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Killing Weeds with Less

How banded herbicide applications can help the environment, and also pay off for potato producers.

Successful weed management is one of the cornerstones of successful commercial potato production, particularly at the start of each growing season. Controlling weeds in potato crops doesn’t appear to be getting any easier—many Canadian growers and researchers alike agree this seems to be more of a challenge with each passing year.

Weeds compete directly with potato plants for the basic natural elements required for growth, namely light, water and nutrients, and can also harbour insects and diseases that attack potatoes. Research shows weeds can have a detrimental impact on tuber yields when compared to those of potatoes grown in weed-free conditions. Weeds present at harvest can reduce yields by increasing mechanical damage to the tubers, as well as by slowing the harvesting operation down and reducing efficiency.

Reducing early season competition with weeds is critical to the success of potato crops. Researchers have found that competition from early season weeds will reduce yields if they are not controlled within four to six weeks after potato plants emerge. Therefore, it is essential that growers ensure minimal competition between potatoes and weeds from planting to the time of full canopy closure.

Growing public concern over pesticide use has intensified efforts by researchers to find ways for growers to cut down on the amount of herbicides applied in potato production.

Reliance on Herbicides

Cultivation and hilling play a large role in weed control with potatoes, but most non-organic potato operations in Canada also rely heavily on herbicides as an important weed management tool. Many growers employ widespread broadcast applications of pre- and post-emergence sprays of broad spectrum herbicides to achieve adequate weed control in potato crops. This has led not only to the use of high amounts of herbicides, but also an increased risk of resistance development.

In recent years, growing public concern over pesticide use has intensified efforts by researchers to find ways for growers to cut down on the amount of herbicides applied in potato production. The rising cost of herbicides is also of concern to producers trying to reduce overall production costs, and a growing number of potato growers in Canada are turning their attention to environmentally-friendly production practices.

As part of integrated pest management, which includes the judicious and reduced use of pesticides, banded herbicide application, also known as banding, is an attractive option. In essence, it involves spraying herbicide only over the potato rows, usually covering a width of about 30 centimetres. Weeds in the spaces between rows are typically controlled mechanically through cultivation. The herbicide is applied at the time of planting, pre-emergence or post-emergence of the crop.

This practice is already used in field crops such as corn and soybeans. Research findings show that when combined with mechanical weeding and hilling, herbicide banding can effectively controls weeds and help produce yields similar to those obtained through conventional production. Indications are it can also dramatically reduce the total amount of herbicide used.

Research Findings

Researchers have shown that herbicide banding can work in potato production, and result in a number or environmental and economic benefits.

During the late 1990s, J.A. Ivany at Agriculture and Agri-Food Canada’s Crops and Livestock Research Centre in Prince Edward Island studied the use of herbicide banding on Russet Burbank potatoes. He tested the combined effect of banded herbicide application on the potato rows and complementary mechanical weeding on crop yield and weed control effectiveness for three species (quackgrass, corn spurry and wild radish).

Ivany’s research findings in Banded Herbicides and Cultivation for Weed Control in Potatoes showed that applying appropriate herbicides in 30-centimetre bands over the potato rows, followed by cultivation to remove weeds between the rows, resulted in acceptable control of broadleaf weeds and quackgrass. Herbicide banding combined with weed cultivation also produced a potato yield similar to that produced by broadcast herbicide application. Other notable findings listed by Ivany include a reduction in the amount of herbicide released into the environment and a 66 per cent reduction in herbicide costs.

Research trials conducted in a number of growers’ fields and at the Deschambault Experimental Farm in Quebec between 2001 and 2004 also demonstrated the feasibility and effectiveness of herbicide banding.

Banded Herbicide Application in Potatoes, a brochure published by the Fédération des producteurs de pommes de terre du Québec, refers to a study in which banding was compared with a treatment using conventional full-width application of herbicide as well as an untreated control group. Two herbicides were tested: linuron and metribuzin. Mechanical weeding and hilling were carried out for all treatments (except for the non-weeded control).

Most non-organic potato producers in Canada rely heavily on herbicides as a weed management tool.

Most non-organic potato producers in Canada rely heavily on herbicides as a weed management tool.

In terms of both weed control and yield, there were no significant differences between herbicide banding and the conventional treatment. When combined with mechanical weeding and hilling, banding was shown to effectively control weeds and provide a yield similar to that obtained through conventional production. The researchers also found that the banded herbicide application cut down on the amount of herbicide used by at least 60 per cent.

Benefits of Banding

Working on the assumption that banding can cut down on the amount of herbicides used by 60 per cent, it follows that this means:

  • lower production costs;
  • reduced risk of contaminated waterways and water tables;
  • fewer risks to human health and the environment; and
  • less chance of weeds developing resistance to herbicides.

When herbicide banding is done at the same time as planting or mechanical weeding, it can also result in:

  • fewer tractor passes in the field;
  • less soil compaction;
  • reduced costs for tractor use (time, fuel, wear, etc.); and
  • lower greenhouse gas emissions.

According to the Centre de référence en agriculture et agroalimentaire du Québec’s 2006 economic guidelines for table stock potatoes, the cost of applying herbicide over 80 hectares drops from $7,882 for broadcast application to $2,627 using banding. Eliminating one tractor and sprayer pass application in the field saves an additional $784, resulting in a total savings of $6,039 with herbicide banding.

Keys to Successful Banding

Successful herbicide banding depends on various factors. It is important that potato growers consider these carefully.

For one, mechanical weeding and hilling always need to be carried out at the right time using appropriate equipment. In addition, if problem weeds have persisted for a number of years in a particular field, the situation should be dealt with prior to considering herbicide banding.

Using cultivars with heavy vegetative growth makes it easier to manage weeds, as rigorous plant growth quickly leads to row cover early in the season, largely preventing weeds from growing between rows. This also makes them good candidates for successful herbicide banding. However, it is important that plants do not collapse prematurely late in the season, as this could lead to weed development at that stage.

Herbicide banding requires precision, especially in the angle and placement of the nozzles on spray equipment. Uneven ground can destabilize equipment and prevent the nozzles from spraying uniformly. To ensure proper herbicide coverage, soil beds should be as level as possible.

As in the case with using conventional treatments, growers should ensure that other herbicide application practices are followed rigorously. These include weed monitoring through scouting, proper sprayer calibration, and compliance with recommendations for tractor speed when applying the herbicide.

Clearly, there are benefits to banded herbicide application for growers. The pay-offs for potato production appear to be not only environmentally positive, but very real in terms of cost savings on a per hectare basis.

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