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Control of Leaf Rusts

This guide outlines effective strategies for controlling leaf rusts and bacterial diseases in greenhouse plants. Regular scouting for infected foliage and the removal of weeds and alternate hosts are essential for managing these diseases. Key fungicides for leaf rusts include myclobutanil, propiconazole, and azoxystrobin. Understanding bacterial leaf spots, distinguishing them from fungal spots, and employing good sanitation practices are crucial. The guide also covers virus management and the impact of foliar nematodes, emphasizing the importance of disease awareness and resistant cultivars for effective plant health management.

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Control of Leaf Rusts

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  1. Control of Leaf Rusts • Scout regularly and remove infected plants or foliage • Remove weeds or alternate hosts • Water when leaves will dry quickly • Fungicides to reduce spread: myclobutanil (Systhane), propiconazole (Banner Maxx), azoxystrobin (Heritage), flutolanil (Contrast), chlorothalonil (Daconil), triadimefon (Strike), oxycarboxin (Plantvax)

  2. Bacterial Leaf Spots • May not be visually distinguished from fungal leaf spots • More active in warmer temperatures than fungi • Common hosts: poinsettia, geranium, impatiens, ivy, mums, petunia, begonia

  3. Bacterial Leaf Spots • Leaves have small, round, water-soaked lesions that turn brown • Water-soaked tissue looks greasy or oily, best seen on underside • Spots may have yellow halo • Center of lesion, tan with purple/red margin R. Lentini T Eaker

  4. GW Moorman Bacterial Leaf Spots • Distinguish from fungal spots by: • Water-soaking • Look for fungal fruiting bodies in center of spots • Texture of the spots T. Eaker

  5. Other Bacterial Diseases • Xanthomonas – Geranium • Erwinia soft rot – dahlia, begonia, primrose • Bad odor GW Moorman

  6. Control of Bacterial Diseases • Good sanitation critical • Discard infected plants • Minimize overhead sprinkler irrigation • Chemical control rarely effective • Labeled for bacteria control: copper hydroxide (Kocide), copper sulfate pentahydrate (Phyton 27) and fosetyl-Al (Aliette)

  7. Viruses • Most common in greenhouse • Impatiens Necrotic Spot Virus – INSV • Tomato Spotted Wilt Virus – TSWV • Spread primarily by Western flower thrips • Wide host range • Cucumber Mosaic Virus (CMV) • Vectored by aphids • Wide host range GA Salsbury

  8. Impatiens Necrotic Spot Virus (INSV)

  9. Tomato Spotted Wilt Virus (TSWV) Agdia Agdia

  10. Other Viruses Agdia Agdia Tospovirus Ringspot virus Agdia Hosta X virus

  11. Virus Management • Symptoms vary with host • Scout regularly and remove infected plants • Monitor and control thrips and aphids • Use caution in carry-over of plants • Quarantine new material (esp. vegetative material) • No chemical control available

  12. Foliar Nematodes GW Moorman • Microscopic, parasitic, roundworms or eelworms • 250 susceptible crops • Begonia, African violets, mums, hosta, verbena, heuchera, helleborus and other perennials

  13. Foliar Nematodes • Symptoms like bacterial leaf spots or downy mildew • To test: • Remove suspected leaf • Chop in water • View under scope (hand lens) for worm-like nematodes in the water

  14. Control of Foliar Nematodes • Do not propagate infested material • Good sanitation • Keep foliage dry • Reduce plant to plant contact • Discard infested plants • No chemical controls available • Hot water dip may help, but plants may be injured by treatment

  15. Disease Management • Verify your purchases are clean • Know your plant • Use resistant cultivars • Know what diseases to expect • History of greenhouse and crop • Know the diseases in your area • Learn about the diseases • Watch the weather • Know your control options

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