Compost for Plant Disease Control

8/3/2019 Compost for Plant Disease Control

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PESTICIDE REDUCTION STRATEGYUSNGCOMPOSTFOR PLANT DlSEASE.CONTRO1

Working on farmsand a t sciencecenters across thenation,researchers aredocumenting therole of compost inprotecting cropsfrom pestswi thou t the useof chemicalagents.Gene LogsdonOhio States Fritz Schmitthenner(left), Sally Miller (middle) andHarry Hoitink (right), have beenexperimenting with compostsdisease suppressive attributesin field crops (above) and in thegreenhouse.BIOCYCLE

RDUCING the amount of pesti-cides used in food production ha sbecome a major objective of agri-cultural policy. Following a re-port by the NationalAcademy ofSciences that stressed dangersfDesticide residues on vegetablesand fruits t o children, federal agen hes an-nounced a coordinated effort to reduce chem-ical applications and develop safer alterna-tives. Compost could well play a significantrole in fulfilling these goals.Scientific research inOhio, Florida, Penn-sylvania, Alabama an d elsewhere is provid-ing almost unbelievable but undeniable ev-idence that compost can effectively replacepar t or in some cases all of the fumigants andfungicides used on some food crops. In oneof our more startling experiments, composta l lbu te l imina te d a funga ld isease ,macrophomima, from a crop of gourmetbeans highly susceptible to it while in near-by untreated plots the disease was severe,says Dr. Herbert Bryan a t The University ofFlorida Research Center in Homestead. Itreally was hard tobelieve.The science of implementing the potentialof compost to suppress plant diseases ishardly 20 years old, with the first practicalproven results achieved by Dr. HarryHoitink, professor of plant pathology at OhioStat e University in the late 970s and early1980s. Working at th eOhio Agricultural Re-search andDevelopment Cen ter of the OhioState University in Wooster, he discoveredtha t when compost was used in pottingmix-es it all buteliminated damping off and root

rot diseases caused by soilborne plantpathogens. Fungicidal drenches of pottingmixes were all but eliminated. This discov-ery led to a breakthrough in thegreenhouseindustry (see B i o C y c l e , J a n u a r y 1990)Those truckloads of fum igants such asmethyl bromide that nur sery men used tohave to buy are all behind us now, saysHoitink. Not only are there ignificant sav-ings in using compost to replace them andpeat, but the environment is a lot safer forthose who work there .A few dedicated scientists, working with-out fanfare, are now busily trying to workout the right techniques to make diseasesuppression induced by compost as practicaland predictable in field crops as it is ingreenhouse culture. Although th e work isonly in its infancy, researchers say the re-su lts are romising enough o justify contin-uing efforts.Here areome of the highlights of researchin compos t disease suppres sion now inprogress:Woods End Research Laboratory, a soiland compost consulting service headquar-tered inMt. Vernon, Maine, as been exper-iment ing successfully with the disease sup-pressive power of compost for several years .We have now achieved some dramatic re-sults in Pennsylvania alfalfa fields, saysWill B rinton, president of the company.Dairymen have been seeing decline in al-falfa vigor which they call clover tiredness.Our research suggests complex of root dis-eases leading to nutrient disorders as thecause, and we wanted to see whatffect com

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Agriculture mus tpay closer attentionto the myriad ife ofthe soil- heunnumberedmasses ofmicroorganismswhich can provide ahealthy repositoryof soil for foodproduction. Toignore the vastpotential involved isan environmentalinsult.

post would have in solving the problem. Af-ter four years of applying high quality com-post to declining alfalfa fields, we doubledthe thickness of the stand andherefore theyield of roughage. Whats more, the compostacted indirectly as an herbicide because theincreased vigor of the alfalfa root and stemgrowth crowded out theweeds. We believe itwas more than just a matter of shading.With compost applications, the alfalfa rootsbecome vigorous and theweed roots decline.OHIO STATE RES EARCH

