ZERO TILLAGE - AFFORDABLE WEED CONTROL

"MAKING THE MOST OF YOUR $'S"

Weed control can be accomplished using 4 major methods. These are:

• Cultural
• Mechanical
• Chemical
• Biological.

In conventional tillage, farmers rely on mechanical and chemical methods with some support from cultivation methods. Biological control methods will become more important in the future as biological herbicides such as Biomal, a fungicide used to control Roundleaf mallow are developed and marketed.

In zero tillage with the exception of some hand picking of weeds to prevent introduction and mowing around field borders to prevent transfer of weeds like brome grass from the margins into the field , zero tillage needs to rely more heavily on cultural methods and then use chemical and biological agents where necessary.

Cultural methods could be defined as those methods for which there is no salesman; methods which you have to develop and methods if used right will return large paybacks. These are the methods which will ensure you receive the most from the dollar inputs you do buy. Farming with large cultivators and discs has allowed us to move away from cultivation control. However, farmers who eliminate or drastically reduce tillage from their crop production will need to re-evaluate cultural control methods.

While not all of the cultural methods described will be applicable to your farm, many techniques will be useful. They include:

1)SANITATION - sanitation involves methods of preventing weed introductions.

Some of the key techniques are:

a)field border sanitation - preventing field border weeds such as brome grass from entering the field. Bromegrass is a bunch grass and tends to stay where it is put unless you help it move. The best way to contaminate a field is to harvest the bromegrass border along with the rest of the crop. The combine will very efficiently move the brome grass 20-30 feet further out into the field. Mowing the field borders prior to brome grass seed set will provide an adequate buffer to prevent spread of the brome grass.

b)weed seed introductions - clean weed free seed and equipment cleaning, particularly of combine is an important way to keep unwanted weeds out of a field. With the development of herbicide resistant weeds combines and trucks will become an increasingly important way for the resistant weed to travel from one field to another.

c)movement of weeds by wind and water. Grassed and hayed water runways are a methods to prevent upstream weeds from taking hold on your farm. Standing stubble can be effective in slowing the movement of some wind blown seeds, however rolling weeds like Kochia or floating weeds like dandelion know no borders.

2)CROP ROTATIONS

Rotations are practiced as a means of weed control to prevent or reduce the buildup of high populations of certain weeds common to a particular crop. Crop rotations help break up the weed growth cycle particularly when crops with different growth habits are used and/or if different herbicides can be used in different crops. Crop rotations also help increase crop vigour (competitiveness) by decreasing disease and insect pressure.

Crop rotations may mean more work and need more ingenuity than mono cropping, however the benefits can often be substantial. While crop rotation is important to achieve the maximum profit from each of the tillage systems employed, the highest profits come from zero tillage when diverse set of crops were grown.

Different farms and areas will have difficult opportunities when it comes to crop rotations. Farmers who can effectively feed or market hay have expanded opportunity to include short term forages into a rotation. Dr. Martin Entz (1992, University of Manitoba) has fine tuned methods of seeding alfalfa directly into standing stubble and then later removing the alfalfa out of the rotation with herbicides while maintaining the improved soil structure developed under the alfalfa. These techniques allow alfalfa to be rotated more frequently, maximizing the benefits of suppressed weed growth and improved soil structure to a greater portion of the farm compared to leaving a forage in the same field for 6 or 7 years.

The use of snow trapping and reduced evaporative losses with zero tillage has also been shown to effectively allow expanded rotations in some of the drier areas of the prairies. Instead of a wheat fallow rotation, zero till combined with enhanced snow trapping systems such as variable height cutting can allow the rotation to include additional crops. Beck (1991) at Redfield, S.D. has found zero till allowed a corn/soybean rotation to be reliable and profitable in an area which traditionally is 50/50 cropping.

Crop rotations also assist us in rotating herbicides. Weed resistances to herbicides is fast becoming a major problem on any farm which has systematically used the same herbicide or family of herbicides year after year. Once the resistant population has become dominant on a farm there are very few good ways of dealing with the problem. In Australia where herbicide resistance has been a problem for a longer period of time than in the Northern Plains, some farmers have no alternative except to sow forages. Unfortunately this is a serious problem and the more comfortable you have become with getting good results from a particular group of herbicides the more likely the problem is to come. In fact with many herbicides it is guaranteed.

3. COMPETITION - the ability of crop to dominate over the weeds.

Competition is one of the most important aspects of weed control a farmer can control. Within a crop rotation system it is imperative to use all the tricks to ensure the crop will dominate.

