Agronomic Information - Weed Control

Chapter I - Introduction

Farmers have been battling weeds ever since man changed from being a nomadic hunter-gatherer to living in permanent agriculture-based communities. Until relatively recently in our history, farmers had few options in controlling weeds in crops, relying primarily on tillage. Herbicides have only been used since the mid-1940's and have provided farmers with another tool in combating weeds. Weeds compete with crops for moisture, light and nutrients, resulting in yield losses in crops. Not only do weeds cost the farmer money in reduced yields, but also in the cost of controlling weeds, not to mention costs associated with cleaning, dockage, etc.

A weed is essentially any plant that is growing where it is not wanted. This includes volunteer crop seedlings that emerge in the current crop. It is important to note all seeding systems, either conventional, minimum, or zero-till, select for certain weeds. Even simple things like seeding a field the same time each year, selects certain weeds that have adapted to that practice. High tillage systems tend to encourage annual weed selection. Low disturbance, zero-till systems that are continuously cropped tend to have less annual weeds, but can develop perennial weed problems if the producer is not regularly inspecting the fields.

What makes weeds start to grow and appear at different times? Well, there are several factors that are involved for weed seeds to germinate. First of all, weed seeds have a dormancy that allows them to survive the winter and also to ensure their survival by not allowing them to all germinate that first year. If all weeds germinated the year following their production, a farmer's life would indeed be much easier. The length of dormancy of weeds is variable, depending on each species. Dormancy can last for a relatively short time of a year or two, or in some cases, last for decades. What conditions are necessary for weeds to begin growing? Generally, weed seeds need something that breaks their dormancy such as exposure to light (even very brief exposure), disturbance of the seed in the soil, breaking down of the seed coat, temperature and moisture. Although we don't know all the secrets involved in breaking dormancy, we do know that tillage is a great way of initiating germination of weed seeds. Tillage does several things at once. First of all, by disturbing the soil and the seed, it will often expose the seed to light and allow lots of oxygen to access the seed. Tillage also can scrape the seed coat (called scarifying) and it can create warmer soil temperatures. Any one or combination of these factors can result in breaking the seed dormancy and initiating weed growth. When the soil is disturbed as little as possible, such as in low disturbance direct seeding (LDS), the optimal conditions needed for the weed seeds to germinate are significantly reduced.

Some weeds can also be propagated by underground stems called rhizomes. Quackgrass and Canada thistle are two good examples of this. Tillage, although it can kill the plant, also breaks off and spreads these rhizomes. A new plant can grow from each of these pieces of rhizome. Therefore, while the parent plant may be killed, some or many of these rhizomes can be spread around the field or to other fields if they are not cleaned off the shanks of the cultivator.

Strategies for controlling weeds in a LDS system are varied, but an integrated approach should be considered. This simply means there are a variety of things that the farmer can do to reduce weed problems. By using a combination of weed control methods and not relying on only one method, weed populations can be kept below economic thresholds.

Weed identification is the first step in an integrated approach to weed control. Before choosing the most appropriate control measures, one has to know what weeds are present. Control measures that may be effective for annual weeds often aren't effective on perennial weeds. In addition, if herbicides are being used, one must know what weeds are present that will cause economic losses so the most appropriate herbicide or tank mix can be selected that will be most effective and cost effective.

Different weed species have different life cycles. Times for germination, flowering, seed set and levels of dormancy differ among weed species. An understanding of the biology of each weed present enables the farmer to implement control measures when each weed is most susceptible. For example, to control perennial weeds like Canada thistle in the cereal crop a pre-harvest application of glyphosate can be very effective. This can be followed up with a post-harvest glyphosate treatment the next year in the broadleaf crop to finish off any remaining perennials.

Weeds like consistency. Consistency allows weeds to select for surviving that particular practice. Seeding a field the same time each year with the same crop and herbicide is a good example of providing consistency. A diverse rotation forces the producer to seed the field at different times each year (for example, seeding early one year with peas and a few weeks later the following year with a cereal). A diverse rotation also forces the farmer to use different herbicide groups, which will significantly reduce the chance of weeds being selected that are resistant to a certain herbicide group.

Using clean seed, free of weeds at seeding time will also help reduce the introduction of weeds onto a field. Good quality seed that is vigorous will germinate and emerge quickly. The growin seedling will then have an advantage over the weeds. The adage "the first one up wins" is very accurate. If the crop emerges before the weeds, the competition of the crop will reduce the number of weeds and their impact on yield. For this reason, a pre-seeding burnoff with glyphosate is very effective in LDS systems. Research has shown that in-crop herbicides applied within the first couple of weeks after crop emergence have the greatest effect on reducing the impact of weeds on the yields of most crops.

To summarize, anything a producer can do to give the crop an advantage over weeds will provide an opportunity for the crop to maximize its yield potential, providing the weather also cooperates.

