PRIN OF WEED SCIENC
PRIN OF WEED SCIENC AGRON 317
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This 3 page Class Notes was uploaded by Daryl Gulgowski on Saturday September 26, 2015. The Class Notes belongs to AGRON 317 at Iowa State University taught by Robert Hartzler in Fall. Since its upload, it has received 58 views. For similar materials see /class/214420/agron-317-iowa-state-university in Agricultural & Resource Econ at Iowa State University.
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Date Created: 09/26/15
Principles of Weed Science Agronomy 317 Biological Control Biological control is de ned as the reduction of pest populations by a biological organism While the growth and reproduction of weeds almost always is affected in some way by other organisms present in the environment the term biological control usually is reserved for when humans take an active role in manipulating the population of the biocontrol agents There are three distinct approaches to this approach Inoculation A Assumptions 1 Many weed species are exotic plants that have been introduced into a new geographical region These plants often are not weedy in their native region 2 Natural enemies may regulate population in native region preventing the species from acting as a weed 3 Introducing these natural enemies to the new region of infestation will control the exotic species B Objective Permanently establish natural enemies in area of weed infestation so that the biocontrol agent will suppress the weed Unlike other control tactics this strategy can provide longterm control and spread outside of the initial area of control release and theoretically can control the pest throughout an entire region C Steps in inoculation approach 1 Identify natural enemies in the native range of the exotic weed For weed control insects have been the primary bio control agent although pathogens have been used occasionally 2 Determine host speci city must make sure that the natural enemy will not move to other plants in the region where it is introduced 3 Evaluate risks of releasing organism in new environment 4 Obtain permits USDAAPHIS Animal and Plant Health Inspection Service is responsible for regulating introduction of any biological control agents 5 Release organism 6 Monitor establishment and impact on weed community and other plants D Limitations 1 Highly specific typically only control one species must not attack native species This limits the usefulness of this tactic for agricultural crops since all fields are infested with several weed species Eliminating one species in most cases will not signi cantly reduce the amount of effort required to control the other weeds 2 Slow acting the biological control agent often takes several years to increase to populations high enough to suppress the weed population In managed ecosystems farms pastures etc people often do not have the patience or economic resources to wait for results 3 Biocontrol agent may not tolerate production practices in highly managed settings eg agricultural or horticultural crops 4 Because of these reasons the inoculation strategy has typically been used to manage weeds that invade rangeland forests aquatic settings etc These areas are less disturbed than agricultural habitats thus they typically have a less diverse weed community where there would be a real bene t to controlling a dominant weed species E Conflicts of interest 1 Weeds may provide services in environment especially ifthey have been a part of the ecosystem for a long time The objective of inoculation is to permanently establish the biocontrol agent and have it spread throughout the range where the weed is present The release of a biocontrol agent beetle to control salt cedar tamarisk in the western US has been held up since the salt cedar is used as nesting habitat for a bird that is on the endangered species list The salt cedar has displaced the native trees that once served this function People are concerned that control of the salt cedar will drive the endangered bird to extinction Biocontrol agent may attack native plants The musk thistle weevil controls musk thistle by feeding on seeds within developing seedheads It has been released across the US and is widely established across lowa Wisconsin banned the release of the weevil because it attacks other biennial thistle species several which are native and at least one dune thistle that is listed as an endangered species N lnundation A Objective Apply biocontrol agent at a high dose so that weed is rapidly killed B Normally a plant pathogen bacteria or fungi C Pathogen doesn t become permanently established in area this isthe primary difference from inoculation along with the rapid control provide with inundation D Mycoherbicides biological agent that is applied like a herbicide A few products have been successful typically involving a weed for which no conventional herbicides are available 1 Collego marketed for northern jointvetch control in rice and soybeans 2 Devine stranglervine in citrus orchards 3 Psuedomonas syn39ngae for Canada thistle this is the organism that is responsible for the whiteyellow CT shoots commonly seen along lA roadsides Attempts to develop more virulent strains that will actually kill thistles have not been successful E Limitations 1 Highly speci c typically only control a single weed species 2 Handling of product since the product is a living organism it must be handled carefully prior to application It can t be placed in the storage shed with the other pesticides May not be compatible with other pesticides for application can t be tankmixed with other products 3 Variable performance depending on environment in order forthe mycoherbicide to be effective there must be a favorable environment for infection following application Considerable research has been conducted to evaluate different formulations and spray additives to enhance the effectiveness of these products IV Conservation A Objective Manipulate environment to enhance native or introduced biocontrol w 0 agents Assumes that natural enemies are already present in the area of the weed infestation but environmental conditions suppress their populations therefore limiting their effectiveness It is well documented that weed populations are influenced by numerous organisms in the environment but as yet there are few if any examples of where the effectiveness of these organisms has been enhanced sufficiently to influence the need for other control tactics Weed suppressive soils 1 Soil microorganisms selectively in uence plant growth 2 Identify organisms that favor crop growth over weeds 3 Fields have been identi ed where the soil suppresses growth of specific weeds In Washington a bacteria has been identified in several field that suppresses growth of downy brome by 50 compared to soils where the bacteria is not present Seed predation Weed seeds have high energy reserves and thus are a valuable food source for insects ants field crickets etc and rodents field mice etc A significant percentage of weed seed is consumed by insects rodentsetc Studies at ISU have shown that 5 to 20 of weed seed laying on the soil surface is consumed per day Tactics that have been proposed to enhance predation a Delay or eliminate fall tillage Weed seeds are most prone to predation when lying on the soil surface Tillage buriesthem within the soil pro le and protects them from predation b Maintain vegetative cover around field borders and within elds grass waterways etc Rodents seek coverto hide from predators and it has been proposed that increasing permanent vegetation around fields would increase weed seed predation However ISU studies have found that seed predation in the center of large fields is as high as that along the borders near grassways so this may not be too important N 00
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