Location:2012 Annual Report
1a. Objectives (from AD-416):
The long-term objective of this project is to reduce the impact of invasive weeds in the Lower Rio Grande Basin (LRGB) and other southwestern watersheds. Over the next 5 years we will focus on the following objectives: Objective 1: Import, culture, and conduct biological studies and host range tests on candidate natural enemies for Arundo donax. Develop mass rearing and mass release methods for permitted agents. Evaluate impacts of biological control agents in the Rio Grande Basin and other watersheds of the Southwestern U.S. Subobjective 1A. Import and evaluate candidate natural enemies of Arundo donax in quarantine for safety and efficacy. Subobjective 1B. Evaluate (1) methods for mass release of biological control agents of Arundo donax and (2) related impacts of introduced natural enemies in the field. Objective 2: Evaluate impacts of tamarisk leaf beetles for biological control of Tamarix spp. saltcedars in the LRGB and in coastal Texas, and develop new agents. Subobjective 2A. Release and evaluate tamarisk leaf beetles (Diorhabda spp.) at sites in the LRGB that contain mainly T. ramosissima and T. chinensis saltcedar, and assess effects on exotic athel trees, Mexican Frankenia species, and native vegetation. Subobjective 2B. Release and evaluate Diorhabda tamarisk beetles for biological control of Tamarix canariensis/T. gallica at coastal sites. Subobjective 2C. Discover and evaluate new agents from the western Mediterranean for biological control of saltcedar. Objective 3: Begin initial foreign exploration and feasibility studies for biological control of guineagrass and elephant ear. Subobjective 3A. Begin initial foreign exploration and feasibility studies for biological control of guineagrass, and determine the distribution and impact of this plant in the LRGB and other watersheds. Subobjective 3B. Begin initial foreign exploration and feasibility studies for biological control of elephant ear, and determine the distribution of this plant in the LRGB and other southwestern watersheds.
1b. Approach (from AD-416):
Giant reed, saltcedar, guineagrass, and elephant ear are invasive, non-native weeds that compete for scarce water resources in arid regions facing critical water shortages for agricultural, municipal, and environmental uses and, in addition, cause many other ecological and economic problems in the Lower Rio Grande Basin (LRGB) of Texas and northern Mexico. The LRGB is the largest watershed in North America, and biological control of these important riparian and terrestrial weeds has not been developed. This project will discover, evaluate, and implement multiple biological control agents to control giant reed along the Rio Grande and throughout the LRGB. Remote sensing and land-based field studies will be used to measure the impact of a biological control program on vegetation change and water use. The project will also evaluate the field efficacy of tamarisk leaf beetles to control saltcedar in south Texas rangelands and coastal grasslands, areas not previously subjected to biological control, as well as evaluate potential non-target effects on related native plants that are relevant to future biological control of saltcedar in Mexico. In addition, the feasibility for biological control of guineagrass, an invasive, fire-promoting weed in LRGB agriculture and rangelands, and of elephant ear, a large, leafy plant that invades the edges of rivers and reservoirs, will be determined by compiling information on the distribution, impact, and uses of these weeds along with preliminary information from the literature and initial explorations for potential biological control agents. This research will produce environmental and economic benefits by conserving water resources associated with giant reed and saltcedar infestations of the LRGB, and by defining new weed targets to achieve further water savings in the future.
3. Progress Report:
This project began October 2010 and terminated in January 2012 due to closure of the research unit. Substantial progress was made during the life of the project. Under Objective 1, the arundo scale, was released and is now established in two locations along the Rio Grande in Texas for biological control of arundo (also known as giant reed or carrizo cane). This was the first use of an armored scale insect for weed biological control. Research in the scale’s native range by collaborators at the USDA-ARS, European Biological Control Laboratory and Alicante University documented the scale’s 50% reduction of above and below ground growth of A. donax. From large collections shipped from Spain and France to U.S. quarantine facilities, over 5 million first instar scale ‘crawlers’ were isolated and released on the Rio Grande near Del Rio and Los Indios, TX and into mass rearing facilities in Weslaco, TX. The arundo scale feeds on root and stem tissues, complementing the stem galling arundo wasp, first released in 2009. More than 500,000 arundo wasps were mass-reared and aerially released in 2010-2011 on the Rio Grande. Field plots were established to examine long-term scale impacts on A. donax. In addition, plots were established to determine the effect of climate on three invasive genotypes of A. donax. Collaborative field work with ARS researchers from Kerrville and Edinburg, TX, revealed that along the Rio Grande, the cattle fever tick survives best in stands of arundo as compared to native riverine forests. This is the first demonstrated link between an invasive weed and an invasive veterinary pest. Also under Objective 1, the arundo leafminer was reared for three generations in quarantine and the conditions for colony production were clarified. The leaf miner is capable of killing leaves in large stands of A. donax and could compliment attack on stems and roots by the arundo wasp and scale. Under Objective 2, vegetation surveys at field sites in south Texas determined that diversity of plants subject to invasion by saltcedar is higher along creeks feeding the Rio Grande than in rangeland. In the Big Bend region of the Rio Grande, tamarisk beetles released by cooperators to control saltcedar removed all of the foliage from exotic athel trees, which, like saltcedar, are invasive but have some value as shade trees. Athel trees recovered their foliage within two months in the first year and experienced little or no attack in the second year. Under Objective 3, collaborators at EBCL in France determined that Texas guineagrass is actually a new species limited to Kenya and Ethiopia in east Africa. New collaborations were developed for exploration in eastern Africa for natural enemies of Texas guineagrass. A lab study showed that guineagrass seed viability is low but production prolific, demonstrating one mechanism of invasion. Field surveys revealed exotic, invasive elephant ear on nine Texas rivers covering over 350 river-miles. Elephant ear showed rapid colony development and high tolerance to artificial damage in experimental plantings.
1. Texas statewide distribution of elephant ear defined. Non-native, invasive elephant ear is widespread throughout the southeastern U.S., and is spreading along rivers and lakes in Texas, hindering access to water resources and displacing native plants and associated food webs. Online resources presented incomplete information on the distribution of elephant ear in Texas. ARS researchers conducted field surveys and compiled online information to reveal the distribution of elephant ear covering nine river systems and at least 350 river-miles in Texas, suggesting tolerance to a wide range of climatic conditions. Experiments with potted plants indicated rapid growth of plant colonies via runner formation and high tolerance of young plants to artificial damage. These results will guide decision making for integrated control of elephant ear in critical Texas watersheds.
Moran, P.J., Patt, J.M., Cabanillas, H.E., Adamczyk Jr, J.J., Jackson, M.A., Dunlap, C.A., Hunter, W.B., Avery, P.B. 2011. Localized autoinoculation and dissemination of Isaria fumosorosea for control of the Asian citrus psyllid in South Texas. Subtropical Plant Science. 63:23-35.