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Control Those Summer Weeds

By K-Line Ag
Published on

A potential problem looms

Uncontrolled heavy weed growth during the summer fallow period can reduce the yield of the next crop by robbing following crops of available soil nitrogen; depleting the soil of stored moisture and reducing crop emergence due to the physical and/or chemical (allelopathic) interference at seeding time.

Controlling summer weeds early will conserve valuable soil nitrogen and moisture for use by the crop during the following season. Growers have gained an average farm crop yield increase of up to 400 kilograms per hectare with consistent summer weed control.

If left uncontrolled, weed burdens of 2.5 tonnes per hectare can cause a loss of available soil nitrogen and burdens of more than 3t/ha can reduce following wheat yields by as much as 40%.

Chemical control of summer weeds

Growers using zero-till or conservation tillage practices commonly treat emerging weeds with chemicals. Chemical control of weeds is also common in conventional tillage systems.

Summer weed control can be expensive but is necessary to prevent problems with excessive growth and/or moisture and nitrogen loss from the soil. When using post emergent herbicides:

  • Water rates should be kept high (at least 60 litres per hectare).
  • Add a surfactant and/or spraying oil unless otherwise directed on the label.
  • Do not spray stressed plants.
  • Spray grazing can be effective at high stocking rates.
  • Glyphosate, 2,4-D, metsulfuron, atrazine and triclopyr are the most common herbicides used for summer weed control.
  • Where summer grasses are present, glyphosate at rates around 2L/ha are generally required.
  • Metsulfuron provides cheap control of wireweed, triclopyr is generally preferred for melon control and atrazine for small crumbweed (also known as mintweed or goosefoot).
  • 2,4-D controls a wide range of broadleaved weeds and is preferred if stock are available for spray grazing. The ester formulations are usually more effective for summer weed control.
  • Moisture stress in weeds is common in summer and reduces the effectiveness of most herbicides. This can be partially overcome by spraying early in the morning. However at this time of day, inversions may be present which could lead to excessive drift. Avoid spraying during still conditions.

Monitor for problem weeds

There are a number of weeds that are likely to present challenges over the coming summer period. The challenges lie in the fact that some of these weeds are spreading through cropping districts to a greater extent, and second, most seriously, some are showing resistance to herbicides.

The weed species likely to cause problems this summer in the major cropping districts are Feather Top Rhodes grass, melons, wire weed, and fleabane.

Let’s briefly consider each in turn.

Fleabane

Fleabane (Conyza spp.) seeds normally germinate at 20°C, so greatest germination occurs in spring and early summer. Following rain there is an initial rapid germination of seed. The seed bank can last for over three years.

Research suggests that most fleabane seeds germinate from the soil surface with very few seeds germinating from below 1cm. This suggests that the recent fleabane problems are made worse as a result of the switch from conventional to minimum tillage systems. These low disturbance tillage systems are less likely to bury seeds below 1cm depth and provide moist conditions for better emergence of seeds that germinate on the soil surface.

Fleabane may often germinate in spring and early summer prior to harvest. Once the crop is removed, the fleabane has no competition for light or moisture and can grow rapidly, especially with further summer rain. By the time there is a window for control, the fleabane are often mature, with a high tolerance to most herbicides.

Control

As is the case for most weeds, fleabane plants can most effectively be controlled with chemicals when they are emerging, mainly in early spring while they are still small. Small fleabane plants are relatively easy to kill and a late post-emergent application of some Group 1 (phenoxy) herbicides during spring can control them in cereals.

Mature fleabane can be difficult and expensive to kill, especially in mid to late summer. Strategic tillage should be considered as an option to chemicals, but if herbicides are the best choice, trials indicate that the best control of large fleabane in stubble used a ‘double-knock’ approach with a range of primary herbicides followed by paraquat 7-10 days later.

The most effective treatment was an application of glyphosate (540g/L) at 2L/ha or a mixture of glyphosate (540g/L) at 2L/ha and 2,4-D amine (625g/L) at 2L/ha with a follow up spray of paraquat at 2L/ha seven days after the initial treatment.

Feathertop Rhodes grass

Feathertop Rhodes grass (Chloris virgata), with its distinctive seed head, is steadily travelling across the country. Its prolific seed production and ability to withstand herbicides makes this weed difficult, but not impossible, to control.

