Chemical and Cultural Control 0/ Tur/grass DiseasesBy JAMES L. HOLMES

Agronomist, Midwestern Region, USGA Green Section

T.he fungi which. are presently recog-,. nized as parasites on turfgrasses

ha.y'~."bee~.widely discussed. We are pri-rriil'fily concerned here with diseases inthe Midwest, but these considerationswill gen~ral1y apply throughout any tem-perate zone of the world.

The plant pathologist is involved inthe recognition of disease-causing fungi,their epidemiology and control, primarilyby chemical means. The agronomist is in-terested in general recognition and con-trol, primarily through cultural means.Through the. years turf growers havecome to realize that chemical diseasecontrol and disease control through cul-tural manipulation are about equal inimportance. It is intimated here thatturf managers can be called neitherpathologists nor agronomists. When deal-ing with turf, consitler all facets of aproblem and then pursue a course whichpromises the greatest results.

Results when dealing with disease con-tr()l of turf. are consistent, inconsistent,ambiguous, complete, incomplete, en-lightening and frequently quite madden-ing. This, of course, points out the in-completeness of our knowledge and un-derstanding in this field.

Listed below are diseasei in a possibleorder of importance in the Midwestern

area and suggested methods for chemicalcontrol. More specific chemical controlinformation is available in numerouspublications from turf fungicide manu-facturers.

COOL SEASON GRASSESFusarium sp. (Fusarium patch; pink

snow mold)Visible symptoms of attacks by this

fungus are most readily detected eitherunder melting snow or in areas of freemoisture resulting from melting snow.Dead areas usually from Y4 to 3 inches indiameter have a characteristic pinkishor reddish periphery.

One of the reasons for the seriousnessof this fungus is that it frequently is not"most readily detected." The author hasfound microscopic evidence of thisfungus and apparent damage to turf,primarily bents and Poa annua, duringall 12 months of the year. Small spotsthe size of a paper match head developon diseased turf especially when the en-vironment is cool and damp and shadeand tree root competition a factor. Thebest way to define this symptom is a"salt and pepper effect." More often thannot these symptoms go unnoticed untilthe mower man or the golf course super-intendent begins to notice that "some-thing is wrong." By this time consider-

USGA JOURNAL AND TURF MANAGEMENT: FEBRUARY, 1962 23

able leaf surface (also perhaps crownand root) has been lost and severedamage may have occurred.

Obviously, spring and fall are the sea-sons when Fusarium sp. will be the mostdamaging. Fungicide applications shouldbe regularly made in early spring as aguard against this serious pathogen. Con-ceivably Fusarium sp. could be indirectlyassociated with the severity of parasiteswhich follow later in the season by ini-tially reducing the natural vigor and re-sistence of turf.

During the warmer and even driermonths Fusarium sp. can be micro-scopically detected in diseased and/ ordead turf areas along with other fungusorganisms. The extent of damage is notdefinitely understood, but surely thisfungus is intimately associated in a com-plex with other leaf disease-causing or-ganisms, and involved in the unexploredarea of root maladies. Mercurials, bothorganic and inorganic, and mixtures ofthese and broad spectrum turf fungicides.seem to give the most positive and longlasting control.Helminthosporium sp. (Leaf spot, melt-

ing out)Visible symptoms of attack by this

fungus are characteristic dead spots onindividual leaf blades and/or dead areasvarying in size from %" to indefinite.Individual dead spots on leaves usuallyhave tan colored centers surrounded byblackened borders. Helminthosporium sp.is known to be parasitic on all thegrasses with which we deal.

Here again, one of the dangers of thisfungus is its subtlety. It often goes un-detected for a period of time and faulty

. diagnosis is common. One of the reasonsit is listed among the most important orsevere pathogens is its tendency to killstems and crowns. No doubt it plays astarring role in the previously men-tioned, little explored area of root mala-dies.

Damage from Helminthosporium sp.has been detected year around but tendsto be most pronounced during cool, hu-mid weather. However, attacks have beensevere during hot, dry periods on high,well-drained areas. Apparently speciesdifferentiation is a factor here. Theauthor believes Helminthosporium sp. isthe most omnipresent and omnivorous

genus of fungi with which we deal. Thefact that hundreds of species of thisgenus of fungus are recognized tends toverify this.