Chapter I | Chapter II | Summary of Opener/Rotation Study

Chapter II

Weed Identification:

Identifying weeds is the first step in weed control. You have to know what are the problem weeds in your fields before you can institute a strategy for control. There are a number of weed identification books that one can purchase to carry while scouting fields. A couple of good books are: Weeds of the West, by Tom D. Whitson, Larry C. Burrill, Steven A. Dewey, David W. Cudney, B.E. Nelson, Richard D. Lee, and Robert Parker, published by The Western Society of Weed Science and Weeds of the Prairies by Alberta Environmental Centre and Alberta Agriculture

There following websites can help identify problem weeds and they also have good information on weed control.

http://www.agr.gov.sk.ca/ (click on crops, then Integrated Pest Management)

http://www.psu.missouri.edu/wheatx/

http://www.gov.mb.ca/agriculture/index.shtml

http://www.agric.gov.ab.ca/

Depending on the growth stage, it can sometimes be difficult to identify a particular weed. Or the guide books may not include the particular plant. In those cases, a sample of the weed can be taken in to an agrologist like such as the local Extension Agrologist with Saskatchewan Agriculture and Food or an agrologist in private industry. When bringing in a weed sample for identification, it is important that the plant is in good condition. Samples that are wilted or dried right out make it difficult or even impossible to identify.

Once the problem weeds are identified, the next step is deciding on the best strategy for controlling the weeds. An integrated approach uses a variety of strategies for weed control and does not rely strictly on herbicides for control. Crop rotation and time of seeding are two good examples of being able to influence weed densities and species. Many producers underestimate the effect crop rotation has on weeds. Different crops have various levels of competition for weeds and differ in when they are most competitive in their life cycle. Herbicides are grouped according to their mode of action. A crop rotation using a diversity of crops allows herbicides from different groups to be used, reducing the odds of resistant weeds developing.

The Guide to Farm Protection is produced by Sask Ag and Food each year and contains good information on each herbicide and it's free! The guide comes out each year in early January at the Crop Production Show in Saskatoon, and each Rural Service Centre will have copies available soon thereafter. It is also available to view online at http://www.agr.gov.sk.ca/ (click on Crops, then Integrated Pest Management then Crop Protection Guide). You will need Acrobat Reader© to read it, but it can also be downloaded free of charge from that same web page.

Since there is good information on herbicides widely available, this section will focus more on problem situations or weeds.

Perennial Weeds:

In low disturbance direct seeding, often there is a shift in weed problems from annual weeds to perennial weeds, such as Canada thistle, quackgrass, foxtail barley or dandelions, to name a few of the worst. To implement a weed control strategy, the first thing to do (and this applies to all farming systems and for monitoring all weeds) is to scout fields regularly. If perennial weeds begin to show up in a field, there is no reason to panic. Although they are difficult weeds to control, control has a greater chance of success if control measures are taken just as the weeds begin to invade a field, before they build a large population.

Glyphosate will play a big role in controlling perennial weeds. Timing of the glyphosate application is most important. Although a pre-seed burn-off occurs in most direct seeding systems, a 0.5 L/ac rate will not control perennial weeds. However, a pre-harvest application of glyphosate of 1-2 L/ac, depending on weed and conditions can be very effective in controlling such weeds. While a higher rate of glyphosate is used, most often, it is the timing of application that makes the treatment so effective.

Many perennial weeds have rhizomes or develop deep taproots. Spring applications of glyphosate can certainly control new perennials that are just developing from seed. However, those established plants that have large and deep taproots or have started from rhizomes or are a couple years old, are very difficult to kill, even with high rates of glyphosate. The reason is that during the early growing season, the plant is using energy and nutrients from the roots as it grows. In other words, the direction of flow is from the roots to the leaves. Herbicides applied early in the spring likely get top-growth suppression, but the roots are still viable. The trick is to apply a herbicide like glyphosate when the perennial plant is most susceptible, late summer or early fall. This is the time when the nutrient flow is moving from the top-growth down into the roots as it stores energy for the winter. Glyphosate applied at this time will be moved down into the roots and rhizomes, thereby killing the whole plant. Pre-harvest tends to be an excellent time for this process to occur. Although post-harvest can also be very effective, the plant generally has to be allowed to re-grow somewhat in order for the glyphosate to be moved through the plant. As a result, the time required for a perennial weed to re-grow after harvest may be limited under very dry conditions or early frosts. Higher water volumes are often required to ensure penetration of the crop canopy when spraying at pre-harvest.

Crop staging is as important as timing of application for effective weed control. Apply too early, and crop yield can be reduced. The crops that glyphosate can be applied to in a pre-harvest application will depend somewhat on manufacturer, as will the weeds registered for control.

For specific perennial pre-harvest weed control timing and crop staging, the Monsanto website www.farmcentral.com offers good information on this subject.

There are some suggestions to keep in mind that the Monsanto site does not cover. One thing to remember is that if post-harvest glyphosate is to be used on Canada thistle, the plant needs to have some time to re-grow before glyphosate should be applied. In addition, it will be necessary to increase the rate of glyphosate since the re-growth tends to have a thicker cuticle and waxier surface. As a result it is more difficult for the herbicide to get into the plant. Although post-harvest treatments of glyphosate can be very effective, the window of opportunity for such an application can be quite short because of weather, especially if the weed needs to re-grow before an application will be effective.