The major factors in ensuring the crop will dominate include:

1. Selection of vigorous seed and cultivars

1. Stobbe et al (1991) have shown the advantages of using vigour seed to produce vigorous crops.
2. Certain varieties are more effective than others in competing with weeds. However there are often trade-offs here. Semidwarf crops compete less effectively than tall varieties however the semidwarf height often has other desirable attributes such as increased yield and decreased straw which make them advantageous.

1. Maximizing early crop vigour

1. seed as shallow as possible. Zero till seedbeds are moist and allow for shallow seeding. Shallow seeded crops emerge quicker, branch or tiller earlier and are less prone to root rots than deeper seeded crops.
2. Use seed treatments to control injury from diseases and insects. Rootrots, wireworm and damping off can cause major plantstand losses or decreased mechanical band or soil fracturing beside the seed can help aerate the soil, increase root growth, decrease rootrot attack and increase crop vigour.
3. Starter +/or precision banded fertilizer will help ensure the crop is adequately fed while at the same time minimizing the amount of fertilizer which is available to the weeds. Adequate and balanced fertility is essential for the production of a healthy crop. Care must be taken to prevent injury if the seedling from fertilizer. Many techniques can be used to efficiently place additional nitrogen. One methods which should be avoided is pre-seeding broadcast as the broadcast fertilizer will stimulate weeds like green foxtail as well as the crop. However using some seed placed fertilizer and broadcasting the remainder as 34-0-0 at the 4-5 leaf stage of the crop, broadcasting can be very effective without stimulating annual weed growth.
4. Biological seed treatments such as legume inoculants or products like Provide may be beneficial to further enhance the nutrient availability to the crop relative to the weeds.
5. Leave the stubble standing. Standing stubble will buffer the crop from drying winds thus resulting in less moisture stress and physical damages and greater crop vigour.
6. Weed free seedbed. Weeds which are left uncontrolled or germinate before the crop is up exert much more pressure on the crop than weeds which germinate after the crop is established. Manitoba Agriculture (1988) has shown that 8 wild oats/m2 which are 1 leaf stage ahead of the crop can reduce yields 26-35% compared to the same wild oats causing 8-10% damage if the crop is ahead of the wild oats by 1 leaf stage. It is important to use burn off herbicide treatments which:

1. control all weeds
2. are timed to ensure the crop is a weed free as possible during the critical phase of development
3. do not injure the crop through toxic residues

1. Planting geometry. Seeding rate and row spacing can be manipulated to produce crops which are more competitive. As with variety selection there may be trade offs to develop a situation which produces the optimal outcome. Generally more equi-distance spacing allows for more competitive crops. This view has been supported by (1992) at Scott Sask., and Rourke and Hargrave (1992) at Minto, MB. Recent studies at Minto indicate that narrow row spacing producted either from narrow spaced double disc openers or paired row systems results in quicker canopy development and higher yields (Rourke and Hargrave 1992). In this study, P205 was seed placed and N broadcast. The broadcast N was also compared to a precision banded under the paired row system. In this instance, the yields were 72 and 69 bu/acre for the broadcast and banded respectfully. Rourke (1992) however also noted wheat grown in narrow row spacing can be more susceptible to foliar leaf diseases than wheat grown under wide rows.

Trials conducted by Dr. Lafond at Indian Head, Sask. Show promising results which may lessen the need for narrow row spacing under zero tillage. Positional availability of nutrients and low soil disturbance may be techniques to move toward the more practical application and use of wider row spacing in zero tillage systems.

2. Good soil seed contact. It is important to use equipment which will consistently place the seed in contact with moist soil and provide adequate cover and packing to ensure rapid germination and emergence. Drills which hair pin straw into the seed row or cause straw bunching and plugging will produce erratic uncompetitive stands.

Adequate chaff and straw spreading is critical to achieving optimum seed drill performance. Problems at seeding translate to problems all year.

3. Manipulation of growing conditions. While most of the points above involving manipulating the situation to the advantage of the crop, there are other techniques, some of which as less proven than others, which involves changing the soil conditions to favour the crop. We all know kochia will dominate on a saline and grow crops which tolerate saline conditions.

Additional of barnyard manure, surface drainage, treatment of recharge area and use of perennial high moisture use crops as well as zero till can all be beneficial to eventually make annual crops more competitive in that situation.

Addition of lime to increase soil pH is another common method of modifying the soil to favour crop growth on low pH soils.

4. Cover crops, living mulches, smother crops, alleopathy and non living mulch are methods which have been used with varying degrees of success to suppress weeds in cropping systems.