Chemical controls for this malady arenot consistent. Here again, this no doubtis dependent upon the particular speciesin question. At times a mixture of zincethylene bisdithiocarbamate (Zineb) andiron sulfate offers the most positiveQontrol. At other times mecurials andmixtures of them and broad spectrumturf fungicides are the most effective.Antibiotic fungicides also offer positivecontrol either alone or in combination.Pythium sp. (Cottony blight, grease spot)

Visible symptoms of attack by thisfungus characteristically follow presenceof free moisture and usually higher tem-perature. Diseased spots which vary insize from 1fz" to include an entire green(or larger) have a black-greasy appear-ance which later turns straw (dead grass)color.

Perhaps many will question the con-sideration of this fungus in importancebefore various other disease causingorganisms. Its importance is not becauseit appears so regularly in the Midwest,but because when it does appear thereseems to be only limited chemical con-trol available. Reports of partial to com-plete control are frequent but no regularor constant control has yet been de-veloped. Daily applications of broadspectrum turf fungicides or a mixtureof Captan and antibiotics are the mostfrequently used chemicals. Concerted ef-forts must be made to dry the diseasedarea in any way possible such as throughthe use of sand or lime and temporarilyimproving surface drainage with hollow-tined forks, etc.Rhizoctonia solani (Brown patch);Sc1erotinia homoeocarpa (Dollar spot);Typhula sp. (Snow mold)

In many respects these pathogens arequite similar and they react similarly tochemical control treatments. Visiblesymptoms of attacks by these fungi arequite similar. The characteristic varia-tion is in temperature. requirements:snow mold-cold; dollar spot-temper-ate; brown patch-hot. (Physiologic racesof Rhizoctonia have been found whichwill thrive under moderate tempera-tures.) The fungi which causes these

24 USGA JOURNAL AND TURF MANAGEMENT: FEBRUARY, 1962

diseases all require free moisture and ingeneral wet, humid conditions in orderto attack and be damaging. They are alleasily controlled by chemical means,which reduced them from the mostdamaging turf disease causer to asecondary role.

A mixture of inorganic mercuries con-tinues to give the most positive and longlasting control. About the only time thischemical mixture fails to give satisfactorycontrol is when excess moisture ispresent for an extended period of time.Thiram, phenyl mercuric acetate andother chemicals also offer control.Gloeocercospora sorghi (Copper spot);Corticium fuciforme (Red thread)

Visible symptoms of attacks by thesefungi are quite similar. Copper spot isjust that, copperish colored spots 2" or3" in diameter appear speckled over theaffected area. Red thread does not ap-pear as regular spots but rather irregu-lar and reddish strands of fungus arevisible. Environmental conditions aresimilar; humid and cool to mild.

These diseases rarely appear in theMidwestern area. Occasionally they arepresent in the Detroit area and rarely inthe Chicago area. Perhaps this is truebecause exact environmental conditionsare lacking. Also, these organisms wouldattack in spring or fall; Cadmium com-pounds are effective long lasting controlsfor these maladies and are generallyused at this time of year in these areas.

WARM SEASON GRASSESConsiderably less has been determined

and thus written about fungus diseasesof the warm season grasses. Zoysia andbermudagrass are the species involvedas far as golf turf in the Midwest is con-cerned.

Some years ago Dr. Frank Howard,Pathologist at the University of RhodeIsland, commented that "the reason littleis said about diseases of warm seasongrasses is that they are relatively newlyintroduced into this country, thus thediseases have not caught up with themyet." To a considerable extent this isstill true. However, it is beginning to ap-pear that a number of fungi are becom-ing increasingly more damaging to ber-mudagrass or are beginning to "catch-up" with it. It is believed that "winterkill" of bermuda grass (primarily U-3) is

largely the result of attacks by parasiticfungi when bermudagrass is in itsdormant stage. Under microscopic ex-amination Helminthosporium sp. andFusarium sp. have been found repeatedlyon dormant stems, leaves, roots andrhizomes of V-3.

