Principles in Weed Management

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Principles in Weed Management : 

Principles in Weed Management Sandra Menasha Vegetable/Potato Specialist Cornell Cooperative Extension

What is a Weed? : 

What is a Weed? A plant growing where it is not wanted “Weeds are plants that are especially successful at colonizing disturbed, but potentially productive sites, and at maintaining their abundance under conditions of repeated disturbance” (Liebman, Mohler and Staver 2001)

Types of Weeds : 

Types of Weeds Annuals Vegetative lifespan <1 year High energy allocated to seed production Establish by seed Lambsquarters, pigweed, galinsoga

Types of Weeds : 

Types of Weeds Stationary Perennials Vegetative lifespan 2 to a few years Medium high energy to seed production Establish by seed Dandelion, curly dock

Types of Weeds : 

Types of Weeds Wandering perennials Vegetative lifespan long to indefinite Low energy to seed production Establish through vegetative reproduction via horizontal roots or underground shoots (rhizomes) which daughter plants emerge Hedge bindweed, quackgrass

Managing Weeds : 

Managing Weeds “Many little hammers” Understand biology and behavior Cultural and mechanical means Chemical controls

Weed Biology and Behavior : 

Weed Biology and Behavior They have adapted to highly disturbed conditions Their biological characteristics are revealed by these adaptations And these characteristics reveal how to manage them For example, many weeds recognize cues like light which allows them to appear after many years of absence

Seed Weights : 

Seed Weights Indication of resources available during establishment Small seeds = small seedlings that are easy to kill with cultivation Correlates to the depth at which germination occurs Small weed seed - commonly germinate with signals associated with near surface conditions, recent soil disturbance, and bare soil Most crops have larger seeds than weeds Corn, soybean, and pea have seed weights 50 to 1000x more than many common agricultural weeds (i.e. pigweed)

Season of Germination : 

Season of Germination Season of year where emergence is most abundant Most seeds dormant when shed Physiological dormancy Cold treatment or aging process to germinate Hard seed coat dormancy Can not germinate unless seed coat cracks or softens Some species high temp thresholds for germination Purslane, summer germinating species, can germinate directly after being shed Spring, summer, and fall germination Lambsquarter and foxtail – spring crops Purslane and pigweed – summer crops Sheperd’s purse – fall crops

Disturbance leads to Germination : 

Disturbance leads to Germination Most weed species have small seeds Seedlings at emergence are tiny and cannot compete well with established vegetation Thus, selected to respond to environmental cues indicating absence of plants In nature, plants only absent when soil has been recently disturbed = tillage

Environmental Cues : 

Environmental Cues Light High light levels at surface when plants removed Exposes covered weed seed to light High soil temperatures Bare soil warmer than covered soil Fluctuations in temperature Bare soil loses more heat to night sky than covered soil cools more rapidly and heats more quickly Nitrate in the soil Slight increases occur when no plants to take it up Chickweed and lambsquarters detect and respond to slight N increases

Seed Longevity : 

Seed Longevity If conditions are not suitable for germination, a seed can remain alive in the soil for many years Survival depends on the species and soil conditions Tillage prompts germination and critical in determining survival Seed survival improves with depth of burial in the soil Velvetleaf and lambsquarters survive well buried Galinsoga survive poorly when buried NO SEED SURVIVES WELL ON SOIL SURFACE

Seed mortality : 

Seed mortality Weed seeds die primarily in three ways; They begin to germinate in conditions that do not allow establishment Germinate deep in soil Germinate, dry out, and die They are eaten by seed predators Effective on seeds near or at soil surface Brids and mice large seeds and ground beetles small seeds Die from physiological breakdown Damage to membranes, genetic mistakes, and toxins Warm temperatures and when seeds damp but not fully moistened

Seed Production : 

