An Introduction to Turfgrass Pathology Part 2

1. An Introduction to Turfgrass Pathology Part 2

2. Knowledge Requirements When you complete this section, you should be able to answer these questions • How do non-spore-forming fungi survive? • How do non-spore-forming fungi infect and cause disease? • In turfgrass pathology what species are hosts? • What are some environmental factors that influence turf disease?

3. Non-Spore-Forming Fungi As the name implies, non-spore-forming fungi are species of fungi that do not form spores or seldom form spores

4. Non-Spore-Forming Fungi Some species of non-spore-forming fungi only form hyphae. Other species of non-spore-forming fungi produce hyphae and specialized survival structures called sclerotia.

5. Non-spore-forming fungi that only form hyphae survive adverse conditions, such as cold winters, as dormant hyphae in leaf, root, stolon or rhizome tissue that was infected in previous seasons. When environmental conditions (temperature, plant wetness) are optimum for fungal growth, new hyphal cells are produced by the dormant hyphae. This new fungal growth can infect plant tissue and reignite disease symptoms.

6. Dollar spot is an example of a disease is caused by a non-spore- forming fungus that produce only hyphae. 1. 2. Next slide Dollar spot occurs in the spring and fall when day- time temperatures range from 50 to 90°F and night temps. are between 45 and 70°F. In addition, leaves must be wet from dew, irrigation or rain for at least 10-14 hrs. The dollar spot fungus forms hyphae that grows among leaf blades inducing white lesions. When many leaves are infected, bleached white spots, about the size of a silver dollar (image 1 above) can be observed on a turf swards such as golf greens, home lawns or athletic fields.

7. 3. 4. The dollar spot fungus stops growing at temps above 90° or below 45° and symptoms appear to vanish due to growth of new turf foliage (see image 3 above). However, the old leaves with dollar spot lesions are still deep in the turf canopy. When leaves are wet and temps become conducive for hyphal growth, the dollar spot fungus grows out of old lesions formed the previous season or year. The hyphae infects new leaves and the dollar spot disease cycle starts again.

8. Gray Snow Mold and Southern Blight are examples of non-spore-forming fungi that produce hyphae and sclerotia.

9. A sclerotium is formed from tightly aggregated hyphal cells. Sclerotia often appear as hard pellet-like structures ranging in size from <1 mm to several mm in diameter

10. Sclerotia on surface of bentgrass leaves infected with the snowmold fungus Typhula incarnata. Unlike spores, sclerotia are often large enough to see with the naked eye.

11. Southern blight of creeping bentgrass caused by Sclerotium rolfsii Note hundreds of sclerotia formed on the surface of the root zone. White mycelium

12. Sclerotia lay dormant in thatch or soil until environmental conditions trigger germination. Sclerotia germinate by producing hyphae that grow in search of a food source such as a living turfgrass plant. Hyphae Sclerotium

13. Hyphae from non-spore-forming fungi grow from sclerotia or from dormant hyphae in previously infected plant tissue. When the hyphae comes in contact with leaves, roots, stolons or rhizomes, it usually penetrates through stomata, wounds or natural opennings. Infection of leaf by spore-forming fungi

14. Examples of turf diseases caused by non-spore-forming fungi Dollar spot - hyphae only Brown patch – hyphae and sclerotia Large patch – hyphae and sclerotia Southern blight – hyphae and sclerotia Gray snow mold – hyphae and sclerotia Pink patch – hyphae only Red Thread – hyphae only White patch – hyphae only

15. Now that we have completed an introduction to the Pathogen side of the Disease Triangle we’ll move on to the Host side. The Host Side of the Disease Triangle Pathogen Host Disease Environment

16. A Host is any plant or animal that is infected by a living pathogen. All species of cool season and warm season grasses can serve as hosts of various pathogens.

17. HOSTS Cool Season Grasses Kentucky bluegrass Creeping bentgrass Perennial ryegrass Fine leaf fescues Tall fescue Rough bluegrass * * * * * *

18. HOSTS Warm Season Grasses Bermudagrass Centipedegrass Zoysiagrass St. Augustinegrass Bahiagrass Seashore Paspalum * * * * * *

19. You should be familiar with the characteristics used to distinguish one turfgrass species from another because: Some diseases occur only on specific grass species, while other diseases affect several species of turf. Some diseases occur on both warm season and cool season grasses. Other diseases are specific to either warm or cool season grasses. Review a turfgrass science text if you’re not familiar with distinguishing features of turfgrass species.

20. The Environment Side of the Disease Triangle Pathogen Host Disease Environment

21. When we talk about environment in reference to disease, we’re referring to all external factors that may influence the interaction between the pathogen and host.

22. Some Environmental Factors that Influence Turf Disease Soil and air temperature *

23. Some Environmental Factors that Influence Turf Disease Soil and air temperature Duration of plant surface wetness * *

24. Most fungi require >10 hrs. of continuous plant surface wetness in order to infect.

25. Some Environmental Factors that Influence Turf Disease Soil and air temperature Duration of plant surface wetness Soil moisture * * *

26. Some Environmental Factors that Influence Turf Disease Soil and air temperature Duration of plant surface wetness Soil moisture Soil pH * * * *

27. Some Environmental Factors that Influence Turf Disease Soil and air temperature Duration of plant surface wetness Soil moisture Soil pH Thatch * * * * *

28. Thatch – An accumulation of living and dead roots, rhizomes and/or stolons.

29. Some Environmental Factors that Influence Turf Disease Soil and air temperature Duration of plant surface wetness Soil moisture Soil pH Thatch Soil compaction * * * * * *

30. Some Environmental Factors that Influence Turf Disease Soil and air temperature Duration of plant surface wetness Soil moisture Soil pH Thatch Soil compaction Nonpathogenic microbes in soil and on plant surfaces * * * * * * *

31. Now that we have completed an introduction to the disease triangle, let’s put everything together. Pathogen Host Disease Environment

32. An Example of a Disease Triangle Pathogen Host Gaeumannomyces graminis var. avenae Creeping bentgrass Take-All Patch Soil temp. 40-60°F Soil pH >6.2 High soil moisture Optimum environmental conditions for disease development

33. Another Example of a Disease Triangle Several species of cool and warm season grasses. Colletotrichum cereale Bentgrasses and annual bluegrass are highly susceptible. Anthracnose High temp. stress on turf Low fertility Soil compaction Leaf wetness >12 hrs.

34. By the end of this course, you should be able to draw a Disease Triangle for each disease that we discuss.

35. End of Introduction to Turfgrass Pathology Part 2