As far as summer diseases of thesegrasses are concerned, they still seem tobe relatively minor. Helminthosporiumsp. appears to be increasing in incidenceand severity on U-3 bermudagrass. Possi-bly V-3 grows so rapidly during hotweather that it simply out-produces thedisease.

Control measures for disease of thesegrasses are the same for correspondingdiseases on cool season grasses at thistime. Perhaps other controls will be de-veloped in the future.

Cultural Control

The turf specialist will note that theleaf spot type of diseases such as Cur-vularia sp., Colletotrichum sp., Septoriasp., Phyllosticta sp. and others have beenomitted. It is believed that by and largethese are not primary turf pathogens butare secondary or damaging only whenthe grass has been weakened throughsome other influence. These influencescan be anything which weakens turf:attacks by other fungi, traffic, shade,tree root competition, excess of mat andthatch or organic matter, lack of air cir-culation, mechanical damage, damagefrom excesses or fertilizers-herbicides-fungicides, presence of insects and short-age of plant nutrients. Therefore, eventhough most of these secondary organismscan be checked or controlled by the useof chemicals, they will rarely be trouble-some if primary parasites are controlledand the various cultural controls arepracticed.

The practice of cultural control alsoaffects the incidence and severity of theprimary pathogens but cannot stop themcompletely. One item is consistent inthe epidemiology of the primary para-sitic fungi (likewise the secondary). Thisis the presence of free moisture. It hasbeen determined that proper drainage isan excellent fungicide. The most im-portant concept of effective culturaldisease control, and one which is regu-larly ignored, is the assurance of ade-

USGA JOURNAL AND TURF MANAGEMENT: FEBRUARY, 1962 2S

quate surface and sub-surface drain-age. Of the fungi known to attack grass,apparently all require free moisture inorder to penetrate the above groundplant parts. Few of these fungi will de~velop to damaging proportions if surfaceand soil water is not in excess. Underwaterlogged conditions all of the knownparasitic fungi can and do develop intoserious problems with which it is diffi-cult to cope. Therefore if water drain-age is assured, our primary culturaldisease control concept is a guarantee.A considerable amount has been done inthis regard; greens and other areas nowcan be constructed so that adequate andpermanent drainage is assured.

The next most important cultural con-trol concept is considered to be traffic,primarily cart and foot. Without thegolfer it would be relatively easy to main-tain golf courses and control the diseasesthereon. However, we must face the factthat golf courses are present for the en-joyment and abuse of the golfer andplan accordingly. Turf, damaged as a re-sult of excessive traffic, is susceptibleto severe attacks from both primary andsecondary organisms. Not only must pro-per and adequate fungicides be appliedbut the golf course superintendent mustmake all efforts to direct traffic overas much of the course as possible thusdispersing it away from localized heavytraffic areas. This is only partially possi-ble and consequently we resort to suchthings as installation of asphalt cartpaths, the building of larger greens andtees (and courses for this matter), theplacing of traps closer to greens thus dis-couraging traffic (foot and cart) andheavy equipment from abusing such re-stricted areas and the placing of signsand ingenious traffic directing devicesin susceptible heavy traffic areas. It isbecoming increasingly, more apparentthat the club must allow its superin-tendent more uninterrupted time in or-der to complete his work if they expecthim to give them a presentable course.This increase in traffic,is reaching alarm-ing proportions. Many clubs are nowclosing the course to all play on Mon-days, as an example.

Other important cultural considera-tions are dependent upon common sense.

1. Apply proper qmounts of plantnutrients. Fungi vary in their pathogenic

severity according to availability ofnutrients to the grass. Brown patch andpythium diseases are more troublesomewhen nutrient levels are high. Therefore,the practice of reducing fertilizer ratesduring hot weather is generally and pro-perly practiced.

Dollar spot is less of a problem whennutrient levels are high. However, Fusari-um patch can be more of a problemwhen nutrients are in excess. As previ-ously stated, possibly Fusarium patch isone of the most damaging diseasesin the Midwestern area. Careful use ofnitrogen in cooler months, regardless ofthe dollar spot picture, is a safeguard.

