What is a Weed? Any plant can be a weed under the right circumstances It all depends on what type of production you are trying to accomplish

Why care? Food costs Aquatic nuisance Allergies Hosts for diseases and insects Increased soil erosion Dandelionالهندباء

Why are they so difficult to control?! Can sprout in many environments Long – lived seed Variable seed dormancy Rapid growth High seed production Burdockنبات الارقطيون http://www.vet.purdue.edu/depts/addl/toxic/plant02.htm

So difficult. Allelopathy Deep root system Milkweedالصقلاب

Classification Grasses Sedges نبات السعد Annual سنوي Perennialمعمرة

Methods of Control Prevention Chemical Biological Mechanical Controlled burning Grazing Crop rotation

Prevention Weed seed may be distributed in a number of ways Crop seed, wind, water, animals, machinery and other ways

Chemical Use of chemicals to control or retard growth of weeds Bull Thistle الثور الشوك Use of chemicals to control or retard growth of weeds http://www.noble.org/imagegallery/Forbhtml/BullThistle.html

Time of Application Preplant: made before crop is planted and is incorporated into the soil Preemergence: Made directly to soil and requries rainfall in order to move into the soil Postemergence: Applied after weed or crop emergence

Types of Herbicide Contact herbicide: sprayed on foliage and only affects area it comes into contact with Systemic herbicide: sprayed on soil

Factors Affecting Herbicide Effectiveness Annual or perennial Tolerance Type of soil Temperature wax on leaves Shape/orientation of leaf

Biological Control Using beneficial creatures such as insects, bacteria and fungi that damage the weeds Not very common

Mechanical Burial دفن Tillage Mowing

Controlled Burning Not very common

Grazing Use of animals such as sheep or goats that will eat weeds and weed seeds.

Crop rotation Rotating your crops from year to year and season to season to take away competitive advantage from weeds of the previous years crop.

Are weeds all bad? Shelter for beneficial insects Lambsquarters Shelter for beneficial insects Beneficial properties for humans Provide food for wildlife http://www.noble.org/imagegallery/Forbhtml/Lambsquarters.html

The word allelopathy derives from two separate words. What is Allelopathy?   The word allelopathy derives from two separate words. They are allelon which means "of each other", and pathos which means "to suffer". Allelopathy refers to the chemical inhibition of one species by another. The "inhibitory" chemical is released into the environment where it affects the development and growth of neighboring plants.

Allelopathic chemicals can be present in any part of the plant. They can be found in leaves, flowers, roots, fruits, or stems. They can also be found in the surrounding soil.

Allelopathy has been defined as the direct or indirect harmful or beneficial effects of one plant on another through the production of chemical compounds that escape into the environment Numerous allelochemicals have been idendified as Phenolic acids, Coumarins, Terpenoids, Flavonoids, Alkaloids, Glycosides, Isothiocyanate,

Target species are affected by these toxins in many different ways Target species are affected by these toxins in many different ways. The toxic chemicals may inhibit shoot/root growth, they may inhibit nutrient uptake, or they may attack a naturally occurring symbiotic relationship thereby destroying the plant's usable source of a nutrient.

Chemical Warfare in the Plant Kingdom   Black Walnutالجوز الاسود - The chemical responsible for the toxicity in Black Walnut is Juglone and is a respiration inhibitor. Tree-Of-Heavenشجرة الجنة - Ailanthone, an allelotoxin. Sorghum الذرة - Sorgolene is found in the root and disrupts mitochondrial functions and inhibits photosynthesis.