2/10/2016. Grassy Weeds Crabgrass, Bermuda grass

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1 Most have large, efficient root systems Grow rapidly Produce tremendous amounts of seed Can tolerate drought or low fertility Little energy is used in producing lush foliage, large seed, or fruit Katie Kammler Horticulture Specialist University of Missouri Extension First identify the weed and consider why it might be thriving Do not overwinter, but must grow from seed each year Summer annuals Germinate in the spring, make seed, and die in the fall Example crabgrass, foxtail, pigweed Winter annuals Germinate in fall or early winter. Make seed in early spring and die before summer Example Henbit, Chickweed Biennial Weeds: two year life cycle Thistle Perennial Weeds: come back year after year Dandelion Tall fescue Bermuda grass Grassy Weeds Crabgrass, Bermuda grass Broadleaf Weeds Dandelion, plantain, pigweed, lambsquarter First identify the weed and consider why it might be thriving Compaction- weeds with tap roots Cultivation- weeds with rhizominous roots Low soil nutrients and organic matter Fallow ground 1

2 Avoidance Tillage Hand pulling Hoeing Mulch Inorganic plastic, etc. Organic Mowing/weed eating Digging Hot water Burning Green mulch (cover crop) Rye, clover, etc Proper depth important Get the root but try not to bring more weed seed to the surface Timing of weed development Get when weeds are small Let weeds germinate before plant main crop Time of day Low humidity, high temperature Keep your weeding tools sharp Don t till deeper than you need to plant Suppresses weed emergence and growth Reduces disease Reduces erosion Warms/cools the soil Moisture Organic Sawdust, leaves, peat moss, wood chips, hay or straw, compost, pine needles, grass clippings Can be incorporated into the soil at the end of the season Some concern about nitrogen depletion in the composting process Living mulches Choosing the right materials for you situation What is available? Grass clippings Leaves Straw Cost Wood chips/bark Appearance Newspaper vs. bark Ease of application 2

3 Inorganic Mulches Black plastic, landscape fabric, white plastic High temperatures can harm plants when mulched with black plastic Black plastic with one side whitelandscape fabric allows water to pass through Advantages Soil warms quickly Weed suppression Moisture retention Possible yield increase Disadvantages Cost Limits irrigation options Difficult to apply soil amendments Provide no food to soil biology Most are not biodegradable Don t apply mulch directly in contact with plants Monitor for disease and overwatering Remove weeds before applying mulch Thickness of mulch important Depends on the material Make sure that seed is not contaminated with weed seed. Prevent weeds from going to seed in the garden Avoid buying topsoil with weed seeds Make sure that manures have been composted completely Do a fall clean up of weedy material from the garden Crop rotation Crop competitiveness Type and timing of tillage & cultivation Water and nutrient management Mulches 3

4 1. Vary the seasonality of planting -- Tillage for spring crops kills off winter annuals like annual bluegrass and shepherd s purse Tillage for summer crops kills off spring germinating weeds like ragweed. Fall crops allow time for a midsummer fallow to fight purslane. 2. Varying crops allows you to vary management practices Can tine weed corn, peas, snap beans Can cultivate root crops very close to the row Hill up potato and corn to kill in-row weeds Flame weed corn & alliums Straw mulch garlic Short season crops like lettuce do not allow seed production act like a fallow period Use short season crops like lettuce and spinach Or easily weeded and competitive crops like potato To clean up after crops like winter squash where weeds often go to seed Many weed species are highly responsive to soil fertility Weeds often have 1.5 to 3 X higher N, P, K, & Ca concentrations than the crops they are growing with Excess fertility increases weed growth rates Standard Management Reduce weed populations below level at which they cause noticeable yield loss Weed populations vary greatly between years Yield loss is hyperbolic no threshold Wild oat in wheat Preventive Management Don t let weeds reproduce Requires constant vigilance Extra management in early years Fallows, hand rogueing 4

5 Herbicides are classified in 3 ways Mode of Action Range of Activity Targeted State of Weed Growth Mode of Action Contact herbicides Kills on contact Not absorbed and translocated Very rapid plant death Temperature dependent activity Little or no soil activity Control annuals but poor control of perennials Usually non-selective Example: Gramoxone (paraquat) RU Mode of Action Systemic Herbicide Absorbed by external tissues and translocated to sites of activity Temperature dependent Variable soil activity Effective on both annuals and perennials Both selective and non-selective forms Example: Roundup (glyphosate) Range of Activity Selective Targets specific range of species Example: Manage (halosulfuron) for nutsedge and 2,4-D for broadleaves Non-selective Targets wide range of species Example: Roundup (glyphosate) Stage of Growth Preemergence Herbicide Inhibits seed germination Usually selective Variable length of activity Most commonly used to control annual weeds Example: Preen Stage of Growth Postemergence Herbicide Kills plants once they have commenced vegetative growth Both selective and non-selective types Example: Roundup #1 rule of herbicides: Plants must be actively growing for herbicides to work. 5

6 Herbicides must disrupt one or more vital plant processes in order to kill the plant *Transpiration & Respiration* *Nucleic Acid Synthesis* *Protein Synthesis* *Lipid Synthesis* *Pigment Synthesis* *Uptake & Translocation of Ions & Molecules* *Energy Transfer* *Photosynthesis* *Cell Division (mitosis & meiosis)* *Amino Acid Synthesis* *Growth* Are any substance in or added to a herbicide that improves herbicide activity, performance, or application characteristics Special Purpose & Activator Compatibility, buffering, antifoam, and drift control agents Can increase absorption and rainfastness Decrease photodegradation Includes surfactants, emulsifiers, diesel fuel, and kerosene Emulsifiers help diesel mix with water Can save costs (time, labor, equipment) Increase control Herbicide tank mixes are the most common ILLEGAL to mix pesticides if such mixtures are EXPRESSLY PROHIBITED ON THE LABEL If no guidance is giving, it is your responsibility to make sure the pesticides will retain their properties Examples: phytotoxicity, reduced activity, excessive foaming, formation of sludge in tank Can have reduced activity of herbicides when hard water is used as the carrier (tends to be more of a problem with insecticides) Binding of herbicide to calcium ions in the hard water which inactivates the herbicide Check the label for water ph recommendations Questions? Identify the critical weed problems Consider why they might be thriving Learn more about the weed Devise a management plan 6