Did you know that MEMBG has classified itself as a "green garden"? This means that we exclude all use of commercially available synthetic pesticides. We have several reasons for following this path. First are health and safety issues, of course, for staff and visitors who would be exposed to these chemicals during and after application. Second are serious concerns about how harsh chemicals applied to plants and soil might affect other critters in the garden. Some chemicals once considered safe have been found to have long-term negative effects on the environment and its inhabitants. At MEMBG alone, for example, our record of regularly observed birds has decreased significantly over the last thirty years.
Another reason relates to the fact that we grow plants from around the globe, with diverse cultural needs that are often difficult to meet. Plants grown under suboptimal conditions generally have lowered resistance, increasing their susceptibility to disease. In addition to the target, pesticides kill beneficial insects that help to control pestiferous insect populations. Thus, by limiting the use of such poisons, we allow beneficial organisms to keep our garden healthy. Additionally, the use of today's biochemically complex pesticides is highly regulated, requiring detailed record-keeping and proper training, certification, and supervision of personnel. Even a single application can be expensive in terms of labor as well as materials, providing yet another motivation for us to use alternative procedures, such as pruning, nutritional strategies, and cultural practices (mulching, plant-specific watering, removal of contaminated leaves) to increase the vigor and natural immunity of plants under attack.
Confirming our decision to stop using synthetic pesticides, we have had good success in controlling plant diseases without these toxins. Our Malesian rhododendrons provide a case in point. The leaves of these plants were badly infected with three fungi: a powdery mildew, a leaf black spot called Colletotrichum lindemuthianum, and another leaf spot and stem canker organism called Phomopsis. Rather than treating the fungi directly with chemicals, our crew first tried clearing out the dense brush that blocked sunlight from this special collection. The results were spectacular! With brighter sun and better airflow, not only did the fungi virtually disappear, but the rhododendrons also experienced their best-ever bloom during late summer!
This year, our most serious infestation came in September, with the arrival of a giant white fly (Aleurodicus dugesii) that first attacked hibiscus and threatened to become an epidemic. This is a new pest that arrived in San Diego in 1992 (California Agriculture 51(6)1997). It attacks many hosts, including banana, bird-of-paradise, begonia, ivy, philodendron, pittosporum, avocado, apricot and plum, citrus, and even morning glory. There is no known chemical control of this beast. MEMBG staff and volunteers worked hard, washing entire plants with our insect wash and pruning infected plants to prevent total infestation. When the white fly expanded its territory and taste beyond Malvaceae, we treated the leaves of infected plants with a thin ultra-fine spray oil called SunSpray, a summer oil that contains a 1:400 solution of Wanis neem seed extract (from the neem tree of India, Azadirachta indica, family Meliaceae). We are also involved in a pilot program to test a potential biological control, now being developed at UC Riverside, that uses parasitic wasps from Mexico, the presumed native home of the giant white fly. I anticipate that the white fly population will decline with the upcoming cool nights and cool days, which may give these natural enemies of Aleurodicus time to establish themselves.
It is commonly believed that economically important commercial crops cannot be grown successfully without the application of pesticides. Cotton, for example, is probably the most heavily sprayed crop on the planet--reportedly receiving about 25 percent of all pesticides applied. An international movement in favor of "green farming methods," however, is challenging this practice. As environmentalists are advocating alternatives to pesticides, we at MEMBG are doing our part.
The next time you visit MEMBG, remember that the insects you see are also part of the experience in our green garden--where we're seeking a golden mean between snacking and feasting!
RAND PLEWAK
Garden Manager