Preventing Diseases on Tomatoes – Late Blight, etc. – By Joanne Rice, Long Beach Community Garden Assn

I read with interest Hein’s e mail regarding early and late blight.  I have
been involved in a large community garden in Long Beach, California for 22
years and pretty much take care of all of our Trials and also vegetable diseases
for our Garden Association. 

In the early 90’s when Late Blight reared its ugly head in earnest again, 
our tomato crop went down big time.  I sought the help of a plant pathologist
from UC Riverside.  The first thing that he said was “stop growing potatoes”. 
We did and fared well.

A couple of years ago, despite my warnings, our board of directors decided
that they wanted to grow potatoes again and guess what, we lost all of our
tomato crop again to late blight and the tomato russet mite.  In a community
garden, you cannot grow potatoes and tomatoes.  One or the other.  I again sought the help of a plant pathologist  from UC Riverside and also the help of an entomologist from UC Riverside.  Their advice was to get rid of all of the host
plants for blight and mite for a period of two months prior to the tomato
planting season.  It was a very big job and there are a lot of host plants for these two conditions.  Amazingly enough, the host plants for both of these
conditions are one and the same.  Their thinking is that if you can rid yourself of all the host plants that the blight spores over winter on and also that the
russet mite over winters on, you will be home free.

We did just that.  We made sure that every host plant was removed and kept
out of our 300 garden plots (8 1/2) acres and also did not allow anyone to plant tomatoes until late March.  We monitored all of the tomato plants to watch
for blight.  Out of thousands of tomato plants,  we only found three with late
blight and those were removed and destroyed.  They had been brought to the
gardens and planted with the disease already on them.

All of what Hein says in his post is true.  You must trim off all leaves that
do not look perfect and keep the tomato plants trimmed of every leaf that
does not look perfect.  In May, we start using a wettable sulfur spray which
takes care of the russet mite and which also takes care of any mildew spores. 
Those of us, and especially trial garden which I oversee, had beautiful disease
free plants.  The secret is keeping the host plants out of your garden area so
that late blight spores cannot over winter.  And, for goodness sakes, do not
plant potatoes.  The late blight spores blow onto your tomato plants and in 10
hours you can have blight. 

Late blight does not seem to affect the other members of the night shade
family–egg plant, peppers, tobacco, however, these plants should also be removed for a period of 2 to 3 months before the tomato season as they too are considered host plants as are many flowers and weeds.  If anyone is interested in a list of host plants, you can e mail me at and I will be happy to forward the list to you.  From the list you can go to Google and type in the name and get info on each host plant and also a picture.

I know this is a long post however, we have been through the blight problems
and they have been very bad.  This past growing season has been such a
revelation as to what good, clean growing conditions can do to promote a perfect tomato patch.

Joanne Rice – First VP, Long Beach Community Garden Assn.