October 2011 Culture

Crop Culture Report: Impatiens Accent Premium Series By Matthew Blanchard

Available in 11 colors that have been improved for branching, uniformity and free flowering, Accents are the impatiens of choice when large blooms and strong garden vigor are what really matters.

The 'gold standard' for bedding impatiens has been updated for today's grower, retailer and landscape demands. Accent Premium impatiens are improved for easier production with more uniform flowering and a better branching habit. Eleven colors are currently available: Bright Eye, Lilac, Deep Orange, Orange Star, Pink, Red, Rose, Salmon, Violet, Violet Star and White. Mix and Limited Edition Mix are also offered. Accent Premium impatiens are ideally suited for 4-inch pots and premium containers, but they're versatile enough to work in large packs. For the retailer, they match the growing trend towards larger plants and containers that can provide instant color and fill in the home garden.

Plug Culture

Production time for finishing 288-cell trays is four to five weeks. Expect radicle emergence in three to five days and a minimum of 95 percent seed germination. Light is necessary for germination, but seeds may be covered with a light layer of vermiculite to maintain moisture levels. If utilizing a chamber, providing a light source of 10 to 100 foot-candles will improve germination and reduce stretch. For optimum germination, media temperature should be 72 to 75¡ F. Maintain 100 percent relative humidity until radicle emergence and then reduce to 40 to 70 percent. The media should be saturated for days 1 to 2 or until radicle emergence. On days 3 through 10, begin slowly reducing media moisture to achieve level medium by cotyledon expansion. Do not allow seedlings to go into nighttime hours with wet foliage, as this may encourage tip abortion.

After emergence, increase light levels to 1,500 to 2,000 foot-candles and begin fertilizing with 25- to 50-ppm nitrogen from a calcium-based fertilizer. Maintain a media pH of 6.2 to 6.5 throughout the plug stage. Until two weeks after sowing, maintain an EC of 0.5 to 0.75 and then increase to 0.75 to 1.0 (2:1 dilution method).

During plug bulking, provide light levels of 3,000 to 4,000 foot-candles. Supplemental lighting at 350 to 450 foot-candles for two weeks will help to produce vigorous, strong-stemmed seedlings in regions where light levels are low. Day and night temperature should be 66 to 68¡ F until development of the first set of true leaves. Temperature can be reduced to 62 to 65¡ F to tone and hold plugs. Alternate between moisture levels wet and medium. Perform a weekly check for actively growing white roots. If needed, apply a Bonzi (paclobutrazol) plant growth regulator spray at 3 to 5 ppm to control stem elongation.

Fertilize at 75- to 100-ppm nitrogen every two to four irrigations with a fertilizer containing both potassium and calcium nitrate. Minimal use of fertilizer will keep seedlings compact. Excess phosphorus may promote stretching of seedlings.

Finishing

At an average daily temperature of 68¡ F, crop time from transplant of 288-cell trays is five to six weeks for finishing in large packs, six to seven weeks in 4-inch pots, seven to eight weeks in 6-inch pots, and eight to nine weeks in 10-inch hanging baskets. Use a well-drained growing media. A day temperature of 70 to 75¡ F and night temperature of 60 to 65¡ F is recommended. However, Accent impatiens are versatile and can be grown at average daily temperatures from 55 to 77¡ F.

To prevent leaf scorch, shading should be provided if light levels exceed 5,000 foot-candles. Maintain relative humidity at 40 to 70 percent and provide air circulation with horizontal airflow fans.

After plants have rooted into the container, the media can be allowed to dry between irrigations as a growth control strategy. However, drying down too much can cause abortion of developing flower buds. Fertilize at 75- to 100-ppm nitrogen every two to four irrigations with a calcium-based fertilizer. Over fertilizing can cause tall, lush, dark-green plants with flowers beneath the foliage, or late flowering.

Foliar spray applications of Bonzi at 5 to 15 ppm are effective at suppressing stem extension. Impatiens are also responsive to A-Rest (ancymidol), B-Nine (daminozide), and Sumagic (uniconazole) plant growth regulators. Management of irrigation, temperature, light, and fertilizer applications can also be used to control growth.

Pests and Diseases

Common insect pests on bedding impatiens include fungus gnats, thrips, aphids and spider mites. Among these, thrips are of most concern due to the physical damage they cause and their ability to transmit tospoviruses such as Impatiens Necrotic Spot Virus (INSV) and Tomato Spotted Wilt (TSWV). A good scouting program that includes monitoring populations and physical examination of the crop is key to catching pest problems early. Some common disease problems on impatiens include root and stem rots caused by Pythium and Rhizoctonia, leaf-spotting diseases caused by Alternaria and Pseudomonas, Botrytis and infections by tospoviruses.