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WEEDS & WEED CONTROL

Understanding weeds and learning how to control them


INDEX


INTRODUCTION

One of the greatest challenges in landscaping and gardening is weed control.  There is an appropriate saying, "Nature despises a void."  This certainly applies to bare, weed-free soil!
     
What you might not have realized is that weeds can attract and harbor destructive insects.   While studying Nursery Plant Culture at Penn State, we learned that a commercial nursery should be weed-free.  Not just for "looks" either. . .

Vectors

We already knew that weeds compete with desirable plants for water, light and nutrients, but what we learned was that weeds can also provide a home for "vectors."
  
A "vector" can be defined as "an organism that carries pathogens from one host to another."  In this case, pathogens would be destructive plant insects, such as aphids, among others.

 


DEFINITION OF A WEED

The definition of a weed is "a plant out of place." OK then, following that line of thinking.... If a dandelion is a weed in a home lawn, grass is a weed on a dandelion farm! (where they grow dandelion greens)

Our choice for the
"National Flower"

 the dandelion 

from flower to seed...
Fast!

 

Dandelion ready to scatter seeds to the wind


LIFE CYCLE: ANNUAL VS. PERENNIAL

ANNUAL WEEDS

Annuals are those weeds which complete their life cycle within one growing season, or year.  The most familiar example of an annual would be crabgrass, which germinates from seed in the spring of the year.  Crabgrass germinates when the soil temperature reaches 50-degrees F.  (An easy way to remember when this occurs is that crabgrass germinates when Forsythia is in full-bloom).

See you next year

Crabgrass completes its life-cycle in the fall; the mature plant produces seeds and is killed-off by the first hard frost of the fall.  The seed remains in the soil to germinate the following spring when growing conditions are right.  This defines a summer annual.  

Winter annuals are very similar, except they germinate in the fall and die in the early heat of summer.  Annual bluegrass would be a good example.

PERENNIAL WEEDS

Perennials are those weeds which live on, from year-to-year, and may appear to die-off in the fall like an annual does, but their roots remain alive, in a semi-dormant state through the winter months.   Fresh foliage reappears from the overwintering root system the following spring.  Dandelions would be a good example of perennial weeds. (It is worth noting that dandelions spread and reproduce from seeds as well)


WEED TYPES: BROADLEAF VS. GRASS

BROADLEAF WEEDS

The dandelion is probably the best example of a broadleaf weed.  The leaves are "broad" as opposed to the "narrow" leaf of a grass plant. In technical terms, broadleaf weeds are 'dicots' having two seed leaves, while grassy weeds are 'monocots' having one seed leaf.

Broadleaf weeds can invade a weak lawn
Plantain is also a very common
broadleaf weed in lawn areas

There are bascially two methods of removing dandelions from a lawn; the first is hand-digging to remove the tuberous root (which will produce another plant if it isn't fully removed), and second, the application of herbicides (commonly known as "weed killers").

GRASSY WEEDS

Weedy grasses share similar appearance to cultivated grasses, while the most noticeable weedy grasses tend to be coarser textured ones.  One of the most bothersome grassy weeds is annual bluegrass (a winter annual), which intermingles with desireable grasses on golf courses, and thrives on the care and maintenance golf course turf receives. 

While annual bluegrass and crabgrass can be controlled with properly timed pre-emergent herbicides (at different times of the year), perennial weedy grasses have to be hand-pulled or treated with non-selective herbicides.  This creates obvious problems when the weedy grasses are intermingled with desirable grasses in a home lawn.


CHEMICAL CONTROLS

INTRODUCTION TO HERBICIDES
 ("weed killer")


Volumes have been written concerning the potential dangers of chemicals in our environment, including herbicides and insecticides, which come under the general heading of "pesticides."  The reader will have to make his or her own determination of whether or not they choose to use chemical weed controls. 

Without implying an endorsement of herbicides here, our purpose is to discuss the basics of chemical weed control used by most professionals in the "Green Industry".  For those of us who have studied pesticides, become state licensed applicators, and applied pesticides commercially, four words become the gospel truth: ALWAYS READ THE LABEL! 

Product labels are full of critical information covering all aspects of use, handling and storage of the product.  Be sure to FOLLOW LABEL INSTRUCTIONS.  For some strange reason, people mistakenly think that if one tablespoon of 'Pesticide X' per gallon is good, two tablespoons has to be better.  WRONG!  The recommended rates have been established through extensive testing and field trials.  Doubling the usage rate of any pesticide is illegal, and probably will be counterproductive, by not producing the desired results.

In summary, labels contain important information you need to know.  Spend the required 10 or 15 minutes necessary to read and understand the label -- this will help ensure desired results.

