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Investigating Silicon Nutrition to Decrease Pythium Root Rot Severity in Snapdragons and New Guinea Impatiens 2010

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Project Leaders: Neil Mattson, Department of Horticulture, Cornell University
Margery Daughtrey, Department of Plant Pathology, Cornell University
Elizabeth Lamb, New York State IPM, Cornell University

Abstract: Control of Pythium root rot in greenhouse production typically involves preventive fungicide applications that are costly, may run off to the environment, and are sometimes ineffective due to pesticide resistance. Adding silicon (Si) to the fertilizer regime has improved the Pythium response of several greenhouse vegetable crops. Anecdotal evidence suggests that Si may also improve the Pythium response of floriculture crops, but no research trials have been conducted. In this project we wanted to determine if silicon can reduce Pythium infection of snapdragons and New Guinea Impatiens.

A greenhouse experiment was conducted in which plants were monitored for five weeks in response to Pythium inoculation. Silicon was applied in two different forms (liquid or substrate-incorporated powder). Snapdragon plants showed increased wilting and decreased plant height within 10 days of exposure to Pythium. At this early stage silicon did show some promise in reducing severity of Pythium. However, by harvest at day 35, there was no improvement in Pythium response for silicon treated plants. It is interesting to note that for snapdragons not inoculated with Pythium, silicon improved plant size, flower number, and root system. New Guinea Impatiens plants began to show symptoms of Pythium infection 24 days after inoculation. Silicon did not improve response of New Guinea Impatiens to Pythium.

There does appear to be some promise for silicon in snapdragon. For plants not infected with Pythium, silicon improved several growth characteristics; and silicon may delay Pythium infection/severity early on. Silicon does not provide clear benefits for New Guinea Impatiens. Overall, this experimental system provided plants with heavy Pythium pressure to test for benefits. This system of inoculating each plant with a virulent strain is not representative of normal greenhouse disease pressure. With a lower level of Pythium inoculum more typical of contamination in a greenhouse, perhaps silicon would be able to delay disease symptoms or decrease their severity: this hypothesis should be tested.