exam 2 - BTNY 304 Lecture Exam 2 Key ...

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Unformatted text preview: BTNY 304 Lecture Exam 2 Key February 23, 2011 ________________________________ Print Name The first rule of intelligent tinkering (with nature) is to save all the parts. - Aldo Leopold 1. A Weed is a plant that interferes with the growth of desirable plants. It negatively impacts human activity and as such is undesirable. There are usually three characteristics needed to make a plant a weed. To be considered a weed, a plant must be: A. __ competitive _______________ B. __ persistent __________________ C. __ pernicious ____________________ 2. The accumulated deposit of seeds on or in the soil is called the Seed Bank. Its survival is affected by two main seed ­related factors: A. Dormancy, a temporary condition in which live seed fail to germinate even when appropriate levels of moisture, air, temperature, and light are available B. Afterripening, the loss of dormancy, which occurs over time in response to favorable environmental conditions by a process called stratification. 3. There are two types of seed dormancy A. Primary dormancy, which the seeds undergo while still attached to parent plant B. Secondary dormancy, which occurs after seeds are dispersed in the seed bank, and is induced over time by unfavorable environmental conditions (over) 1 4. There are three main mechanisms of seed dormancy: A. Hard seed coats that requires mechanical or microbial attack on the seed coat before the seed will germinate B. Chemical inhibitors that must be leached out of the seed coat before germination will occur 5. The Critical Period for Weed Control can be defined as the early weeks of crop growth (plant establishment) when weeds need to be controlled to prevent yield reductions. Describe two ways of defining (looking at) the critical period of weed control that is used in developing a weed control strategy: C. Exposure of buried seeds to Red light, a phytochrome regulated process 1. The time span when weeds present from the beginning of the crop cycle must be removed in order to prevent negative impacts on the crop plants 2. The time span from the beginning of the crop cycle in which a crop plants must be kept weed ­free, after which occurring weed growth no longer affect crop yields. 2 6. Weed Interference describes the total impact of one plant on another plant or the ability of weeds to adversely affect crop growth. There are three main components involved in weed interference name each and describe their differences: 1. Competition – mutual struggle for growth factors 2. Allelopathy – inhibition through biological toxins 3. Parasitism – plants form protoplasmic connections with their host plant (over) 3 7. Effects of weed competition can be measured by determining the weed’s threshold level. In a weed control program we are concerned with two types of threshold levels. Give the definition of the two terms below. Crop Response Threshold: the level of weed infestation (in terms of weed biomass, weed number, or period of weed infestation) at which a measurable effect on the crop begins Economic Threshold: the level of weed infestation at which the increase in crop production from weed control will pay the cost of the control The economic threshold is always higher than the crop response threshold. 8. When studying weeds Weed biology is concerned with the taxonomy, genetics, establishment, growth and reproduction of a weed species, while Weed ecology is concerned with the development of a single species within a population of plants and the development of all plant population within a community on a given site. Collectively, the environment and the living community are considered an ecosystem. 4 9. Define an invasive plant and list 2 ways it will differ from and agronomic weed. INVASIVE PLANT: a non ­indigenous species or strain that becomes established in natural plant communities and wild areas, replacing native vegetation Agricultural Weeds: • • • • Disturbance dependent Easily distinguishable from crop Usually controlled by tillage and/or broadcast herbicides Rarely are beneficial or intentionally planted Invasive Plants: • • • Often invading relatively undisturbed habitats Often overlooked or not easily identified in diverse natural areas Control options much more limited due to presence of native species and need to minimize disturbance May be intentionally planted and have beneficial uses Very little funding for controls or research • • 10. Species that are able to grow under a broad range of light, moisture or other environmental conditions are more likely to be successful invaders into new habitats (True, False). These types of species are referred to as exhibiting plasticity 5 ...
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