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Seedling Disease Control 5 Things You Can Do to Stay On Top This Season

GERMINATING SEEDS AND SEEDLINGS face many hurdles before becoming the strong, healthy, and mature plants that customers buy in the spring. Some of the toughest obstacles include those posed by diseases: damping-off, root and crown rots, and Botrytis, to name a few. What makes these diseases so difficult to fight is their pervasiveness. The Botrytis fungus and the fungi that cause damping-off—Pythium, Rhizoctonia, and Fusarium—are nearly always present in the greenhouse and cannot be completely eliminated from the environment. Yet the damage they can do is extraordinary. They can rapidly attack a flat, leaving devastating plant losses in their wake. Faced with such determined foes, what’s a grower to do? 

We’ve pulled together a list of five things you can do now to help your seed and cutting production prevent losses caused by disease so you can enjoy a profitable season this year.

1) Make sure to first clean, then sanitize all used pots and trays. Two of the common culprits in damping-off, Pythium and Rhizoctonia, can live in soil or root debris commonly found in used pots and trays. Because organic matter can block the penetration of sanitizing chemicals, effectively shielding the pathogens, it’s imperative to wash any used containers thoroughly with soap and water before sanitizing.[i] Once containers are clean and free of debris, sanitize them with a disinfectant that’s made for the greenhouse. Use the product according to labeled instructions. If using X3, which is a safe and effective sanitizer for pots, trays, and all greenhouse surfaces, apply it at a rate of 25.6 ounces per 100 gallons and soak for at least 10 minutes.

2) Use seeds and soil that are disease-free and use soil mix that drains well. Because these fungi survive in the soil, on plant debris, or on seeds, it’s critical to use a disease-free, soilless growing media, or a soil mix that has been pasteurized, and to plant only high-quality seeds, preferably those that have been treated with a fungicide to help protect them during the germination phase. Since diseases thrive in high-moisture environments, make sure the soil media drains well and do not over-water. Ventilation and proper temperature control are equally important. For further protection, you can also drench seeds after transplanting to kill any disease organisms on the seeds, soil, or containers. Labeled for Pythium, Rhizoctonia, Fusarium, and Botrytis, X3 is plant-safe and will kill diseases on the seed, in the soil, and on other surfaces. Drench X3 at a rate of 25.6 ounces per 100 gallons.

3) Be careful to not re-contaminate your soil through poor sanitation practices. Poor sanitation and poor disease control go hand-in-hand. A clean, disease-free germinating area is essential to good germination. Be mindful of re-contaminating planting media; do not set it or the flats on a dirty floor or other unclean surface. Tools, equipment, potting benches—anything that could come into contact with the seeds or the potting mix—need to be cleaned and sanitized before use. If using X3, use at the rate listed above. Following other good cultural practices will also go a long way toward guarding your seedlings against disease. For example, make it a habit to hang hose ends and not let them touch the ground; if they do, clean and sanitize as indicated above.

4) Fertilize sparingly. Excess nitrogen fertilizer can cause soft growth instead of maturation, leaving seedlings more susceptible to damping off. Nitrogen and potassium fertilizer should be properly balanced with enough phosphorus to speed maturation (NPK 1:2:1).[ii]

5) Take proactive, preventive measures to control disease. Again, prevention is key. Inspect flats frequently and remove suspicious-looking seedlings promptly. Flats where damping-off has occurred should be discarded. Even seedlings that look healthy may carry contaminated soil and will often suffer from stunted growth or root rot in the future.[iii] Irrigate in the morning to allow enough time for the soil and leaf surfaces to dry, making a less hospitable environment for disease. To stay ahead of disease while seeds are germinating, X3 can be injected into your mist lines on a constant basis at an injected rate of 1:5000 or 2.45 ounces per 100 gallons. Note that X3 is safe to use over plant material and has a zero-hour REI. Once seeds are germinated, a fungicide spray, such as Phyton 27 (ornamentals) or Phyton 35 (ornamentals, fruits, and herbs), can be applied for lasting disease prevention. To help avoid repeat problems in the future, it’s always a good idea to save all information on seed purchases in case problems develop at any stage of production.[iv]

Getting your seedlings off to a good, strong start is one of the most important things you can do to ensure their long-term health. Strong, healthy plants are more resistant to disease over the long run and tend to perform better in the home or commercial garden throughout the entire season. In today’s market of tight margins and high expectations, there is simply no room for lackluster plants. Doing all you can now, in the early stages, will pay off in the future in terms of satisfied customers and repeat sales.

[i] Tina Smith, “Cleaning and Disinfecting the Greenhouse,” University of Massachusetts Amherst, The College of Natural Sciences, Agriculture & Landscape Program, Greenhouse Crops and Floriculture Program,

[ii] Daniel S. Egel, “Preventing Seedling Diseases in the Greenhouse,” Purdue University, Purdue University Cooperative Extension Service,

[iii] Tina Smith, “Damping-Off of Bedding Plants and Vegetables,” University of Massachusetts Amherst, The College of Natural Sciences, Agriculture & Landscape Program, Greenhouse Crops and Floriculture Program,

[iv] Egel, “Preventing Seedling Disease in the Greenhouse.”

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