There is so little proven through scien-tific endeavor along this line that theassumptions and practices followed havebeen determined through observation bygolf course superintendents. This is asubject about which more information isneeded.

2. Remove trees in order to decreaseshade and tree root competition. If en-tire trees are not removed, prune treeroots and limbs as necessary. Not onlyare fungi more damaging to tendershaded grass but evaporation of surfacemoisture is reduced in shaded areaswhich increases activity of fungi.

3. All of the fungi discussed areknown to be facultative organisms. Thatis, they can subsist on both living anddead material. If a thick layer of matand thatch or organic matter is presentdisease-causing organisms are alsopresent-either in a growing or dormantstage in this layer of organic matter.\\Then turf loses its resistance to theseomnipresent disease-causing organismsbecause environmental conditions favorthe fungi or when turf is weakenedthrough some cultural aspect such asexcessive traffic, trees, etc., the fungiare then capable of attacking and causingdisease.

A thick layer of organic matter alsointerferes with water movement downto and through the soil. This layer willsometimes absorb and hold free mois-ture while under other conditions it willshed applied water and become dry.

Thus the entire irrigation or water re-lationship is confounded. However, ourinterest here rests in the accumulationand presence of surface moisture. As we

26 , USGA JOURNAL. AND TURF MANAGEMENT: FEBRUARY, 1962

previously discussed, fungi benefitgreatly as a result of this moisture.

Spiking, aeration, aerothatching, andrebuilding greens are often done in aneffort to reduce this organic layer andthus effect cultural disease control.Basic soil consistency is a considerationhere and was discussed under moisture.

CONCLUSION

All turf management practices areeither directly or indirectly associatedwith incidence of disease. As can be seen,chemical control and cultural control ofdisease-causing fungi are intrinsicallyinterwoven. Cultural control goes a longway in keeping turfgrass disease free(or disease reduced) and unless propermanagement practices are pursued, eventhe best chemical controls often fail tostop disease spread. On the other hand,chemical control measures are frequentlyand regularly necessary especially duringperiods when adverse environmental con-ditions prevail, even though the bestknown cultural practices are followed.

The frustrating aspects of disease con-trol mentioned earlier arise primarily asa result of the lack of basic knowledge.As examples, why will a green, eventhough located in a similar area or adja-cent to other greens, be constantly sus-ceptible to disease while its neighborsremain relatively disease free. The

author has seen examples of courses lo-cated in the same general area; onecourse receives the best possible manage-ment known, yet disease is a problemeven though fungicides are regularly andfrequently used. The other course re-ceives far inferior management and lessfrequent and regular fungicide applica-tions, yet diseases are much less of aproblem and in general, turf is healthier.Of course, these are exceptions. Nonethe-less, they exist.

COMING EVENTSFebruary 26-March 1

Cornell Turfgrass ConferenceCornell UniversityIthaca, N. Y.

March 5.6-7Midwest Regional Turfgrass ConferenceMemorial Center, Purdue UniversityLafayette, Indiana

March 8-9Massachusetts Turfgrass ConferenceUniversity of MassachusettsAmherst, Mass.

March 13-14-15Iowa Turfgrass ConferenceMemorial Union BuildingIowa State UniversityAmes, Iowa

March 22-23Michigan Turfgrass ConferenceMichigan State UniversityEast Lansing, Mich.

Potassium - That Mysterious MacronutrientBy CHARLES E. CROLEY

Agronomist, Southwestern Region, USGA Green Section

Of the various soil minerals known tobe essential to plant growth, potas-

sium was among the first to be recog-nized. One of the first ohservations ofpotassium-plant relationships was thatpotassium is required in relatively largequantities by plants. Yet, since thoseearly observations, progress has beenslow in understanding the specific partpotassium plays in plant growth and de-velopment. Through scientific investiga-tions and practical observations we havelearned that plant uptake of potassiumis .often higher than any other mineraland that a deficiency of. potassium willgive a very marked decrease in growth

and, if the potassium level is low enough,even death of the plant. Since the begin-ning of the 20th century, emphasis onquality of crop production, especially inturf management, .has increased to aprime factor. Here, too, potassium andplant quality are very closely related. Itseems only profitable, then, to surveybriefly what is known of the potassium-plant relationships.

