Controlling Turf Diseases Daniel Tremblay

THE ROLE OF SILICA IN IMPROVING TURF'S NATURAL DEFENSES

Fungal diseases are a regular turf problem for golf course superintendents.And the problem is made even worse by often appearing during the summerseason when the course is at its busiest. Control methods are presently few innumber, basically boiling down to the use of fungicides. Studies presentlyunderway at Laval University's Horticultural Research Centre, however, areworking on alternatives to pesticide use.

n spite of all the money and effort in-vested over the last few years inresearch into the biological control ofturf diseases, few new solutions arepresently available that golf course

superintendents could actually use. Im-proved turf care and the use of newdisease-resistant cultivars can help preventthe appearance of diseases, but are not al-ways sufficient.

During the summer, heat and humiditystimulate the growth of several fungi ca-pable of attacking turf grasses. At the sametime, golf turf is undergoing intense main-tenance and suffers from several forms of

severe stress. Among them, heat, drought,predatory insects, foot traffic from golf-ers, and frequent low mowings not onlymake turf more vulnerable to various in-festations, but also wound the plantsleaving the door wide open to pathogens.It is the combination of these factors thatexplains why diseases are so commonduring the summer months. ,".. page 9

Below: Plants were sown in University ofGuelph greenhouses. Half were given fer-tilizer without silica while the other half re-ceived fertilizer with silica. Resultsobtainedwere conclusive. See page 9 for more ...

Cover Story Continued ... The Role of Silica in Controlling Turf DiseasesDANIEL TREMBLAY, MASTERS STUDENT AT LAVAL UNIVERSITY, DISCUSSES CURRENT TURF RESEARCH

Golf Turf is UniqueFortunately, plants have the ability to

defend themselves against harmful fungi.They are, in fact, usually extremely goodat preventing fungal colonization. Amongothers, their defense arsenal includesthickened cell walls and the productionof compounds that are toxic to harmfulfungi. These means are usually highlyefficient. However, golf turf, alreadyhighly stressed, is particularly vulnerableand therefore less efficient at preventingfungal infestation.

One avenue of research that is worthexploring is developing and improving thenatural defenses of turf grasses. It wouldalso be interesting to look into increasingthe speed with which the plants deploytheir defense arsenal and into improvingthe intensity of their defense response toaggressions. Over the last few years, vari-ous research teams have noted that addingsilica to the mineral nutrition of certainplants decreases the incidence of severalfungal diseases.

What is Silica?Silica is a mineral element, much like

carbon, nitrogen, and calcium. It is an el-ement that is found in great quantities onthe surface of our planet and is, in fact,the second most abundant element afteroxygen. Concrete, sand and glass· aresilica polymers. But silica is insoluble andtherefore cannot be absorbed by plant rootsystems. It is therefore important to add

it in a soluble form so plants can absorbit. .Since silica is not considered an ele-ment that is essential to plant nutrition, itis generally omitted from current fertili-zation programs ..With more and moreobservations that silica has the potentialto decrease the frequency of disease inseveral types of culture, it would seemworthwhile to include silica in regularplant fertilization situations.

For example, European growers ofgreenhouse cucumbers and roses who ap-ply daily doses of silica report a decreasein mildew (Sphaerotheca sp.), a foliar fun-gal disease common in greenhouse

Researching Silica in Turf CultureThe goal of this research project, lead

by Laval University-in collaboration withthe University of Guelph, is, in the firstphase, to verify that silica actually is ab-sorbed and translocated by turf grasses.The second phase attempts to determinethe effect of silica on fungal turf diseasesboth in greenhouse experiments and infield tests, more precisely on golf coursegreens and fairways. Finally, the researchshould help make it possible to improvethe know ledge of turf defense mechanismsand to understand the effects of silica onplant defense systems.