Using compost at 40 tons per acre, Dr.A.F.(Fritz) Schmitthenner t Ohio State, hascontrolled P h y t o p h t h o r a rot in soybeans.Schmitthenner, one of the worlds foremostauthor ities on the plan t disease, became in-terested in ompost after experience led himto believe that pure chemical control was notgoing to work on Phytophthora and the newno-tillage methods coming into vogue only n-creased its incidences in heavy clay soils.Hedoubts, however, whether compost alonewould solve he problem even if enough com-post became available to trea t all affectedsoybean acreage. What we willprobably endup with is a combination of controls: plant re-sistance, soil management techniques, com-post, maybe some fungicides, says Schmit-thenner. One things for sure: Phytophthorais a very serious and vicious disease in someof its strains.The one that attac kspumpkincan reduce a fully grownfruit to a little lumpof rind in shortrder.A combination of P h y t o p h t h o r a controlmethods is whatDr. SallyMiller, a colleagueof Schmit thenner andHoitink, is studying inher experimental pepper plots at the OhioState University Muck Farm Branch nearWillard, Ohio. The Phytophthora strain thatattacks pepper plants can kill them in dayor two. She is omparing yard waste ompostat 40 ton per acrerates to the culturalrac-tice of hilling the plan t rows, along with orwithout the use of a fungicide, Ridomil, tosee which one-practice or combination ofpractices is most effective. Its too early totell much yet, she sa id in early July whenBioCycZe visited the plots. The pepperplants grown in a commercial compost mix(originally formulated by Hoitink) were cer-tainly more vigorous than the othe rs when

we set them out over a month ago but thatdifference is not as apparentnow. Phytoph-thora is us t beginning to appearn the lots.Well know more afte r harvest.My feeling atthis point is that hilling the plants alongwith composting will be bett er than eitherpractice alone.Hilling prevents water from standing onthe soil surface around the plant. A tinypuddle makes a great swimming hole forPhytophthora zoospores, says Schmitthen-ner. If the puddle lasts only 15 minutes,thats enough or a many-fold increase in thorganisms. Then they can migrate to theplant roots and infect them with in anour.The compost could help at least physical-ly by increasing soil porosity which in turnwould eliminate standing water faster, Miller. Also with hilling, we can mechani-cally concentrate the compost right into theplant area where its most needed. The mi-croflora in compost supports Phytophthoraas well.COMPOST MULCH STUDIES ON FLORIDA FARM

We experienced a really horrible P h y -tophthora outbreak this year, says NancyRoe of the University of Florida who hasbeen working with Ted Winsberg on his pep-per farm nearBoynton Beach, Florida. Butsurvival rateswere definitely bet ter in pep-pers on a MSW compost mulch (43 percent),or on a n aged wood chip mulch (46 percent),than on white polyethylene (8 percent).Roe had previously experienced anotherinteres ting response to MSW compost in asimilar experiment with squash plants at -tacked by gummy stem blight and dampingoff diseases. Thirty six days aftereeding, 69percent of the squash standemained on thecompost mulch, 49 percent on the aged woodchip mulch, 24 percent on the dried sewagesludge mulch, and only 8 percent on thepolyethylene. Its importan t to stress thatthis was an experiment with mulches, cautions Roe. The compost was not worked intothe soil. I t is still to e determined how muchof the disease reduction is due to protectiveeffects of the compost and how much is re-lated to differences in the environment cre-ated by the mulches. The empe rature, mois-ture, etc. around and under polyethylenemay be more conducive to development ofthese diseases.INCREASED PLANT VIGOR

Dr. Herbert Bryan at the University ofFlorida (Homestead) has been studyingom-post and vegetable diseases for severalyears. I lways believed that heal thy plan tshould have built-in resistance to diseaseand my initial curiosity about compost wasto see f it would increase overall plant vigorto this end, says Bryan, In 1990, we con-ducted our first field tests with sludge com-post at five, 10 and 15 tons per acre rates.The first thing we learned was that withcompost we could cut fertilizer rates in alfand s t i l l ge t the same y ie lds . But theseedlings where ompost was applied did notgrow as fast at first. It appeared that the

