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lecture 01

lecture 01 - Introductory Weed Science BTNY 304 What...

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Unformatted text preview: 1/11/11 Introductory Weed Science BTNY 304 What is a Weed? Some photographs were taken off various websites and are intended for instruc8onal purposes only Witchweed (Striga asia)ca) What is a Weed? •  Plant growing where it is not wanted •  Plant out of place •  Plant whose virtues have yet to be discovered Wild Carrot Daucus pusillus Michx. Maypop passionflower (Passiflora incarnata L.) 1 1/11/11 Bull Thistle (Cirsium vulgare) Trumpet Creeper (Campsis radicans) Bu1erfly Milkweed (Asclepias Tuberosa) Common Milkweed (Asclepias syriaca) BiDersweet Nightshade Solanum dulcamara L Cup Plant Silphium perfoliatum L. 2 1/11/11 A beRer definiIon: A weed is a weed because it possesses certain definable characterisIcs that set it apart from other plants:  ­ Abundant seed producIon  ­ Rapid populaIon establishment  ­ Seed dormancy  ­ Long survival period of buried seeds  ­ Presence of vegetaIve reproducIon structures  ­ Capacity to occupy sites disturbed by human acIviIes A Weed is a plant that interferes with the growth of desirable plants (compe88ve) and is unusually persistent and pernicious. It nega8vely impacts human ac8vity and as such is undesirable.  ­ Pernicious – highly injurious or destruc8ve – syn. Noxious, detrimental, exceedingly harmful Cost of Weeds to Humans Of the approx. 250,000 plant species, only a few thousand behave as weeds. Approx. 200 species (0.8 % of the total) are recognized as major problems in world agriculture. These 200 species account for 90 % of the loss in world food crop producIon. Only about 25 species (0.01 % of the total) cause major weed problems in any one crop. Regardless of the crop, only a handful of weeds cause conInuing problems. 1998 – total loss US crops due to weeds  ­ $32 billion/yr.  ­ $6.6 Billion from cost of herbicides This represents 12% loss of potenIal crop yield based on herbicides being used on 85% of the total cropland Losses – Crop quality –  Odor – wild garlic in wheat and milk –  Staining of edible seeds – nightshade berries –  Prohibited noxious seed in cer8fied crop seed Weeds Should Be Controlled Because: 1. Weeds compete with crops for: a) space  ­ only so much plant maRer can grow on a given area of land b) ferIlity (nutrients) c) light d) moisture Limits choices of crop rotaIon and cultural pracIces Harbors other pest – pathogens, nematodes, insects Interferes with crop harvest Increases cost of cleaning crops at and aPer harvest Overall increase in crop producIon and transportaIon –  Hort crops planted into fields infested with perennial weeds –  The inability to establish no ­8ll 3 1/11/11 Weeds Should Be Controlled Because: Weeds Produce Seeds Weed seeds are usually small in comparison to crop seeds. A single weed plant commonly produces from hundreds to hundreds of thousands of seed per year. These seeds infest cropland soils in the amount of millions per acre. The number of seeds produced per plant is apparently related to the total weight of the seeds produced: the smaller the seed, the more seed produced per plant. 2. Weeds reduce yield and quality of crops. 3. Weeds produce seeds. 4. Weeds are alternate host for diseases & insects. Weeds Produce Seeds Weed seeds can be found throughout a deep profile of the soil but the majority of the seeds are found within the top 6 inches. In undisturbed soil, seeds are mainly found in greatest quanIty in the top 2 inches of soil. The length of Ime that a seed is viable varies widely with plant species and environmental condiIons. However, many weed seeds can remain viable for 40 years or longer when buried 2 inches or deeper in the soil where the oxygen supply is reduced. 4 1/11/11 5 ...
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