Over-watered lawns will quickly become mold factories and will shower everyone near them with an abundance of mold spores. Plant Diseases and Spores Many pests of our plants are not insects but are fungal type diseases such as mildew, rust, black spot, scab, and leaf blight. These organisms also produce allergenic airborne spores. The very best way to avoid these diseases and their spores is by planting disease resistant plants. The second most valuable approach is to keep plants growing cleanly and strongly.
Healthy plants go a long way to keeping our air clean.
Certain plants if grown in the wrong area can almost be counted on to harbor disease. Evergreen viburnum growing in the shade will certainly get moldy and full of mildew. Crape Myrtle trees grown in an area that doesn't have hot summers will always have mildew. A cold, wet spring frequently brings out a huge flush of both mildew and anthracnose on the leaves of California Sycamore trees. In areas with cool, foggy nights and warm days, rust will surely grow on any roses, hollyhocks, or snapdragons that are not rust-resistant.