Purdue News

June 24, 1991 New Compounds Curb Aquatic Weeds Without Eliminating Them West Lafayette, Ind. – Purdue University researchers report that a common garden herbicide may keep aquatic weeds at bay, a watershed discovery for the world's food supply and recreation industry. Carole Lembi, professor of botany, has found that the compound flurprimidol, which is currently used as a growth regulator for some flowers and bushes, also controls aquatic plants, but does not destroy the vegetation as many other herbicides do. "That is crucial because if a herbicide kills the plants, other animals in the water that depend on the vegetation for food, oxygen and shelter can also suffer," Lembi says. "In areas such as the Midwest, aquatic weeds are only a problem when they interfere with recreation. However, in many areas, such as the Third World where people depend on clear lakes and rivers to supply food, the problem is much more serious." The weeds can starve the fish of oxygen. As with land plants, aquatic plants release oxygen as a by-product of photosynthesis, but at night they also take in oxygen. This dramatic fluctuation in the oxygen levels in the water can stress or kill aquatic fauna. "Also, in some severe cases, the weeds can even clog hydroelectric dams, irrigation systems and navigable waterways," Lembi says. "For example, the Army Corps of Engineers estimates that if they left the weeds to grow in the Panama Canal, the weeds would force the canal to close within two years." One approach to controlling aquatic vegetation in this country is to stop nutrients from getting to the ponds or lakes. Bans on phosphate detergents, the switch to no-till farming and cautions against over-fertilizing lawns all aim to reduce the nutrient load. These measures help, but such measures are rarely found in developing countries. And in this country, for bodies of water as small as farm ponds or lakes by apartment complexes or houses, they are not enough because nutrients still get through, and weeds still grow. "Even if we could shut off all sources of nutrients, rooted plants would flourish on nutrients stored in sediment at the bottom of the pond or lake and continue to present problems," Lembi says. Although having too much vegetation in an aquatic environment is a problem, so too is having too little, which often occurs when today's herbicides are used. Fish depend upon aquatic plantlife for shelter and food. Without some aquatic plants there is also no producer of oxygen for fish and other life. Lembi has found that the compound flurprimidol solves this problem by limiting the vegetation growth instead of eliminating it. The research, funded by the U.S. Army Corps of Engineers, was published recently in the Journal of Plant Growth Regulation. For several years nursery and greenhouse growers have used plant-growth regulators, including flurprimidol, to stop flowers and bushes from getting spindly. Chrysanthemums, for example, keep a tight, round form when certain growth regulators are used. Some of these growth regulators inhibit a plant's ability to create the plant hormones called gibberellins. Plants make most of their gibberellins in young leaves and roots. From there, these hormones travel throughout the plant and cause stems to grow longer. When plant-growth regulators stop plants from producing gibberellins, stem length between leaves stays short and plants are dwarfed. Lembi has found that the plant-growth regulators work as well on aquatic plants as they do on nursery plants. In barrels used in the testing, untreated aquatic weeds entirely fill the available space; weeds treated with growth regulators form a soft carpet on the bottom. Having proved the efficacy of the compound in controlled environments, Lembi will begin using the compounds in real-world experiments. The first experiment will be conducted in small ponds at an Army Corps of Engineers facility in Texas next spring. Purdue News Service: (765) 494-2096; purduenews@purdue.edu