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Managing Herbaceous Perennial Diseases in the Nursery and Landscape
Cornell University – Long Island Horticultural Research & Extension Center
is found on all plants, B. elliptica
on lilies, B. paeoniae
Avoid excessive leaf wetness, low Ca or excess N; remove dead plants or plant parts.
Protect plants with Decree, Chipco 26019/Sextant, Daconil/Pathguard/Echo/Spectro, or
Medallion; Endorse; Coppers, mancozebs, strobilurins (Compass, Cygnus, Heritage, Insignia,
Pageant), CEASE, MycoStop, PlantShield HC also reduce Botrytis diseases.
Fungal leaf spots and anthracnoses
Septoria leaf spots on phlox, rudbeckia, aegopodium, mum; Ascochyta leaf spot on clematis =
“clematis wilt”; Heterosporium leaf spot on iris; Pyricularia leaf spot on hakonechloa;
Colletotrichum anthracnose diseases on bergenia and lupine. Scout for first symptoms of these
diseases and begin treatment promptly. Control by watering early, reducing leaf wetness duration,
spacing plants, removing badly spotted plants, cultivar choices. Control with contact fungicides:
Dithane/Protect DF/Zyban, Daconil/Echo/Pathguard/Spectro or systemics: 3336/6672/Spectro,
26/36; strobilurins (see Botrytis for list) or Eagle/Strike/Terraguard/BannerMAXX—best to use
both contact and systemic products in a rotation. Leaf spots are also caused by bacteria, downy
mildews and foliar nematodes: get a lab diagnosis!
Bacterial spots and stem rots
Stem rots are caused by Pectobacterium carotovorum
); leaf spots are due toXanthomonas
species. Reduce leaf wetness duration, don’t over-water or plant
deeply; control fungus gnats. Use coppers (e.g. Camelot, Kocide, Phyton 27) or CEASE.
Seen on solidago, campanula, viola, panicum. mum, daylily, veronica, etc. Keep leaf surfaces as
dry as possible. Find less susceptible cultivars. Use contact (copper, mancozeb) fungicides in
rotation with systemics: strobilurins (see above); and/or BannerMAXX/Eagle/Strike/TerraguardSmuts:
Round pale spots that turn brown on dahlia & gaillardia. Use rust controls.
Downy mildews (DM)
Seen on iberis, veronica, geum, agastache, lamium, geranium, coreopsis, rudbeckia (Goldsturm
esp.). High humidity favors: keep plants spaced. Contact fungicides: coppers and mancozebs.
Systemic fungicides: Stature DM, FenStop, Disarm (coming soon); strobilurins (see list above);
Aliette/Alude and other phos acids. Related plants may share the same downy mildew: agastache
is susceptible to the new coleus DM.
Foliar nematode (Aphelenchoides
) seen especially on Japanese anemone, bergenia, heuchera,
hosta, lamium, peony, ferns. Stem and bulb nematode (Ditylenchus
) common on creeping phlox.
Avoid excess shading or overhead watering. Inspect incoming plants. Pylon treatment may help.
Powdery mildew (PM)
Powdery mildew prone plants include phlox, monarda, asters, sedum (watch for scabby
symptoms that are not easily recognizeable as PM), verbena, delphinium, columbine and peony.
Phlox cvs. less susceptible to PM include David, Orange Perfection, Prime Minister, Starfire,
Blue Boy, Miss Elie, Miss Universe, Laura, Nicky. Monardas Blue Stocking and Marshall’s
Delight have been disappointingly disease-prone in my experience, but Violet Queen, JacobCline, Fishes and Snow White have done better. For fungicides, both systemics and contacts areavailable: Systemics BannerMAXX/Terraguard/Strike/Eagle may be rotated with strobilurinsCompass/Cygnus/Heritage/Insignia/Pageant and with contacts: MilStop; Pipron; Coppers; hortoil; neem oil; Actinovate; CEASE; Plant Shield HC
Viruses on perennials include tomato spotted wilt virus (TSWV) & impatiens necrotic spot virus
(INSV), both thrips-borne; tobacco rattle virus (TRV), shown on anemone, hosta and epimedium
(nematode-borne); dahlia mosaic virus; potyviruses e.g. one shown in phlox (aphid-borne); hosta
virus X (HVX) common in Gold Edger, Gold Standard, Golden Tiara and Sum and Substance is
spread by handling. Immunostrip test from Agdia available for HVX (www.agdia.com).
Phytoplasmas are bacterium-like organisms without cell walls that cause virus-like symptoms in
their hosts. This often includes stunting and yellowing of foliage and weird flower abnormalities
such as virescence (greening of normally colored flower petals, as shown on coreopsis). Control
weeds in the aster family that may be reservoirs of the phytoplasma, as well as aster leafhopper.
Dodder is a parasitic plant that will persist easily in any flower planting once it has become
established: remove it before it flowers and sets seed.
Pythium and Phytophthora
Avoid overwatering, poor drainage, deep planting, overfertilization—especially with lavender.
Treat preventively with PlantShield, CEASE, Mycostop or Actinovate biofungicides and/or with
Truban/Terrazole/Banrot for Pythium
, alternated with SubdueMAXX/Hurricane. ForPhytophthora
, use these materials but also rotate in Stature DM, strobilurins, FenStop and phos
acid materials (Aliette/Alude/K-Phite, etc).
Don’t mulch up to stem; keep field soil out of soilless mixes. Use PlantShield HC, CEASE,
Actinovate preventively. Use Terraclor, Medallion, Heritage, Medallion, Hurricane,
3336/6672/Banrot or 26/36, Sextant/Chipco 26019/Chipco 26GT.
Be alert to stunting and chlorosis: have roots checked for black root rot. Keep pH below 6.0 and
use 3336/6672/Banrot/2636, Medallion or Terraguard. Don’t reuse pots without first disinfecting.
Southern blight (Sclerotium rolfsii)
Look for mustard-seed sclerotia. Use Heritage, Medallion, Hurricane, Contrast or Terraclor.
Grow chrysanthemum cultivars not as prone to Fusarium wilt and relocate plants the year after an
outbreak to avoid overwintered inoculum. Suppressive fungicides include 3336/6672, Medallion,
Terraguard, Heritage. Keep pH above 6.2 and use nitrate forms of nitrogen in fertilizer.
Diseases of Herbaceous Perennials
from the plant pathologists’ society is newly available from
APS PRESS: http://www.shopapspress.org/diofhepe1.html (281 pages text + 800 illus.)
(Also available in bookstore at New England Grows
For chemical control details
(NY State): http://ipmguidelines.org/HerbaceousPerennials/
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