Three Findings from the SAF Pest and Production Management Conference
At the recent Society of American Florists’ Pest and Production Management Conference in Orlando, I presented some results of research conducted at the University of Maryland, and thought I would share some others as well.
The “Big Gorilla Disease” for Basil Growers
Basil is a huge money-maker for many horticulture operations. One large New Jersey greenhouse said their demand for sweet basil exceeds their ability to produce it in New Jersey, and they’re now looking at buying 15-20 acres of greenhouse in Florida to grow more basil. Attendees surveyed at the SAF meeting said that sweet basil is the most in demand.
Margery Daughtrey of Cornell University spoke on the “big gorilla disease” of basil: downy mildew.
Downy mildew of basil is known to be carried in seed. The trick is finding a seed producer who sells clean seed. Margery and her team found that if the seed is treated with steam, the downy mildew can be killed without damaging the seed. Hot water treatment doesn’t work because of troublesome seed exudates. She mentioned one Dutch company that can supply steam-treated seed called Enza Zaden.
The long-range way to deal with this disease is to use resistant varieties. There is one called ‘Eleonora’ which Margery called a good first try, but we still have a ways to go to find a really good downy mildew-resistant cultivar. Some promising new ones are under development at Rutgers.
Margery suggested that fungicides be applied preventatively. In greenhouses the materials to use would be Revus, Ranman, or phosphorus acid fungicides such as FosPhite or K-Phite. Other materials registered for use on basil outdoors are not labeled for greenhouse use, but the materials available for the greenhouse will do the job, unless you grow organically.
One of the physical controls you can use is to keep the relatively humidity under 85%, which can be a real challenge later in the spring and early summer when greenhouse humidities tend to rise.
Margery mentioned that in Israel researchers are trying a novel way of dealing with this disease by using incandescent light bulbs suspended over basil, kept on overnight. In the first couple of weeks after germination they are able to protect 96-100% of the basil from downy mildew. In the following weeks this beneficial impact from nighttime lighting drops off gradually because the canopies fill in and much of the leaf area is no longer directly exposed to light.Margery also emphasized the importance of regular monitoring, and destroying infested plants immediately.
Growers producing basil as micro-greens for use in salad bars must really stay on top of monitoring with a fast-turning crop like this.
Banker Plants and Biological Control
Lance Osborne of the University of Florida presented a session describing several banker plant systems for growers. One was new to me—using papayas as banker plants. Lance, Ashton Dickey, and Cindy McKenzie published a paper in 2011 about infesting papaya plants with papaya whitefly. This pest limits its feeding activity to papaya and plants in its family, which are not generally grown in a greenhouse environment. Lance told me he purchased papaya fruit from the grocery store (easy to do in Florida where he is located), removed the seeds, and started them in pots. The papaya plant is then infested with whitefly, Bemisia tabaci.
The parasitic wasps Encarsia sophia (transvena) are released on the plants, and the females sting the sessile stage of the whitefly and lay eggs inside. The banker plant is then moved out into the greenhouse, and the parasitic wasp adults migrate out into the greenhouse to search for and sting sessile stages of whiteflies. Biological supply houses are now investigating what is required to ship out papaya whitefly to states other than Florida, where it already exists. Once this hurdle is crossed we will have a potentially very cool banker plant system to deal with whitefly in greenhouses.
Grass Mites Useful for Two-spotted Spider Mite Control
One of the major pests damaging greenhouse plants is the two-spotted spider mite. Lance Osborne said that in Florida, growers raise field corn plants in pots and infest the foliage with grass mites that feed only on monocots such as corn and grasses. Once the mite population is established, two predatory mites, Amblyseius californicus and Phytoseilus persimilis, are released on to the corn plants. They feed on the grass mites, reproduce, and when the banker plant is moved into the greenhouse, migrate off the corn and search for spider mites on the crop. Grass mites are found in many states so shipping them from biological supply houses should be a smaller hurdle to get over.
Stanton Gill is an extension specialist (professor-ranked principal agent) in IPM and entomology with the University of Maryland Extension, based at the Central Maryland Research and Education Center in Ellicott City. He is also a professor in the Landscape Technology Program at the Germantown Campus of Montgomery College. Contact him at [email protected]