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United States Department of Agriculture

Agricultural Research Service

Research Project: Aquatic and Riparian Weed Management to Protect U.S. Water Resources in the Far West United States

Location: Exotic and Invasive Weeds Research

2011 Annual Report


1a. Objectives (from AD-416)
Objective 1: Improve understanding of weed life history and population dynamics (including effects of habitat alteration and assessment in canals and managed wetlands), biosystematics, and molecular biology to develop tools to undermine the success of weeds such as water primrose-willow species, perennial pepperweed, purple loosestrife, cordgrass, giant reed, and Eurasian milfoil, and to restore invaded riparian, marsh, and aquatic ecosystems. Objective 2: Determine the effectiveness of integrated weed management, including potential new herbicides on weeds such as hydrilla (Hydrilla verticillata), pondweeds (Potamogeton, nodosus, P. crispus, Stuckenia pectinata), Eurasian watermilfoil (Myriophyllum spicatum) and exposed sediments during seasonal drawdown (dewatering) for weeds such as M. spicatum, Western milfoil (M. hippuroides) in irrigation systems. Objective 3: Determine the applicability of biological control agents for water primrose-willows, Mexican mosquito fern, Brazilian waterweed, giant reed (including tricin host production effects on natural enemies), M. spicatum, and water hyacinth (Eichhornia crassipes), including plant ecology in relation to biological control for L. hexapetala and E. crassipes. Objective 4: Develop effective rapid response methods for new introductions of aquatic invasive weeds such as E. densa, P. crispus, and Undaria, or Japanese kelp (Undaria pinnatifida), and adapt these technologies to control invasive freshwater plant species, marine macroalgae and invasive marine plants.


1b. Approach (from AD-416)
1) A demographic study will determine how temporal and spatial variation in factors affecting Uruguayan water primrose contribute to overall population dynamics and improved management and restoration at Lagun de Santa Rosa. 2) Egeria Carbon Hydrogen Nitrogen (CHN) and associated insect communities will be determined monthly at invaded/ non-invaded sites at in the Sacramento/San Joaquin Delta using presence/absence and hydroacoustical and videographic methods. 3) Eurasian watermilfoil will be sampled (weekly to monthly) in the Truckee and Fall Rivers along streamflow gradients. 4) Effects of simulated herbivory on Giant reed and effects on root growth (abundance, life span) will be quantified from images recorded with a video camera system within the minirhizotrons at weekly intervals. Success of active (planting desirable species) versus passive (recruitment from resident propagules) re-vegetation will be assessed in giant reed managed sites. 5) Effects of native and non-native submersed plants on rhizosphere microflora will be assessed in replicated mesocosms and natural populations. 6) Replicated applications of fluridone, copper will be made in water and with penoxsulam, or acetic acid to canals and canal sediment. 7) Methods to eradicate Curlyleaf pondweed will be evaluated in indoor and outdoor tanks using diquat, endothall, and penoxsulam under short and long-day conditions. Formerly 5325-22000-019-00D (02/1/2011)


3. Progress Report
Research on six non-native and invasive aquatic plants was conducted. Giant Reed: Over 1,700 Giant Reed (Arundo) buds, were tracked, their locations on stems noted, and their contribution to expansion of clones (clumps) was determined. Data showed that the leading edge of bud advance on stem about 17 cm/year and that clones can persist in a wide range of moisture and temperature. Growth models showed that optimal control and prevention of expansion may be achieved by either complete stem removal and by blocking growth of rhizome. Experiments were conducted near Davis and Fresno, California detailing the response of Giant Reed (Arundo) to the herbicide glyphosate applied in spring, summer and fall. Leaf greenness, number of living and dead stems, and the number of newly emerging stems were measured monthly. Results indicates that best control is achieved with fall treatment with 1.5% glyphosate. Primrose Willows (Ludwigia): Genetic characteristic such as chromosome numbers were determined in California and Oregon populations of Primrose willows (Ludwigia species) to determine how these characteristics may be associated with plant structure. Studies on relationships between Ludwigia and a Primrose-eating native flee beetle showed that volatile chemicals were produced in response to feeding by this insect, which may be a protective response. Follow up study sites and their nutrient characteristics were identified for field research in the Russian River watershed. South American Spongeplant: Growth of South American spongeplant, a non-native invasive floating-type weed newly established in the Sacramento-San Joaquin River Delta, was compare in controlled condition under late winter, early spring and in outdoor mid-summer conditions in natural Delta water and in Delta water diluted to produced 25% of natural nutrients. Results and field observations suggest that South American spongeplant will easily survive typical winters in the Delta and may be protected from hard frost since the growing tissues are partially in the water, which provides insulation. Eurasian watermilfoil Biological Control: Cultures of Eurasian watermilfoil were established under controlled conditions and inoculated with a native insect herbivore, the “Milfoil weevil”. Feeding activity was quantified, and studies on the reproduction and other life-cycle traits were begun. Field sites for potential augmentative release were evaluated including the Fall River in Northern California. Curlyleaf pondweed Control: Baseline studies were completed in several sites at Lake Tahoe that are infested with Eurasian watermilfoil and curlyleaf pondweed. The distribution and abundance of these invasive plants were determined. Sites will be used in assessing various non-chemical control actions including use of natural (jute) and synthetic materials (“bottom barriers”) to cover the plants, and mechanical harvesting. Sampling stations were established in the Sacramento-San Joaquin Delta and Lake Tahoe to compare the dispersal, growth and reproductive characteristics of curlyleaf pondweed.


4. Accomplishments

Last Modified: 10/19/2017
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