Foxtail Barley

Foxtail barley, like other perennials, can be effectively controlled with a pre-harvest treatment, provided some of the plant is still active and has not gone into dormancy. Drought and extended periods of heat do cause this weed to go dormant, at which time no herbicide will be taken up. However, late summer or early fall precipitation will cause foxtail barley to become active again thereby making it susceptible to a glyphosate treatment.

Winter Annual Weed Control

Although the practice of applying a herbicide in the fall for winter annual weeds has been around for quite some time, it isn't practiced as much as it could be. A phenoxy type of herbicide such as 2,4-D or Banvel can be effective in controlling winter annual weeds like stinkweed and flixweed. These two weeds can create significant problems in the spring due to their early development. A caution is necessary when deciding what herbicide to use for winter annual control. The choice will depend on what weeds are the target and the crop being planted the following spring. If a perennial like dandelion is also being targeted, a glyphosate will need to be included in a tank mix. 2,4-D or Banvel are good choices for fall winter annual control if a cereal crop is being planted the following year. Due to their residual properties, they should not be used in the fall before crops such as pulses or oilseed crops are to be planted. However, research is showing that low rates of 2,4-D (up to 6 oz/ac) can be used the fall before field peas are planted. However, bear in mind that clay soils have more buffering capacity than sandy soils.

Narrow-Leaved Hawk's-Beard

Narrow-leaved hawk's-beard is a growing weed problem. It has the unusual ability to be an annual or a winter annual weed. Pre-seeding burnoff, in-crop herbicide treatment, coupled with a fall application of 2,4-D, Banvel or glyphosate can be very effective in controlling this weed. However, it does tend to take a fairly high rate of 2,4-D in the fall for control. As a result, if a pulse or oilseed is to be planted the spring following the fall treatment, glyphosate should be used instead of Banvel or 2,4-D as the residuals left by these herbicides, especially at the higher rates, can cause serious problems for next spring's crop.

Weed Control in Chickpeas

Few other crops have so few herbicide options for broadleaf weeds as chickpeas. To date, only Sencor® has been registered for broadleaf control in-crop, but unfortunately, it does not control some key problem weeds, namely kochia, flixweed, wild buckwheat, Russian thistle, and redroot pigweed. Another complication is that few crops are as sensitive to herbicide damage as are chickpeas.

Rick Holm et al. has prepared a report entitled "In Search of Effective Herbicides for Chickpeas." First published in the proceedings of the 2001 Western Canadian Agronomy Workshop in Lethbridge, this report answers many of the questions associated with weed control in chickpeas. It is included below in its entirety.

In Search of Effective Herbicides for Chickpeas.

F.A. Holm1, K. Sapsford1, E. N. Johnson2, R. McVicar3 and K. Kirkland4.

1Crop Development Centre, University of Saskatchewan, Saskatoon, SK,

2Agriculture and Agri-Food Canada, Scott, SK.,

3Saskatchewan Agriculture and Food, Regina, SK.

4Kirkland Crop Tech, Vermilion, AB

Introduction:

In general, chickpeas are poor competitors with weeds and are more sensitive to many herbicides than other pulse crops such as field peas and lentils. This is especially true in the case of post-emergence herbicides for the control of broad-leaved weeds. Therefore, herbicide choices for broadleaved weed control are limited and hard to control broad-leaved species can cause significant problems for chickpea producers. To date, relatively few herbicides have been registered on this crop. The responses to the following 13 questions provide a summary of our experience to date with the use of herbicides on this crop.

Question 1. Are any pre-emergence herbicides safe to use on chickpeas?

Chickpeas have good tolerance to both trifluralin (Treflan®, Rival®, several other trade names) and to ethalfluralin (Edge®). In extensive testing of pre-plant incorporated applications at Saskatoon and other locations in Saskatchewan, Edge® has been safe to use on the crop. In some cases, very slight effects on the crop have been noted from spring applications but this has not affected time to maturity or seed yield. No crop injury has been noted when Edge® was applied in the fall. Desi and Kabuli types appear to be equally tolerant to these herbicides.

Question 2. Are any of these products registered for use on chickpeas?

No. New use patterns for these herbicides have not been approved in Canada for a considerable length of time. We do not know if or when Edge® will be registered for use on this crop.

Question 3. Could I use Avadex® or Fortress® on chickpeas?

To our knowledge, these products have not been tested on chickpeas. Based on their mode of actions and their use patterns in other crops, we would not expect them to injure chickpeas. However, they are not registered and, therefore, should not be used.

Question 4. What about post-emergence products for annual grass control?

Chickpeas have excellent tolerance to Group 1 herbicides. Both Poast® and Select® are registered for use on both types of chickpeas. Rates are the same as for other crops and applications should be timed for optimum grass control, as crop safety is not affected by crop stage.

