Tuesday, April 24, 2012

How to Control Those Pesky Weeds



What is a weed?  Dandelion is cultivated for salad greens, but in a lawn, it is a weed.  Cantaloupe is a very tasty fruit, but growing in your flower bed, it would be a weed.  A weed is simply a plant growing where it is not wanted or, a plant out of place (p.o.o.p.)!  In some agricultural areas, more money is spent on weed control than any other pest.   

What’s so bad about weeds? 
·        They compete with our crops for space, nutrients, water and sunlight.  As a result, the crop may appear stunted with reduced yields and lower quality.  
·        Weeds can serve as hosts for insect pests and disease organisms.  
·        They provide cover and food for many rodent pests. 
·        Many people are allergic to certain weeds.
·        Some weeds are poisonous to livestock. 

On the other hand, here are some redeeming features of weeds:
§  They reduce dust and soil erosion.
§   Provide cover and food for birds, nectar for honeybees and a habitat and food for beneficial insects.    
§  Some, with an extensive root system, penetrate deep into the subsoil to improve drainage and bring nutrients to the surface.

Strategies for control:
 Prevention don’t allow weeds to go to seed!  Get rid of existing weeds before they flower and produce seed. The average number of weed seeds in soil is 30,000 – 350,000 seeds/square meter, or 120 million to 1.4 billion per acre. 
Cultural – modify the environment to improve the crops competitive advantage and decrease the weeds advantage. This includes, proper soil preparation, crop rotation, maintaining good soil fertility and moisture, choosing the best varieties for your area and planting at the proper time of the year.  In turf, watering deeply and infrequently discourages many weeds as does maintaining the proper mowing height.

 Mechanical – this method includes hoeing, hand pulling, and mowing. Flaming is also a method of weed control - using a propane tank, hose and appropriate applicator; best when weeds are less than three inches tall.
 Although time consuming, here is another effective method using mechanical weed control: first work up the ground to be planted, water it and allow weeds to grow.  Then either spade them out or spray with a contact herbicide. Repeat this process again, then plant, disturbing the area as little as possible.  This will rid the area of a high percentage of annual weeds.

 Physical – this method includes placing a layer of opaque material over the soil surface.  Examples - inorganic (synthetic) material such as plastic sheeting, or organic material like bark, wood chips, straw and compost. Place 3-6 inches of an organic mulch for best results.  Living mulches, such as grass or a clover cover crop, are used by many growers. Clovers have an extra benefit in that they can supply nitrogen to the soil.

Biological – employs the use of insects and diseases that would normally attack weed plants and their seeds in order to reduce the weed population. Sheep, goats and geese are also used to chew down many weeds.  Geese prefer grass seedlings, but have been known to feed on the crop when the grass is gone. Chinese weeder geese are preferred to other geese because they walk around the crop and not on it. 

Chemical control – products can be categorized as either a pre-emergent or post emergent herbicide. Preemergent herbicides, also known as soil-residual herbicides, are applied to the soil before the weeds appear in order to prevent their germination.  The residual effect of the herbicide will last from several weeks to a number of years, depending on the particular herbicide used, the rate of application, and soil characteristics. The more common preemergent herbicides will persist in the soil from 1- 12 months.

Post emergent herbicides, sprayed on the weed itself, are either contact or systemic. A contact herbicide, such as weed oil, literally burns the plant. The weed however, could recover if it had a significant root system.  On the other hand, a systemic herbicide, such as RoundUp, will kill the weed as it is absorbed and  taken into the root system.

Cinnamon, clove and thyme oils are contact herbicides and have been used as an organic approach in controlling weeds. They are most effective on small annual seedlings and more effective on broadleaf weeds than grasses.  They are strictly contact herbicides.  If the root system of the weed is old enough or strong enough, the plant will regrow, making repeat applications necessary. In general, they do a moderately good job. However, they are not economical for controlling weeds in large areas (acres).