Diseases Affecting Herbaceous Perennials

Disease

Favorable Environmental Conditions for Development

Typical Symptoms

Cultural Management

Chemical Management

Agrobacterium tumefaciens Crown Gall

Symptoms of infection usually most evident mid to end of summer

Galls at crown or base of plant; callus or shoot proliferations along stem; systemic

Clean stock

None

Alternaria Leaf Spot

Warm temps, humidity, prolonged standing  water on leaf surface

Reddish or purple spots usually with brown/ necrotic centers

Good air flow around plants, keep free water on leaf surface to a minimum, remove diseased foliage

Medallion, Compass Heritage, Daconil Ultrex, Chipco 26019, Pageant, Veranda O

Anthracnose Leaf Spot

Warm temps, prolonged standing  water on leaf surface

Tan, black, or brown leaf spots irregular spots; some- times spores can be observed in spot with hand lens

Good air flow around plants, keep free water on leaf surface
to a minimum, remove diseased foliage

Daconil Ultrex, Heritage, Compass, Pageant, Medallion, Cease

Aster Yellows

Symptoms of infection usually most evident
mid-spring thru summer

Flowers become  green and distorted; new shoots are yellow, spindly, & stunted.

Clean stock

Use yellow sticky cards
to monitor for 6-spotted Aster leafhopper (the Aster Yellows vector) and start control
early in spring.

Bacteria Leaf Spots (ex: Xanthamonas, Pseudomonas)

Warm temps, prolonged standing  water on leaf surface and high humidity

Red, brown, black, purple irregular or round shaped spots with yellow halo

Clean stock

Copper-based products  such as Phyton 27, Camelot, or Kocide can reduce disease symptoms, but will not eliminate bacteria

Botrytis

Moderate to cool temps, high humidity or prolonged standing water on leaf surface

White/grey spores; primarily attacks dead, decay- ing, or diseased plant parts and spreads to healthy plant tissue when disease is not controlled.

Good air flow around plants to dry out decaying plant tissue

Decree, Terragaurd, Medallion, Daconil Ultrex, Heritage, Compass, Chipco
26GT

Cercospora Leaf Spot

Moderate to cool temps and prolonged leaf wetness

Spots with tan centers and purple borders; sometimes small black spores visible in center

Good air flow around plants, keep free water on leaf surface to a minimum,
remove diseased foliage

Daconil Ultrex, Heritage

Downy Mildew

Warm to cool temperatures, prolonged standing  water on leaf surface, high relative humidity, cloudy days

Faint or bright red/purple/ tan angular leaf spots (can resemble foliar nematode symptoms); white fuzzy spores may be seen underneath leaf if disease is advanced

Good air flow around plants; keep free water on leaf surface to a minimum, monitor relative humidity & attempt to decrease  if too
high, remove diseased foliage

Aliette, Heritage, Alude, Stature DM, mancozeb-based fungicide, Subdue Maxx

Fusarium Crown or Root Rot

Warm soil, excess water and/or fertilizer

Initially older leaves yellow
& wilt; in time, roots & crown
become  completely brown
with rot

Avoid overwatering, reduce fertilization

Terraguard, Cleary 3336

Powdery Mildew

Moderate or cool temps, high humidity, cloudy days

Starts out as round white/ grey spots on leaf surface, spots quickly coalesce to cover entire leaf

Good air flow; remove diseased foliage

Compass, Eagle, Terraguard, Cleary 3336, Heritage, Milstop, Pageant

Pythium
or Phytophthora
Root/Crown Rot

Excess soil moisture or root tips in standing  water under pots, excess fertilizer, plant stress

Yellow, stunted or wilted plants, roots turn brown, sometimes  outer root tissue pulls away, leaving only vascular tube

Avoid overwatering, reduce fertilization, avoid plant stress

Subdue Maxx, Aliette, Truban, Banrot, Alude

Rhizoctonia Crown Rot

Warm temps, high humidity, excess water and/or fertilizer, plant stress

Foliage may turn yellow and wilt; reddish brown lesions/ cankers on infected roots and crown

Avoid overwatering, reduce fertilization

Compass, Medallion, Chipco 26GT, Cleary 3336, Terraguard, Heritage, Veranda O

Rhizoctonia Web Blight
(Foliar Blight)

Warm temps, prolonged standing  water on leaf surace, dense canopy

Foliage becomes  water- soaked and rots, sometimes the brown web-like growth if the fungus is noticible,
sometimes  leads to crown rot if left untreated

Good air flow around plants, keep free water on leaf surface to a minimum, remove diseased foliage

Compass, Heritage, Cleary
3336, Daconil Ultrex, Pageant,
Eagle, Veranda O

Rust

Moderate temps, prolonged standing  water on leaf surface & high humidity

Sometimes brown, red, or orange leaf spots on upper leaf; round, raised brown
or orange pustules on the underside  of leaf

Good air flow around plants; keep free water on leaf surface to a minimum, remove disease foliage

Eagle, Compass, Heritage, Cleary 3336, Daconil Ultrex, Protect DF, Pageant

Septoria Leaf Spot

Moderate temps, prolonged standing  water on leaf surface & high humidity

Spots have red/purple mar- gins with tan, necrotic centers (can look similar to Alternaria) or brown necrotic angular spots

Good air flow around plants, keep free water on leaf surface to a minimum, remove diseased foliage

Compass, Heritage, Cleary
3336, Daconil Ultrex

Thielaviopsis
Root/Crown Rot

Excess soil moisture, high soil pH (>6.0), cool soil temps, plant stress

Lower leaves turn yellow & wilt; roots start with dark brown or black spots & even- tually turn completely black with rot

Keep soil pH≤6.0, warm soil temps (>65 degreees); avoid overwatering, do not reuse soil

Amendments to adjust soil pH if needed;  Terraguard, Medallion, Banrot, Cleary
3336

Virus

Symptoms usually most evident mid-spring thru early summer, can persist or disappear  during summer

Ringspots, mosaic, mottling, stunted growth, necrotic or chlorotic spots, leaf distortion

Clean stock

None