Question 5. What about post-emergence herbicides for broad-leaved weeds?

Sencor® is the only post-emergence product that is registered for control of broad-leaved weeds in chickpeas. Both types of chickpea are considerably more sensitive to this herbicide than are lentils. Early application is critical in order to minimize crop injury. Apply the herbicide any time from ground crack (crop just starting to emerge) until the plants are about 6 cm (2.5 inches) tall (plants have 1 - 3 above ground nodes). Delaying application past this stage will result in excessive leaf burning that can delay maturity and, in some cases, reduce yield. Application of Sencor® to 15 cm (6 inch) tall chickpeas has reduced yield by up to 40% in our trials. Sencor® is not registered for use on soils with less than 4 % organic matter and chickpeas should be seeded at least 5 cm (2 inches) deep.

Early application is also necessary in order to achieve acceptable weed control. Delaying application in order to control late emerging weeds is not recommended as the earliest emerging weeds compete most strongly with the crop and will be the most difficult to control if treatment is delayed. Weeds should be no more than 5 cm (2 inches) in height or diameter.

In chickpeas, Sencor® is registered for suppression of: ball mustard, chickweed, corn spurry, green smartweed, hemp nettle, lamb's quarters, stinkweed, tartary buckwheat, volunteer canola and wild mustard.

Question 6. Can I mix Sencor® with a post-emergence herbicide for annual grass control?

These tank-mixes are not registered and are not recommended as the optimum timing of the two products does not coincide and a tank-mix of the two will result in significantly more crop damage than will result from Sencor® applied alone. Apply the Sencor® first and then apply the grass killer after the crop shows significant recovery from any Sencor® injury.

Question 7. Products like MCPA, Tropotox Plus® Pea Pack® and Basagran® can all be used to control broad-leaved weeds in field peas. Can I also use them on chickpeas?

No. All of these products cause serious injury to chickpeas, even at relatively low rates.

Question 8. Is it safe to apply Odyssey® or Pursuit® post-emergence to chickpeas?

No. In our trials, post-emergence applications of these products, even at reduced rates, have resulted in severe injury to chickpeas that has delayed maturity and, in some cases, reduced yield.

Question 9. Are there any other potential post-emergence options for broad-leaved weeds?

There are two other products that show promise but the prospects of them ever being registered in Canada seem remote.

Pyridate (Lentagran® in Canada, Tough® in the USA) is very safe on the crop and controls a fairly wide spectrum of broad-leaved weeds including Russian thistle and kochia. In other countries it is used on crops such as peanuts, cole crops, oilseed rape, asparagus, alfalfa, red clover, and chickpeas. Application rates twice that needed for acceptable weed control have not caused crop injury in our trials and the product does not leave any soil residues that will interfere with rotational crops. The crop appears to be tolerant at all stages of application.

Sulfentrazone (Authority®) is a pre-emergence or pre-plant incorporated product for control of annual grasses and broad-leaved weeds that has shown promise in more limited testing. It is used on soybean in the USA and is being developed for use on sunflower. Crop tolerance was good in preliminary trials in 2000 but its weed spectrum has not yet been well defined.

A major concern is that this product persists in the soil. In the USA, cereals, alfalfa, and dry beans can be grown the year following application but there is an 18-month re-cropping interval for flax, lentil and mustard and a 30 month re-cropping interval for canola and potatoes. We are conducting re-crop trials this summer to identify potential re-crop problems.

Question 10. I've heard that some growers apply a light rate of imazethapyr (Pursuit®) along with the glyphosate burn-off prior to emergence of chickpeas. What has the research experience been?

Yes, some growers are using an unregistered tank-mix of glyphosate + 25% - 50% of the recommended rate of Pursuit® for their direct-seeding burn-off treatment. This treatment has shown mixed results in research trials. When light rain falls shortly after (within a few days) application, residual weed control from the Pursuit® has often been quite good. However, if no rain falls for an extended period after spraying, weeds can emerge through the herbicide. At 25% of the recommended rate, weed control has not been satisfactory in the majority of cases in our trials. Growers should be reminded that Pursuit® is not registered for use on chickpeas and not on any other crop in the area where chickpeas are grown.

Some crop injury has been noted with this treatment and this has often been temporary but growth of the crop can be slowed down or even stopped for a period of time and this can result in delayed maturity. The greatest amount of crop damage has been noted when heavy rain has fallen shortly after application. It is believed that this results in the herbicide leaching into the root zone of the young crop plants, thus increasing the amount of herbicide taken up by the crop.

Tolerant legume crops are not injured by these herbicides because they can metabolize the herbicide, thus breaking it down into harmless compounds. Some legumes, such as peas and alfalfa, apparently can break down the herbicide more quickly than other, more sensitive, species such as lentils and chickpeas. Therefore, the degree of damage suffered by these more sensitive crops is very likely influenced by the rate of uptake of the herbicide into the plants and the rate of breakdown of the herbicide in the plant, both of which will be affected by soil moisture and air temperature. Conditions that result in slow plant growth (therefore low rates of metabolism) may result in increased crop injury and a prolonged recovery period and yield loss.