Function of Potassium in PlantsVoluminous amounts of investigations

on potassium-plant relationships haveclearly indicated that unlike nitrogen,Iphosphorus, calcium, and magnesium,

USGA JOURNAL AND TURF MANAGEMENT: FEBRUARY, 1962 27

28

pota.ssium is not a permanent component and calcium in the plant sap increasesof any organic compound or structural the uptake of nitrate nitrogen. Thesepart of plants. Its total apparent existence same investigators state further thatis in the form of soluble inorganic and such activity does not seem to hold trueorganic salts, the greater portion being with all species of plants.the inorganic forms. There is considerable belief, however,

Recent investigations have indicated that potassium definitely influences thethat potassium affects the metabolic ac- synthesis of proteins in plants. Some in-tivities of plants in several ways, most vestigators believe there is a direct rela-of which appear to be enzymatic. Law- tionship between potassium and proteinton and Cook report that evidence now synthesis while others hold that the rela-available shows that potassium affects tionship is an indirect one. The overallthe following processes: (1) synthesis of effect agreed upon is that potassium-de-carbohydrates, (2) translocation of car- ficient plants are generally lower thanbohydrates, (3) reduction of nitrates and normal in protein content. Along thissynthesis of proteins, particularly in same line it is suggested that with highmeristem tissues, and (4) normal cell nitrogen supply and deficiency of potassi-division. It is also suggested that potas- urn there may result a toxic conditionsium plays a part in maintaining turgor to plants from a too high a.ccumulationin plant cells as well as increasing of ammonia in the plant.disease resistance. Research further indi-cates to some investigators that potassi- A number of reports have been made

. that potassium is in some way as-urn may affect photosynthesis through Its sociated with cell division and activelyinfluence on chlorophyll. growing plant tissues. Often it has been

Concerning carbohydrate synthesis, it found that in potassium deficient plantshas been reported that a decrease in the potassium is moved from older tis-available potassium is associated with a sues to the actively dividing cells of thedecrease in carbohydrate content of the meristematic tissues. The effects of thisplant and that high potassium content phenomenon are observed in grasses byis necessary for high carbohydrate syn- a yellowing of the margins and tips ofthesis. It has been suggested that po- grass blades. In such a case the potassi-tassium may play a major part in the urn, being deficient in the plant, has mi-formation of more complex sugars and grated to the base of the leaves where in-starches from the simple sugars in tercalary meristematic tissues exist.plants-a lack of potassium appeared to There is still a great deal of doubt as tocause an increase in simple sugars as the function of potassium in cell division,compared to total carbohydrate. but the feeling is that it is associated

Practically coupled with potassium- with protein synthesis.carbohydrate studies has been the in- Adequate levels of potassium in thevestigations of potassium as related to plant have been reported to maintainthe structure of stems and cell walls. It and in some cases increase disease re-is generally held that adequate supplies sistence in the plant. Here again justof potassium are necessary for the forma- how potassi.um causes this effect is nottion of stiff straw or stalk. Researchers known. A general belief is that it ishave reported that when carbohydrates brought about by the ability of potassi-are present in high amounts, stem struc- urn to regulate chemical reactions in thetures are likely to be strongest. Such a cells of the plant. When potassium isreport strongly supports the potassium- deficient, there usually exists excess ni-stiff straw relationship. But if carbohy- trate and phosphorus, thinner cell wallsdrates are used up in protein synthesis in epidermal tissues, reduced productionas when high amounts of available nitro- of amino acids because nitrate reductiongen are present, stems and plant tissue is suppressed, a marked decrease or haltmay not be stiff even though there is an in the accumulation of carbohydrates, aabundant amount of potassium present failure to' produce new cells for want ofin the plant. essential amino acids for the protoplasm,

There are a few workers who have sug- and slower growth of meristematic tis-gested that the presence of potassium sues that would permit replacement of

USGA JOURNAL AND TURF MANAGEMENT: FEBRUARY, 1962

diseased tissues. Under such conditionscaused by potassium deficiency, diseaseorganisms can more easily enter the thincell walls, obtain the abundantly avail-able nitrogen necessary for their growth,and more easily damage plant tissueswhich the plant is unable to replace ata competitive rate.

