Monday, September 30, 2013

Organic Weed Control

Cinnamon, clove and thyme oils, acetic acid (vinegar), citric acid, d-limonene (a component of the oil extracted from citrus rind) and lemongrass have all been used as an organic approach in controlling weeds. They are strictly contact herbicides with no residual activity; good coverage is essential. These products are most effective on small annual seedlings; weeds in the first true leaf stage are easier to control. They are also more effective on broadleaf weeds than grasses.  These compounds will burn the tops of perennial weeds, but they will quickly recover.  Repeat applications are needed for perennial weeds.

This type of herbicide will damage any green vegetation they contact but are safe against woody stems and trunks.  In general, the organics listed above do a moderately good job. In trying to control weeds in large areas like acres, however, the economics of using these products is poor. It is expensive.

Many of the organic herbicides work better when temperatures are above 75 Fahrenheit; sunlight may also improve the effectiveness of some.
Adding a spray adjuvant, a product added to the herbicide mix to enhance the effectiveness of the herbicide, will result in improved control. 

As stated, the age of the weed is important, the younger the better. A group of organic herbicides were tested and found to control broadleaf weeds between 80 to 100 percent when the weeds were 12 days old. But after 26 days of age, control was between 17 and 38 percent. For grasses, control was between 25 – 42 percent for 12 day old seedlings; for 26 day old seedlings control dropped to 0-8 percent control.

In addition to the chemical sprays, other approaches in controlling weeds include mechanical, physical and biological.  Mechanical weed control involves hoeing, hand pulling, and mowing. Burning is another mechanical method – the use of a propane tank with attached hose and nozzle. This application is best when weeds are less than three inches tall.

Physical weed control consists of placing a layer of opaque material over the soil surface.  This may include inorganic (synthetic) material like plastic sheeting, or organic material like bark, wood chips, straw and compost. Place 4-6 inches of an organic mulch for best results.  Biological weed control is where sheep, goats and geese are used to chew down the weeds.

The main point to stress is: do not 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.