Question11. Are there any residue carry-over concerns when using Pursuit® at these reduced rates?

It depends. In re-crop trials on a heavy clay soil with 3.5 - 4.0% organic matter and a soil pH of 7.8, cereals and canola have not been injured the year following treatment. However, on lighter textured soils with lower organic matter and/or low pH (below 7.0), these crops can be injured when they are grown the following year. We would expect canola (except Clearfield canola) to be severely injured and we would not recommend seeding oats the following year. Barley, durum and spring wheat could also be affected. Reduced tillering, delayed maturity and reduced yield can be expected on lighter textured soils, especially those with lower organic matter levels and/or a pH below 7.0. Barley and durum appear to be more sensitive to Pursuit® residues in soil than does spring wheat.

Application of 1/3 the recommended rate of Pursuit® is approximately equal to application of the recommended rate of Odyssey® in terms of soil residual potential. The degree of risk to susceptible rotational crops cannot be accurately predicted because it is the result of a combination of herbicide application rate, soil texture, soil organic matter, soil pH and the soil moisture content throughout the year of application and the subsequent year. Breakdown of the herbicide in soil is most rapid when the soil is moist; therefore, residue carry-over will be greater following a dry growing season. Lowest risk would be with a combination of fine textured soil, relatively high organic matter, pH above 7.0 and good moisture throughout the growing season and into the next year. Conversely, a sandy soil, low organic matter, pH less than 7.0 and dry weather would be high risk for susceptible crops grown in the rotation. Notwithstanding all of the above, we would expect that a dry growing season following application of a 1/3 recommended rate of Pursuit® will likely result in herbicide carry-over levels that will damage cereals or canola planted in the following year. It should be remembered that is not registered for use in the brown and dark brown soil zones.

Question 12. What can I use to control perennial broad-leaved weeds like Canada thistle and sow-thistle in chickpeas?

Nothing. There are no selective herbicides that will control these weeds in this crop. If perennial weeds are a problem in fields intended for chickpeas, they should be controlled in other years of the rotation. Products containing clopyralid (Lontrel® based products) should not be used because of soil residue concerns. Thus, the only practical alternative is a glyphosate treatment. Pre-harvest is the preferred timing.

Question 13. Can I use Reglone Pro® to desiccate chickpeas?

Data to support the registration of Reglone Pro® for desiccation of chickpeas has been submitted. Chickpea is a long season crop so it is important to remember that use of a desiccant does not speed up the maturity of the crop. The seed MUST be mature before the desiccant is applied. Desiccants merely speed the dry-down of the vegetation and can reduce the time from seed maturity to harvest. In general, in our trials, treatment with Reglone Pro® has had minimal effect on the rate of dry-down on the pod material of the Kabuli type. It was much more effective on the Desi type.

Growers should not use this treatment unless and until it becomes a registered treatment.

Acknowledgements:

The authors acknowledge the technical assistance of Mr. Gerry Stuber and Ms. Teri Ife, Crop Development Centre, University of Saskatchewan, Mr. Herb Schnell, Agriculture and Agri-Food Canada, Scott, SK, personnel at various Spoke Sites throughout Saskatchewan and the financial support of the Agri-Food Innovation Fund.

On behalf of SSCA, we acknowledge and are grateful of Mr. Holm et al. and the Crop Development Centre at the U of S for permission to re-print this report.

Wick Applicators

An ongoing problem that causes a lot of grief in chickpea and lentil crops is a late flush of kochia. Kochia can cause all sorts of problems at harvest time. Combining green kochia can easily plug a combine and can also stain the seed of the crop, resulting in a loss of grade. Although glyphosate or Reglone Pro® can be used on lentils to kill and dry down kochia, these herbicides cannot be used on chickpeas. Residues of these herbicides are being aggressively being checked and a positive result of a check will result in rejection of your chickpeas for human consumption. However, a wick applicator can be effective in applying a herbicide like glyphosate to the kochia that is taller than the crop. The wick applicator is simply a horizontal wick that is attached to a tube that contains a herbicide. The applicator is attached to a frame with wheels and the height of the wick can be adjusted. Like the wick in a lamp, the wick soaks up the herbicide and the height is set to clear the height of the crop. As the wick comes in contact with the weeds, the herbicide is applied to the weed. Unfortunately, the reduction to crop yield from weed pressure of kochia has already occurred by that time. However, using a wick applicator is intended to kill and dry down weeds like kochia before harvest and minimize harvest difficulties that kochia would cause.

