Watermelon Research

Watermelon is the largest acreage vegetable crop grown in South Carolina. Watermelon is produced in all 46 counties, with the bulk of the crop coming from the Central Savannah River Area. The 7,900 acres of watermelon in 2014 make South Carolina the fifth largest watermelon-producing state in the country. Part of the success of the SC watermelon industry is due to the partnerships between growers and researchers at Coastal REC. Current watermelon research focuses on seedless transplant production, grafting, and sustainable disease management.

Approximately 80% of the watermelons produced in South Carolina are seedless. Production costs are greater for seedless watermelon than traditional seeded watermelon, but the price growers receive for them also is higher. One of the higher costs is the seed. Seedless watermelon production starts with transplants, or seedlings grown from seed in a greenhouse. Precise control of temperature and moisture during seed germination is critical to get 100% emergence. A step-by-step guide to seedless transplant production is available to growers and home gardeners.

Grafting watermelon is a technique used to combat root and wilt diseases without applying chemicals. Watermelon seedlings are grafted onto (joined to) stems of bottle gourd or hybrid squash seedlings. After the seedlings heal and the two parts grow together, the grafted plants are ready to transplant in the field. Grafting makes watermelon plants resistant to Fusarium wilt, because the bottle gourd and hybrid squash are resistant. When grafted plants are grown in a field infested with the Fusarium wilt fungus, there is almost no wilt, and grafted plants produce more and larger fruit. Growing grafted watermelon means that herbicides and between-plant spacing may have to be adjusted compared to growing standard watermelon, so these cultural practices are re-examined with grafted plants. Fruit produced on grafted plants is often firmer than fruit from non-grafted plants. The vitamins, minerals, and anti-oxidants, such as lycopene, in fruit are tested in cooperation with North Carolina State University’s Plants for Human Health Institute.

Disease management is crucial for growing watermelons successfully, as there are no cultivars with resistance to four common leaf diseases: gummy stem blight, anthracnose, powdery mildew, and downy mildew. Sustainable disease management includes:

• using disease-free seeds and transplants
• rotating crops to different fields each year
• burying crop debris at the end of the season
• identifying which diseases are present before fungicides are applied

Yearly fungicide tests are done to compare new fungicides to ones currently used. Different fungicides must be used for each watermelon disease to manage them effectively. An important recent finding is that the gummy stem blight fungus in South Carolina is resistant to tebuconazole. Up-to-date spray recommendations are made each spring in the Watermelon Fungicide Guide. The sensitivity of cucurbit downy mildew to fungicides also is checked yearly, as this organism easily becomes resistant to over-used fungicides. Current recommendations are in Cucurbit Downy Mildew Management.