RESEARCHQuestions and answers aboutbiostimulantsSuperintendents are often in the dark about the best ways to use biostimulants and whattypes of results to expect.

R.E. Schmidt, Ph.D.; E.H. Ervin, Ph.D.; and Xunzhong Zhang, Ph.D.

Several golf course superintendents haveexpressed some confusion about how todetermine the best way to incorporate bio-stimulant treatments in a turfgrass nutrientprogram. Our conversations were reminis-cent of a recent research article written by agood friend, who said that research is like agood mystery story (1). She indicated thatSherlock Holmes would have made a goodresearch agronomist, as he would thor-oughly understand the hazards of a rush tojudgment.

In ''A Scandal in Bohemia," Holmes tellsDr. Watson, "It is a capital mistake to the-orize before one has data. Insensibly onebegins to twist facts to theories, instead ofthe theories to suit facts." Some superin-tendents are much like Sherlock Holmes: Acultural practice becomes elementary onlywhen the facts are realized.

From the 10 years of biostimulant datathat we have amassed in field, greenhouseand laboratory studies, a number of factshave emerged. A biostimulant is an organicmaterial that, when applied in small quan-tities, enhances plant growth and develop-ment such that the response cannot beattributed to application of traditionalplant nutrients. Biostimulants also may bereferred to as "positive plant growth regula-tors," or as James Beard, Ph.D., recentlycoined, "metabolic enhancers."

Our research has documented thatapplications of biostimulants have condi-tioned turf grasses to tolerate environmentalstresses and improve grass growth, particu-

Root growth in drought-stressed L-93 creeping bent-grass treated with humic acid, seaweed extract or acombination of the two was signifcantly greater thanroot growth in untreated turf.

larly root development. Biostimulants havebeen shown to improve turf grass photo-chemical activity (an estimate of photosyn-thetic efficiency) and overall quality whenthe turf is subjected to low soil moisture,

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Biostimulants are organic materialsthat, when applied in small quanti-ties, enhance plant growth anddevelopment.

Seaweed and humic acid are thetwo most commonly usedingredients in biostimulants.

Superintendents should useindependent researcH.reportsto verify tHe efficacy of a commercialbiostimulant.

If. applied before stress occurs, bio-stimulants can help plantstolerate stress.

dollar spot, nontarget pesticide applications,nematode infestation, high soil salinity, highUV light intensity and heat.

How much and how often?How does a superintendent know how

much of which material to use? How oftenshould a biostimulant be applied? Thesequestions are difficult to answer becausebiostimulants are manufactured from dif-ferent materials and formulated at variousconcentrations. (Some that have low con-centrations ofbiostimulating materials mayseem less expensive, but they actually costmore in the long run because more mater-ial is required to realize stress-tolerance ben-efits. Economic comparisons should bedone on the basis of cost per unit area.)

Confusion concerning biostimulantsseems to arise because many materials areclassified as biostimulants but have not per-formed as advertised. At Virginia Tech wehave shown that seaweed extracts, humicacids, triazole fungicides, amino acids,potassium silicate and, most recently, lowdoses of salicylic acid have demonstratedbiostimulant properties. However, the twomost commonly used biologically activeingredients - seaweed and humic acid -have different sources, and different proce-dures are used to extract these materialsfrom their sources.

SeaweedsThe chemical composition of seaweed is

determined by the conditions under which

GCM 91June 2003

RESEARCHit is grown. T.L. Senn, Ph.D., fromClemson University, has studied the influ-ence of seaweed products on plants formany years. He has indicated that brownseaweed, Ascophyllum nodosum, prepared byalkaline hydrolysis from Norwegian waters,is a stable product when subjected to rigidquality control.

We have found that seaweed extractsobtained from a similar latitude in NovaScotian waters provide similar biologicalactivity (12,13). Hormones such ascytokinins and auxins have been isolatedand quantified from these extracts (2) andmay be the active ingredients.

Humic acidsHumic substances can be extracted

from soils, peat, coal (leonardite) and lig-nite in an alkaline solution. These extrac-tions are separated into humic acid andfulvic acid fractions by acidification.Humic acids are precipitated under a pH of2 or lower. Fulvic acids, soluble at all pHs,

have lower molecular weights and are themost biologically active fraction. The twomain aspects of these humic fractions thatinfluence plant growth are the auxincontent and the ability to chelate certaininorganic nutrients such as iron.

