detergent soap/leaf scorch
I am a first time grower learning the hard way. My two Giant Atlantic
Pumpkins plants are in deep trouble. Some type of leaf disorder. I had been
feeding the little guys with a fish emulsion. (Probably over feeding is more
exact.) This attracted a lot of flies to the plants. I became worried about
the flies being a vector for pathogens so I washed the plants with soapy
water. (Ajax dish washing liquid.) The flies headed for the hills. The
plants looked great. Several hours after their bath, however, the leaves
closest to the stump started developing rusty/grayish blotches which quickly
spread to newer leaves farther down the vine. The most seriously discolored
leaves also began curling up at the edges. Prior to my Ajaxing 'em, the main
vines on both plants were about 4-5 feet long with the biggest leaves a foot
in width and all a beautiful healthy green.
I found an image on the Texas A&M horticulture site of a cucurbit with a
leaf disorder closely matching the appearance of the damaged leaves on my
AGPs indicating the problem could have resulted from a pesticide injury.
Somewhere in a Rodale organic gardening book I found a sentence about using
"non-detergent" soap to clean leaves from invading pests. The soap I used
was apparently a detergent soap, i.e., one that cuts grease and oil. My
amateur guess is that the detergent may have been absorbed through the roots
and possibly created the damage by acting like a broadleaf herbicide. Small
amounts of residual herbicides apparently can cause leaf scorch, dwarf plant
growth and reduce vigor. (See
http://aggie-horticulture.tamu.edu/cucurbit/leaf/39.2.html for image and
text.)
This occurred several days ago. Since then, new growth appears to be
unscorched or minimally scorched. Most scorched areas have dried up and
turned gray in color. Don't know whether to prune damaged leaves or not. I
am not even sure about my hypothesis that this event was caused by my use of
a detergent soap.
Any opinions and/or advice from listmembers are greatly appreciated.
______________________________________
bob johnson
holbrook, ma usa rjohnson@thecia.net
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