Today’s vincas are better than ever before, offering hybrid vigor and dramatically enhanced disease resistance and performance. Two examples are Goldsmith Seeds’ Cora and Cora Cascade vincas, which have been thriving in landscapes and field trials nationwide with their high tolerance to aerial phytophthora.
But even with superior varieties, growers still need to pay attention to growing practices. Best practices can help eliminate greenhouse disease issues like Thielaviopsis and Pythium, which commonly affect vinca and most other bedding plants. Ken Harr, grower account manager for Syngenta Flowers/Goldsmith Seeds presents best practices for success with vincas in a 12-step program:
1. Provide a well-aerated media. Finish plants in areas with protection from seasonal rains and adequate dryback within 18-24 hours to reduce susceptibility to root disease.
2. Maintain an EC range of 1.2-2.0 to finish plants. An EC less than 1.2 stresses plants and may cause susceptibility to disease. EC greater than 2.0 in a dry substrate for longer than four to eight hours could result in iron-deficient plants with stunted roots and shoots.
3.A slow-release fertilizer can be added. Plants treated with these should not be allowed to dry down. Drying down could result in iron-deficient plants with stunted roots and shoots.
4.Provide a pH no greater than 5.5. When pH exceeds 5.5, vinca may become susceptible to Thielaviopsis, creating an environment for secondary infections, such as Phytophthora and Pythium.
5. Monitor pH weekly. Vincas can raise the pH of the growing substrate by as much as one unit in 10-14 days.
6. If Thielaviopsis is prevalent in your greenhouse, treat plants with a preventive fungicide of Medallion, Terraguard or a thiophanate methyl product during the first seven days after transplant.
7. Grow vincas in soil temperatures no less than 70°F day and night. An average daily temperature of 80°F is optimum.
8. Grow vincas in humidity of 40-70 percent. If growing in greenhouses, avoid many foliage diseases, such as Botrytis and Rhizopus, with horizontal fans to lower humidity.
9. Review and employ methods to eliminate Thielaviopsis. Keep pH at 5.5. If this disease has infected your greenhouse, maintain an EC less than 1.5. Use a preventive fungicide following label directions. Keep phosphorous under 12 ppm and ammonium under 10 ppm.
10. Fertilize with iron at 2 ppm and ammoniacal nitrogen at 20 percent on a trial basis if light intensity is greater than 5,000 footcandles (18 mols).
11. Use a reputable plant lab to diagnose problems so an effective treatment plan can be applied.
12. Only use new plug trays and finish containers.