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ARS Home » Pacific West Area » Albany, California » Western Regional Research Center » Invasive Species and Pollinator Health » Research » Research Project #433288

Research Project: Aquatic Weeds Associated with Agricultural Water Supply

Location: Invasive Species and Pollinator Health

Project Number: 2030-22300-032-021-S
Project Type: Non-Assistance Cooperative Agreement

Start Date: Sep 5, 2017
End Date: Jul 30, 2022

Water quantity and quality are both significant issues related to agriculture, and nowhere are these two issues more critical than in drought-beleaguered California. Water flows from surface-storage reservoirs, rivers, and lined canals through smaller irrigation ditches and aqueducts. The shallow ditches and canals are often occluded during the growing season with dense growths of nuisance aquatic plants and algae, which clog intakes and outflows, impede flow rates, and displace water. Aquatic plants significantly reduce the flow of water through these distributary systems. The goals of the irrigation conveyance portion of the project are to quantify the impact of dense vegetation on water conveyance, and to evaluate weed control options for both de-watered canals and flooded canals to improve weed management at reduced cost or environmental impact. Once the water reaches the intended users, the water quality may impact the crop condition or affect crop protection. For one crop, excess nutrients in the water may contribute to the growth of a novel problem. In water-seeded rice, dense growths of algae may reduce seedling survivorship and condition. This research will examine the nutrient loads and sources, as well as other factors contributing to the eruption of algal blooms in seeded rice fields. The management options for controlling algae in rice fields will be investigated, with the goal of reducing copper loadings resulting from the use of inorganic granular copper sulfate.

One issue of water delivery is the growth of weeds in irrigation canals and feeders. Growth of submersed weeds, no matter the species, adversely affects water delivery by reducing the available volume to hold water, reducing the flow velocity due to hydraulic resistance, and increasing the potential for canal flooding and water loss. Because of these factors, irrigation canals are intensively managed to reduce weed growth. The available methods are restricted. Pesticides must have food tolerances, and have relatively short contact time requirements. The list of herbicides for use in flowing irrigation ditches is therefore very short. Mechanical methods are often used, but they are very expensive. Currently, little research is being done on irrigation canal weed issues, such as predicting the amount of water movement capacity, or investigating methods to improve weed management at reduced costs. Evaluations of pesticide application methods and trials of existing aquatic herbicides for irrigation use will be investigated, as well as the use of bareground treatments on dewatered canals to provide season-long control from aquatic weeds. Some options for bareground spring or fall treatments on dewatered canals include acetic acid, diuron, flumioxazin, imazamox, fluridone, and penoxsulam. The main options for controlling weeds in flowing canals are complexed copper compounds, two different formulations of endothall, and acrolein. Therefore, predicting water carrying capacity related to volume of aquatic weed growth will also be evaluated. These would involve examining plant height and biomass related to water discharge and canal cross-sectional area. An additional issue related to the use of irrigation water is that, in California, the seeding of rice by plane into flooded fields has become more popular. One drawback is that algal growth may reduce seedling survival and crop yields early in the cultivation process. Currently, the only active ingredient used are copper-based algaecides. Farmers typically use “blue rock,” inorganic granular copper sulfate. This is inefficient and introduces more copper into the environment than necessary. The nutrient loads and sources that produce algal bloom issues will be investigated, and evaluations of new chelated copper formulations as well as other potential algaecides for use in controlling algae in cultivated rice fields will be studied. Influent nutrient concentrations, particularly phosphorus, will be analyzed, and field nutrient and fertilization rates will be examined to consider the relationship of nutrient availability to algae growth. Very little is known regarding the environmental drivers of algae growth in flooded rice fields, which would lead directly to integrated pest management approaches to reduce algal issues in seeded rice fields.