1. Avoidance of weed stimulation.

1. minimize soil disturbance. Many weed seeds left on the surface of a zero till field will quickly be weathered, eaten by birds, insects or attacked by fungi, etc. to come non viable. Undisturbed mulch of a zero till soil will help prevent germination of weed seeds which need light as a stimulus of those which require warmer seedbeds such as green foxtail.

Minimizing soil disturbance needs to be balanced with good soil seed contact to ensure crop vigour. Crop vigour is of course the primary objective. In using some drills such as a paired row opener on an air seeder, 40-50% of the soil will be disturbed, however some drill designs allow loose soil to fall between the seed rows. The unpacked loose soils generally will make poor seedbed for weeds.

2. restrict access to fertilizer. Pre-emergent broadcast fertilizer will be beneficial not only to crops but also to weeds, thus fertilizer should be sidebanded, seed placed, broadcast post emergent or applied in such a way as to restrict its use to weeds.

MECHANICAL WEED CONTROL

Mechanical weed control is a second form of weed control which in certain cases can compliment zero till crop production.

Mowing is the most complimentary form of mechanical weed control in a zero tillage system. Situations where mowing will be advantageous is in:

1. mowing of field borders
2. mowing to harvest annual or perennial forage can also be used to control weed growth.

A second form of mechanical weed control is hand picking. While this form of weed control has a certain lack of appeal, it can be extremely effective in eradicating new and small infections of weeds. For example on our farm we have used this method to eliminate cleavers and milkweed from the farm. It requires close scrutiny of a field to make this method viable.

Tillage is a third form of mechanical weed control which is generally avoided in zero till field. However even the best zero till farmers has been known to use some discretionary tillage to eliminate a problem which otherwise has no economical solution. Every year it appears as if there are less and less need to use even a small amount of tillage. Some farmers have successfully zero tilled all of their land without any tillage for up to 19 years. These farmers have been successful in using cultural and chemical methods to overcome problems as they have arisen.

Tillage as we know can have many deleterious side effects which if practiced in excess will certainly lead to soil degradation.

CHEMICAL AND BIOLOGICAL WEED CONTROL

These methods should be reserved to compliment other weed control methods particularly cultural methods. Many farmers have in the past tried zero till but many have gone back to conventional methods. There are many reasons for their lack of success. For some it was lack of suitable machinery, for others it was the high cost of Roundup however for many it was lack of understanding the system. The long term zero tillage have been successful due to their ability to adapt machinery to the purpose, fine tune the use of Roundup and other chemicals to keep costs down and weeds under control and perhaps most importantly develop a system which used the advantages of cultural weed control practices which automatically results in successful crops.

Today we have suitable machinery, affordable Roundup and a much enhanced understanding of the zero tillage system.

Because we largely remove tillage as a weed control method in zero tillage, we automatically need to use other methods to control weeds. Obviously herbicides have been shown to be very effective and cost effective in Western Canada and are especially effective when combined with previously mentioned cultural and mechanical measures.

Chemical weed control in zero tillage can occur at various phases of crop growth. These include:

1. Pre-harvest. Preharvest weed control has only just become a practical alternative with the recent registration of the preharvest use of glyphosate. Pre-harvest applications of Roundup have been shown to be especially effective in controlling perennial weeds as quackgrass, Canada thistle and sow thistle (Monsanto 1992). The pre-harvest timing allows for application to weeds at a more susceptible stage and should become an important method to provide cost effective control of many troublesome weeds. Further refinements weeds. Further refinement of this technique may allow for fine tuning of rate at a later date, generally 1 1/acre is recommended.
2. Post-harvest. With the recent registration of pre-harvest Roundup the use of post harvest weed control for perennial weeds will likely be diminished and will be reserved for cleanup of small weed patches.

 

Late fall herbicide applications will be continued for control of winter annuals such as stinkweed, flixweed and downy brome. Low rates of 2-4D can be very effective in controlling many broadleaf winter annuals. Occasionally herbicides may be required to control heavy growth of volunteer crops after harvest. This will only be economical where moisture and nutrient loss would be considered to be excessive or where it is important to break the green bridge so that disease and insect cycles could be broken. An example of this would be the transfer of wheat streak mosaic from spring wheat volunteers onto newly planted winter wheat. The green bridge would have to be disrupted for at least 2-3 weeks (i.e. no green plant growth on the field for 2-3 weeks) for the disease cycle to be broken (Cook & Veseth, 1991).