Soil Disturbance and its Effect on Weeds

Low disturbance direct seeding (LDS) also has an impact on weeds and weed densities. Weeds need something to break dormancy. As was mentioned in the introduction of the weeds section, tillage is an excellent method of breaking dormancy of weeds and initiating growth. Low disturbance openers minimize the disturbance of the soil under most conditions. As a result, the less the soil is disturbed, the fewer weeds will grow. As a result, the low disturbance disc openers tend to have to lowest weed densities. However, these disc openers, like most openers, are not suited to every situation and region. They work very well in the Brown and Dark Brown Soil Zones. However, in the Black Soil Zone, there tends to be much more surface mulch. Under moist conditions, this mulch is difficult to penetrate with most disc openers. In addition, an opener that moves this mulch aside and causes the seed row to be relatively free of residue will cause the soil to warm faster and the crop can get a quicker start over the weeds. The old adage of "Whichever one gets out of the ground first wins" is very true.

A study (unpublished) in the Brown Soil Zone at Aneroid looked at varying levels of soil disturbance and its effect on weed densities and on four different crops in a rotation. The low disturbance disc opener tended to result in the lowest weed densities for all crops and tended to have higher yields. The knife, although a low disturbance opener, seemed to take about three years before the weed densities became significantly lower than the spoon and sweep. Although it took three years for the weed densities of the knife to lower, it may take less time for this to occur in the Dark Brown and especially in the Black Soil Zones.

Chapter I | Chapter II | Summary of Opener/Rotation Study

Summary of Opener/Rotation Study

1998-2001

Aneroid, Saskatchewan

Eric Oliver, PAg

Saskatchewan Soil Conservation Association

The objective of this study was to evaluate the effect of soil and seedbed disturbance on weed populations and crop establishment in the Dry Brown Soil Zone. The study also evaluated the agronomic performance of a diverse, extended rotation, with different levels of soil disturbance.

The site is located six miles southwest of Aneroid on a sandy loam soil. The four openers used in this study included an angle disc (Barton Generation I disc), 0.75-inch knife, 2.25-inch spoon and a 12-inch sweep. All openers were on 9-inch row spacings. Four crops (durum, field peas, barley, and desi chickpeas) were used in the study in a four-year, zero-till rotation. Field scale equipment was used to seed this study (a 15-foot Flexi-Coil 5000 was used on the knife spoon and sweep, a 30-foot unit seeded with the Barton Disc). Plots were the width of the seeding implement (15 or 30 feet wide) and 100 feet long. The four crops (Kyle durum, Delta peas, Harrington barley, and Myles desi chickpeas) were seeded side-by-side with all four openers seeding each crop and the plots were replicated four times for statistical accuracy. The rotation followed a cereal/broadleaf rotation over the four years of the study. Although the crops were in rotation between the plots, the openers were not. In other words, a specific opener seeded a particular plot the entire four years of the study so comparisons between weed densities and yields could be made.

On each plot, weed population counts, crop establishment counts and yields were taken. There was a burnoff treatment with glyphosate (Roundup Transorb) and a no burnoff treatment. Weed counts and crop establishment counts were taken on both treatments to provide an indication of weed populations and its effect on the crop, based on the amount of soil disturbance occurring in the seeding process. Both the pre-emergent burnoff treatment and the non-burnoff treatment had in-crop herbicides applied as required. Two weed counts were taken. The first weed count was conducted just prior to spraying and the second weed count was taken about five or six weeks after the in-crop spraying treatment. The weed counts involved 20-half metre square counts per plot, in which the numbers of each weed species was recorded. Yields of each crop and treatment were taken with a plot harvester.

Results and Conclusions:

Over the four years of the study, the angle disc resulted in having the highest level of crop establishment in all crops and in wet or dry years (Table 1). This was particularly evident in dry years. However, the trend was that over the last two years of the study, the crop establishment of the knife was usually quite close to that of the angle disc. The angle disc also resulted in the greatest reduction of crop establishment when there was no burnoff with a glyphosate. Overall, although the burnoff benefited all crops and all openers, it is evident that the burnoff becomes more important when a lower disturbance opener is being used.

Table 1: 1998 to 2001 crop establishment means (plants/m2).

Burnoff Treatment

No Burnoff Treatment

 

Angle Disc

Knife

Spoon

Sweep

Angle Disc

Knife

Spoon

Sweep

Chickpeas

54.29

43.60

40.63

39.82

46.33

39.96

36.57

36.40

Peas

71.77

57.68

55.67

55.80

63.91

56.47

55.08

54.33

Barley

110.81

92.52

75.43

70.24

100.18

86.52

64.64

66.85

Durum

103.84

97.35

88.87

84.28

96.35

90.06

81.91

79.81


First Weed Count:

The first weed counts were taken just prior to the in-crop herbicide treatment. Over the four years of the study, the general trend was that the higher the level of soil disturbance at the time of seeding, the higher the weed density, particularly in the last two years of the study. The means of this four-year study can be a little misleading in that it is too short-term to reflect and indicate the effects of using each opener over the long term. As an example, the four-year average (Table 2) doesn't indicate it, but the trend observed over the last two years of the study indicated

Table 2: 1998 to 2001 first weed count means (weeds/m2).

