Diseases of Alfalfa and Orchardgrass

1. Diseases of Alfalfa and Orchardgrass Erik L. Stromberg Professor and Extension Plant Pathologist, Agronomic Crops Department of Plant Pathology, Physiology and Weed Science Virginia Polytechnic Institute and State University Blacksburg, Virginia

2. Promoting Healthy Alfalfa Stands Use good cultural and management practices Rhizobia-treated, high quality seed Locally adapted disease resistant cultivars Weed free seedbed Well drained soil at pH 6.5-8.0 Soil fertility adjusted according laboratory analysis before planting

3. Promoting Healthy Alfalfa Stands Seeds are small and require shallow planting Firm, moist seedbed Stands persist by regenerative growth from healthy crowns Plants are subject multiple wounds � mower blades, machinery tires during harvest Harvests should be timed to maintain plant vigor

4. Phytophthora Root Rot Phytophthora medicaginis Survives in organic debris active in wet soil --- produces zoospores which �swim� to roots Yellow, red, or purple discoloration of leaves --- dark lesions on tap roots -- rotting lateral roots Control: Well-drained fields, crop rotation, resistant cultivars

5. Verticillium Wilt of Alfalfa Verticillium albo-atrum � vascular wilt Found in Maryland in May 1986 Spread by contaminated farm machinery, seed, or air- borne spores Once in field it spreads with cuttings Can survive in weeds Can be spread by insects

6. Verticillium Wilt of Alfalfa Symptoms do not usually appear until 3rd year of production Affected plants scattered or in patches Early stages leaflets wilt during slight water deficit A yellow, V-shaped discoloration at leaflet tip Eventually, leaflets turn yellow or pink, and curl or twist

7. Control of Verticillium Wilt of Alfalfa On farms where this disease is present resistant cultivars must be used Crop rotation � 2-3 years out of alfalfa Small grains or corn crops are not hosts Movement infested hay off farm is not good Pathogen does not survive passage through livestock

8. Sclerotinia Crown and Stem Rot Sclerotinia trifoliorum Problem with no-tillage stand establishment Survives as sclerotia in soil In fall sclerotia produce apothecia that release spores that infect leaves From leaf infection fungus moves down stem as white cottony mass to crown and kills young plants Produce sclerotia that persist in soil

9. Sclerotinia Crown and Stem Rot Often associated with no- tillage establishment in fescue/clover pastures Can cause complete stand failures Rotations of 3-4 years Rotate with cereal or grass crops (non- hosts)

10. Crown Rot of Alfalfa Complex of Fusarium, Phoma and Rhizoctonia species Bacteria and nematodes maybe associated Brown areas develop in crown tissue or root cortex Core of crown and tap root rotted or hollow Poor fertility, low potassium, low pH Damage to crowns from harvest equipment and grazing animals Choose adapted cultivars

11. Foliar Diseases of Alfalfa Cause defoliation Reduce hay quality Pathogens survive on dead leaves and/or stems Produce spores from leaves on the ground Spores infect new growth Infection favored by periods of moisture Some may be spread by harvest machinery

12. Common Leaf Spot Pseudopezia medicaginis Survives on dead leaves between cuttings where it produces spores that spread to new growth Favored by prolonged periods of cool, wet weather Most alfalfa cultivars have low levels of resistance Control: Early harvest to reduce leaf drop to reduce inoculum for regrowth

13. Lepto (or Pepper) Leaf Spot Leptosphaerulina briosiana Overwinters on leaf and stem debris Lesions small brown surrounded by yellow halo Favored by cool, wet weather Most common in spring, early summer, and fall Early harvest before leaflet drop reduces inoculum for regowth

14. Spring Black Stem Phoma medicaginis Dark brown to black spots on leaves and stems Leaves turn yellow and tend to wilt before dropping Most common in spring and fall Often common in first cutting Favored by cool, wet weather Early harvest can reduce disease development and quality of hay

15. Summer Black Stem and Leaf Spot Cercospora medicaginis Overwinters on infested stems Lesions on leaves and stems are chocolate to reddish brown, large, with fuzzy yellow margins Occurs on or after second cutting Favored by hot, wet and humid weather Early harvest to prevent loss of quality and yield

16. Anthracnose Colletotrichum trifolii Survives on stems, crowns, and crop debris Straw colored dead shoots scattered in field known as shepherd�s crook Lesions straw colored and diamond shaped, dark bordered, and tiny black structures that produce spores Favored by warm, humid conditions Clean debris from harvest equipment Harvest young fields before older stands Rotate out of alfalfa at least one year Select cultivars resistant to anthracnose

17. Diseases of Orchardgrass

18. Disease control strategies Sow only disease-free seed of improved, well-adapted cultivars Careful, controlled burning of dead grass in early spring if pastures are severely affected

19. Disease control strategies Rotate at least two years with non- grass crops where practical Suppress weed grasses by cultural or chemical means

20. Practices to avoid Excessive rates of fertilizers high in quickly available nitrogen Pure, dense stands of a single cultivar

21. Practices to avoid Leaving a heavy mat of hay on grass during wet weather Close grazing and/or mowing

22. Anthracnose � summer depression Colletotrichum graminicola Lesions first observed as water- soaked spots Lesions expand to reddish brown to orange Associated with warm, wet conditions

23. Brown stripe Scolecetrichum graminis Overwinters as masses of mycelia in living leaves and crop debris Produce spores in spring Rain splashed and wind-blown rain Ceases during hot, dry summer Resumes in wet fall conditions

24. Stagonospora leaf blotch Stagonospora arenaria Overwinter as pycnidia in dead leaf tissue Infection takes place during cool, wet, spring weather Small, slightly elongate-to-ellipitcal lesions form on leaves, leaf sheath early in growing season Pynidia (fruiting bodies), golden-brown to black form in the dead tissue of lesions

25. Powdery mildew Blumeria graminis f.sp. dactylidis Lesion are at first small and white effuse patches Pathogen is entirely superficial except for haustoria which penetrate the epidermal cells Disease is favored by cool, damp weather and high rates of nitrogen

26. Summer blight Drechslera dactylidis Associated with rainy conditions Lesions first appear irregular and spindle shaped, faint brick color to gray surrounded by chlorotic tissue Under severe conditions lesions fuse to blight entire leaf Wind-blown conidia Pathogen survives in colonized dead tissue

27. Barley yellow dwarf virus BYDV, luteovirus Aphid transmitted Infection adds stress to orchardgrass Cummulative effect over life of stand

28. Keys to reducing impact of disease Maintain proper fertility Well adapted orchardgrass cultivars Rotate with non-grass host for two years before establishing Follow recommended mowing and grazing practices Mixtures of grasses or cultivars Suppress weed species in stand

29. Questions?