CHEMICAL PROTECTION OF COOL-SEASON TURFGRASSES TO WATER STRESS. John E. Kaufmann Crop and Soil Sciences, M.S.U. Introduction

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1 CHEMICAL PROTECTIO OF COOL-SEASO TURFGRASSES TO WATER STRESS Jhn E. Kaufmann Crp and Sil Sciences, M.S.U. Intrductin Thrughut mst f the cl-humid regin f the United States, lng dry perids during the summer present prblems t the glf superintendent. Inadequacies f the irrigatin system becme mst apparent at this time. Water has generally been available in sufficient quantity t allw fr ver watering f sme areas fr the purpse f supplying mdest, badly needed amunts t ther areas. Sme displacement and cmpactin prblems are ccurring in ver-watered areas. Additinally, qutas may be placed n the amunt f water available t turfgrass irrigatin. Clearly, if grasses culd be maintained at reduced irrigatin time and frequency, and at the same time imprve the unifrmity f appearance f the glf curse, it wuld be f great value t the glf industry. One f the mst bvius ways t minimize water use is t reduce the transpiratin rate f the turfgrasses. When this becmes pssible, turfgrasses receiving marginal quantities f water will be able t survive and prvide an acceptable playing surface. One methd f slving a high water use prblem is thrugh the applicatin f antitranspirants. These materials wrk thrugh external chemical clsure f stmata, r by cating the leaves with a chemical layer impervius t water vapr. Because f mwing and traffic, these layers d nt persist lng (1). And while they persist, water vapr cannt escape causing leaf temperatures t rise (5), pssibly t the pint where damage culd ccur. In additin, carbn dixide exchange appears t be inhibited, resulting in a greater reductin in phtsynthesis than transpiratin (6). The use f antitranspirants may tend t put the plant int a type f drmancy. This culd be useful t prevent winter desiccatin f a near drmant plant, but wuld nt be as applicable fr actively grwing turfgrasses. A secnd methd is thrugh the use f wetting agents r surfactants. Hwever, surfactants als need t be used carefully. In water slutins, surfactants are txic t turfgrasses, but are less s in sil slutins where absrptin apparently binds the surfactant t the sil (2). It has been shwn that surfactants can imprve pesticide mbility int the sil (3) and that surfactants aid in the wetting f hydrphbic sils (4). Where lcalized dry spt prblems ccur, a unifrm playing surface has been restred thrugh the use f surfactants. A third methd fr reducing water cnsumptin is thrugh systemic chemical alteratin f the physilgy f the turfgrass plant t make it use less water. Several systemic fungicides having a chemistry similar t kinetin, have been bserved t have kinetin-like activity. Kinetins are knwn t reduce senescence and preserve cell integrity. The bjective f this investigatin was t determine the effect f fur cmmnly used turf grass chemicals n transpiratin and phtsynthesis f leaves f intact Kentucky bluegrass plants. Materials and Methds Mature Merin Kentucky bluegrass was btained frm the MSU Experimental Field Labratry and acclimated in styrfam cups in the greenhuse fr tw weeks. A full nutrient slutin was then supplied tw times per week in the check plts while treatments included the additin f 5 ppm f Aquagr, Hydrwet, Tersan 1991, r Chipc These treatments cntinued biweekly fr three weeks. Even 38

2 thugh the applicatin rate was extremely high t determine if the plants were affected by the treatment, n phyttxicity was bserved thrughut the study. Fr gas exchange measurements, leaves were put int a water jacketed aluminum chamber that had a windw t admit light. The chamber allwed the air stream t pass ver 1.19 cm L leaf tissue. There was a separate air stream fr the upper and lwer surfaces f the leaf, each with a flw rate f 5 l/hr. The air stream was humidified, then passed thrugh a glass cndenser in a water bath kept at 18C t keep the dew pint f the air cnstant. Als, the air was passed thrugh tw sda lime twers, after which C2 was added t give the aesired C2 cncentratin. An infrared gas analyzer (URAS 2, Hartmann & Hraun, Frankfurt A.M., W. Germany) was used t mnitr the C2 cncentratin. The mlar fluxes f C2 and H2 fr bth the upper and lwer leaf surfaces were measured with a fine thermcuple pressed against the nn-illuminated side. Thrughut all analyses the temperature and the water vapr pressure deficit f the leaf were held at 26C +.5C and.5 mill respectively. White light was prvided by an Osram XHF 6 w water cled xenn arc lamp shining thrugh a Crning n. 46 infrared-absrbing glass filter. The irradiance was reduced with neutral density Plexiglas filters (n. 8 and 38, Rhm and Haas, Darmstradt, Germany). Irradiance was mnitred with a silicn cell in the same plane as the leaf chambers that had been calibrated with an Eppley pyranmeter. Irradiance was cntrlled at 13 w/ml thrughut the investigatin. Assimilatin and transpiratin rates, stmatal cnductance, and intercellular C2 cncentratin were calculated by cmputer. The figures cnsist f quartic predictin curves f stmatal aperature and gas exchange mnitred every 2 minutes fr the first 3 minutes after irradiance was initiated. Each predictin curve was based n 3 replicatins, and thus a ttal f 45 bservatin pints. The experiment was repeated three weeks later with similar results. Results Maximum cnductance (stmatal aperature) was fund in the nn-treated check 15 minutes after the light was turned n (Figure 1). Maximum cnductance fr Aquagr, Chipc 261 and Hydrwet ccurred within a similar time span as the check. hwever, maximum stmatal aperature f Tersan 1991 treated plants did nt ccur until 2 minutes after light treatment. In Figure 2, assimilatin f C2 was greatest in the nn-treated check. Maximum phtsynthesis ccurred within 1-15 minutes in all treatments except in Tersan 1991 treated plants which did nt reach maximum until the end f the 3 minute analysis perid. The Aquagr and Chipe 2619 treatments resulted in the least reductin f phtsynthesis, while Hydrwet and Tersan 1991 reduced peak phtsynthesis by 5% r mre cmpared t the check. It is interesting t nte that 1 minutes f light was required befre phtsynthesis vercame respiratin in the Tersan 1991 treated plants. The quartic curves fr transpiratin in Figure 3 are nearly identical t the stmatal cnductance curves in Figure 1. Since gas exchange is the basis fr determining stmatal aperature, and since up t 1 times as much water passes thrugh stmates cmpared t C2, it is nt surprising that these curves are similar. Table 1 is a summary f the effects f the fur turfgrass chemicals. The percentages are calculated n the average cnductance, transpiratin r assimilatin f each treatment during the secnd half f the 3 minute analysis perid. Tersan 1991 and Hydrwet exhibited the greatest reductin f gas exchange including a large reductin in phtsynthesis. Chipc 2619 reduced transpiratin t 58% while lwering phtsynthesis t 76% f the untreated check. Aquagr 39

