Re: Red blotches on hawthorn leaves

I admit I passed over your message owing to the fact that plant diseases
are generally localized and I despaired of identifying any pathogen 7,000
miles away....but after further reflection I decided, what the heck, why
not take a crack at it.  So I consulted my reference books for US plant
pathogens.  We have a marvelous reference in this country called Wescott's
Plant Disease Handbook, which has attempted for decades to provide a
catalogue of every reported plant disease in the US, listed by state. I
wondered if one of our organisms might also be about in Spain.j

There really are only two possibilities, both fungal.
The most unlikely is Septoria leaf spot.  There are a zillion Septoria
organisms in the US affecting just about any plant you can name.  Most
cause roughly circular spotting on leaves and/or fruit.  The most common in
California forms reddish blotches on english ivy(*Hedera helix*).  There is
a septoria reported on Hawthorn but the text doesn't give any description
and it has been reported only in the extreme north part of the country in
Michigan, Wisconsin and North Dakota.

A more reasonable choice is *Fabraea thuemenii*, Hawthorn Leaf Blight.
Wescott describes the symptoms:
"Small dark brown or reddish brown spots , with raised black dots, are
numerous over leaves, which drop prematurely in August.  In wet seasons
trees may be naked by late August."  We have a related disease,
*Entomosporium leaf spot* in the San Francisco Bay Area affecting
ornamental pear(Pyrus kawakamii* and *P.calleryana*), *Photinia fraserii*
and *Raphiolepis indica*.  It has become such a problem that people are
just beginning to shy away from the latter plant; probably a good thing as
Raph's are greatly overused.
Jerry Heverly, Oakland, CA





At 9:43 AM 4/29/99, Damian Martin wrote:
>I planted a few local hawthorns (Crataegus monogyna) last year.After a
>short burst of healthy spring growth, they came out in red blotches,
>specially oin the tender young leaves at the tips of branches. Later, in
>the summer, the blotches spread to older leaves infesting most of the
>plant. The centre of the botch finally turned into a root-like outgrowth
>on the leaf's underside. The result was a set of very sad hawthorns with
>no post-summer growth at all. I treated with fungicide to no avail. I
>cut back in winter but, on inspecting the new shoots yesterday I found
>the same little red spots appearing. Help!
>
>This is probably a well-known disease... but not to me. Any suggestions
>most welcome.
>
>Damian Martin
>Talavera, Spain
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