Weed Sprayer Safety Tips

  • Keep pesticides out of the reach of children
  • Don't use the same sprayer for weed control and insect control applications. Mark one sprayer "WEEDS."
  • Use a low pressure regulator to help prevent spray "drift" onto desirable plants.
  • Make applications in the cool of the day when there is little to no wind.
  • Spray when no rain is forecast for 24 hours unless the product calls for watering-in.
  • Dress properly: Protect eyes and skin, wear approved chemical resistant gloves and boots, and wear an approved respirator if possible.
  • One of the greatest risks is handling the concentrate, so wear approved gloves and be sure to protect your eyes from splashing.
  • Triple-rinse empty pesticide containers into your sprayer and dispose of containers properly.

POISON CONTROL CENTER
National toll-free number
1-800-222-1222

  

PESTICIDE TOXICITY

Labels contain signal words which tell the user the level of toxicity:  The least toxic chemical pesticides are labeled CAUTION.
Middle level toxicity is indicated by the word WARNING.
The most toxic pesticides are labeled DANGER/POISON.

The most toxic pesticides usually require a pesticide license to purchase or apply.  It is always advisable to use the LEAST toxic pesticide available to treat your particular need.
   
   

ARE YOUR CHILDREN SAFE?
The #1 cause of pesticide poisoning in children is oral exposure. NEVER transfer a pesticide from its original packaging and never put a pesticide in an old beverage container!

    


HYPERSENSITIVE INDIVIDUALS

Some individuals are "hypersensitive" to pesticides that cause little to no reaction in other people.  The State of Pennsylvania sends a quarterly "Pesticide Hypersensitivity Registry" of hypersensitive individuals to all commercial pesticide applicators in the state.  There is a mandatory process for commercial applicators to provide advance notice to these individuals when an application is to be made within 500 feet of their work, school or residence.

If your doctor can medically certify that your name should appear on this hypersensitivity registry list, contact:

Pennsylvania Dept. of Agriculture (PDA)
Bureau of Plant Industry
2301 N. Cameron St.
Harrisburg, PA  17110-9408
Main Phone: (717) 772-5231
-or- Peg Zubeck (717) 772-5207

If someone in your family is hypersensitive, it would also be a good idea to notify your neighbors.  Commercial applicators know about registered individuals, but your neighbors might not.


TYPES OF HERBICIDES

These two terms describe the "action" of a particular herbicide.

SELECTIVE HERBICIDES

Some "selective" herbicides are those types used to control broadleaf weeds (like dandelions) in your home lawn.  They are considered selective since they only kill selected, or target weeds, when they are properly applied. 

Note: Applying the proper rate is very important since a higher rate may not be selective, killing more than just the target weeds.  In other words, your lawn grass may tolerate the labeled rate of weed killer it takes to kill a dandelion, but at a higher rate, the grass could be burned and adversely affected as well. 

NON-SELECTIVE HERBICIDES

"Non-selective" herbicides can kill any plant they touch, without being at all selective.  These herbicides are most commonly used for controlling weeds that aren't intermingled with desireable plants (weeds that are "out in the open" so to speak).  Non-selective herbicides are used to control vegetation along highways, power lines and railroad right-of-ways. 


TYPE OF APPLICATIONS

Learning these terms helps to understand the type of herbicide you need to control a particular weed. 

PRE-EMERGENT HERBICIDES

Pre-emergent implies controlling the weed, or weed seed, before it "emerges" or germinates.   In actuality, some pre-emergents control the weed seed right after it germinates, by killing the young, delicate, emerging roots.

POST-EMERGENT HERBICIDES

Post-emergent implies controlling the weed after it has "emerged" or germinated. 

TIP: Post-emergent weed controls are most effective when applied to a weed that is "actively growing" (not to a weed that is under drought stress or in a semi-dormant state).  Many herbicides have "systemic action", moving from the plant leaf down to the root, and throughout the plant.  This movement occurs best during periods of rapid plant growth.

 


    
 IMPORTANT 
This page attempted to cover the basics of a very complex subject and the information may be incomplete. We're not responsible for any errors or omissions.

REMEMBER: ALWAYS READ AND FOLLOW LABEL DIRECTIONS!


DISPOSING OF OLD OR UNUSED PESTICIDES

Since 1993, the Pennsylvania Department of Agriculture has hosted a program known as CHEMSWEEP. On a rotating basis from county to county, and year to year, individuals can safely turn over their old or unwanted pesticides to authorized personnel for safe disposal. Protect our environment by safely disposing of your pesticides.

CHEMSWEEP Program
Phone: 717-772-5210


MORE

Controlling weeds

Pesticide Storage

Using herbicides and pesticides

    


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