3 reduced transpiratin by 32% while reducing phtsynthesis by nly 13%. Discussin The data in this reprt indicated that high rates f cmmnly used turfgrass chemicals reduce transpiratin and phtsynthesis f Kentucky bluegrass. It is recgnized frm the start that the rate f applicatin is abut 1 times what might be experienced in nrmal field cnditins. T achieve field results in the rder f magnitude shwn by this data wuld be cst prhibitive. Data needs t be cllected that indicates the level f effect fund fr nrmally ccurring rates f these chemicals in field cnditins. Hwevert these data indicate the ptential fr reducing water cnsumptin while maintaining adequate phtsynthesis. Since the plants were treated with a sil drencht rt impairmentt particularly fr high rates f Tersan 1991t may have caused a plant water deficit and subsequent lw transpiratin measurements. Hwevert the plants were peridically examined thrughut the treatment perid and did nt exhibit the zermrphic features typical fr Kentucky bluegrass experiencing a plant water deficit. AdditinallYt the surfactant Aquagrt shwn by End (2) t cause rt damage in slutin culturet exhibited the lwest transpiratin reductin f any f the chemicals. Thust there is evidence t suggest that surfactants are translcated frm sil slutins int turf grass leaves where stmatal behavir is alteredt and that systemic fungicides may alter hst resistance t a disease by reducing water cnsumptin and the subsequent severity f drught stress. References 1. Beardt J. B. ly73. Turfgrass: Science and Culture. Prentice Hallt ew JerseYt pp Endt R. M. t J. LeteYt. Valras and J. F. Osbrn Effects f nninic surfactants n mncts. Agrn. J.t Vl. 61: Huggenbergert F.t J. Letey and W. J. Farmer Effect f tw nninic surfactants n absrptin and mbility f selected pesticides in a sil-system. Sil Sci. Sc. Amer. Prc.t Vl. 37: Rieket P. E Sils research: carrierst ptassium studies and rewetting f a hydrphbic sil. 45th Annual Michigan Turfgrass Cnference Prceedingst Vl. 4: Tanne r, C. H Plant temperatures. Ag rn, J. t Vl. 55: WlleYt J. T kelative permeabilities f plastic films t water and carbn dixide. Plant Physil.t Vl 42(5):

4 Table 1. The effect f fur turfgrass chemicals n transpiratin, phtsynthesis and stmatal cnductance f Merin Kentucky bluegrass. (percent f untreated check) Chemical cnductance transpiratin phtsynthesis Aquagr Hydrwet Tersan Chip c Check Fig. 1 The effect f turfgrass chemicals n stmatal cnductance f intact leaves f Merin Kentucky Bluegrass CJ <1J 45 Cll e r-i CJ <1J CJ d ec 4.1 CJ 25 ::l "' d U r-i ec ec S Cf.l Time in Minutes 41

5 Fig. 2 The effect f turfgrass chemicals n assimilatin f intact leaves f Merin Kntucky Bluegrass ȯq) 8 '- a '- U ):: '-'" ') Time in Hinutes Fig. 3 The effect f turfgrass chemicals n transpiratin f intact leaves f Merin Kentucky Bluegrass. 7 r 6,...,. Q) s 5 4 '- M '-'" 3 s::: '1'1 "-' III H c, c III H f-l Time in Minutes 42