MSU Extension

Each year, the Western Michigan Greenhouse Association and Metro Detroit Flower Growers Association partially fund floriculture projects performed by Michigan State University faculty and staff. In 2016, the associations awarded grants for seven projects in the MSU Departments of Horticulture, Entomology and Plant, Soil and Microbial Sciences. Here is a short summary of three of those research projects and results.

Assessment and mitigation of tomato spotted wilt virus on chrysanthemums

Tomato spotted wilt virus is vectored by western flower thrips to a wide variety of plants, and infection of chrysanthemum is increasingly problematic. Symptomatic chrysanthemum plants at two commercial greenhouses were scouted and sampled to better understand the interaction between thrips populations, incoming plant material, carryover between crops and other risk factors for tomato spotted wilt virus. Ten percent of 110 samples tested for tomato spotted wilt virus were found to be positive for the plant virus, and it was most prevalent during the last week of July and first week of August. Based partly on this project, we recommend growers minimize plant stress, manage thrips populations less than or equal to 30 thrips per card per week), scout for early detection, perform consistent in-greenhouse viral testing, and immediately dispose of plants testing positive for tomato spotted wilt virus.

Based partly on this project, we recommend growers minimize plant stress, manage thrips populations less than or equal to 30 thrips per card per week), scout for early detection, perform consistent in-greenhouse viral testing, and immediately dispose of plants testing positive for tomato spotted wilt virus.

Read the full research summary, “Assessment and Mitigation of Tomato Spotted Wilt Virus (TSWV) on Chrysanthemums,” by Heidi Lindberg, MSU Extension.

Comparing LEDs vs. HPS lamps in greenhouse production of seedlings

The objective of the experiment was to determine the effectiveness of lighting from light-emitting diodes (LEDs) and high-pressure sodium (HPS) lamps on growth and subsequent flowering of popular bedding plants. Geranium, pepper, petunia, snapdragon and tomato were grown as seedlings, and also after transplant, under each of six different greenhouse lighting treatments. Five of the six lighting treatments had different ratios of light from red + blue, red + white, or red + white + far-red LEDs using fixtures from Philips. All LED treatments delivered 90 μmol·m^–2·s^–1 of photosynthetic light, while one treatment delivered 10 μmol·m^–2·s^–1 of light from an HPS lamp. The air temperature was maintained at 68 degrees Fahrenheit and lights operated continuously for 16 hours per day.

Plants under the five high-intensity light treatments had more root and shoot growth than under the low light intensity, but there were no consistent differences between those under HPS lamps or the LEDs. Also, the flowering time was generally similar under the high-intensity LED light treatments, and all flowered substantially earlier than under the low-intensity control. Therefore, the LEDs could be a suitable replacement for HPS lamps and also reduce energy consumption by 53 to 64 percent.

Read the full research summary, “Comparing LEDs vs. HPS Lamps in Greenhouse Production of Seedlings,” by Brian Poel and Erik Runkle, MSU Department of Horticulture.

Increasing height of chrysanthemum with Fresco drenches

Chrysanthemums can induce flowers early, which occurs when temperatures during the summer are relatively cool, especially at night. When flowers induce early, or when plant growth retardants are over-applied, there is a need to increase plant height. One technique to increase stem elongation is to make an application of a product (Fresco) that contains gibberellic acid (GA) and benzyladenine (BA). Fresco applications increased height in ‘Barbie Lavender,’ ‘Eventide Dark Bronze’ and ‘Gigi Coral’: plants were 2-3.5 centimeters (1-1.5 inches) taller at first flower than untreated plants. Height of ‘Chelsey Coral’ and ‘Jacqueline Pearl’ was not affected by the treatments. Sprays were more effective in some varieties while drenches were more effective in others; overall, when applied at the same rate, responses were similar. Therefore, Fresco drenches offer potential advantages compared to spray applications with potentially less delay in flowering, more flowers and no chlorosis.

Read the full research summary, “Increasing Height of Chrysanthemum with Fresco® Drenches,” by Cathy Whitman, Nate DuRussel and Erik Runkle, MSU Department of Horticulture.