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compost seedlings were developing a biggercluster of roots however and, after flowering,the plants stayed a rich green while theplants in oncompost plots paled s they us-tomarily do. This delayed action held trueright on through harvest: at the first har-vest, the noncompost plots yielded better ,but in the second and third harvests theom-posted plots outyielded the controls. Thegrower was not to o impressed with the com-post performance however because the firstharvest is thene th at brings the best price.But what caught Bryanseye was the ab-sence of bacterial spot lesions on the com-posted plants, while the uncompostedshowed about a 15 percent infection. Thatfed my curiosity t o try more controlled andfocused experiments.In his next experim ent, Bryan workedwith beans and peas using ompost applica-tion rates of from 36 t o 72 tons per acre. Onthe LaBelMSW gourmet beans, which areparticularly susceptible, he achieved almostcomplete control of macrophomima in thebeans as mentioned above. The disease wasonly slightly reduced where sludgead beenapplied. Yield in the omposted plots was l-most twice tha t of the untreated plots, saysBryan. The sludge treated plots were com-parable to the untreated plots.After the bean crop, Bryan planted black-eye peas (California Blackeye No. 5) whichmade better s t a d s , greener foliage, tallerheight and more than twice the yield in theMSW compost plots compared to either thesludge treated or untreated plots, saysBryan. Rhizoctonia severely affected rootsin untreated and sludge treated areas, hesays, but disease was reduced 0 percent inthe areaswhere the highest ratesf compostwere applied and 40 percent where the in-

term-ediate rates were applied. The controlplots yielded 75 bushels per acre, the com-post plots 200 bushels per acre.In yet another experiment conducted by agraduate student studying plantesponse t ovarious compost ra tes atdifferent irrigationrates, an unexpected resu lt occurred. SaysBryan: Where ompost was used even with-out a fumigant, there was a significant re-duction in rootknot nematode, somethingthat might have gone unnoticed were it notfor the fact tha t this Ph.D. candidate has abackground in nematology.MATURE COMPOST AND TOMATO CROPS

Dr. Tom Obreza, asoil and water scientistat theSouthwest Florida Research nd Edu-cation Center in Immokalee, says he is en-couraged enough y first year resu ltsf com-posts disease suppression t o continue hisexperiments. When we applied dried andpartially composted sewage sludge to atomato field in Dade County, primarilyo seewe could get by with less irrigation, earlydisease was significantly less th anwhere no compost was used, he says. In asecond go around with that experiment, wen into bacterial leaf spot, but infectionslower in the ompost treated plots. So Idecided t o get serious about experimenting

specifically in disease suppression.Last October, he grew tomatoes in com-posts from several different commercialsources and compared them all to controlplots treated with the usual fertilizers. Atleast one of the composts, he later realized,was not mature, the factor that compost sci-entists increasingly believe is critical t o ef-fective results. Where composts were ma-ture, plant rowth just took of f from the verybeginning. Where it was not, growth wasslow and early yields noto good. But the sit-uation completely reversed itself when theplots were planted t o a second crop. Thenwhere th e imm ature composts had finallymatured, the plants fairly leaped out of theground. I assume this was partially becausethe compost was sucking nitrogen awayromthe plants when it was immature, but afterseveral months all th at nitrogen was avail-able for the plants. In general, it appearsthat compost, and especially mature com-post, allows the grower t o cut standard fer-tilizer application rates by at least a thirdwithout negatively affecting yields.There were no disease problems in any ofthe plots except or one interesting incident.We had a little invasion of rootknot nema-tode in one corner of the field. The infectionwas evident in the plants right up t o th ecompost treated plots and stopped rightthere. The difference was as plain as nightand day. Diseased plants on one side, plantsgrowing vigorously on the other. Obrezadoesnt know why, but he intends t o repeatthe experiments again next year. We canmeasure the hydrologic benefits of compost- he wate r conserving propert ies it pro-vides by increasing soil porosity and waterand nutri ent absorption- ut disease sup-pression is anew ballgame, a t least for me.APPLICATIONS OF MSW COMPOST

