From Clemson Plant Pathologist Tony Keinath.
Southern blight has become more common on tomatoes grown without fumigation throughout the southern United States. A joint project between the University of Georgia and Clemson University looked at grafting as a management option. In the 2021 trial in Charleston, SC, grafting reduced the percentage of diseased plants from 44% on nongrafted ‘Roadster’ to 7% on ‘Roadster’ grafted on ‘Maxifort’ rootstock. Even better, marketable weight was 71% greater on the grafted plants than on the nongrafted. The extra yield was mostly in the extra-large red and pink fruit categories, based on weights of fruits from 8 plants per plot.
For growers unsure about grafting, we also saw that ‘BHN 602’ was somewhat tolerant to southern blight. Although nongrafted ‘BHN 602’ had 33% diseased plants by the end of the season, marketable weight was not significantly lower than on the grafted plants, although there were fewer extra-large fruit. For information about grafted tomatoes, see trihishtil.com or vegetablegrafting.org. Note that grafted plants need to be ordered 60 days before delivery.