Red blotch on bulbs, Stagonospora curtsii

Joe Shaw
Thu, 23 Nov 2006 10:22:54 PST
Hi Gang,

    Stagonospora can be a nasty pathogen of some bulbs (e.g., Narcissus 
hybrids) where is destroys foliage in the leaf scorch stage.  In amaryllids 
Stagonospora can cause leaf spots and the familiar ugly red blotch on leaves 
and bulbs.

    Stagonospora is the only recurrent fungal problem I have in the bulbs 
that I grow and I control it with twice yearly applications of myclobutanil 
(a.k.a., ziram).   Myclobutanil does not cure the problem for me (at least 
not when applied only twice a year), but it sure controls the problem.  I 
use myclobutanil because it is a systemic fungicide and because I understand 
it to be of moderate or low toxicity for mammals, birds, and fish. 
Additionally, it does break down in time in soil or water.

    Of course, I take care to remove infested debris, and cut off leaves 
that are showing symptoms (especially Crinum).  Debris removal is always a 
part of my fungal control efforts.

    I use a Spectracide product called Immunox that contains myclobutanil. 
The Spectracide products come in liquid of dry forms.  All new plants coming 
into my garden (even cacti and germinating seeds, etc.) are treated with an 
overnight dip in a myclobutanil solution.

    For potted plants, I sprinkle about 1 tablespoon of dry powder (the lawn 
granules) on top of the soil of a gallon container.  I scale up accordingly 
for larger containers.  Large bulbs in the ground (e.g., a big Crinum) get 
about 6-8 ounces (about a cup) of the granules sprinkled over the soil 
around the plant.  I apply the granules in fall and spring.  The fungus is 
controlled and I've learned to accept minor blemishes and spots.

    There is a catch with fungicides along the Gulf Coast:  some plants 
(including many Cape bulbs) are going to die from fungal disease unless they 
are protected from too much rain and humidity.  Thus, I don't expect 
fungicides to perform miracles.

    As always, I encourage anyone using a pesticide to read up about it and 
make informed decisions.  And all garden chemicals need to be stored away 
from pets and children.



Conroe TX

LINK:  Fungal diseases of Narcissus

LINK:  Narcissus leaf scorch

LINK:  ExToxNet Info about myclobutanil (ziram) 

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