Dosage and frequencyResults from independent research

reports should be used to verify the efficacyof commercial biostimulant materials andalso to confirm that suppliers are providingformulations with proper dose and appli-cation frequency recommendations. Ourexperience is that frequent, low-dose appli-cations are more beneficial than infrequenthigh-dose treatments. One should be awarethat most of the biostimulants are hor-monal in nature, and excess applicationscould be harmful to plants. For frequentapplications (once a month or less), weobtained excellent results when 0.5 ounceof humic acid, 0.2 ounce of seaweed extractand 0.5 ounce of rriazole fungicide

were applied in combination per 1,000square feet. When these materials areapplied alone, the dosage may be doubled.(Because oflabeling laws, triazole fungicideswill not be packaged with other biostimu-lants. The superintendent will have to dothe blending.)

The effect of a single biostimulantapplication can be expected to decreasegradually with time. There are some indi-cations that better results are obtained whensequential treatments are made, and the sec-ond year is better than the first. Monthlyapplications before and during the stressperiods (three to six applications per year)should be programmed.

Many biostimulant products list themineral nutrient content in order toqualify in labeling. Sometimes these arelisted as auxiliary to the biologicallyactive substances (such as hormones). The"bonus" major nutrients are generally smallamounts and contribute little to plantgrowth and development.

What can reasonably be expected frombiostimulant treatments?

Let us begin with an explanation of howenvironmental stress damages plant tissuesand then discuss what we have observedand documented regarding the ability ofbiostimulants to diminish these damagingprocesses.

Environmental stressUnder favorable conditions, molecular

oxygen accepts electrons during metabolicprocesses, producing water as a byproduct.However, under unfavorable conditions, thisoxygen-accepting electron process can beoverwhelmed, resulting in the production ofa number of toxic oxygen species. Thesetoxic oxygen species are often referred to asfree radicals and go by names such as super-oxide, singlet oxygen, hydrogen peroxideand the hydroxyl radical. These radicals, leftas they are, cause pigment breakdown(bleaching) and major damage to cell walls,mitochondria and chloroplasts, which leadsto a loss of photosynthetic efficiency, cell'death and eventually plant death.

Plants deal with these damagingbyproducts of metabolism by producingchemical compounds that are appropriatelycalled antioxidants. These compounds reactwith oxygen radicals to produce nontoxic

a

Humic acid

• Root mass (grams)

SeaweedControl

The application of seaweed and a combination ofseaweed and humic acid resulted in significantlygreater leaf moisture and root mass in drought-stressed Penncross creeping bentgrass than theapplication of humic acid alone or of seaweedalone.

• Leaf moisture (%)

o

40

20

80

60

Seaweed+humic acid

Columns with different letters are significantly different from each other. (Graph from Zhang and Schmidt 2003.)

120

160

100

140

SEAWEED AND HUMIC ACID ON PENNCROSS

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RESEARCH

Columns with different letters are significantly different from each other. (Graph from Zhang and Schmidt 2003.)

SEAWEED AND HUMIC ACID ON KENTUCKY BLUEGRASS

treated with biostimulants (11).Possibly, the tolerance of low soil mois-

ture could be the most evident and benefi-cial aspect associated with biostimulanttreatments of turfgrasses (12). Bio-stimulant-treated plants retain more mois-ture than nontreated grasses under dry soilconditions. Turf treated with biostimulantsmay tolerate longer periods between irri-gations and require lessafternoon syringingto prevent wilting. This practice could helpalleviate the formation of algae and moss soprevalent on some overwatered greens.

At Virginia Tech, we have shown that,in addition to treatments with seaweedextracts, humic acid, triazole fungicides oramino acids, applications of potassium sil-icate (8) and low doses of salicylic acid (7)have demonstrated biostimulant properties.However, there are different sources of sea-weed and humic acid, and different proce-dures for extraction of these sources.Commercial products also differ in theirconcentrations of amino acids and silicates.

a

Seaweed+humic acid

Humic acid

Pre-emergence herbicidesSafer use of pre-emergence herbicides

may be obtained with biostimulant treat-ments (6). Our recent research has shownthat applications of biostimulants appliedseparately or in tank-mixes with post-emergence herbicides increased the effi-cacy of the herbicide (15). This indicatedthat lower dosages of these herbicidescould be employed. We postulate that thebiostimulant increased translocation of theherbicide. In addition, we obtainedreduced phytotoxicity to nontarget plantswhen a biostimulant was applied in con-junction with certain pre-emergence orpost-emegence herbicides. The injuryreduction apparently was related to theincreased antioxidant activity associatedwith the biostimulant treatment.