Potassium is also given partial creditfor the maintenance of proper turgor inplant cells. Turgor is the state of livingcells being plump and swollen as a re-sult of internal water pressure. In thisrespect it is reported that potassium af-fects the cell sap and helps to regulatethe degree of swelling and the watereconomy of cells.

Concerning potassium and photosyn-thesis, some workers suggest that po-tassium has an indirect effect. It isknown that photosynthesis takes place inthe chlorophyll molecule, and that C02as well as water and light are needed forthe process. Some scientists feel thatpotassium enables the chlorophyll mole-cule to accept C02 more readily, whichin turn affects the photosynthesis pro-cess-the process from which plant foodis derived. It is also thought that po-tassium, perhaps by way of activatingenzymes, plays a definite role in themanufacture of the chlorophyll molecule.

A. G. Kennelly has been quoted as sum-marizing the role of potassium in plantsas follows: "Potassium is important inthe general health of the plant, par-ticularly in developing sturdiness anddisease resistance. It helps to promotethe growth of woody tissues and usuallyimproves texture, color, and quality."

Supply of Potassium to the Plant

The plant receives its potassium fromthe soil. It is generally known thatheavy soils or soils high in clay contenthave the ability to hold more availablepotassium than light soils or those highin sand content. The available potassiumis supplied to the soil from the weather-ing of potassium minerals, which con-tain unavailable potassium. Generallythe unavailable potassium makes up ap-proximately 99% of the total potassiumin the soil. In many cases the amountof such mi nerals in the soil and the rateof weathc:"ing of these minerals is great

enough to supply adequate amounts ofavailable potassium to the plant. How-ever, when the weathering of enoughminerals is too slow or the available po-tassium is lost at too rapid a rate byplant removel, leaching, and erosion, po-tassium must be added to the soil in theform of fertilizer.

The available potassium is taken intothe plant by the root. There is wide-spread belief that the root cells im-mediately associated with the uptake ofpotassium and other minerals as wellmust exert a considerable amount ofenergy in order to absorb the potassium.

It has been well recognized that soilaeration is necessary for normal rootgrowth and nutrient absorption by roots.And it has been observed that poor aera-tion apparently has more pronounced in-hibitory effects on potassium than onany other elements. The effects of aera-tion on potassium absorption are pri-marily on the plant roots and not on thestatus of potassium in the soil. The ef-fects of a lack or adequate aeration aredue to either a lack of oxygen to theroots, or a toxic effect of too much car-bon dioxide on the roots, or both. Thi~point still remains a mystery. Excess soilmoisture and soil compaction affect theabsorption of potassium in that theylimit soil aeration. Unless a soil can beadequately drained and relieved of com-paction, areation will be limited.

A number of investigators have foundthat very low soil moisture considerablyreduces the absorption of potassium bythe plant. This effect is a result of boththe dehydration of the plant and a re-duced availability of the soil potassium.

Most workers have concluded thatmineral nutrient absorption is reducedunder low environmental temperatures.,It has been found that within the rangeof 50° F. and 77° F. potassium absorptionchanged directly as the temperaturechanged.

Potassium Fertilization ofTurfgrass Areas

There are a number of potassium ferti-lizer materials. The most widely usedmaterial, however, is potassium chloride,commonly called muriate of potash,which contains from 50 to 60 per cent

USGA !OURNAL AND TURF MANAGEMENT: FEBRUARY, 1962 29

K20. This fertilizer can be applied aloneor in a fertilizer mixture with phospho-rus and/or nitrogen materials.