3. SPRING BURN-OFF

Spring burn-off is the practice we most associate with replacing the tillage in a crop production system. Roundup is the preferred herbicide in that it is:

1. wide spectrum
2. non residual
3. safe to use
4. relatively cost effective
5. seems not to readily be susceptible to herbicide resistance.

Since Roundup was once very expensive and still is a significant cost in the zero tillage system researchers and farmers have worked hard to make it more effective and less costly to use.

It is imperative that we control all weeds prior to crop emergence. Weeds which are in place and growing before the crop emerges are very damaging. For the most part we can afford weed escapes at this time.

As a general recommendation Roundup used to burnoff annual weeds should be used at .5 1/acre with 1 lb. of 21-0-0 (24) from Sherrit Gordon or equivalent quality product. Water volume should be 5 gallons/acre or less. Kirkland (1989) showed Roundup activity could be enhanced by using water volumes as low as 1 gallon/acre. Kirkland uses extremely small nozzles to achieve 1 gallon/acre compared to using larger nozzles and increased ground speed. Research is currently indicating that additional surfactant may not be beneficial with this combination (Rourke and Hargrave 1992). Water quality is important and ideally should contain <20 ppm of Ca +/or Mg. A fact sheet is being prepared which will give more detailed information on water quality guidelines for herbicides use (Holms and Henry 1992). The .5 1/acre rate will be very effective in controlling a wide range of annual weeds as well as non sod bound quackgrass (Rourke and Hargrave 1992).

Weeds should not be more than 6" tall or smaller if possible. The timing of the spray should be close to seeding, usually not more than 12-24 hours prior to seeding or 3-4 days after seeding but prior to crop emergence. Spraying too early could allow a second flush of weeds to emerge before the crop resulting in a competitive advantage for the weeds.

Lower and higher rate are sometimes necessary. Lower rate (.3 1/acre) could be used if the weeds are small (<4 inches) and only include green foxtail, volunteer cereals, wild oats, wild mustard, stinkweed, lady's thumb and volunteer canola. Weeds such as wild buckwheat require the .5 1/acre rate. Foxtail barley, brome grass, alfalfa, dandelion and dense quackgrass may require higher rates and/or a tank mix with another herbicide such as dicamba. Again 21-0-0 (24) ammonium sulfate has proven to be valuable in boosting control with the lower rates.

Development of weed resistance to Roundup has not be reported, however we cannot rule out the possibility that weeds could develop tolerance, therefore future research will need to focus on developing alternative to help us ensure Roundup will be an effective tool in the future. Other herbicides which may eventually be used to compliment Roundup include glufosinate (Harvest - Hoechst), sulfonate (Touchdown - ICI) and paraquat (Sweep - ICI).

The continual use of Roundup can also lead to weed shifts by selecting for weeds which are not susceptible to Roundup. Wild pansy and wild vetch are examples of two weeds which Roundup cannot control. Tank mixes or use of other herbicides will be necessary in some cases to deal with these problem weeds.

1. IN CROP WEED CONTROL

POST EMERGENT HERBICIDES

During that last 15 years we have been privileged to have access to many effective post emergent herbicides. Further development of new herbicides and herbicide resistant crops will continue to provide us with increasingly good options for in crop weed control.

New products which will fill gaps left existing products include:

1. Pursuit (Imazethapyr) is a residual herbicide which will be effective in controlling weeds such as wild buckwheat, kochia and other weeds in peas, soybeans and possibly lentils. Pursuit has both pre-emergent and post-emergent activity.
2. Fluroxypur is a broadleaf herbicide designed to be tank mixed with other broadleaf herbicides for control of hemp nettle and cleavers in cereal crops.
3. Roundup tolerant canola will offer broad spectrum weed control in canola at a very competitive price. It will also allow other options to the use of Accase herbicide for the control of grassy weeds in canola
4. Glufosinate resistant canola will also allow for broad spectrum weed control in canola again with a different mode of action which should further prevent development of Accase herbicide resistance.
5. Other companies are developing other herbicide resistant crops which will increase our ability to control weeds postemergently.
6. Biomal is a biological fungal herbicide which selectively controls roundleaf mallow in a wide variety of crops.

PRE EMERGENT HERBICIDES

This group of herbicides including trifluralin, ethalfluralin and triallate are not normally associated with zero till due to a need for soil incorporation. New research has shown that triallate can be surface applied. Evidence also exists that trifluralin may be effective in a zero tillage or limited tillage system (Rourke and Hargrave 1992). Initial work at Minto (Rourke and Hargrave 1992) illustrates some of the results obtained using trifluralin/ethalfluralin compared to Poast/Pursuit for weed control in lentils. The Pursuit was effective but damaging to the lentils.