Burnoff Treatment

No Burnoff Treatment

 

Angle Disc

Knife

Spoon

Sweep

Angle Disc

Knife

Spoon

Sweep

Chickpeas

59.64

92.63

101.09

99.26

87.55

108.28

102.40

105.55

Peas

68.58

92.83

103.88

125.10

134.90

110.48

102.75

150.85

Barley

53.94

80.81

123.56

116.74

78.08

99.15

124.78

147.23

Durum

65.13

112.33

112.60

120.68

83.45

130.55

128.83

132.40

there was an increasing density of weeds associated with higher levels of soil disturbance at time of seeding which is also reflected at the time of the first weed count (Figure 1). The short-term advantages of the sweep and the time required for the weed densities of the knife to become reduced mask what the trend was clearly showing over the past two years.

Figure 1: 2000-2001 1st Weed count means (weed/m2) in burnoff treatment.

The study also indicated that the advantages of the sweep are more short-term and over the longer term, sweeps do not provide the weed control as many producers expect. As with crop establishment, all openers had fewer weed densities with a Roundup burnoff treatment compared to no burnoff in most years. The less soil disturbance caused by the opener, the more important the burnoff becomes (Table 2).

Another trend was that there was more of a separation in weed densities between the lower disturbance openers and the higher disturbance openers. In addition, although the angle disc still had lower weed densities overall, the difference between weed densities of the knife and the angle disc had become much less. A noticeable improvement in the knife began in 2000 and was much closer to those numbers produced by the angle disc by 2001. The difference in time between the knife and angle disc in response to reducing weed populations is likely due to the angle disc having so little soil disturbance. With the angle disc, it is immediately evident that fewer weeds germinate in response to low soil disturbance. The knife, although it is a low disturbance opener, does cause much higher level of soil disturbance than the angle disc, but generally not enough disturbance to cause significant weed control as compared to the sweep. After a few years, the weed seed bank is reduced under lower soil disturbance. This results in a lower weed density, but it took a few years before this occurred with the knife.

Second Weed Count:

The second weed count was undertaken about five or six weeks after the in-crop herbicide treatment to all the plots. The second weed count can indicate the level of control and the level of potential weed problems that may be encountered in the subsequent year.

As observed in the first weed count, the less the opener disturbs the soil, the lower the weed populations (Table 3). The benefits of the burnoff treatments also tended to carry over throughout the growing season with all openers in most years. Another trend observed was that

Table 3: 1998 to 2001 second weed count means (weeds/m2).

Burnoff Treatment

No Burnoff Treatment

 

Angle Disc

Knife

Spoon

Sweep

Angle Disc

Knife

Spoon

Sweep

Chickpeas

37.9

65.7

63.5

58.0

42.4

74.9

65.7

65.7

Peas

21.0

28.4

35.2

39.6

24.1

26.8

36.1

39.2

Barley

18.7

31.4

69.2

55.0

30.5

41.0

76.8

63.1

Durum

28.9

55.5

52.9

59.8

33.5

58.9

59.2

66.4


over time, there were increasing densities of perennial weeds like foxtail barley and Canada thistle occurring in the no burnoff treatments, primarily with the angle disc treatments and to a lesser degree, the knife. The annual Roundup burnoff tended to keep these perennial weeds at bay. This reinforces the importance of a burnoff with low disturbance openers.

Crop rotation also had a major impact on weed densities. Peas consistently had the lowest weed densities throughout the study (Table 3). Although peas provide very good competition to weeds, the type of herbicide used also had a significant effect on weed densities and on the subsequent cereal re-crop. The peas were treated in-crop with Odyssey and as a result, usually had significantly lower weed densities. This herbicide has residual aspects that resulted in far fewer broadleaf weeds in the peas as compared to other crops. Cereals had significantly lower broadleaf weed densities when they were seeded onto pea stubble that had been treated with the herbicide Odyssey. When comparing the grassy vs. broadleaf weeds, it was evident that broadleaf weed densities were significantly lower in the cereal crop on pea stubble than those in the other crops and was observed at the first weed count (data not shown). Chickpeas provide very little competition to weeds and also have very limited broadleaf herbicide options. As a result, there are usually higher weed densities found in chickpeas. In addition, the cereal crop following chickpeas will also have higher weed populations to deal with.

Yields:

Over the four years of this study, the very low disturbance angle disc consistently produced the highest yields in all crops (Table 4). The yields using the knife have become closer to those of the angle disc, but it took three years before this gap began to narrow. As noted earlier, it appears that there is a delay in realizing the benefits of a knife whereas the response to using a low disturbance disc is immediate.

Table 4: 1998 to 2001 yield means (bu/ac).

