10/16/1991

Nursery Field Day Held at Ornamental Substation in Mobile

MOBILE, Ala.—Water quality and water management, disease control for ornamental plants and container research were just a few of the topics addressed during the Nursery Field Day held Oct. 8 at the Ornamental Horticulture Substation in Mobile.
The Field Day drew a crowd of more than 100 people who came to learn about results of research conducted at the Substation, an outlying research unit of the Alabama Agricultural Experiment Station at Auburn University.

Donna Fare, a research associate at Auburn, discussed the results of a study of the best irrigation cycles for nursery production. "Water quality has become a big issue with environmentalists and also with the nursery industry," she said. "We have abundant water in the Southeast so we are not as concerned about conserving water, but we are concerned about runoff water and its potential for pollution."

Her study evaluated several different irrigation cycles to see how much water was used by plants grown in containers and how much runoff occurred. Four regimes were tested -- a 60-minute cycle of continuous watering; a 60-minute cycle divided into three 20-minute watering periods; a 45-minute continuous cycle; and a 45-minute cycle divided into three 15-minute waterings.

Data from the study showed that reducing watering time from 60 minutes to 45 minutes of continuous watering reduced runoff by 28 percent. Using the 60-minute split-interval cycle reduced runoff 11 percent, even though the same amount of water was used, and the 45-minute split-interval cycle reduced runoff by 14 percent.

There was no difference in plant quality among the various regimes, which, Fare said, indicates that the optional cycles could be used without harming the plants.

Another irrigation study conducted at the Substation compared a sub-irrigation system to hand and drip irrigation systems for plants produced in a greenhouse. Bridget Behe, a horticultural researcher at Auburn, explained the study looked closely at ebb-and-flow irrigation, a sub-irrigation system which puts water at the base of plant containers, allowing the plants to take water up from the base rather than applying it over the tops of plants.

The ebb-and-flow system uses water stored in a tank to flood the platform on which the plants are standing, then drains the water back into the tank when the process is complete. "This is a closed system," Behe said. "There is no problem with runoff, which is the major advantage of the system."

Other advantages of an ebb-and-flow system include savings of labor, water, fertilizer, and fungicide inputs and less disease problems. The greatest disadvantage to the system, Behe said, is its installation expense.

Fred Deneke, also an Auburn horticulturist, noted that evaluation of sub-irrigation on poinsettias showed that sub-irrigated plants
were slightly poorer in quality than plants irrigated by drip or hand methods. He noted further research is needed to verify if the irrigation system caused this or if other factors are involved.

Deneke also noted that poinsettia variety research at the Substation indicates that Pink Peppermint and Glory varieties did well both in the nursery and in home environments.

Pest and disease control also were addressed during the Field Day. Austin Hagan, a plant pathologist from Auburn, noted that spray trials of various materials to control southern blight on acuba showed that Folicur, Prostar and Spotless all performed well. Spot anthracnose on dogwoods was controlled using Daconil, an experimental pesticide named ASC 66791, Rally and Folicur. Fireblight on cotoneaster was controlled using Agristrep, Kocide and a combination of Kocide and Manzate.

Hagan said evaluation of some biological controls on leafspot in photinia, such as using leaf litter and cotton waste, showed little promise for commercial production, but might be useful for homeowners.

Mike Williams, an Auburn entomologist, told visitors that the whitefly now has four potential candidates for problems in Alabama nurseries. He noted three whitefly species -- the greenhouse, citrus and sweetpotato whiteflies -- all are already in Alabama causing problems. Now, he said, the banded-wing whitefly is a threat, though it has not yet caused any major problems in the state.

Williams said a greenhouse test of whitefly controls on hibiscus plants revealed that Danitol and Orthene could control this pest and that Orthene mixed with Sunspray ultrafine oil also controlled whiteflies and cleaned debris left by whitefly activity from the leaves.

Jimmy Stephenson, associate superintendent at the Substation, also told the group that other types of entomological research was underway at the Substation, including work with control of azalea lacebugs, spider mites and fire ants.

Fertilizer work on ornamentals was reported by John Olive, superintendent at the Substation. Olive said studies are underway to compare eight- to nine-month release fertilizers to 12- to 14-month release fertilizers. Emphasis in the study is to determine which fertilizer provides the most benefit and at what stage of plant production fertilizers are best utilized. He noted the study has already shown that potting date influences plant growth, regardless of the type of fertilizer used.

Ken Tilt, also an Auburn horticulturist, discussed his studies comparing different types of containers for nursery production. "Container production of trees is not a new idea, but more and more people are doing it on a bigger scale," he said. "We have found there are some problems with this, including concerns about runoff, labor costs and problems with heat buildup inside the black plastic containers most commonly used for this purpose."

Tilt's study has been looking at different types of containers and also different types of irrigation with these containers. The traditional black container, an "environmental friendly" black container with holes bored high in the plastic to avoid water runoff, a foam-rubber and wire "soil sock" container and a "low-profile" container built with a wide base and low sides all were evaluated. Both over-the-top irrigation and sub-irrigation were used with all these options.

So far studies have shown no differences in ornamental pear trees grown in any of these containers or irrigation options. However, pecan trees performed best with sub-irrigation in the soil sock or traditional containers.

Dr. Lowell Frobish, director of the Experiment Station, also addressed the group and expressed optimism about the horticultural industry. "There has been a steady increase in ornamental and turfgrass industries in the past few years," he said. "Our goal is to do research and get the results out to you. We want to help you find out how to move your industry ahead."

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By:
Katie Smith