· Brent Wilson's Answer
· Dennis - It could be some type of pest, such as spider mites or could be fertilizer burn, but I doubt it. There is a bacterial wilt pathogen called Pseudomonas solanacearum that could be causing the browning/burning of the edges of the leaves. This disease can be found in some growing facilities. If your plants have this disease, there's a possibility they came from one of these sources? As this bacterial disease advances in the rhizomes of the plant it will cause the edges, and eventually the centers, of the leaves to turn brown. Eventually the entire leaf turns dark brown with an oily appearance and then dies. As the plants die and decompose, bacteria is released into the soil. Affected plants should be removed. If dead plants are replaced with new plants the disease can spread to the new plants. It can also be spread to other areas in the landscape by runoff from heavy rainfall. If there is a bacterial problem, about the only thing I know to do is remove the plants and wait at least 12 months before replanting. Unfortunately, there is no method of chemical control.
But, before going to the extent of removing the plants, I would suggest getting with your local extension service to see if they can test the soil for pathogens. At the same time, they can test it for nutrient deficiencies.
Hope this information was helpful,