Seed Production Big lambsquarters or barnyard grass can produce over 100,000 seeds Hairy galinsoga (basketball size) 40,000 seeds Big plants have more seeds than small plants Removing large individual weeds important for long term weed management Remove from field Many weed species can set seeds after uprooted if flowers have opened Dandelion flowers will set seed even if severed from the plant and incorporated in the soil

Cultural Weed Management : 

Cultural Weed Management Depends on: The weed species present The crop The time of year the crop is planted The type of equipment available Understanding the species you have can help effectively match your tactics to the weed problem

Target Nutrients and Water : 

Target Nutrients and Water Feed the crop not the weeds Band fertilizer in the crop row Avoid broadcasting fertilizer Water the crop not the weeds Drip irrigation favors crop plants Overhead irrigation waters weeds

Crop Competition : 

Crop Competition Important element of weed management and should be encouraged where possible Transplants offer a competitive edge over weeds Use high quality transplants that are vigorous and at appropriate growth stage Crop uniformity and vigor Keep planter in good repair and adjustment, uniform depth and without skips

Crop Competition : 

Crop Competition Dense Planting and narrow row spacing The closer plantings come to a square grid arrangement, the more competitive against weeds Difficult to do with row crops but good tactic for cover crops Use competitive varieties Vigorous early growth, speed of canopy closure, foliage density, etc.

Cover Crops : 

Cover Crops Winter cover crops Compete directly with weeds Chickweed and shepherd’s purse thrive in cool weather Winter wheat, rye, and hairy vetch Survive the winter well Summer cover crops Used to “fill-in” time between vegetable crops Buckwheat, sorghum-sudangrass

Crop Rotation : 

Crop Rotation Rotate between spring, summer, and fall planted crops Interferes with life cycle of weeds with preferred seasons of germination Spring germinating weeds destroyed during seedbed prep of summer planted crops Alternate crops to allow for different weed control tactics Prevents strong dominance by a single hard to control species Lowers average abundance of most or all species Row crops can be intensively cultivated Hilling potatoes can kill inter-row weeds Late germinating weeds in onions can be killed with flame weeding Rotate between short cycle and long cycle crops Helps keep weed populations in check Short cycle crops like lettuce reduce weed populations by preventing seed set Long cycle crops like winter squash difficult to weed late in growth cycle

Mulch : 

Mulch Organic mulches Effective for suppressing small seeded annuals Majority of agricultural weeds Ineffective for controlling perennial weeds Sufficient energy stored in roots or rhizomes to push through Synthetic Mulches Plastics, landscapers cloth

Sanitation : 

Sanitation Aids in preventing new weeds and reducing populations Clean up as quickly as possible after harvest Delaying clean-up as little as 1 week can increase weed seed shed by several fold, 1 month 100 fold Maintain clean field margins Mow field margins and driveways frequently to prevent seed production and force perennials to put energy into shoots rather than roots Buy certified cover crop and grain seed Test compost and manures for weeds Clean farm equipment between fields to prevent transport of weed species

Mechanical Weed Management : 

Mechanical Weed Management Tillage and cultivation directly affects weeds by: burying shoots uprooting plants so they dry out breaking both shoots and roots changing vertical distribution of weed seeds affecting survival, germination, and emergence

Slide 24: 

Tillage Implements

Cultivated Fallow : 

Cultivated Fallow A period where no crop is planted and the soil is regularly cultivated to eliminate weeds Bare soil and regular tillage prompts seed germination Shallow, regular cultivations to eliminate germinating weeds near surface Avoid any deep tillage after to prevent bringing up more seeds before the next cash crop Cultivate about once every 2 to 3 weeks When targeting perennials, kill them before they have more than 3 leaves

Chemical Weed Management : 

Chemical Weed Management Herbicides Important, useful tool Selection may be limiting in some crops Should be integrated with other management strategies to effectively manage weed populations

“Many Little Hammers” : 

“Many Little Hammers” Important to know the biology and the behavior of weeds for effective management Implement cultural, mechanical, and chemical weed management tactics to effectively control weed populations on your farm No one strategy is 100% effective

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