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Home , Poa, Red, Shades of purple

Why Putting Appear or in Winter and Spring

Peter H. Dernoeden completely moved out of the and they accumulate. There are many types of . Glucose is a common he first frosty nights in autumn bring about some pro- and sometimes glucose molecules are chemi- Tnounced physiological changes in . In creeping cally bound with . Anthocyanins are bentgrass ( stolonifera), especially on lower-cut and their function in plants is unclear. They provide the putting greens, the leaves may develop a reddish-, red, purple, and in flowers. Anthocyanins are purple, or blue-gray . The discoloration may be uni- always present in leaves, but normally are masked by the form, but frequently the various , red, or presence of . They are expressed in the foliage blue appear in circular patches. These patches constitute of trees during cool and bright weather to provide the different clones within the bentgrass polystand. The col- spectacular colors in autumn leaves. Hence, bentgrasses ors are most prevalent on older greens, especially those may experience a similar accumulation of sugar, and there- seeded to Seaside or "South German" bentgrasses. These fore anthocyanins, following the first cool or frosty night varieties were genetically variable and as a result not all of fall. Frost injury may denature the chlorophyll, plants emerging from seed were true to type. Hence, indi- thereby exposing the . These colors vidual plants would grow and the more aggressive types may intensify and persist throughout winter months and would dominate to produce circular patches. These patches slowly disappear in mid-spring after the turf begins active are not unlike the circular areas of blighted turf associated growth. with some diseases. The purplish discoloration often is A similar phenomenon can occur on bentgrass greens, misdiagnosed as red (Drechslera erythrospila) tees, and fairways in the spring. This usually coincides by some golf course superintendents. Helminthosporium with unseasonably warm in late winter or diseases that cause leaf spot and melting-out are not com- early spring, which stimulates a premature green-up of monplace on creeping bentgrass, but leaf lesioning can bentgrass and annual bluegrass. Should night tempera- cause a reddish-brown discoloration and subsequent se- tures plummet into the low 20s°F (-7°C), or if there are vere thinning in Kentucky bluegrass () and several nights of frost following a premature green-up, perennial ryegrass (.Lolium perenne) turfs. The purpling the bentgrass and annual bluegrass again may develop a from frost often is prominent in Penncross greens. Since reddish-brown, brick-red, or dark-purple color. This con- Penncross has three parents, at least three different types dition is aggravated by topdressing, brushing, core culti- of color patches or clones can appear on greens. Similar vation, foot traffic (especially around the hole, and in color changes can appear in older stands of Pennlinks, entrances and exit areas), and other grooming practices Southshore, Providence, and all of the newer seeded performed at the time cold temperatures recur following bentgrass cultivars. Some cultivars, such as Crenshaw, may an early green-up. Use of plant growth regulators, and display a more uniform, purplish color in winter. The dry and windy weather further contribute to the redden- same purple color also can occur in annual bluegrass (Poa ing or purpling of creeping bentgrass. Helminthosporium- annua), but seems to be more commonly associated with like lesions may develop on these leaves, but it should be the perennial types rather than the annual types. noted that water-soaked leaf lesions can develop in re- Why do putting green grasses turn red, blue, or purple? sponse to many different kinds of injury mechanisms. The cool to cold temperatures trigger the color responses. Therefore, the lesions observed on red or purple leaves During mid to late October, many regions experience rela- during cold periods most likely are caused by mechanical tively warm days (65 to 75°F; 17 to 24°C), but cool nights injury associated with grooming, topdressing, or mowing (32 to 55°F; 0 to 13°C). The sunny, bright, and warm greens too early in the morning following a frosty night. days stimulate plants to produce large amounts of sugars The bentgrass will recover rapidly with the advent of con- (through ) in leaf blades and sheaths. At sistently warmer weather (i.e., days >70°F; 21°C and night night, the sugars must be translocated out of the leaves to >45°F; 7°C). An application of about 0.1 to 0.2 lb N/1000 crowns for storage or use in other physiological processes. ft2 (5 to 10 kg N/ha) from a water-soluble nitrogen source When nights are very cool or frosty the sugars are not will speed recovery as daily temperatures rise. ...Putting Greens... Continued from page 4

