I spent some time these past few days reviewing a chapter of the excellent publication Mineral Nutrition and Plant Disease. This book is a review of the scientific literature, and while we should not see any of this as recommendations for crop production practice, it does give us plenty to think about as far as what direction we can go experimentally:
Manganese (Mn) has a consistent record in the scientific literature as reducing vascular diseases in crop plants caused by soil pathogens such as Verticillium and Fusarium. Physiologically, this makes sense because of the role that manganese plays in the production of phenolic compounds, phytoalexins and other plant defense mechanisms.
An increase then in the amount of Mn applied to the soil (foliar applied does not work well, since Mn does not move downwards in the plant to the roots) seems to be a straightforward approach in obtaining the disease reducing qualities of this element into the plant. For example, one study (Dutta and Bremner, 1981), achieved greatly reduced Verticillium wilt by dipping tomato roots in a Mn solution before transplanting.
However, there are other strategies to increase plant tissue Mn, especially in the soil right around the roots. Lowering the pH of that soil through the use of ammonium fertilizers such as ammonium sulfate (ammonium acidifies more than nitrate), has reduced Verticillium wilt from moderately infested soils in eggplant (Elmer and Ferradino, 1994), and the combination of a rotation with oats with ammonium fertility (Elmer and LaMondia, 1999) has been shown to double the Mn tissue concentration in subsequent plantings of strawberry and reduce black root rot incidence (but not, unfortunately, increase plant growth or yield).
Again, some of this might be worth a look experimentally in strawberry on the Central Coast.
Several of the papers mentioned in the text above are available online – links provided below.
1. Dutta, B.K. and Bremner, E. 1981. Trace elements and plant chemo therapeutants to control Verticillum albo-atrum wilt. Z. Pflanzenkankh. Pflanzenschutz 88:405-412
2. Elmer and LaMondia. 1994. Comparison of Ammonium Sulfate and Calcium Nitrate Fertilization Effects on Verticillium Wilt on Eggplant. Plant Disease 78: 811-816 https://www.apsnet.org/publications/PlantDisease/
3. Elmer W.H. and LaMondia, J. A. 1999. Influence of ammonium sulfate and rotation crops on strawberry black root rot. Plant Disease 83: 119-123. http://apsjournals.apsnet.org/doi/pdf/10.1094/PDIS.1999.83.2.119