Your potatoes are more liable to scab on an alkaline soil than an acid one, for potatoes a Ph of 6 is recommended, plus the use of manures.
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Scientists with Agriculture and Agrifood Canada have shown swine manure fertilizer has the potential to control disease in potatoes grown in soil with a low pH.
In the past using manure fertilizer in potato crops has been discouraged because of the fear it would contribute to disease, particularly scab.
Researchers working in London Ontario, looking to test this theory, applied liquid swine manure to potato plots at two locations and found the manure significantly reduced disease at one site.
Dr. George Lazarovits says the determining factor turned out to be the pH of the soil.
"We took the soil where the manure worked and we took the manure that was effective and we started testing to see what made it work in this particular soil.
We discovered the mechanism of action was really based on the presence of volatile fatty acids. Volatile fatty acids, one of the ones that everybody will know of is vinegar.
Manure has a very high vinegar content plus a whole bunch of other related compounds. As it turns out, all of these materials are biologically active.
That is they act as disease control agents only in soils that have low pH but they do not work in soils that are neutral or in high pH soils.
Now we can fingerprint the manures that work and we can get and idea, based on soil pH, in which soils they work.
As a result we think these liquid manures can be used as a cheap method of delivering materials to soil that control diseases".
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a useful chart for the ph for any particular vegetable can be found at
http://web.ukonline.co.uk/fred.moor/soil/ph/p010601.htmRegards
MikeB
