July 2008

Crop Culture Report: Vinca Cobra Series By Bill Wilson

Vinca (Catharanthus roseus) originated in Madagascar, a large island off the African coast. Vinca has been bred since the 1920s, but it has been available only as an open-pollinated (OP) variety until recently. In 2003, Floranova brought the first complete F1 vinca series to the market. Floranova has since become a leader when it comes to F1 vinca by providing four separate series to meet the needs of the marketplace. The benefits of an F1 vinca over an OP vinca are very apparent in production, plant habit (increased branching and flower size), landscape performance and sell-through at the retail level.

The major segment of the vinca market is found in pack production, so we will focus on Cobra today. The colors available in the Cobra series are Orchid Eye, Passion Fruit, Rose, Purple Eye, Peppermint, Red, Red with Eye and White.

Plug Production

When sowing, use a well-drained, disease-free, peat-based plug media. The media should have a pH of 5.5-5.8 and EC of less than 0.75 (saturated paste). For best results, cover the seed with coarse vermiculite after sowing to provide dark conditions for better germination.

During Stages 1 and 2 (germination), keep media uniformly moist until seedlings are hooking above the vermiculite covering. Once you see this, dry down covering to control stretch and improve rooting. Soil temperature should be 75-80¡ F; vinca likes warm temperatures during germination. Keep light levels less than 1,500 foot-candles until cotyledons are open. Complete germination time is seven to 10 days.

During Stage 3, the soil temperature should be no lower than 68-72¡ F. Keep media on the drier side, and lower humidity for best rooting, height and disease control. Light levels should be around 3,000 foot-candles. Feed every other watering with 100- to 150-ppm nitrogen from 15-5-15, 17-5-17 or 13-2-13. Keep media pH at 5.5-5.8 and EC at 1.0-1.5.

During Stage 4, soil temperature can be lowered to 65-68¡ F. Avoid cooler temperatures, which will promote poor rooting and increase risk of root rot. Keep media on the drier side, with light levels at 3,000-4,000 foot-candles. Use low-ammonium feeds, but monitor media pH closely to keep it less than 6.5.

During plug production, use B-Nine (daminozide) at 800-2,500 ppm, A-Rest (ancymidol) at 2-7 ppm or Sumagic (uniconazole) at 1-3 ppm in warmer climates only, as effective growth regulators. This is not a requirement; you should set up your own trials to determine which work best, as weather and cultural practices directly affect how much growth regulators to use.

The crop time for plugs is five to seven weeks for 512 plugs and six to eight weeks for a 288-plug tray, depending on temperature and light levels. Using HID lights during low light periods will speed up growth thanks to warmer leaf temperatures.

Transplant to Finish

Most vinca production is in cell packs to 4-inch pots. Transplant plugs into a well-drained, disease-free, peat-based media with a pH of 5.5-5.8 and an EC less than 1.5. Avoid saturating the media with water after transplanting to help control root rot. Use the half-saturation technique for watering until roots reach the sides of the container.

Keep the soil temperature around 70-72¡ F to ensure strong rooting. Once the roots are established, keep temperatures above 68¡ F, as vinca grow best in warmer environments. Maintain light levels at 3,000-5,000 foot-candles or higher.

Vinca do not like to be kept too wet; grow on the drier side with some wilt. Watering lightly but frequently will only create more foliar diseases. Feed once a week with 150-ppm nitrogen from 15-5-15, 17-5-17 or 13-2-13. Keep the media pH around 5.5-5.8, and the media EC at no more than 1.0-1.5.

You can effectively use growth regulators such as B-Nine at 1,000-5,000 ppm, A-Rest at 2-7 ppm, or Sumagic at 2-5 ppm in warmer climates as needed. Bonzi (paclobutrazol) can cause black spotting on leaves.

The most common problems you may experience include Pythium, Rhizoctonia, Thielaviopsis, aerial Phytophthora, Botrytis, Alternaria leafspot and yellowing of the upper leaves. This yellowing is caused by low iron or media pH greater than 6.5.

The crop time for cell packs and 4-inch production is five to seven weeks, depending on plug and container size, temperature and light levels.