The key is to concentrate on preventing seed set. Feathertop Rhodes grass seed is relatively short-lived in the soil, so with a dedicated focus it is possible to run down the seed bank reasonably quickly.

This requires an integrated and intensive management approach; there are no silver bullets for easy management.

Control

As mentioned, for successful control, seed set must be stopped or minimised to break the life cycle and reduce future weed burdens.

Large weeds (>10 cm, tillering or with seed heads) are very difficult to kill with knockdown herbicides.

Small, actively growing weeds (< 5 cm, pre-tillering) should be targeted when using post-emergence herbicides.

The double-knock tactic is very effective, particularly with a Group A herbicide followed by a Group L herbicide. The knock interval should be at least 7 days for maximum effectiveness; adding residual herbicides to the second knock may improve the Group L knockdown.

The effectiveness of pre-emergence herbicides (residuals) can be maximised by applying them when the soil surface has very little or no weed cover.

Escapees and survivors should be monitored and spot treated as soon as possible.

Strategic tillage, to bury seed or control large plants, has a role to play. Removing mature plants by cultivation can be very effective. Burial of seed below 5cm can also reduce emergence and this seed will lose viability within about 12 months (providing it is not subsequently returned to the soil surface by further tillage).

While an effective cultivation may bury the vast majority of seed, there is always a small percent of seed remaining at the soil surface in the preferred germination zone. If something is not done to prevent these seeds from germinating and establishing, then the cycle recommences.

A plan should be in place to manage these subsequent germinations via either tillage, knockdown or residual herbicides.

Competitive crops and cultivars should be planted, and narrow row spacings and high crop populations used where possible.

Commitment to two summers of 100% control of Feathertop Rhodes grass should deplete the seed bank in the soil.

Melons

Paddy melon (Cucumis myriocarpus) and Afghan melon (Citrullus lanatus) are both prostrate annual melons germinating in spring and summer. Their growth is favored by good moisture relations and bare or fallowed paddocks. Horse, sheep and cattle losses have been associated with eating the melon but the smell of the plants generally makes them unpalatable.

Control

Grazing is an effective control method after applying low rates of a hormone herbicide to make the melons more palatable.

Another example for melon control in summer might be a mixture of triclopyr, 2,4-D and metsulfuron in the early morning when plants are not stressed. Graze heavily five days after spraying. Increase rates if grazing is not possible.

Prevention of seed set by mechanical removal is feasible on small areas.

Integrated management the key

As you will note from the examples above, many weeds are showing resistance to commonly used herbicides.

To deal with this problem, an integrated management approach should be adopted. This involves having a number of tools in your spraying and cultivation arsenal that you can use as the occasion and weed species demands.

Departments of Primary industries and research and advisory agencies can provide detailed advice on just how each of the resistant weeds should be dealt with.

Common grassy weeds that are showing resistance to Glyphosate are:

  • Annual ryegrass (Lolium rigidum)
  • Annual veld grass (Ehrharta longiflora)
  • Awnless barnyard grass (Echinochloa colona)
  • Barnyard grass (Echinochloa crus-galli)
  • Barley grass (Hordeum spp.)
  • Brome grass (Bromus spp.)
  • Crabgrass (Digitaria sanguinalis)
  • Crowsfoot grass (Eleusine indica).

In most cases, an important tool in an integrated management approach is strategic tillage. Choosing an implement that enables chopping and burying of mature weed plants before seed set, and/or burying weed seed to depths that hinder germination are features that you should look for in a tillage implement.

Two implements that effectively deal with a summer weed problem and also handle carryover stubble are the Speedtiller® by K-Line Ag and its smaller brother, the K-Line Ag Flexi-Mulch®. The Speedtiller® is a high-performing, high speed dual purpose disc-tillage machine that will efficiently cut, size and incorporate high levels of mature or emerging weeds as well as crop residue. Both have the flexibility and adjustments to suit most trash burdens and soil conditions. Soil erosion from wind and water is drastically reduced by the excellent incorporation ability of these implements.

The Flexi-Mulch® is designed specifically for multipurpose use in mid-sized farming operations with 70 to 125 horsepower, 3PL tractors. Both machines are fitted with a crumbler roller that leaves the soil with an even, level tilth, ready for sowing the next crop.

