| Disease |
Symptoms |
Pathogen/Cause |
Management |
| Bacterial Leaf Blight |
Faint, water-soaked spots on leaves enlarge along
the leaf when weather is wet but cease activity when it is dry. |
Xanthomonas campestris
pv. tardicrescens |
Remove infected leaves. Avoid overhead irrigation. |
| Botrytis Rhizome Rot |
Few leaves emerge in the spring. Leaves are yellowed,
turn brown, and die. Gray masses of fungal spores form on infected
leaf tissue. Rhizomes have a dry, mealy rot. Large, shiny, black,
granule-like structures (sclerotia) form on the surface of infected
rhizomes. |
Botrytis convoluta |
Do not plant infected rhizomes. Destroy infected
plants. |
| Crown Rot |
Leaves die slowly from the tips. White fungal
threads can be found at the leaf bases. Tan, spherical structures
(sclerotia) form between rotting leaves. |
Corticium rolfsii |
Discard infected bulbs. Apply PCNB to plants
not yet affected. |
Ink Spot
(Bulbous Iris) |
Tiny spots and streaks on leaves enlarge and
become dark reddish brown. Spots may become gray in the center.
During wet weather, dark masses of spores form in the spots.
The plants yellow and die prematurely. Heavily infected bulbs
may rot before flowering occurs. |
Drechslera iridis |
Destroy leaf debris at the end of the season.
Apply iprodione, triadimefon, chlorothalonil, or mancozeb when
leaves are 6-8 inches long. Repeat at 10-day intervals until
dry weather prevails. Remove and destroy infected bulbs |
| Leaf Spot |
Small
brown spots with water soaked margins turn yellow, enlarge
and develop reddish-brown
borders. Leaves die. Dark fungal spores can be seen within the
spots with a magnifying glass |
Mycosphaerella macrospora
(Didymellina) |
Remove and destroy infected leaves and leaf debris.
Apply chlorothalonil, myclobutanil, thiophanate methyl, triadimefon
or mancozeb when leaves are 6-8 inches long. Repeat at 10-day
intervals until dry weather prevails. |
| Nematodes |
Black streaks develop along the veins of outer
leaves of bulbs. The basal plate is gray and separated from
the outer scales by a dark sunken groove. |
Ditylenchus destructor |
Destroy infected bulbs and do not replant in
that location until the soil has been fumigated or heat treated. |
| Soft Rot |
Leaves collapse suddenly or die gradually from
the tips. The base of infected leaves and infected rhizomes
have a foul smelling soft rot. |
Erwinia carotovora
PVcarotovora |
Destroy infected rhizomes. Control iris borers,
which often cause the injury where the bacteria initially gain
entry. |
| Virus |
Mild mosaic on flower stalks and spathe (mild
mosaic virus). Yellow green stippling and stunting (severe mosaic
virus). Flower color breaking and puckering can occur. |
Iris mild mosaic, iris severe mosaic, cucumber
mosaic (all aphid transmitted), broad bean wilt, tobacco ringspot,
tobacco rattle, bean yellow mosaic, narcissus latent virus,
bearded iris mosaic, beardless iris mosaic |
Most iris cultivars tolerate viruses. Destroy
severely affected plants. |
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