April 2021 - 27

PLANT HEALTH
Eryngium with yellow leaf
spots due to white smut
(Entyloma ho-chunkii)
infection.
In some cases, there may be an opportunity to
eliminate an alternate host which is essential for the
rust's lifecycle, but often it seems that the lifecycle
allows repeated infection on the crop without need
for an alternate host (as for the rush rust described
above). In other cases, the alternate host for a
herbaceous perennial may be a tree (some of the
goldenrod rusts have pine trees as alternate hosts).
WHITE SMUT
White smuts, caused by Entyloma species, are lessfamiliar
relatives of rusts. White smut on dahlia (E.
dahliae) and gaillardia (E. polysporum) are two of the
more common of these diseases. Both show leaf spots,
whitish to pale green, and the spots eventually turn
tan to brown as they mature. The pathogens must be
identified by examining sporulation inside the brown leaf
lesions with a microscope. This past year a distinctive
white smut pathogen, E. ho-chunkii, came to light in
the Midwest and Northeast, appearing on Eryngium
yuccifolium. The symptoms begin as small, veinbounded,
bright yellow spots, turning brown with time.
Fungicide labels do not usually mention white smuts.
Plants being treated with fungicides that control rust
will probably have reduced white smut symptoms, but
you may need to rely on sanitation (prompt and careful
disposal of infected plants) to keep this disease from
becoming a problem in production. White smuts are
known to be seedborne in some cases, and spores can
overwinter in plant debris. It's important to clean up
thoroughly after an outbreak!
Margery Daughtrey is senior Extension associate in the Long
Island Horticultural Research & Extension Center at Cornell
University. She can be reached at mld9@cornell.edu.
21_0488_Greenhouse Product News_APR Mod: March 1, 2021 9:23 AM
Print: 03/02/21 2:17:36 PM page 1 v7
as pathogens in the U.S. Rusts are also
seen commonly on monarda. A rust with
brown sporulation (Puccinia chrysanthemi)
and another with white cushion-like spore
pustules (P. horiana) are seen occasionally on
chrysanthemums; chrysanthemum white rust
is subject to federal quarantine.
Perhaps the most famous of rust diseases
Chocolate brown rust spores of
Puccinia chrysanthemi (chrysanthemum
brown rust) produced in rings on a
chrysanthemum leaf.
Saxifrage family as well (e.g., saxifraga,
tellima, tiarella, tolmiea). Goldenrod often
shows a rust that is yellow-orange; veronica
may show dark chocolate brown pustules.
Growers of Panicum virgatum may have
noticed leaf spots that sporulate in pustules
when examined closely; for this host Uromyces
graminicola and Puccinia spp. are known
on perennials is daylily rust, which happens
to affect two different herbaceous perennials:
Hemerocallis and Patrinia. The " repeating "
stage is on daylily, so Patrinia is not essential
for the disease to perpetuate itself. Recently
we saw a rust on soft rush, Juncus effusus,
a wetland plant that is used for restoration
- and to make tatami mats in Japan. The
widespread rust Uromyces junci-effusi has its
" repeating " and overwintering stages on the
rush - and no alternate host is known.
Rusts are sensitive to some contact
materials including neem oil and mancozebs,
and to systemic materials in FRAC groups 11
and 3, similarly to powdery mildews. Reducing
leaf wetness duration helps with rust control.
π
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GREENHOUSE PRODUCT NEWS 25
April 2021

Table of Contents for the Digital Edition of April 2021
