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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
1. Rapid response to South American sponge plant. The highly diverse natural aquatic habitats in California, including the Sacramento-San Joaquin Delta (Delta) are threatened by an increased spread of South American sponge plant, a newly introduced floating aquatic plant native to South and Central America. To understand the environmental limits to its dispersal, ARS scientists from Davis, California, examined its growth rate under three temperature and day-length conditions that represent late winter, early summer and mid-summer in the Delta. Winter conditions did not kill the plant, but rather increased its surface cover at 10 to 12 C. Levels of nitrogen in the leaves varied with external levels and suggest that increased nutrient inputs will greatly increase growth rates. These results along with the persistence of plants throughout winter months, have prompted state agencies to initiate regulatory actions and rapid responses in an attempt to prevent further impacts.

2. Improving control of giant reed (Arundo). Arundo donax, is a tall perennial invasive grass that in the U.S., spreads exclusively by vegetative (especially clonal) means and can invade and alter many riparian ecosystems in the western U.S. Improved management strategies can result from better understanding the dynamics of its vegetative growth and the mechanisms by which annual growth expands its cover. Results of extensive analysis of growth patterns, the role of new “buds” on shoots, coupled with understanding herbicide efficacy showed that optimal control can be achieved by complete removal of shoots and by methods that can affect the rhizomes. These studies by ARS scientists at Davis, CA also showed that Giant Reed is capable of establishing in a wide range of temperature and moisture conditions. These results provide a basis for development of models that may predict the types of sites that are likely to become invaded by Arundo, and sites that should be monitored for new incursions.

3. Management of water primrose willows (Ludwigia). Several species commonly known as “water primrose” or “primrose willows” have spread dramatically over the past 10 years in the western US waters; yet, little is known about their genetic make-up, growth characteristics and habitat requirements. Studies were completed by ARS scientists in Davis, CA that better characterize the genetic differences among Ludwigia species, and their nutrient requirements. In addition, the interaction between some Ludwigia species and insect herbivores suggest that chemical substances released or found in these plants may serve as cues, or deterrents to potential biological control agents. This information will be helpful in searches for effective biocontrol agents in South America where the Ludwigia species are native.

4. Management of aquatic weeds at Lake Tahoe. Lake Tahoe, the second deepest lake in the US, is an Outstanding National Resource Water, and has been impacted by two non-native aquatic weeds which are the Eurasian watermilfoil and Curlyleaf pondweed. Multi-year surveys and assessment of infested sites have been made over the past 16 years showing an increase spread of these aquatic weeds in several marinas and along several areas of the lake shoreline. The long-term assessment by ARS scientists in Davis, CA showed the continued spread of invasive plants, and this, coupled with new threats from quagga and zebra mussels prompted new management actions and regulatory changes that form the basis of an integrated aquatic invasive species program for the Tahoe Basin (Lake Tahoe Basin Aquatic Invasive Species Plan). The Plan helps protect Lake Tahoe from further infestations and insures that the full benefit of public uses for commerce and recreation will be sustained, while improving ecological functions in the lake. Thus, the benefit accrues to millions of annual tourists and local residents who value this alpine lake.

5. Expanded control of Brazilian waterweed. The non-native submersed plant “Egeria” or Brazilian waterweed has impacted commercial navigation, recreation and water delivery from the Sacramento-San Joaquin Delta for many years. Successful control in over 3,000 acres was achieved in past years through collaborative efforts of ARS, state and other federal agencies. In 2011, methods were refined and expanded to encompass another 700 acres of highly infested areas. Control of Brazilian waterweed is now expected to encompass over 5,000 acres with reductions of over 75% of biomass.

Last Modified: 05/23/2017
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