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Strategic tillage a winner in no-till cropping

By K-Line Ag
Published on

What is strategic tillage?

Conservation farming and no-till cropping are now widely practised by the majority of Australian farmers. Most importantly, this approach preserves soil structure, making for less erosion, better moisture penetration and infiltration and improved soil conditions for plant growth. Retained crop stubble can add to the store of soil carbon.

But no-till or zero-till farming can introduce some drawbacks, and strategic tillage seeks to overcome these. The question is: will strategic ploughing cause long-term damage to the soil structure that no-till has sought to improve?

Why use strategic tillage in a no-till system?

A number of research trials have sought to answer this question. Problems with no-till can arise from weed species developing resistance to common herbicides; soil acidity buildup; a deficit of nitrogen in the top soil layers and the possibility of fungal diseases building up on the stubble. Retained stubble can become habitat for mice and slugs and each of these issues can adversely affect following crops.

Some potential advantages of strategic tillage include integrated weed control for weeds that are developing resistance to key herbicides, and the incorporation of lime to depth on acid subsoils. Tillage can also address mice and slug buildup in residue.

Studies throughout the cropping zones show few short term and environmental costs from strategic tillage. Concerns include destruction of soil macro-and micro aggregates that can lead to water erosion and loss through dust. There is no doubt that soil macro-aggregates (larger groups of soil particles with large pore spaces) are temporarily damaged by cultivation. And dust (which is the micro-aggregate portion of soil) can also be lost if conditions allow.

But the research consistently shows that these changes are temporary. Soil physical, chemical and biological fertility in the surface layers (0–20 cm), as well as crop growth and yield were monitored for 5 years.

Trial results give a ‘thumbs up’

The results of several long-term trials suggest that strategic tillage can be a useful strategy to manage limitations of NT systems. Tillage at the right intervals can give benefits such as short term yield improvement, greater profitability and reduced reliance on herbicides.

Soil carbon is certainly reduced initially by tillage, but recovers to previous levels after two years. Soil aggregates were reduced in the top 0-5 cm of soil, but these also recovered within 1-2 years after tillage. Soil pH, total carbon and nitrogen that were confined to the surface layer of soil were redistributed more evenly through the topsoil and remained that way for the 5 years of the trials.

Crop yields of strategic tillage and no-till treatments during the 5 years of the experiment remained the same. Overall, the minor short-term negative impacts on soil structure, the definite beneficial effects on soil chemistry and biology, and absence of impacts on crop production suggest that strategic tillage can be a valuable agronomic tool in sustainable production in many cropping and mixed farming enterprises.

Choosing machinery for strategic tillage

Trials suggest that in most cases, there were no great differences between various strategic tillage implements. In north-eastern Australia, most growers use non-inversion cultivation based on tyne and disc implements. It seems that the type of tillage is less important than the frequency. And in an otherwise no-till cropping program, tillage can be used to address specific issues such as weed control or stubble buildup or allow for deep nutrient placement. Tyne tillage lifts and shatters the soil, removing shallow compacted layers for in-crop weed management, deep placement of nutrients and breaking up hard pans. Disc tillage cuts and mixes stubble and soil clods to leave a fine tilth, considered effective for reducing disease and pests and weed management during the fallow period. Discs are useful for incorporating either lime or gypsum. Both tillage operations are shallow as compared to mouldboard tillage which is seldom used in farming these days.

K-Line Agriculture produces two machines specifically designed to carry out the operations described here: the Speedtiller® and Flexi-Mulch®. The Flexi-Mulch® is the smaller brother to the Speedtiller®. They are both high performance disc implements designed to efficiently cut, size and incorporate high levels of crop residue. Soil erosion from wind and water is drastically reduced by their excellent incorporation ability.

K-Line Ag’s Speedtiller® penetrates soil at the ideal depth and cuts to the desired disc angle. The high-speed discs allow for better trash flow and incorporation, while simultaneously lifting the soil for less compaction. This effectively improves the quality of the soil and helps maximise crop yields.

The Speedtiller® handles heavy residue with ease, moves the soil with a set of fully adjustable offset discs, and the trailing roller bar is an excellent finishing tool for levelling and one-pass seedbed preparation.

