Transcript A weed is a
Agronomy Weed Plants and Seeds What is a Weed? Plant that is out of place Plant not intentionally grown Plant that decreases aesthetic value Why are Weeds Troublesome? Reduce Crop Yield Steal light, water, nutrients, space, and time Can produce toxic substances (Allelopathic) Why are Weeds Troublesome cont’d? Hosts for plant diseases Shelter for insects and diseases Reduce crop quality/taste Multiply rapidly Why are Weeds Troublesome cont’d? Clog equipment Decrease future stands and longevity Add to frustration and safety concerns Groups of Weeds Annuals 1 year – Summer (germinates in May and June) – Winter (germinate in late summer or fall) Biennials Perennials 1-2 years > 2 years Groups of Weeds cont’d. Grassy Weeds –Simple leaves, monocots Broadleaf Weeds –Complex leaves, dicots Groups of Weeds cont’d. Early Late Season Season Monocots VS. Dicots Simple leaves One seed cotyledon Complex leaves Two seed cotyledons How To Manage Weeds Field Scouting Proper Identification and Recording of Weeds Economic Threshold Economic Threshold The amount of weeds in a given area that is needed to justify taking action to reduce their impact Weed Control Good Weed control requires an integrated approach system Cultural Controls Forces the plant being grown to be more competitive against the weed Cultural Control cont’d. Seed Preparation Planting date Fertilization Crop Rotation Row Spacing Seeding Rate Seed Variety Mechanical Control Physical action completed to reduce the rate of weed growth and spreading Mechanical Control cont’d. Plowing Disking Field Cultivating Chemical Control The use of chemical pesticides (Herbicides) to control weeds Chemical Control Issues? Safety and Handling Cost of Chemical and Equipment Crop and Chemical Rotation Environmental Hazards Carryover and Residual Effect Herbicide Resistance Reduced and Conservation Tillage Chemical Herbicides Pre-Emergent –Applied before the crop or weed plant emerges through the soil –Must be timed perfectly Chemical Herbicides Post-Emergent –Applied after the crop or weed plant emerges through the soil –Timing not as critical Noxious Weeds A noxious weed is a plant defined by law as being troublesome, undesirable, and difficult to control List of Noxious Weeds in PA There are currently 13 noxious weed species on PA’s list Herbicide Characteristics Contact Herbicides –A chemical that kills on contact of any plant tissue Herbicide Characteristics Systemic Herbicides –A chemical that is absorbed or translocated in a plant Selective VS. Nonselective Selective Herbicides –Selective herbicides kill weeds without significant damage to desirable plants Selective VS. Nonselective Nonselective Herbicides –Nonselective herbicides kill ALL plants present when applied Herbicide Resistance Herbicide resistant plants are uninjured or unaffected by certain chemical applications Herbicide Resistance Resistant plants are becoming more common Begins with a few tolerant plants that survive These plants then reproduce and spread Herbicide Resistance Prevention Minimize tillage of the soil Rotate crops Use various chemicals The perfect herbicide does not exist!!! Carryover Chemical carryover or residue may affect future crops in the rotation Occurs due to excessive applications Managing Organic Weeds Organic Farming is the growth of crops without the use of chemicals and synthetic fertilizers How can an organic farm manage weeds without pesticides and synthetic fertilizers? Waging war with weeds Weeds compete with crops for moisture and plant nutrients. Gardeners pull or hoe weeds. Farmers use tillage and cultivation. Conventional farmers use chemical treatments. ARS photo by Scott Bauer. Farmers are in a fight with nature … Nature wants a diversity of plant growth. Farmers want to limit nature to grow just one crop. Conventional tillage and fertilization increases crop production and also encourages weeds. The battle heats up! The organic approach is different … The organic farmer tries to work with nature. An organic grower tries to "manage" the crop ecosystem to help the crop thrive while suppressing weeds. This requires observing and understanding nature. A weed is a “plant out of place.” Annual weeds Grow one season Reproduce from many seeds Thrive under same conditions as annual crops. Perennial weeds: Grow for several seasons Reproduce from roots, stolons, bulbs, tubers, rhizomes or fewer seeds Do best in areas with less cultivation Defining succession: Natural diversity will result in either forest or prairie. First step: annual weeds Second step: perennials Third step: brush and young trees in forest regions or perennial grasses in prairie regions During succession plants compete for moisture, nutrients and light. Organic farmers grow crops and create conditions in which weeds cannot compete. Using cover crops … Cover crops hold down weed growth and add organic matter to the soil. Allelopathic cover crops produce a chemical in the soil that inhibits the growth of other plants. Rye is allelopathic, winter hardy, and grows almost anywhere. Rye crop residues leach allelopathic chemicals into the soil and prevent the germination of smallseeded weeds. ARS photo by Scott Bauer Shows rye cover crop. More on allelopathic effects: Some large-seeded food crops can tolerate the allelopathic effects (corn, cucumbers, peas, snapbeans). Smaller-seeded crops had less tolerance (cabbage and lettuce). More crops with allelopathic effects: sunflowers, sorghum and rapeseed. Mulches and cover crops: Cover crops can be used to physically smother weeds by growing faster and out-competing the weeds. Mulches can be black plastic, or plant material such as wheat straw. ARS photo by Scott Bauer shows wheat straw mulch. More weapons: crop rotation and intercropping Crop rotation changes the growing conditions each year, breaking the weed cycle. A good rotation for weed control will include clean-cultivated annual crops, tightly spaced grain crops, and mowed or grazed perennial sod crops. Add a short-season crop to smother weeds, if needed. Intercropping is another alternative … Growing two or more crops together to give weeds more competition Often established by planting a row crop into a standing grain crop Example: interplant soybeans into standing green wheat Ideal organic farming minimizes tillage … Tillage leaves soil exposed, allowing annual weeds to sprout and grow. Can lead to soil erosion Speeds decomposition and increases runoff Can damage soil structure Adds equipment, fuel and labor costs. Ways tillage can be used: Preplant tillage clears away annual weeds and reduces perennial weeds. Blind cultivation works the soil to kill weeds with minimum damage to seedling crops. Between-row cultivation cleans out more weeds emerging as crop begins to grow. More weapons in the war on weeds: Flame weeding works on broadleaf weeds. Hand weeding and topping require hand labor. Weeder geese are good for grassy weeds.