Since silica is not considered anelementthatises~~ntialto plant nutrition, it is generallyomitted ..from currentfertili~ation programs.

production. Other beneficial effects havealso been observed in the culture of cer-tain other types of grass. Rice producersin the southern United States, for exam-ple, use silica as an amendment and areable to reduce the appearance of severaldiseases that decrease their harvest suchas rice blast disease iPyricularia oryzae).Other than disease resistance, leaves ofplants fertilized with silica stand moreupright, which improves light absorptionand thus increases yields. Also silica ac-cumulates in cell walls, allowing a generalstrengthening of plant tissues and, there-fore, of the entire plant.

The grass chosen .for.theproject wasbentgrass (Agrostis palusN-is), the speciesmost commonly used in~()lf greens. Thefirst phase consisted 9£ verifying thatbentgrass does absorbsjilisa. ,To beginwith, plants were sown in University ofGuelph greenhouses . Aftera week ofgrowth, half the plants were given a liq-uid fertilizer without silica while the otherhalf received a liquid fertilizer with silica.The plants were fertilized three times aweek.

The results obtained were conclusive.The plants receiving fertilizer enriched insilica contain a very large amount of that

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www.sportsturfassociation.comISPRING 2003 9

Top: Testsare presently underway inexperimental plots on the greens andfairways of two golf clubs in the Guelphregion. Above: Experimental plot at theGuelph Turfgrass Institute of the Universityof Guelph. Photos by Tremblay.

on the incidence of fungal diseases suchas dollar spot, caused by Sclerotiniahomoeocarpa, and pythium blight(Pythium sp.). The results obtained up tonow indicate that the addition of silica toturf fertilization delays the appearance ofsymptoms and, in some cases, decreasesthe incident of disease. Tests are presentlyunderway in experimental plots at theUniversity of Guelph and on the greensand fairways of two golf clubs in theGuelph region (Guelph Lake Golf andCountry Club and Victoria Park GolfCourse) in order to confirm the results

element in their aerial parts compared toplants not receiving silica.

The goal of the second phase of theexperiment, on which the research teamis presently working, is to determinewhether the absorbed silica has an effect

10 SPRING 2003 I Sports TurfManager

obtained under controlled conditions.The last phase of this experiment con-

sists of studying how silica acts in turfdisease resistance. The interest in the roleof silica in decreasing the incidence ofdisease is recent. The first hypotheses con-sidered that the strengthening of plant cellwalls (limiting the penetration of thepathogen) was the only role silica played.However, over the last few years, anotherrole is coming to light. Studies carried outat Laval University by the team of Dr. Ri-chard Belanger suggest an entirelydifferent means of action: it appears silicastimulates the plant's own defense mecha-nisms and thus make it more capable ofdefending itself against the aggressions ofpathogenic fungi.

When attacked by a pathogen, the re-sponse of plant cells seems to be farsuperior when they have undergone pre-vious treatments with silica. It is thesedefense strategies that still have to be iden-tified and quantified in order to betterunderstand the inductive role of silica inplants. Similar studies have been carriedout on cucumbers, but so far no other studyhas been done on turf grasses and silica.This research project is therefore innova-tive and should help point out the defensecompounds of bentgrass during attacks bypathogens as well as verify the effect ofsilica on the production of these com-pounds.

When Will Results be Available?Complete results should be known by

next summer. Other than their contribu-tion to the advancement of scientificknow ledge, the results could provide aninteresting tool to golf course superintend-ents. Eventually silica might well beintegrated into turf maintenance programsas a means of reducing the use of pesti-cides, notably fungicides. •

- Volume 24 (6), Quebec Vert,September 2002

About the author. Daniel Tremblay is an agrono-mist and a student working on his Masters Degreein Plant Biology at Laval University. He wrotethis article in collaboration with Dr. Julie Dionne,a professor specializing in turfgrass managementat the University of Guelph, and Dr. RichardBelanger, a professor and phytopathologist atLaval University's Horticultural Research Centre.