.1 b 0.0 b 0.0 b 0.0 b UTC a 4.3 a 7.9 a 1.0 a 2.0 a Conclusions: This test provided little useful information because the weed pressure was light at the time the only weed control rating was made but it does show that 30 gallons per treated acre of PPO controls light weed pressures as well as the MB/PIC standard. The 15 gal per acre rate was ineffective even for control of the light populations of the annual weeds that were present. PPO should not be used at rates lower than 30 gallons per acre based on these results.

13 -13- Michael McKenry, University of California, Riverside. Field Application of Propylene Oxide by Shanks and by Drenching for Control of Plant Parasitic Nematodes in Walnuts (Carpathion spp.), Parlier, CA, PPO was applied by shank injection and by drenching at 330 and 500 lbs ai per acre in walnuts for control of one of the causal agents of re-plant disorder of perennial crops, plant parasitic nematodes. The PPO treatments were compared to an untreated control. MB/PIC was not included in these tests. Telone II at 332 lbs ai per acre was used as the standard in the test where PPO was shank-applied. The shank-applied treatments were tarped with standard plastic film as one test variable, and left without tarping as a second variable for these treatments. The depth of shanking was 20 inches, using a standard Methyl Bromide Rig. The drench treatments a total six acre inches of water ( ~ 165,000 gallons per acre) was used and the treatments went out over a period of 8 ½ hours. Treatments Nematode Control 45 Days after Treatment/Shanked-in Treatments Average Number 5 Depth % Control Telone 332 lbs/ A- Tarped a 100 a Telone 332 lbs/a-nontarped a 99.9 a 500 lbs/a------nontarped ab 89.4 ab 330 lbs/a------nontarped ab 85.9 ab 330 lbs/a------tarped ab 78.0 ab 500 lbs/a------tarped b 56.9 b UTC c 00.0 c Treatments Nematode Control 45 Days after Treatment, Drenched Treatments Average Number 5 Depth % Control 500 lbs/a, Drenched In a 64.0 a 330 lbs/a, Drenched In a 65.9 a UTC b 00.0 b Nematodes represented in samples: Root knot, Root Lesion, Stunt, Citrus, Stubby Root.

14 -14- Conclusions: A higher percentage of nematode control resulted in the shanked-in treatments of PPO compared to drenching but in both cases there was a significant reduction in plant parasitic nematodes compared to the numbers in the untreated controls. In the shanked-in treatments, PPO performed statistically as well as the Telone II standard at both rates where no tarp was used, but tarping might have caused a deleterious effect on PPO since the nematode numbers higher in the tarped plots compared to the nontarped PPO treatments. GENERAL OVERVIEW Propylene oxide has the potential of being an excellent replacement for MB with it s versatility of use (both post harvest as it is now registered and for future soil uses if registered), its broad spectrum pest control potential and its safety. Adding to its versatility is the fact that PPO may be applied either by shank injection or through drip-tapes for good control of soil borne pests. This product has been used many years as a post harvest fumigant and there have been no reported adverse effects to man from this use. It converts rapidly to propylene glycol (GRAS) and would not persist at ph levels in man s stomach Propylene oxide controls plant parasitic nematodes, fungal and bacterial plant diseases, and many weed species when applied within the rate range of gallons of product per treated acre. It controls Cyperus spp. (Nut sedges) at rates of gallons product per acre. Rates lower than this would require the use of a registered herbicide for full spectrum pest control if heavy pressure from Cyperus spp exists. Literature Cited 1. W. Meylan, et. al Chemical of Current Interest: Propylene Oxide, Health and Environmental Profile, Syracuse Research Corporation, Syracuse, NY. Toxicology and Industrial Health, Vol. 2, No. 3. P Todhunter, J Analysis of a Definitive Study of the Stability of Propylene Oxide in Human Gastric and Rat Forestomach Juice: Implications for Propylene Oxide and for Nature of Gastric Metabolites. Final Unpublished Report. EPA MRID #

15