Identification and Management of Ornamental Plant Diseases – Fall Update

1. Identification and Management of Ornamental Plant Diseases – Fall Update Jean Williams-Woodward Extension Plant Pathology UGA - Athens

2. What are we seeing now? • Black root rot caused by Thielaviopsisbasicola • Cercospora leaf spot • Downy mildew of impatiens • Boxwood blight

3. Black root rot – Thielaviopsisbasicola Cooler temperatures, wet soils, alkaline soil pH favor disease development Plants often infected during production Fungus survives in soil for years

4. Black root rot control • Maintain soil pH at 5.8 or below • Do not over water and plant in well-draining mix • Discard infected plants • Fungicide drenches can help reduce infection • Thiophanate methyl (3336, 6672) – high labeled rates • Fludioxonil (Medallion) • Polyoxin-D (Veranda) • Use less susceptible plants

5. Black root rot plant susceptibility Vinca Pansy/Viola Snapdragon Impatiens Petunia Calibrachoa Verbena Begonia Salvia Geranium Marigold Zinnia Dusty Miller Coleus Celosia SUSCEPTIBLE LESS SUSCEPTIBLE

6. Fungal Leaf Spots • Warm days, cool nights, high humidity favor leaf spot diseases caused by the fungi, especiallyCercosporaand relatives (Passalora, Pseudocercospora) • Fungi survive on leaf debris from previous crops • Defoliation is common

7. Fungal leaf spot control • Reduce leaf wetness • Remove infected leaves, plants • Use resistant cultivars or less susceptible plants • Use fungicides preventively and to reduce spread Cercospora leaf spot on pansy

8. Cercospora - Resistant Pansy Cultivars Bingo Red & Yellow Crown Blue Crown Golden Crystal Bowl Supreme Yellow Crystal Bowl True Blue Dynamite Red & Yellow Majestic Giants Yellow Viola ‘Sorbet Blackberry Cream’

9. More resistant pansies… • Pansy Patiolaseries cultivars • Purple Passion mix • Pure Yellow • Pure Lemon • Pure Orange were less susceptible to leaf spot than Colossus series cultivars

10. Cercospora Fungicides • Coppers (CuPRO) • Mancozeb (Fore, Dithane) • Chlorothalonil(Daconil) • Myclobutanil (Systhane, Eagle) • Propiconazole (Banner MAXX) • Thiophanate methyl (3336, 6672) • Strobilurins: • Azoxystrobin, pyraclostrobin, trifloxystrobin (Heritage, Insignia, Compass)

11. Impatiens Downy Mildew Caused by Plasmoparaobducens Affects all varieties and intraspecific hybrids of I. walleriana

12. Symptoms and Signs • Rapid defoliation • Subtle leaf discoloration • Leaf cupping • Sporulation on leaf underside

14. Rapid defoliation and plant collapse • Survival in landscapes, infected re-seeded plants

15. Systemic infection of plant • Oospores produced within leaf, stem, root tissue enables survival year to year, season to season • Windblown and water-splashed sporangia spread disease within current season

16. Landscape Considerations • Has occurred in GA this past summer, due to cooler and wetter conditions • Could occur where impatiens are grown as winter annuals • Needs cool, wet conditions! • Could occur in landscapes with no disease history • Blown in during storms or from infected plant material • Once a landscape bed becomes infected, it will remain infested with pathogen • Impatiens cannot be safely planted in bed again • Use begonias, New Guinea impatiens, coleus

17. Nursery Considerations • Demand for impatiens will decrease • Growers must change in product mix • Supply of impatiens plugs will decrease • Follow best management practices (BMPs) • Scout plants regularly • Discard infected immediately • Preventive fungicide sprays provide short-term protection

18. Downy mildew fungicidesfor impatiens downy mildew • Adorn (fluopicolide) • Fenstop (fenamidone) • Heritage (azoxystrobin) • Orvego (ametoctradin + dimethomorph) • Pageant (boscalid + pyraclostrobin) • Protect (mancozeb) • Stature (dimethopmorph) • Segway (cyazofamid) • Vital (potassium phosphite) • Aliette (fosetyl-AL) is ineffective

19. Boxwood or Box Blight • Caused by Cylindrocladiumpseudonaviculatum(syn. C. buxicola) • New to US in 2011 (September-October) • Now in CT, VA, NC, MA, MD, OR, OH • Still not widespread, but in nurseries and landscapes • Great concern for the green industry • Infects all species and cultivars of boxwood • Also infects Pachysandra (ground spurge) • Has not been identified in GA (yet)

20. Boxwood blight in CT (fall 2011)

21. Disease Development • This is a scary disease • Time from infection to leaf spot symptoms to defoliation can be 2 days • Introduction of an infected plant can spread disease to established landscape very quickly • Plants can become infected just by traveling in the same truck or sitting on the same loading dock with an infected plant

22. Symptoms and Signs • Leaf spots • Dark stem lesions • Foliage browning • Rapid defoliation • Tufting, white sporulation

24. Nursery Concerns • Spread easily via water-splashed spores, tools, workers (spores are very sticky) • Profuse sporulation • Microsclerotia allow for survival

25. Management • Very difficult to control • Discard infected plants immediately • Bag and dispose • Don’t place in compost or cull piles • Remove all fallen leaf litter and dispose • Treat area with propane torch to burn litter • Preventive fungicide treatments • Medallion (fludioxonil), Daconil (chlorothalonil), Insignia (pyraclostrobin) • Fungicides after infection are ineffective

26. Look-a-like • Volutella Blight (Volutellabuxi) • Often associated with weakened plants

27. Questions?