07/29/1996

Pretty Flowering Vincas Susceptible to Deadly Disease

BREWTON, Ala.- Vincas are flowering annual bedding plants that have become a mainstay for many Alabama landscapes each spring and summer. They seem to withstand heat, drought, and floods equally well, and they come in a multitude of flower color combinations. For most growers vincas are trouble free, but when trouble comes, it's devastating to these hardy flowers.

Phytophthora stem and shoot blight, a fungal disease in vincas, has shown up sporadically around the state, but for home and business owners who have invested time and money in planting vincas it can be frustrating and costly. For example, Atmore city planners planted large areas of vincas around their town as part of a beautification program. Virtually all the vincas died from the blight.

A critical thing for growers to remember, according to Auburn researcher Austin Hagan, is that once phytophthora gets into the soil, vincas are at risk in subsequent years. It is a rapidly spreading fungal disease, which can kill large areas of vincas surprisingly fast.

Hagan and other Auburn University researchers are looking at some bedding plant options to plant in soil infected with the phytophthora disease organism. In tests at the Brewton Experiment Field, diseased vincas were planted, quickly died, and the plant residue was incorporated into the soil.

"We wanted to be sure the disease-causing organism was present in the soil, and it certainly is," noted Randy Akridge, superintendent of the Alabama Agricultural Experiment Station research facility in Brewton. Akridge pointed out that some varieties of vincas, which are in the periwinkle family, were killed by the disease almost immediately when transplanted into the diseased soil. Other varieties had slightly more tolerance, but were also killed by the disease.

To determine some alternatives for planting into soil infected with phytophthora stem and shoot blight, researchers planted 32 different bedding plants, including such popular flowers as geraniums, impatiens, marigolds, pansies, daisies, and salvia. All these plants survived in the infected soil, but some, like salvias, showed some susceptibility to the disease.

For those who have vincas in plantings, the disease begins in a single shoot of a plant, which starts to wilt and droop. The leaf will then turn black and usually stick to the plant. One diseased plant will rapidly infect nearby plants, probably as rainfall or watering splashes the organism around on the foliage. The disease can appear a few days after transplanting, or it can affect mature plants. Removing diseased shoots will help slow down the disease, but the fungal organism is soilborne, so it will infect other vinca plants in the area.

"There is some evidence that the use of ammonia-based fertilizers on vinca may create some stress on the plant that opens it up to the disease quicker," Hagan noted. "We will be switching to calcium nitrate to see what affect the non-ammonia source has on the spread of this disease in vincas. We also think that some of the sensitivity of salvia to the disease may actually be its sensitivity to ammonia in the fertilizer we used in the tests at Brewton," Hagan concluded.

Though there are some fungicide combinations that will control phytophthora in vincas, these materials are so specific to nursery use and so expensive that they are not practical to use in most home and business plantings.

Based on tests with vincas and phytophthora at Brewton, Hagan and Akridge agree the best bet with vincas is to be sure you get healthy plants to transplant, and if you do get the disease in your flowers plant something else there next year. Homeowners who notice signs of wilting and sticking of dead leaves in vincas should contact their county Extension office to more precisely identify the disease. The good news is that phytophthora stem and shoot blight seems to be very specific to vincas, and all the other 32 bedding plant varieties planted in the test at Brewton have survived.

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News from:

Office of Ag Communications & Marketing

Auburn University College of Agriculture
Alabama Agricultural Experiment Station
3 Comer Hall, Auburn University
Auburn, AL 36849
334-844-4877 (PHONE) 334-844-5892 (FAX)

Contact Jamie Creamer, 334-844-2783 or jcreamer@auburn.edu
by Roy Roberson

07/29/96