This summer early warm weather and frequent rain alternating with sunny days have created conditions allowing vegetable gardens to flourish. Many gardeners are amazed at the size of their tomato and corn plants. Recently, however, gardeners have been noticing yellowing and spotting of their prized plants, especially on the lower leaves. This discoloration is caused by several different fungal and bacterial leaf spot pathogens. Unfortunately warm wet weather also favors growth of these pathogens.
Leaf spot fungi and bacteria come into the garden on infected seed or transplants or are blown in on the wind. Many of these pathogens can survive from one season to the next on infected plant debris. Splashing rain carries fungal spores and bacteria from the soil and plant debris onto this year’s leaves. Moisture in the plant canopy then allows these pathogens to start new infections. Established leaf spots create a whole new generation of bacteria and fungal spores, starting the cycle all over again.
Luckily several basic cultural control practices can help to keep leaf spot pathogens in check.