PRIN OF WEED SCIENC
PRIN OF WEED SCIENC AGRON 317
Popular in Course
Popular in Agricultural & Resource Econ
This 2 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 Staff in Fall. Since its upload, it has received 21 views. For similar materials see /class/214424/agron-317-iowa-state-university in Agricultural & Resource Econ at Iowa State University.
Reviews for PRIN OF WEED SCIENC
Report this Material
What is Karma?
Karma is the currency of StudySoup.
Date Created: 09/26/15
Principles of Weed Science Agronomy 317 Vegetative Reproduction De nition A Production of new individuals without formation of seeds or spores B No recombination of genes resulting in clones C Vegetative reproduction most common in perennials but some annual weeds can form new plants through fragmentation common purslane Types of reproductive structures A Stem structure possessing nodes and internodes 1 Rhizome underground horizontal stem quackgrass swamp smartweed 2 Stolon aboveground horizontal stem bermudagrass 3 Tuber swollen stem tissue yellow nutsedge 4 Bulb stem with shortened internodes and fleshy modi ed leaves wild garlic B Vegetative rootstocks common milkweed Canada thistle 1 2 Lack nodes and internodes Adventitious buds form to produce new plants Advantages A Tolerance to control tactics 1 l Most vegetative reproductive structures have considerable more energy reserves than seed thus newly emerged perennials can survive more stress than annual weeds If the shoot ofa perennial is removed by mowing grazing or herbicide the plant can regenerate via the stored energy reserves in the vegetative reproductive organs whereas most annuals would simply die Perennials often are able to emerge from greater depths in the soil profile due to the high level of energy reserves This allows them to survive control tactics such as tillage that typically only disturb the upper area top 46 ofthe soil profile B Enhanced competitiveness 1 The large energy reserves available to each bud allows the plant to grow very rapidly immediately following emergence whereas seedlings developing from small seeds generally have low relative growth rates when transitioning from stored reserves in the seed to energy produced via photosynthesis The rapid growth of perennials allows them to get a head start on the crop plant and provides them a competitive edge for the growing season Many perennial weeds can form new reproductive structures ie rhizomes etc within a few weeks of emergence whereas an annual typically requires a full growing season to produce new seed O E Perpetuate successful genotypes since a plant that forms from a bud on a rhizome stolon or a vegetative rootstock is a clone of the parent plant genotypes that are best adapted to the current habitat will be maintained and reproduce more rapidly than less adapted geneotypes Disadvantages A Most perennial weed species produce far fewer reproductive units seeds buds nodes w 0 lt w 0 U than annual weeds Example 1 Quackgrass perennial grass 200 buds 2 Giant foxtail annual grass 4000 seed Perennial weeds typically spread less rapidly than annual weeds since the perennial reproductive structures are less adapted to longdistance dispersal than seeds Because ofthis perennial weeds are often found in distinct patches within fields However if left unmanaged a perennial can eventually cover an entire field Most perennial weeds reproduce within a field primarily via vegetative reproductive structures thus there typically is much less genetic variation within the population than is found with annual weeds This makes them much less adaptive to change than annuals However most perennials do produce seed thus there is a source of recombination of genes to create different biotypes Management of perennials A Perennial weeds are often the most difficult weed species to manage due to the large energy reserves stored within the soil profile In order to bring the plant under control the energy reserves must be depleted Prior to systemic herbicides it wasn t unusual to take land heavily infested with troublesome perennials Canada thistle eld bindweed Johnsongrass out of production for 23 years and repeatedly till the eld every 34 weeks whenever new shoots developed in an attempt to drain the energy reserves of the vegetative reproductive structure Systemic herbicides offer an opportunity to control perennials since the chemical can be translocated from shoot to the perennial root system However for effective control herbicide must be applied at a time when shoots are transporting energy reserves into the root This often doesn t coincide with typical herbicide application timings in cropping systems thus reducing the effectiveness of the herbicide In addition there is limited translocation to dormant buds which in an established perennial patch there are lots of thus complete control usually is not achieved with a single application even at optimum timings Smother crops typically plants with rapid growth rates and dense canopy characteristics have been used to suppress perennial and reduce energy reserves They provide an alternative to the repeated tillage described above and are usually beneficial to soil quality rather than detrimental as is tillage Most commonly used in organic systems