I have 12 heirloom tomato plants in my community garden in Toronto. They are planted in full sun, properly spaced (35 inches apart) watered properly in soil that is augmented with mushroom/turkey litter compost. I have been planting these heirlooms for over 12 years and pretty much every year I run into early/late blight or fungas on the leaves that turns them brown and rots them. I understand that this is a common problem but would like to do something to eliminate or at least curtail the spread of this annual problem. A well known gardening expert here in Toronto recently suggested Boron to curtail this disease. However, after looking this chemical up, it looks way too scary to me since it appears that the application of this substance has to be exactly correct in quantity and is highly poisioness to humans. Is there another product or method I can use to help me with this disease on the leaves of my tomato plants.
So annoying to have your tomato crop struck with blight! As you can imagine, we get questions about this every year. Here is a link to a previous answer you may find helpful: http://www.torontomastergardeners.ca/askagardener/verticillium-fusarium-or-another-ium/
As for techniques for improving yield, we recommend good compost and proper pruning. There is an excellent paper on pruning techniques published by the University of New Hampshire here: https://extension.unh.edu/resources/files/Resource000598_Rep620.pdf
We are proponents of the no-till approach to gardening. Excessive tillage destroys the soil structure which is the foundation for healthy plant roots that interact with the living component of the soil. For an excellent guide to no-till vegetable gardens, see Michigan State University’s paper here: https://www.canr.msu.edu/news/preparing_the_smart_vegetable_garden
Hope your tomatoes are healthy and happy next year!