by Elaine Roddy, OMAFRA and Cheryl Trueman, University of Guelph – Ridgetown Campus
Seed borne diseases represent a real threat to pumpkin and squash production. Commercial seed is typically grown under arid conditions, and is carefully monitored to ensure it is disease-free. It is difficult to employ those precautions to saved seed produced on the farm here in Ontario.
A new disease that is cause for considerable concern is bacterial leaf spot (Xanthomonas cucurbitae). While it has only been identified in 2 locations in Ontario (Kent County in 2012 and Elgin County in 2014), experience in the mid-western US has shown that field infestation levels of 60-80% are not uncommon.
In 2014, we investigated methods of on-farm seed treatment to disinfest saved-seed. Both the hot water treatment and the chlorine treatment effectively killed the bacteria present on the batches of seed infested with X. cucurbitae. There was a 5% reduction in germination of the chlorine-treated compared to untreated seed. Germination rates in the hot-water treated seed were similar to those in the untreated seed.
The methodology used in the 2014 study is outlined below. **Note: test a small batch of seed for each cultivar to be treated. The 2014 study was conducted on Waltham butternut squash. Other varieties or types of cucurbits could potentially be more sensitive to either the chlorine or hot water treatments. In particular, other researchers have reported negative effects of hot water treatment on cucurbit seedling emergence (Miller and Ivey, 2005).
Chlorine Seed Treatment
Use 25 oz of Chlorox (5.25% hypochlorite) and 1 tsp of surfactant in 100 oz of water. 1 gallon of solution will treat 1 lb of seed. Agitate the seed in the solution for one minute. Immediately rinse the seed in cold, running tap water for 5 minutes. Spread it into a single layer on a screen and allow it to dry completely.
Use fresh solution for each batch of seed.
Hot Water Treatment
Place seeds in a 37°C water bath for 10 minutes. Then move them into a 50°C water bath for 20 minutes. Place a thermometer in each water bath to monitor any temperature changes. After treatment, move the seeds into a cold water bath for 5 minutes; then spread them in single layer to dry. It is important to immediately cool seeds in a cold water bath to end the heat cycle.
Ohio State University Extension has an excellent factsheet on Hot Water and Chlorine Treatment of Vegetable Seeds to Eradicate Bacterial Plant Pathogens (Miller and Ivey, 2005).