Basically, biostimulants enhance plant

Our research indicates that the correctdosage of salicylic acid is important forobtaining positive results.

Seaweed

• Root mass (grams)

Control

The combination of seaweed and humic acid signifi-cantly increased concentrations of vitamin E (an impor-tant antioxidant in plants) and root mass of drought-stressed Kentucky bluegrass over a control and theapplication of seaweed alone and humic acid alone.

• Vitamin E

o

500

600

400

300

100

200

end products such as water and molecularoxygen. Generally, under nonstress condi-tions, enough antioxidants are producedto quench or detoxify these ever-presentfree radicals.

Any type of environmental stress cangreatly increase the generation of free radi-cals, overwhelming the ability of the antiox-idant system to stop their damaging effects.If this happens and the stress continues, theplant goes into a survivalmode that can cul-minate in semidormancy or plant death.During this high-stressphase, the plant pro-duces greater levels of the hormone ethyl-ene, which signals the beginning of leafsenescence and conservation of energyreserves in plant growing points (turfgrasscrowns). Photosynthesis halts, and respira-tion is greatly reduced, continuing only toa minor extent in the crowns and roots.Higher levels of ethylene almost alwayscoincide with reductions in the growthhormones cyrokinins and auxin.

Treatment with biostimulantsWe postulate that pretreatment with the

biostimulant active ingredients - seaweedextract and humic acid - may change thehormonal balance to favor cytokinins andauxin over ethylene enough so that antiox-idant production can continue when stressoccurs. In effect, the turf may be "triggered"into continuing to grow and protect itselfduring periods of stress when it normallywould begin to shut down.

According to our research, the para-mount impact that biostimulants haveon turfgrassstressedby drought (12,13,14),salinity (4,11), heat (14), cold (5), dollarspot (14), high UV light intensity (7),herbicides (6,15) and nematodes (9) isassociated with the stimulation of endoge-nous antioxidant development that protectsthe plant during the formation of excessfree radicals.

For example, many warm- andcool-season turf areas now are beingirrigated with brackish water. As water islost through evapotranspiration, salt accu-mulates in the soil and plant free radicalsincrease because of salinity stress. Theantioxidants stimulated by biostimulanttreatments will help offset the toxic influ-ence of the free radicals (10). In addition,we have some evidence that uptake ofsodium and chloride is reduced in grass

GeM 93June 2003

RESEARCHmetabolic activity to condition the plant totolerate stresses. Therefore, biostimulantshave a greater impact when they areapplied before the turf is subjected to ananticipated stress.

What about mixing the different typesof materials that have biostimulantproperties?

TriazolefungicideOur research has shown mixing different

biostimulating materials to be a good practicein some cases. For example, the combinationof a triazole fungicide, humic acid and sea-weed extract has provided excellent results(12). Dosages of each of the materials whenblended may be lowered and yet retain theefficacy of the biostimulant effect and diseasecontrol. This combination reduces the needfor high rates of triazole fungicide to controlcertain diseases. Higher triazole rates may bedetrimental to turf grasses under certainconditions. The combination of seaweed andhumic acid generally has better biostimulantproperties than either material alone.

Trinexapac-ethylThe use of trinexapac-ethyl (Primo)

to suppress turfgrass top growth hasincreased in popularity. We have shown thatapplications of trinexapac-ethyl haveincreased endogenous antioxidants, butnot root growth as other biostimulantmaterials have. The addition of seaweedextract with trinexapac-ethyl may encouragethe development of roots under stressperiods. Our current research has shownthat the incorporation of salicylic acidwith seaweed and humic acid enhancesbiostimulant properties.

Do biostimulants affect turfgrassfertilization programs?

Biostimulants, even those containingsome mineral fertilizers, do not supply allthe essential nutrients in the quantities aplant needs. Their main function is to con-dition the grass to tolerate environmentalstresses. Therefore, biostimulants should beused in conjunction with proper mineralfertilization.

We believe that biostimulantsenhance the effectiveness of conventionalfertilizers. Research indicates that lessmineral fertilizer is required when

94 GCMJune 2003

biostimulants are used (3). This has both apractical and environmental impact. Anexample of the practical aspect is that, in ourexperience, applying less nitrogen than theconventional rates to the newer creepingbentgrasses results in reduced thatchdevelopment and possible subsequent dete-rioration of the turf associated with heavynitrogen fertilization.

