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Disease SymptomsAnd Identification

Helminthosporium or leaf blight can be identifiedfrom the characteristic circular lesions on the leaves(Figure 2, page 1). Leaf spots are more numerous nearthe collar of the leaf blade. Leaf lesions are irregularlyshaped and brownish green to black in color. Infectedplants may occur in irregular patches. Extensive dam-age occurs when the pathogen attacks crowns, stolonsand rhizomes. Severely affected hayfields may becomebrown and thin. Under a microscope or hand lens thefruiting bodies (conidia or conidiophores) of B. cyno-dontis are cylindrical and multi-celled (inset of Figure2). This clearly distinguishes Helminthosporium fromrust urediniospores. The disease cycle of bermudagrassleaf spot/blotch is depicted in Figure 3.

Leaf rust or Puccinia looks similar in nature to thenaked eye as Helminthosporium (Figure 4, page 3), butcan be identified microscopically by the more circularfruiting bodies in the inset. Numerous, small, red toorange lesions can be observed on leaf and stem tissue.Puccinia or rust lesions start as a small raised area orblister (pustule). The blister ruptures reveal a powderymass of orange red urediniospores. Identification of thespecific pathogen is interesting. For example, rubbingan infected leaf will leave rusty colored areas on yourfingers or clothing. Disease management for leaf blight

and leaf rust are similar, so both diseases will be broad-ly referred to as leaf spot in this bulletin.

Disease ManagementThe most effective way to treat bermudagrass leaf

spot or blotch is avoidance. There are five managementpractices that are effective in decreasing risk of diseaseinfection including: a) selecting a resistant bermuda-grass variety, b) maintaining soil fertility, c) managingirrigation, d) removing thatch and e) harvesting foragein a timely manner.

VARIETY SELECTION. Without a doubt the mosteffective practice to control leaf spot is to select aresistant variety. All selections that were released fromDr. Glenn Burton’s breeding program in Tifton,Georgia, were screened for leaf spot resistance. Thismeans that Coastal, Tifton 44 and Tifton 85 all havesome degree of disease resistance. While infected fieldsof Coastal or Tifton 85 are occasionally seen inGeorgia, infections are not typically severe. Observa-tions indicate that poor soil fertility or extremely dampweather has contributed to the problem.

Russell also appears to have good resistance to theleaf spot diseases. While there is no formal data on thisresistance, few or no reports have surfaced regardingleaf spot diseases on this variety in Alabama orGeorgia. On the other hand, some bermudagrass

Figure 3. Bermudagrass leaf spot disease cycle.

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varieties are highly susceptible. While not a formalvariety, common bermudagrass is often infected withleaf spot and is probably the most commonly reportedsusceptible “variety.” Most reported problems are inunder-grazed pastures during late summer. Twoimproved varieties also appear to be extremely suscep-tible: Alicia and World Feeder. Note that both of thesecultivars were introduced to Georgia from more aridareas of central Texas and Oklahoma. It is not uncom-mon to observe increased disease susceptibility whenvarieties originating from arid climates are introducedinto more humid areas.

SOIL FERTILITY. Resistant varieties can still be in-fected with leaf diseases, particularly when soil fertilityis low. The severity of leaf spot can be minimized usingmanagement practices once the stand is established.The most important practice is to sample soil andmaintain adequate levels of fertility. Soil potassium iscritical for leaf spot resistance. Most reported leaf spotcases are directly related to low soil potash. Nutrientsare removed from bermudagrass hay fields in approx-imately a 4-1-3 ratio of N, P2O5, and K2O with hayharvest. That means that 75 percent as much potash asnitrogen should be applied each season. Potash can beapplied in single applications in the heavy soils of northGeorgia or in split applications in any portion of thestate. Split applications are particularly helpful in sandysoils.

Please note that soil tests can be misleading. Therehave been cases where adequate soil levels were pre-sent, but plant tissue samples indicate a nutrient defi-ciency. If leaf spot has become a problem and soil testsdo not recommend potassium, submit a clipped sample

of hay for plant tissue analysis. If the sample analysisindicates a potassium level less than 1.8 percent on adry matter basis, then apply additional potash.

IRRIGATION MANAGEMENT. Fungal diseases thrivein warm and wet environments. While it is impossibleto control moisture in dryland situations, with irrigatedsituations some control is possible. Leaf spot diseasesneed several hours of continual leaf wetness to thrive.Several producers have effectively decreased the pre-valence of leaf spot infections on Alicia bermudagrassin southeast Georgia by turning off irrigation waterfrom mid-afternoon until the following morning. Thisallows bermudagrass leaves to dry and prevents plantsfrom staying wet through mid-morning the followingday.

MINIMIZE THATCH. Some leaf spot infectionsappear to be associated with the amount of thatch pre-sent in hay fields, with heavy thatch loads producinghigher incidences of leaf spot. Thatch ties up nutrientsand contains abundant decaying material, which mayserve as a “spore reservoir.” In addition, thatch retainswater and reduces air circulation, creating humid con-ditions and promoting leaf spot incidence. The onlypractical way to reduce thatch is to burn in springmonths just prior to bermudagrass green-up. Consultyour local forestry group to make sure that all precau-tions are taken, as fires can easily escape.

MAINTAIN A FREQUENT CUTTING INTERVAL.Maintaining a proper cutting interval does more thankeep nutrient quality of hay high. Timely cutting mayimprove leaf spot resistance, at least indirectly. Thepotassium necessary for leaf spot resistance is mobile inplants and typically moves from older to younger tissuewhen there is a nutrient deficiency. This predisposesolder tissue to infection from leaf spot diseases. Thistopic has not been formally researched, but a wealth ofinformation on other plant systems supports the logicbehind this theory in bermudagrass species.

What if I FailTo Prevent the Disease?

There are no legal, effective or economical fungi-cides to control leaf spot in forage bermudagrass. Thisremoves any possibility of chemical control. The onlyeffective management practice in cases of severe infec-tion is to remove the infected tissue and fertilize lowfertility fields. Ideally, enough material is present toharvest as hay so that material can be removed from thefield. Resulting hay quality will be decreased and pala-

Figure 4. Puccinia or leaf rust on bermudagrass. Insetshows magnified conidiophores of leaf rust.

Reviewed March 2012