Question
I am within 25' of a black walnut tree!  Now what??



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Followup To
Question -
My peppers started first - green leaves turning to a yellow (on the bottom) dropping off then tghe rest still green dropping off , nothing left but a stem that looks like it is a piece of wood!

Now migrating into my yellow squash which was doing good and started from seed not like the peppers, potted from Home Depot.

Tomato plants are next to the peppers and have a little bit of this going on, but the leaves are turning a black or dark color.

1st year gargen, brought in topsoil from garden center, little lime, little 10/10/10 and exisiting ground.


Answer -
Scott, it sounds like you have a soil-borne disease causing the foliage to die off.  Normally, the yellowing of leaves can be attributed to a lack of essential nutrients in the soil.  But this will not cause plants to suddenly turn black, drop leaves, and die.  This is only caused by diseases such as blight, anthracose, club root, or one of several wilting viruses.  

The only extraneous source would be a black walnut tree planted within 40 yards of your vegetables.  These trees exude a substance through their roots that will kill off many vegetable plants.

It's impossible to diagnose which disease is present, or how it was introduced. But at this stage, your only alternative is to remove the soil and solarize the sub-soil.  This is accomplished by covering the area with black plastic for a period of 6-8 weeks.  The heat that is generated will kill off the disease.  I would then till in ample quantities of organic matter such as shredded leaves, peat moss, aged manure, and compost.  These amendments will neutralizre the ph balance as well as add all of the necessary nutrients necessary for a healthy garden.

I realize this is probably not the answer you were hoping for.  But once a soil-borne disease enters the bed, there are very few chemicals that can counter the disease.  If it was simply a fungus related disease, copper or lime could be used.  In this case, you must totally eradicate the disease to prevent it from spreading.

Good luck, and please write again if I can ever be of assistance.

Regards,

Mike

Answer
Scott, there is not much that can be done besides moving the garden to another area of the property or taking down the tree. The walnut tree produces a toxin called juglone that is fatal to tomatoes, peppers, eggplants, and many other vegetables.  Once this substance is in the soil, it takes two to three years for it to dissipate after the tree is removed.

Attached is a good article from the Ohio State University Extension.  This should give you all of the information you need on this subject.

http://ohioline.osu.edu/hyg-fact/1000/1148.html

Regards,

Mike