Kirkland (1992)(Ag.Canada, Scott, Sask.) has found the surface (non incorporated) application of trifluralin to be generally effective in controlling green foxtail. Generally wild oat control with triallate was less consistent when no incorporation was done; results range from 40-85% control. Work is continuing in an effort to increase consistency.

Increased moisture with zero tillage , shallower weed seeds plus late fall application may offer new opportunities to use these old compounds in zero tillage, however the consistency of performance is still not known.

Zero tillage, enhanced cultural control and vigorous crops have the potential to reduce the need for herbicide used within our cropping rotations. For example, establishment of a vigorous cereal crop which emerges prior to weed emergence and has overall reduced weed pressure due to zero till establishment may in some case be competitive enough that weeds will not cause any significant yield loss. If this potential can be achieved herbicide costs will of course decrease and the chances of developing herbicide resistance should also decrease. We will then be saving the use of our best herbicides for the situation where they are most needed; example - grassy weed control in lentils or flax.

1. Fallow weed control.

Chemicals increasingly play an important role in providing for weed control in fallow situations. Coming from the black soil zone this author has little knowledge of the practical applications of herbicides used for fallow weed control. However it is obvious even from afar that tilled fallow can be the cause of considerable soil erosion, loss of soil organic matter and increased soil salinization. Extended rotations with the aid of enhanced snow trapping, reduced evaporation losses with zero tillage in combinations with chemical or chemical/tillage fallow will continue to offer new opportunities for innovative farmers.

CONCLUSIONS

Zero tillage is one of the best answers available to achieve sustainable production of high yielding crops. Not only does zero tillage protect and improve soil quality but it provides economic advantages as well. Weed control is one of the key factors influencing the success of zero tillage on any given farm. The integration of cultural and mechanical weed control methods with chemical and biological control methods is the best way to get the most out of your herbicide dollar and guarantee long-term success.

REFERENCES

Beck, D.L., and R.Doerr 1992. No-Till Guidelines for the Arid and Semi-arid Prairies, B712 Dakota Lakes Research Farm, Pierre, South Dakota

Cook, R.J., and R.J. Veseth 1991. Wheat Health Management, APS Press, American Phytopathological Society, 3340 pilot Knob Road, St. Paul, Minnesota 55121 USA

Derschoid, L.A. 1978. Controlling field bindweed while growing adaptable crops.Proceedings of North Central Weed Control Conference. 33: 144-150.

Entz, M. 1992. Short term alfalfa rotations. Personal communications, Dept. of Plant Science, University of Manitoba, Winnipeg, MB.

Holms, R., L.Henry 1992. Water Quality Guidelines for Herbicide use, Personal Communications, University of Sask., Saskatoon, Sask. December 1992.

Kirkland, K.J. 1989 The Effect of Water Volume on Herbicide Activity, Proceedings of 11^th Annual Manitoba-North Dakota Zero Tillage Workshop, Winnipeg, MB.

Kirkland, K. 1992 Soil Incorporated Herbicides Without Incorporation, Personal Communication, Agriculture Canada, Scott, Sask.

Kirkland, K. 1992 Row Spacing, Seeding Density and Herbicide Rate Influence Weed Competition on Various Crops. Personal Communication, Agriculture Canada, Scott, Sask.

Manitoba Agriculture 1988, Knowing when it pays to spray wild oats. Manitoba Agriculture, Agdex No. 641.

Monsanto, 1992 Preharvest Weed Control with Roundup, Personal Communication, Monsanto Canada, 55 Murray Park Road, Winnipeg, MB.

Putnam, A.R. 1988 Alleopathy: Problems and Opportunities in Weed Management. P.77-88 in M.A. Altreri and M. Liebman eds. Weed Management in Agro ecosystems: Ecological approaches CRC Press Boca Raton, FL.

Rourke, D. 1992 Intensive Wheat Management - Production Guide, Canada Grains Coucil, 760-360 Main Street, Winnipeg, MB.

Rourke, D. and A. Hergrave 1992 Annual Report of Conservation Tillage Productivity Centre, Minto, MB.

Stobbe, E.H., J.Moes, M.H. Entz, Y Gan, R.Wytinck, H. Ngoma, L. Bouregeois, M. Empey and A. Iverson, 1991 Crop Management for High Quality Wheat and Barley Seed Production, Dept. of Plant Science, University of Manitoba, Winnipeg, MB.