Dean Richardson a t Reuter Recycling Inc.in Pembroke Pines, Florida, has suppliedcompost for some of the Florida experimentsand has een conducting is own research aswell. We have gained a reduction inmosaicvirus spread by white fly, and in control ofcrown rot in tomatoes, a real problem inFlorida, he says. The most dramatic s ightIve seen was rom an airplane over a field in-fected with Rhizoctonia root rot. This disease

In some Florida research, MScompost (facing page) hasbeen appliedwith a custombuilt spreader (above).

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Not only are thersignificant savingsin using compostreplace fumigantsand fungicides, butthe greenhouse snow a ot safer forthose wh o wo rkthere.

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ompost actedindirectly asanherbicide becausethe increased vigorof the alfalfa rootand stem growthcrowded out theweeds.

spreads sometimes in almostperfect circles,and from the air hows up learly. But wherecompost had been app lied in strips, therewere straight green lines of healthy plantsright through the diseaseings.Whats more, he continues, we areachieving some effective weed suppressionby mulching MSW compost two t o threeinches thick around papaya. We are in factnow thinking aboutMSW compost mulch asa possible replacement for plastic.REDUCTION IN WEED GRASSES

Dr. Jim Edwards, a SDA soil scientis t a tthe National Soil Lab in Auburn, Alabama,has been experimenting with farmland ap-

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plications of MSW and composting it insitu, as he puts it.When he uses mixturecontaining newsprint, he gets a noticeablreduction in weed grasses in orn and cottonIn the first year f work, Edwards observestun ting in crop plants as well as reductioin grassy weeds but the stunting did no treappear theollowing year. We are not positive yet s t o the cause, though it appeabe that the MSW, turning t o compost, immobilized the nitrogen available for p lanlife, says Edwards. But we increased organic matter content rom about one perct o 1.8 percent and in subsequent applica-tions, there wa s no stunting of crop plantswhile reduction of weed grass germinationcontinued. Ive duplica ted the experimentwith the same resul ts. ts no fluke.He is now conducting various experimento find out why. If we can reduce nd replacherbicides with a resource we have beenprone t o calling waste, that would surely ban accomplishment, he says. (See Dr. Edwards report, Applying Organics t o Agricultural Land, in this issue.)A N I M P O R T A N T F R O N TI E R

Hoitink believes compost science, and infact the whole science of soil microbiologwhich holds the secrets t o composts actionis barely in its infancy, a frontier which scentis ts will continue t o push back with accomplishments that can scarcely be dreameof today. There is some interesting newwork being tried using oliar applications owater extracts from compost to control fungal diseases, he says, a sortf modern scentific application of the traditional use ocompost tea by organic gardeners. It appeathat such liquids can induce protection bumuch work needs to be done and potent iaproblems resolved. Obviously if you ad a ecal problem in the tea, foliar applicationwould be a great way t o spread it. Also, yocant control mycotoxins this way, and (foexample , aflatoxin on peanuts) these toxinaremore angerous han ungicideresidues.He is also excited by cultural practices hobserved in Brazil l ast year . Those who believe composting is not practical for largacreages would find Brazil interesting. I visited a sugar cane farmf some 150,000acrewhere the bagasse [stalkseft after harveswas composted and applied back on the lanEvery acre got a treatm ent once every fivyears with 15 percent increases in yield.Some of that increase is apparently dueosuppression of dise ase organi sms. Cornstover is baled, composted in the bale analso returned t o the farmland.Hoitink believes that agriculture in theuture must pay closer attention t o the myrialife of the soil: the unnumberedmasses of mcroorganisms which, inompetition with eaother, canprovide a healthy epository of sofor food production. We are learninghow tmanipulate thepopulations of these microorganisms to achieve plant protection more oless naturally. To ignore the vast otential involved isn environmental insult.OCTOBER99

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Compost for Plant Disease Control