Weed characteristics and morphology

• Weeds are unwanted plants that compete with cultivated crops, disrupting land use and thriving in disturbed environments.
• Sustainable weed management integrates various methods to protect crop yields and the environment.

Characteristics of Weeds

• Rapid growth compared to cultivated crops.
• High reproductive output, producing numerous seeds.
• Seed dormancy allows seeds to remain dormant for extended periods.
• Adaptability to various environments and conditions.
• Allelopathy, where weeds exude chemicals that inhibit surrounding plant growth.

Gross Morphology: Grasses, Sedges, and Broadleaves

• Grasses belong to the family Poaceae.
• Grasses have round, hollow, jointed stems, long, narrow, parallel-veined leaves arising from nodes, fibrous root systems, and small, inconspicuous flowers grouped in spikelets.
• Examples of grasses: Leptochloa chinensis, Eleusine indica, and Echinocloa colona.
• Sedges belong to the family Cyperaceae.
• Sedges have triangular stems, leaves arranged in three ranks with parallel veins, dense fibrous root systems, and small, inconspicuous flowers grouped in spikelets or umbels.
• Examples of sedges: Cyperus rotundus, Cyperus iria, and Fimbristyllis miliaceae.
• Broadleaves have generally round or polygonal stems, broad leaves with reticulate venation, taproot or fibrous root systems, and typically larger, conspicuous flowers.
• Examples of broadleaves: Sphenoclea zeylanica, Amaranthus spinosus, and Portulaca oleraceae.

Life Cycle

• Annual weeds complete their life cycle within one year, such as crabgrass and barnyard grass.
• Biennial weeds take two years to complete their life cycle, like wild carrot and bull thistle.
• Perennial weeds live for multiple years and reproduce by seeds and vegetative means, such as cogon grass and Bermuda grass.

Habitats

• Weeds compete with crops in agricultural fields, with ornamental and vegetable plants in gardens, and thrive in disturbed soils along roadsides.
• Weeds grow in nutrient-poor and harsh waste areas.
• Weeds can invade and disrupt native plant communities in natural ecosystems.

Importance in Weed Competition

• Weeds compete with crops for resources like light, water, nutrients, and space.
• Weed competition leads to significant crop yield reduction.
• Weed control measures result in increased costs and reduced crop quality.

Biology and Behavior

• High seed production and vegetative propagation are reproductive strategies of weeds.
• Weed germination is adapted to various conditions.
• Weeds have rapid growth rates, often outcompeting crops.
• Weeds develop resistance to herbicides.

Dispersal Mechanisms

• Wind carries seeds, for example, cogon grass.
• Water disperses seeds or plant parts, such as barnyard grass.
• Animals spread seeds via attachment to fur or through ingestion and excretion.
• Human activity spreads weeds through contaminated equipment, seed stock, or soil movement.

Why Weeds Are Problems in Agriculture

• Weeds reduce crop yield by competing for essential resources.
• Weed management increases costs.
• Weeds harbor pests.
• Dense weed growth can impede harvesting equipment.

Beneficial Contributions of Weeds

• Weeds prevent soil erosion.
• Weeds provide habitats for wildlife and beneficial insects.
• Weeds can act as indicator species, reflecting soil conditions and environmental changes.
• Some weeds have medicinal properties like tawa-tawa and paragis.
• Weeds contribute organic matter to the soil when decomposed.

Reproductive Capacity of Selected Weeds

• Understanding seed production and germination rates helps design effective control strategies.
• Weeds like Amaranthus spinosus that produce a large number of seeds require more rigorous management to prevent seed spread.
• Knowing germination rates helps in timing herbicide or mechanical control interventions.
• Echinochloa crusgalli is a significant competitor in rice fields due to its high seed production and germination rates.
• Weeds with a high seed bank in the soil, such as Leptochloa chinensis, persist for years, requiring long-term management strategies.
• Species with high seed production and germination, like Rottboellia conchinchinensis, are more likely to become invasive.
• Understanding the reproductive capacity of species like Ipomoea triloba can guide decisions on managing invasive species to protect endangered plants.

Weed Management Impact

• Weed management is impacted through control strategies based on seed production and germination understanding.
• Agricultural impact is determined by competition affected by weed seed production and germination.
• Invasive potential is determined by seed production and germination.

Weed Control

• Habitat restoration in influenced by knowledge of the seed characteristics of invasive and native species.
• Conservation planning is influenced by knowledge of reproductive capacity of species.
• Ecological studies utilize reporductive traits to model population dynamics.
• Educating public about weed characteristics lead to proactive mangement.

Fundamental Guide to Creating Integrated Weed Management Plans

• Weed spectrum includes identifying weed species and understanding weed ecology.
• Cultural control involves crop rotation, cover crops, adjusted planting dates, and mulching.
• Mechanical control includes tillage, hand weeding, and mowing/cutting.
• Chemical control requires herbicide selection based on weed species, crop type, and growth stage.
• Herbicide use per crop: rice(butachlor, pretilachlor, cyhalofop, metamifop, pyribenzoxim), corn (glyphosate-tolerant corn varieties and atrazine), vegetables (selective herbicides), sugarcane (pre- and post-emergent herbicides), and banana (glyphosate).
• Herbicide resistance management involves rotating herbicides with different modes of action.
• Biological control involves introducing natural predators or using allelopathy.
• Monitoring and evaluation requires regular scouting, record keeping, and adjustments to the management plan.
• Integrated approaches combine cultural, mechanical, chemical, and biological methods.
• Education and training educate farmers on weed identification and IWM strategies.
• Environmental considerations involve minimizing herbicide use, buffer zones, and maintaining soil health.