Despite the aforementioned explanation, many per- autumn to spring for controlling winter diseases on greens sist in believing that the reddish color of greens must be (e.g., snow molds) also may help explain why leaf spot- disease. After all, textbook photos or red leaf spot dis- ting and melting-out diseases are uncommon in the spring ease on greens depict symptoms almost identical to frost on creeping bentgrass. injury. To explain this better it may be helpful to re- During the summer Bipolaris sorokiniana can attach view the Helminthosporium diseases and their incitants. bentgrass, but the melting-out phase is uncommon in Many of the fungi that cause leaf spotting and melting- creeping bentgrass. Colonial bentgrass, however, may out diseases of turfgrasses once belonged in the taxo- exhibit melting-out in the summer, particularly when nomic Helminthosporium. Today, these fungi are treated routinely with sterol-inhibitor (DMI) or benz- more appropriately referred to as of Drechslera imidazole fungicides. Again, this is probably due to the or Bipolaris. Because these diseases have been known routine use of the aforementioned fungicides for com- for decades as Helminthosporium leaf spot and melting- bating summer diseases. Regardless, it is not unusual to out, most people do not recognize names other than find a few zonate lesions (i.e., circular to oblong, brown- "Helminthosporium." Thus, Helminthosporium often is ish-purple lesions with or without a spot in the cen- used as a generic name for all the Drechslera and ter) produced in response to B. sorokiniana spore Bipolaris species that can cause leaf spot or melting-out penetration on bentgrass leaves during summer stress diseases. Drechslera erythrospila is the causal agent of periods. red leaf spot. Most turf grass pathologists (Couch, 1995; Some golf course superintendents have reported see- Smiley et al., 1992; Smith et al., 1989; and Vargas, ing a positive response from a broad fungicide 1994) agree that red leaf spot is a warm weather disease applied in the spring to red, frost-injured greens. This that develops in late spring or early summer. In Ken- would be more convincing if an untreated strip were tucky, Vincelli and Doney (1995) reported that colo- left for comparative purposes! Assuming, however, that nial, brown top and dryland bentgrasses were very a positive response occurs, it may be due to the chemi- susceptible to red leaf spot, but all 15 cultivars of creep- cal impacting populations of "weak," secondary patho- ing bentgrass evaluated in their trial showed high levels gens or the activity of saprophytes. During cool weather, of resistance to D. erythrospila. There are other these organisms may be enhancing leaf senescence at a Drechslera species known to be associated with time when plants are not actively producing new leaves bentgrasses; they include D. catenaria and D. gigantea. and tillers for replacement of either frost-damaged or D. catenaria is the most likely species to attack bentgrass naturally senescing leaf tissue. in the spring, especially Toronto creeping bentgrass. A somewhat similar blackening or purpling of leaves Since our diagnostic lab opened in 1980, none of the also may be elicited by the following: iron applications, aforementioned Drechslera spp. have been associated low soil phosphorus levels, ammonium sulfate applica- with creeping bentgrass in Maryland. In mid-May of tion, high application rate of fungicides classified as ste- 1997, however, we did find D. dictyoides producing pro- rol inhibitors, some plant growth regulators, and arsenic digious numbers of spores on senescent or dead leaves toxicity. These responses are well known and can occur of Penncross creeping bentgrass from a new tee. The at any time of the year.^ sodded Penncross turf also was heavily infected with tuft disease. In this case, D. dictyoides likely Literature Cited was acting as an opportunistic saprophyte, because there Couch, H.B. 1995. Diseases of Turfgrasses. Krieger Pub- were no lesions on green leaves and spores were only lishing Co. Malabar, FL. found on dying or dead leaves. We also find red leaf Smiley, R.W., P.H. Dernoeden, and B.B. Clarke. 1992. spot (D. erythrospila) in late May and June on colonial Compendium of Turf grass Diseases. APS Press. St. bentgrass. Paul, MN. Most reports of Helminthosporium diseases in Agrostis Smith, J.D., N. Jackson, and A.R. Woolhouse. 1989. species have involved colonial bentgrass, redtop or veg- Fungal Diseases of Amenity Turf Grasses. E.&F.N. etatively propagated creeping bentgrass (e.g., Toronto). Spon. London and New York. Hence, the relative rarity of Helminthosporium diseases Vargas, J.M. 1994. Management of Turf grass Diseases. in creeping bentgrasses today may be due in part to bet- Lewis Publishers, Boca Raton, FL. ter resistance in Penncross and the many newer cultivars Vincelli, P. and J.C. Doney. 1995. Reaction of released in recent years. Furthermore, the widespread bentgrasses to Drechslera leaf blight. Biological and usage of broad spectrum fungicides applied from late Cultural Tests. 10:36.