Question
I planted potatoes in February; they are now about 6" to 8" tall and are developing brown spots on the leaves. I am concerned: my soil was mixed with horse manure back in September , 08. i just planted and additional crop of potatoes they are just coming through. First, are the brown spots of concern? And secondly will it jump to my new plants?

Answer
Daniel, when leaves turn brown it is usually an indication of too much water or fertilizer.  Excess water tends to saturate the roots, making it difficult for the roots to absorb oxygen and nutrients. The best approach is to only water the plants when the soil completely dries out. You then want to water them deeply so that the roots reach down. Shallow watering causes the roots to reach for the surface resulting in a weakened plant.  

Excess fertilizer will burn the roots of young plants, causing random brown spots on the foliage. In your case, it may have been caused by the horse manure. Manure should be aged at least 6 months before mixing in the soil. Otherwise, it is too strong, resulting in a very high concentration of nitrogen, which can burn the roots. Potato tubers are very hardy and gradually will adjust. By now, the manure should have aged sufficiently where it should not cause a problem going forward. I would add some ground sulfur to the soil to help neutralize the ph.

I hope this answered your question. Please write again if I can ever be of assistance.  

Regards,  

Mike