The amount of potassium fertilizer toapply and the time to apply it will de-pend on several factors. These factorsare: (1) The amount of available po-tassium in the soil. If, at any time dur-ing the growing period of the turf theavailable potassium is not sufficient, po-tassium will need to be added in aquantity high enough to adequately raisethe potassium level. (2) The kind andamount of clay in the soil. Some typesof clays hold more potassium thanothers, and some clay types hold potassi-um in a more available form than others.If a soil is high in clay, it will be ableto hold more potassium than a soil whichis primarily sandy. A sandy soil willneed small but frequent applications ofpotassium whereas a soil high in claymay be able to provide sufficient po-tassium with larger but less frequentpotassium applications. (3) The type ofwatering program. Where the wateringprogram is heavy, potassium will tend toleach out of the soil more readily thanwhere the watering program is light.(4) Whether or not clippings are re-moved. Grass clippings contain a con-siderable amount of nitrogen, phospho-rus, and potassium. O. J. Noel' has re-ported that clippings removed from agolf green in Memphis, Tennessee con-tained nitrogen, phosphoric acid, and pot-ash in the approximate ratio of 3-1-2,respectively. If the clippings are removedinstead of being allowed to remain onthe turf, potassium will be depletedmore rapidly. (5) The kind of grassgrown. All turfgrass species and varie-ties need available supplies of essentialnutrients. However, some turfgrasses arecool season types and others are warmseason types, and because of this dif-ference the various types require greateramounts of nutrients at different timesof the year. (6) The particular manage-ment of the turf. In general a turf thatis mowed close and frequently will needmore potash than one that is mowedhigher and less frequently. A turf areathat is designed to be kept in an activegrowing state the year round by eitheroverseeding warm season grasses or bythe use of permanent cool seasongrasses will more than likely need

to be fertilized with potash morefrequently and with an overall increasein amount of potash. On the other handa turf area that is allowed to go dormantor partially so in the winter will not needan addition of potassium during the win-ter. In many cases the winter dormantperiod gives the potassium minerals timeto weather, the result of which is at leasta partial replenishment of the availablepotassium in the soil. If such weatheringis inadequate to supply all the neededavailable potassium for the followinggrowing season, applications of potassi-um will need to be made in the springand anytime thereafter if the availablepotassium supply becomes short. It isalso a good policy to have sufficientquantities of available potassium in thesoil in the fall in order that the turf canbecome "hardened" for the cold wintertemperatures. It is felt that plants wellsupplied in potassium and not overlytender due to high applications of nitro-gen in the fall will be more capable ofsurviving freezing temperatures of thewinter. There is also the possibility ofgetting too much available potassium inthe soil. Plants are apparently unable toregulate the uptake of potassium; and iftte soil supply is high enough, a so calledluxury consumption may result. Undersuch conditions, the high potassium con-tent in the grass plant may cause an ex-cessive amount of stiffness in the stemsand leaves as well as other undesirableor harmful effects. (7) The generalweather conditions of the area. If thereis a great amount of rainfall there is aptto be a need for more available potassiumin the soil to replace that lost by leach-ing.

REFERENCES

BLACK, C. A. Soil.Plant Relationships. JohnWiley & Sons, Inc. 1957; FERGUSON, M. H.>Fer-tilization of Turfgrasses. U.S.G.A. Journal andTurf Management: 3()"32. August, 1955; LAWTON,K. and COOK, R. L.> Potassium in Plant Nutri-tion. Advances in Agronomy VI: 253-303, 1954;MCNEW, G. L. The Effects of Soil Fertility. PlantDiseases the Yearbook of Agriculture: 100-114.1953; MUSSER, H. B. Getting the Most out ofFertilizer. The Golf Course Reporter: 5.8.> May,1955; NOER, O. J. Fertilizer-When, Where, HowMuch. The Golf Course Reporter Conference Is-sue: 52-55, 1956; REITEMEIER, R. F. Soil Potassi-um and Fertility. Soils the Yearbook of Agricul-ture: 101-106, 1957; WORLEY, R. E. Growth andComposition of Three Grasses as Affected by Po-tassium and Nitrogen.> Ph.D. Thesis. VirginiaPolytechnic Institute. 1960.

30 USGA JOURNAL AND TURF MANAGEMENT: FEBRUARY, 1962