Burnoff Treatment

No Burnoff Treatment

 

Angle Disc

Knife

Spoon

Sweep

Angle Disc

Knife

Spoon

Sweep

Chickpeas

22.43

20.47

18.92

17.42

18.71

18.56

16.41

17.34

Peas

35.82

31.49

31.46

31.59

31.48

29.85

32.04

30.20

Barley

30.59

28.02

24.26

24.82

27.08

26.57

26.08

24.48

Durum

21.40

19.91

17.53

18.37

17.75

17.01

16.94

16.71


Over the four years of the study, a Roundup burnoff resulted in a yield benefit in all openers regardless of level of soil disturbance in most years. However, the lower the level of soil disturbance by the opener, the more important it is to include a pre-emergent burnoff in the operation. Not all years showed a yield benefit in the burnoff treatment for the high disturbance openers. A longer study would indicate whether a pre-seed burnoff is necessary for high disturbance openers. Another trend that would require a longer study to confirm is that the advantages of the sweep tends to be rather short-term. The longer a sweep is used, the higher the weed densities become in comparison to lower disturbance openers, and the yields are correspondingly lower. In addition, a longer study would also indicate how close to the yields and weed densities of the angle disc openers the other openers could become.

Table 5 shows the differences in yields from Table 4 for each opener when compared to the angle disc with the burnoff treatment. For example, the chickpea yield using the knife with a burnoff treatment had 1.96 bu/ac less yield than the angle disc. The sweep yielded an average of 5.01 bu/ac less than the angle disc. This table indicates that over time, the knife will yield close to that of the very low disturbance angle disc. Under dry years, the difference in yields between low and high disturbance openers can be much higher.

Table 5: Yield difference (bu/ac) between angle disc in burnoff treatment and other openers, 1998-2001.

Burnoff Treatment

No Burnoff Treatment

 

Knife

Spoon

Sweep

Angle Disc

Knife

Spoon

Sweep

Chickpeas

1.96

4.33

2.57

1.50

3.52

5.01

3.72

3.87

6.02

5.09

Peas

4.36

4.23

4.34

5.97

3.78

5.62

Barley

6.33

5.77

3.51

4.02

4.51

6.11

Durum

3.88

3.04

3.65

4.39

4.46

4.69


If we attach a value to the yield differences, a more definite economic picture can be observed (Table 6). For comparison purposes, the average price per bushel for each crop over the four years of the study is as follows:

Desi chickpeas $7.80/bu

Field peas $3.75/bu

Malt barley $3.25/bu

Durum $4.00/bu

Table 6: Value of yield difference between angle disc in burnoff treatment and other openers, 1998-2001 ($/ac).

Burnoff Treatment

No Burnoff Treatment

 

Knife

Spoon

Sweep

Angle Disc

Knife

Spoon

Sweep

Chickpeas

15.29

16.24

8.35

6.00

27.46

39.08

29.02

30.19

46.96

39.70

Peas

16.35

15.86

16.28

22.39

14.18

21.08

Barley

20.57

18.75

11.41

13.07

14.66

19.86

Durum

15.52

12.16

14.60

17.56

17.84

18.76


Table 6 indicates the average dollar value per acre of the various crops and openers. The table shows some significant differences in return based simply on the opener used. For example, the sweep returned an average of $39.08/acre less than the angle disc in chickpeas. The two high disturbance openers consistently produced much less return than the angle disc or even the knife.

Conclusions:

A very low disturbance disc openers, such as was used in this study, has shown significant advantages in lower weed densities, higher crop establishments and yields in most years and in wet and dry years in the Dry Brown Soil Zone. These advantages occurred immediately with the angle disc opener. Although the knife opener eventually produced lower weed densities and higher yields than the spoon or sweep, these improvements didn't occur until the third year of the study. The advantages of the spoon and sweep tend to be relatively short-lived and consistently produced significantly higher weed densities and lower yields on all crops, especially in the last two years of the study. A longer study would have more accurately shown the long-term potential of the knife in comparison to the much lower soil disturbance opener of the angle disc. A longer study would also more accurately reflect the effects of high disturbance openers like the sweep.

Overall, the angle disc or any similar very low disturbance disc opener has a tremendous potential for the Dry Brown, Brown and likely the drier parts of the Dark Brown Soil Zones. However, personal anecdotal experience using the angle disc indicated problems with consistent seed depth in stony soil and with very dry soil conditions. The knife also has shown to have very good potential in maximizing yields while initiating less weed growth as compared to high disturbance openers. However, unlike the angle disc, there is a lag time before this occurs and producers need to be aware of this lag when making opener choices. The high disturbance openers are often the first choice of producers who switch from conventional farming practices and move into a single pass seeding system. The choice of the sweep is often based on the premise that good weed control will be obtained by using the sweep and there won't be any consequence to yield. However, as this study indicates, any advantage to the high disturbance opener is generally short-lived and after two years, experiences much higher weed densities and lower yields. In addition, under dry years, crop establishment is significantly reduced due to drying down of the seedbed.

Funding for this study included:

1998: Saskatchewan Agriculture and Food, Saskatchewan Soil Conservation Association, SW Regional Council of ADD Boards, and District index.php/weed-control#4 ADD Board.

1999-2001: Canada-Saskatchewan Agri-Food Innovation Fund.