Weed control cultivations

To control weeds, approximately 90% of U.S. agricultural acreage is treated with nonchemical, mechanical weed controls, such as mechanical cultivation and rotary hoes (15), whereas only about 25% receives treatment with herbicides (13). 

An annual estimated cost of approximately 938,835,000 is required for labor and equipment to apply 204.5 million kilograms of herbicides to 147.6 million hectares of cropland in the United States (Table IV). Mechanical tillage to control weeds between cropping seasons and interrow tillage of crops has been used for centuries as a very effective method of weed control. Approximately 50% of all tillage between crops is done to control weeds. The number of cultivations required for effective weed control within a row crop varies from two to five during a cropping season. 

Mulch tillage or mulch ripping the soil is tilled prior to planting with chisels, disks, sweeps or blades weed control is obtained with herbicides and/or cultivation... 

No tillage or zero tillage the soil is left undisturbed from harvest to planting except for nutrient injection. Planting or drilling is accomplished in a narrow seedbed or slot created by coulters, row cleaners, disk openers, in-row chisels. Weed control is accomplished primarily with herbicides. Cultivation may be used for emergency weed control... 

Pollen allelopathy can find utilization in field cultivations that could contain pollen of allelopathic crops or weeds. Pollen allelopathy could be an effective method for annual weed control that reproduce, at least in part, via wind pollination and flower concurrently with the allelopathic species. The effects of allelopathy should result in the loss of genetic variation and so in reduction of reproductive ability, but some plants are probably able to detoxify the pollen allelochemicals (Murphy and Aarssen 1995a, b). Murphy and Aarssen (1989) suggested possible delaying of weed flowering at later, less favorable times of the season or diurnal period, so decrease in weed pressure. However, infestation by perennial weeds can worsen due to compensation of pollen allelopathy through increase in the formation of rhizomes. 

Organic farming systems rely more on mechanical weed control and in certain crops on considerably more intensive soil tillage as the use of synthetic herbicides is prohibited. This can have negative effects on other key species of soil meso-fauna, i.e. a reduction of population of Collembola with organic cultivation (Krogh 1994). 

Allelopathic crop plants have already been used experimentally in weed control. Leather (70) found one of thirteen genotypes of the cultivated sunflower tested to be very allelopathic to several weeds. In a 5-year field study with oats and sunflower grown in rotation, the weed density was significantly less than in controi piots with oats only. 

The move into continuous cereal production and away from mixed farming with firm rotations meant that farmers could cultivate high value crops on all available land without the need for fallow. This could not have been achieved without the use of chemical herbicides. The movement of people from the land to the urban environment during the industrial revolution and thereafter reduced the available labour for hand weeding and weed control became a real problem for the farmer. The revolution was the introduction of 2,4-D and MCPA that allowed broad-leaved weeds to be controlled selectively in the previously dirty cereal crops. 

Fogelberg, F. 1999. Night-time soil cultivation and intra-row brush weeding for weed control in carrots (Daucus carota L.). Biological Agriculture and Horticulture 17(1) 31-45. 

Melander, B. 1998b. Interactions between soil cultivation in darkness, flaming and brush weeding when used for in-row weed control in vegetables. Biological Agriculture and Horticulture 16(1) 1-14. 

Rasmussen, J. 2004. Guidelines for Pphysical Weed Control Research. Flame Weeding, Weed Harrowing and Intra-row Cultivation. Proceedings of the 6th EWRS Workshop on Physical and Cultural Weed Control, Lillehammer. pp. 194-225. 

The historical record reveals that herbicides have replaced or reduced the use of hand weeding and cultivation for weed control, with an associated reduction in cost and an increase in yield. Today herbicides are used routinely on more than 90% of the area of most US crops, representing 87 million ha of cropland (Gianessi and Reigner, 2007). 

Many of our current technical innovations in mechanical weed control can trace their development from earlier forms of the same tillage device. Even the plows and cultivators used through the 1900s tended to be little more than large, hardened steel replacements of the wooden tools used centuries earlier. On the other hand, herbicides radically changed agricultural production within a few years of their introduction. Novel application equipment is now required by the herbicide user, as is the knowledge to use each new herbicide product effectively. 

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