Biostimulant treatments should be ben-eficial when used in conjunction with thespoon-feeding technique of fertilizing creep-ing bentgrass putting greens. This is esp-cially true when summer application ofnitrogen is scheduled. Reducing applicationsof mineral nutrients reduces the potential ofsoil-water contamination, resulting in goodenvironmental practices.

ConclusionsResearch on biostimulants permits

advances in turfgrass nutrition.Understanding the organic metabolismimpact as well as mineral functions within agrass will enable enhancement of nutritionof turf grass subjected to stresses. Organicaspects of a grass are as important asmineral aspects in proper plant nutrition.The difference in mineral content betweenplants of the same cultivar with differentgrowth responses is relatively small. Mineralnutrition is poorly correlated with toleranceto stresses. However, knowing the impactthat biologically active materials have onturfgrass metabolism allows superinten-dents to condition turf grasses better to tol-erate environmental stress. Using thisknowledge provides an additional tool forproducing high-quality turf under adverseenvironments.

Literature cited1. Allen, VAG. 2000. Foragesfor grazing animals. p.

65-69. In: A spectrum of achievements inAgronomy: Women fellows of the Tri-Societies.ASA Special Publication No. 62. American Societyof Agronomy, Crop Science Society of America,and Soil Science of America, Madison, Wis.

2. Crouch, I.J., and J. VanStaden. 1993. Evidenceforthe presence of plant growth regulators in com-mercial seaweed products. Plant GrowthRegulators 13:21-29.

3. Frankenberger, WT. Jr., and M. Arshad. 1995.Phytohormones in soils. Marcel Dekker,New York.

4. Nabati, D.A., RE. Schmidt and D.J. Parish. 1994.Alleviation of salinity stress in Kentucky bluegrassby plant growth regulators and iron. Crop Science43:198-202.

5. Schmidt, RE., and D.R. Chalmers. 1993. Latesummer to early fall applications of fertilizer and

biostimulants on bermudagrass. InternationalTurfgrassSociety Research Journal 7:715-721.

6. Schmidt, RE., and W.-J. Lui. 1993 Pendimethalininfluence on seedlingly' Kentucky bluegrassdeveloped from plant growth regulator-treatedseed. International Turfgrass Society ResearchJournaI7:708-714.

7. Schmidt, RE., and X. Zhang. 2001. Alleviation ofphotochemical activity decline of turfgrassesexposed to soil moisture stress or UV radiation.International Turfgrass Society Research Journal9:340-346.

8. Schmidt, RE., X. Zhang and D.R.Chalmers. 1999.Response of photosynthesis and superoxididedismutase to silica applied to creeping bentgrassgrown under two fertility levels. Journal of PlantNutrition 22:1763-1773.

9. Sun, H., RE. Schmidt and J.D. Eisenback 1997.The effect of seaweed concentrate on the growthof nematode-infected bent grown under low soilmoisture. International Turfgrass SocietyResearch Journal 8:1336-1342.

10. Winston, G.W 1990. Physiochemical basis for freeradical formation in cells production and defense.p. 57-86. In: R.G.Alsher and J.R. Cumming (eds.),Stress responses in plants: Adaptation and accli-mation mechanisms. Wiley-Liss, New York.

11. Yan,J. 1993. Influence of plant growth regulatorson turfgrass polar lipid composition, tolerance todrought and salinity stresses and nutrient effi-ciency. Ph.D. dissertation. Department Crop andSoil Environmental Sciences, Virginia PolytechnicInstitute and State University, Blacksburg.

12. Zhang X., and R.E. Schmidt. 1999. Antioxidantresponse to hormone-containing products inKentucky bluegrass subjected to drought. CropScience 39:545-551.

13. Zhang, X., and R.E.Schmidt. 2000a. Application oftrinexapac-ethyl and proiconazole enhances pho-tochemical activity in creeping bentgrass(Agrostis stoloniferous var. palustris). Journal ofthe American Society of Horticulture 125:47-51.

14. Zhang, X., and RE. Schmidt. 2000b. Hormone-containing products' impact on antioxidant statusof tall fescue and creeping bentgrass subjected todrought. Crop Science 40:1344-1348.

15. Zhang, X., R.E. Schmidt and P.L. Hipkins. 2001.The influence of selected PGRs on postemer-gence herbicide efficacy. International TurfgrassSociety Research Journal 9:1056-1 061.

R.E.Schmidt, Ph.D.(rschmidt@vt.edu),is professoremeritus; E.H.Ervin,Ph.D., is assistant professor;andXunzhongZhang,Ph.D., is a researchassociate in thedepartment of crop and soil environmentalscience,VirginiaTech,Blacksburg.