Economic and Definition Considerations of CPWC

• Cost-effectiveness weighs control costs with benefits.
• Risk management considers herbicide resistance, crop damage, and environmental impact.
• The critical period of crop-weed competition (CPWC) is the time frame when weeds must be controlled to prevent yield loss.
• Yield protection and efficient resource use through weed management during CPWC.
• Cost reduction results from focusing on CPWC to reduce herbicide applications.

Herbicide Window of application

• Pre-emergent herbicides are applied before weed seeds germinate.
• Critical timing and adequate rainfall or irrigation are needed for pre-emergent herbicides.
• Post-emergent herbicides are applied after weeds emerge.
• Timing to apply when weeds are young and are actively growing.
• Weather influences efficacy of herbicides

Herbicide Mobility/Immobility

• Pre-emergent mobility applications include advantages of broader coverage but risks of leaching.
• Pre-emergent immobility applications include advantages of less leaching but requires precise application.
• Post-emergent mobility applications include advantages of systemic movement but influenced by weather.
• Post-emergent immobility applications include advantages of reduced risk to nearby crops but requires thorough coverage.

Rainfall, Sunlight, and Weather Effects

• Rainfastness is the time a herbicide needs to resist being washed off.
• Leaching is herbicide movement through the soil profile with water.
• Volatility is the tendency of a herbicide to vaporize and move.

Definition of Herbicide Resistance

• Herbicide resistance is the inherited ability of a weed population to survive herbicide application.
• Genetic variations within the weed population determine resistance.

Kinds of Herbicide Resistance

• Target-site resistance (TSR) involves genetic mutation preventing herbicide binding.
• Non-target-site resistance (NTSR) includes enhanced metabolism, reduced absorption, or sequestration.
• Cross-resistance is resistance to one herbicide conferring resistance to others.
• Multiple resistance is resistance to different modes of action.

Herbicide Overview

• Group 1 (A): ACCase inhibitors target lipid synthesis in grasses (e.g., Cyhalofop-butyl, fluazifop-butyl).
• Group 2 (B): ALS inhibitors block branched-chain amino acids (e.g., Pyribenzoxim, Bispyribac-sodium).
• Group 3 (K1): Microtubule assembly inhibitors interfere with cell division (e.g., Pendimethalin, Trifluralin).
• Group 5 (C1): Photosystem II inhibitors block electron transport (e.g., Atrazine, Diuron).
• Group 9 (G): EPSP synthase inhibitors block shikimic acid pathway (e.g., Glyphosate).
• Group 14 (E): PPO inhibitors disrupt cell membranes (e.g., Oxyfluorfen, Flumioxazim, Carfentrozone).
• Group 15 (K3): Inhibitors disrupt cell membrane formation (e.g., S-metolachlor, Dimethenamid).
• Group 22 (D): Photosystem electron diverters generate reactive oxygen species that damage cell membranes (e.g., Paraquat, Diquat).
• Group 27 (F2): HPPD inhibitors block carotenoid biosynthesis (e.g., Mesotrione, Tembotrione).

Common Herbicides

• Glyphosate targets EPSP Synthase
• Atrazine targets Photosystem II
• Pendimethalin targets Microtubule Assembly
• Clethodim targets ACCase
• 2,4-D is a Synthetic Auxin
• Metribuzin inhibits Photosystem II
• S-metolachlor inhibits VLCFA Synthesis
• Imazethapyr inhibits ALS Enzyme
• Paraquat is a Photosystem 1 Electron diverter
• Carfentrazone inhibits PPO enzyme
• Flumioxazim inhibits PPO enzyme
• Clomazone inhibits DOXP Synthase
• Mesotrione inhibits HPPD enzyme
• Bentazon inhibits Photosystem II
• Sulfentrazone inhibits PPO enzyme

Future of Weed Science and Technology

• Precision agriculture, new herbicide technologies, biological control, and advanced detection systems improve weed management.

Weed Photos

• Economically important lowland rice weeds: Leptochloa chinensis (Chinese sprangletop) and Echinochloa crusgalli (Barnyard grass).
• Additional economically important weeds: Echinochloa glabrescens (Barnyard grass), Echinochloa colona (Jungle rice), Ischaemum rugosum (Saramollagrass), and Ludwigia octovalvis (Mexican Primrose Willow).
• More economically important weeds: Ludwigia perennis (Indian Primrose), Sphenoclea zeylanica (Gooseweed), Monochoria vaginalis (Pickerel weed), and Pistia stratiotes (Water lettuce).
• Additional weeds: Cyperus iria (Rice flatsedge), Cyperus difformis (Small-flower umbrella sedge), and Fimbristylis miliaceae (Fimbry).
• Weeds in banana, corn, sugarcane, & vegetables: Cynodon dactylon (Bermuda grass), Eleusine indica (Goosegrass, wiregrass), and Rottboellia cochinchinensis (Itchgrass).
• More weeds: Echinochloa colona (Barnyard grass), Brachiaria distachya (Armgrass millet), and Ipomoea triloba (Three-lobe morning glory).
• Additional weeds: Ageratum conyzoides (Billy goat weed), Cleome rutidosperma (Spindle top), and Amaranthus spinosus (Spiny amaranth).
• Additional weeds: Portulaca oleracea (Common purslane), Cyperus rotundus (Purple nutsedge), and Trianthema portulacastrum (Horse purslane).
• Additional weeds: Cyperus kyllingia (Spike sedge), Galinsoga quadriradiata (hairy galinsoga), and Ageratum conyzoides (billy goat weed).
• Other weeds: Spilanthes acmella (toothache plant), Crassocephalum crepidioides (thickhead/fireweed), and Commelina benghalensis (dayflower).
• Final weeds: Portulaca oleracea (common purslane), Oxalis corymbosa (pink shamrock/sleeper weed), and Bidens pilosa (blackjack/beggarticks).