The right machine, the right time

Strategic tillage is an invaluable tool for no-till cropping programs. Timing of cultivation has a major impact on the success of any tillage operation.

Soils differ in their reaction to tillage, and there are a number of factors to take into account when deciding if and when to cultivate a no-till paddock. These factors include:

  • the amount of trash or stubble present. This will govern the amount of chopping and incorporation required;
  • the weed burden, weed history, and the likelihood of herbicide resistance;
  • soil type. The most common soils of the cropping zone, Vertosols, are resilient to one-time tillage, while soils with texture contrast (Sodosol) and weakly structured A-horizons (Dermosol) are likely to suffer more temporary damage in the first 3 months of cultivation;
  • soil moisture at the time of tillage. You will want to avoid the risk of soil smearing, compaction and aggregate breakdown;
  • the amount of stored moisture available for plant establishment;
  • the need to incorporate soil amendments such as lime or gypsum. Both need to be incorporated to be effective.

Fortunately, the tools for a flexible program of strategic tillage are on hand. K-Line Ag’s Speedtiller® and Flexi-Mulch® disc tillage implements allow farmers to design a strategic tillage program to meet the conditions they need for success. These machines, designed specifically for Australian farms, can fulfill the needs for a successful strategic tillage operation, producing the benefits of occasional cultivation without cancelling the advantages of a no-till cropping program.

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Time To Think Lime

By K-Line Ag
Published on

Have you got a plan to address acid soils?

Even in conservation farming or no-till programs, strategic tillage can be used for various reasons, but lime incorporation is one of the most compelling.

Applying lime to the subsoil through incorporation with a suitable tillage machine ensures the lime can react with the soil to give the benefits needed for optimum plant growth. Just spreading lime on the soil surface is not recommended, as it may take years for surface-applied lime to do the job, and crop yields may suffer in the meantime.

So if you are preparing to cultivate the soil for this coming season, now is the time to consider whether lime will benefit the coming crop and those that follow.

Assess the need

Soil acidification has been recognised by all state agricultural agencies as a growing problem in Australian cropping and grazing regions. The reasons can be quite complex, but are associated with clearing of native vegetation, movement of groundwater and the geology of a catchment, and the focus on annual crops over perennials.

Ironically, a buildup of soil organic matter, while overwhelmingly beneficial, can eventually lead to soil acidity.

Some crops are much more sensitive to acid conditions than others. Some crops are much more sensitive to acid conditions than others. Cereal crops are more tolerant, while pulse crops such as lentils and faba beans are acid-sensitive. These crops can indicate early the areas that need to be tested for acidity, especially in the subsoil. Until they are grown, however, it is possible for any acidity issues to remain hidden. But by that time, even yields of tolerant crops will have suffered yield losses.

Symptoms in the crop can be confusing, as they may look similar to drought stress or nitrogen deficiency, however, those problems will often occur across the whole paddock, whereas soil acidification is typically patchy.

To assess the need for lime, state agencies have a range of useful tools and calculators available to farmers. These can show the cost of lime, how much return you can receive by investing in lime and also how much lime is needed to treat a paddock for an initial ‘fix’ and then by applying maintenance levels over following years. A single initial application can give benefits that may last up to five years.

A simple soil testing kit is useful, but both topsoil and surface soil in each horizon should be tested to give an accurate indication of the need for lime. Results below a pH of 5.5 will signal a need to raise the levels with lime.

Getting the lime into the soil

Lime moves into the soil very slowly, and if not incorporated can lie, inactive, on the soil surface for a long time. There is no doubt that incorporation, where possible, is the best way of getting the benefits from applying lime.

The neutralising value of lime and its ability to dissolve depends on its fineness and purity, so the source of lime that you use will also be important.

Research has shown that strategic tillage to incorporate lime will speed up the effectiveness of the lime and help neutralise subsurface acidification.

Machinery to incorporate lime is available, and the ideal machines, specifically developed for strategic tillage and lime incorporation are K-Line Ag’s Speedtiller® and Flexi-Mulch® disc tillage implements. Designed in Australia for Australian farmers, these machines are among a suite of implements developed by K-Line Agriculture that will help reverse the problem of acid soils by incorporating lime into the soil where it can do its work.

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