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1 November 2019 Gary Bosley

Controlling yellow bristle grass

I am receiving an increasing number of calls from across the North Island especially the Waikato and Manawatu, about Yellow Bristle Grass (YBG) being found in both pasture and crops, and more particularly maize.

This weed is part of the family of annual grasses known as Seteria, which includes foxtails and millets. YBG originally came from Asia and has spread through Europe, North America and Australasia.Over the last few years, possibly driven by wet winter pugging,

YBG has spread through Taranaki, Waikato, Auckland and the Bay of Plenty, moving from roadsides into paddocks.

YBG does not provide good quality late summer/autumn feed. It is a C4 photosynthetic plant that grows more vigorously at higher temperatures than ryegrass. It becomes dominant through the summer months, reducing the quality of your pasture. Then with winter frosts, the YBG dies out leaving gaps for weed and more YBG infiltration the following spring. 

Germination of YBG seeds typically starts around mid-October when soils are about 16 degrees Celsius and peaks by mid-November when soil temperatures are over 20 degrees Celsius. This is a  similar timing to other C4 weed grasses, such as summer grass, crowsfoot grass, and smooth witchgrass, however due to the size and seed numbers per plant, YBG is far more invasive and  competitive.

The seed heads can normally be seen from late December onwards, but more commonly through January and February. Once these seed heads appear, the seeds are viable and cannot be killed by sprays. Seeds are hard coated and dispersed in water,in hay, on animals and in contaminated crops such as maize. They are dormant for about three months before they can germinate. Germination is driven by soil temperature, so usually new germination doesn’t happen until the following spring. The seeds can last in the soil for up to ten years, although generally only viable for just a few  years.

Because YBG and other weed C4 grasses readily invade run-out or pugged pastures, the best form of control is not to get into the situation in the first place. Avoid allowing flat weeds to dominate and then spray them out, as this leaves a bare patch in the pasture for weeds including grasses to invade.

Top control tips

  • Learn to identify YBG and how it differs from other summer grasses, especially at the vegetative growth stage. One of the most recognisable features of YBG is a bright red stem base. Once identified, you can then isolate the area and treat accordingly.
  • Avoid pasture damage at the key germination timing, from October to December.
  • Remove seed-heads through topping during the summer or tight grazing before the seed-heads appear. Seeds pass through the rumen and land on the ground in a pile of dung ready to germinate the following spring.
  • Spray non-selective herbicide, such as glyphosate, before seed-heads are produced.
  • Whether the YBG is in pasture or crop, for example maize or brassica, there are selective herbicides available that kill the YBG and other summer grasses before they go to seed-head preventing damage to your pasture or crop. Speak to your local PGG Wrightson Technical Field Representative for guidance. 
  • YBG seeds can be killed in a good quality silage pit where increase in temperature and the correct acidic conditions are created during the ensiling process.

For more information on YBG control, get in touch with your local PGG Wrightson Technical Field Representative.


Gary Bosley

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Different soil types require unique management

30 October 2019

This is the third article of a three-part series that takes a closer look at New Zealand soils. This month, I focus on the different management strategies that are required for the four distinct soil types that were discussed in the last issue.

New Zealand soils are generally young (comparatively worldwide), made from inherently different parent materials of different origins. Soil types have varying nutrient availability and respond to applied fertiliser uniquely.

Pumice soils
Pumice soils can recover quickly from intensive grazing, and soil compaction of the topsoil is usually not a problem. However, protecting them from pugging damage is important as they can erode  easily if the pasture is exposed by stock. Cultivation should also be kept to a minimum. These soils are loose, friable, and have a low bulk density which makes them perfect for low/no till methods of planting. Pumice soils are naturally deficient in Phosphorus (P), Potassium (K), Magnesium (Mg) and Sulphur (S) and always need yearly applications of these nutrients if they are to remain  productive. Cobalt (Co) and Selenium (Se) are two trace elements that are lacking in pumice soils and need to be added to yearly fertiliser applications. 

Organic/peat soils 
These soils usually need  some kind of artificial drainage to be productive. Over drainage (drains that are too deep) of these soils can make them dry in summer. This can cause subsidence (sinking soil), poor summer growth and hydrophobicity. By keeping drains shallow and/or controlling the water table, you minimise many of these problems. As for pumice soils, cultivation should be kept to a minimum, and low/no tillage methods are recommended. These soils have high cation exchange capacities, and a naturally low pH. Accordingly, they need larger lime applications to increase or maintain pH than other New Zealand soil types. As these soils often have small amounts of mineral material, nutrient deficiencies are common, especially P and S and some trace elements.

Sedimentary soils
This soil type is the most common soil in New Zealand. It is no surprise it is comprised of many soil orders and groups. So the  management of these soils can only be described at a generic level.  Some sedimentary soils naturally provide considerable amounts of K (from soil clay minerals) for plant growth. Some of these soils are unlikely to require capital applications of K and may not even  require maintenance K applications. Sedimentary soils tend to have medium-to-low Anion Storage Capacity (ASC), and therefore require lower rates of maintenance or capital P fertilisers compared  to other soil types. Given the low ASC, they tend to be responsive to S fertiliser in the spring, especially after a wet winter. Some sedimentary soils are poorly or imperfectly drained and prone to soil damage from grazing animals. Cultivation also has to be carefully timed to avoid soil damage as these soils take longer to dry out than other soil types. Some sedimentary soils can be low in  Molybdenum (Mo) and need periodic applications of this nutrient to ensure optimal clover growth. 

Ash soils
Ash soils include some of New Zealand’s most productive soils, and have naturally good soil structure and bulk density. These soils tend to tolerate the impacts of machinery and grazing animals better than other soil types. Cultivation still needs careful management to preserve topsoil structure, as some of these soils have limited workability when wet. Ash soils generally have naturally low levels of K, and can respond well to K fertiliser. These soils usually have a higher ASC than the other soil types, and therefore need larger amounts of maintenance and capital P fertiliser compared to the other soil groups. These soils also generally tend to have higher sulphate-sulphur levels, again due to the higher ASC.

For more information on your property’s soil type or to arrange a soil test, talk to your local PGG Wrightson Technical Field Representative.

Weed control in new pastures

01 November 2019

New pastures are a great opportunity to lift production and fine tune the production dynamics on your farm.

After sowing your new pasture paddocks, ensure you monitor them as they emerge. Once the clovers are at the two trifoliate stage, it is a good time to assess the weed pressure. Some paddocks can be clean during establishment but many have a resident weed population that emerges at the same time as sowing down the new pasture. Checking the paddock at this early stage allows selection from a range of herbicides that can prevent the weeds competing for nutrient, moisture and light.

Weeds are much easier to control when they are small, so once your clovers have got two trifoliate leaves, check the paddock for weeds. Identifying the weeds at this early stage can be tricky but I  recommend a copy of “A Guide to the Identification of New Zealand Common Weeds in Colour” by E. A. Upritchard. This little red book is a good investment to have in the truck, and shows the most common weeds at the seedling stages. Identification of weeds is required so the correct herbicide can be selected.

A couple of common weeds seen in new pasture are shepherd’s purse and spurrey/yara. Both these weeds have distinctive characteristics. The shepherd’s purse seedlings have distinctive white hair on their leaves in a cross shape, these can be seen with a hand lens. Spurrey/Yara is an interesting weed, the seedling has upright, round leaves which can be mistaken for grass, but it has a distinctive pattern of four upright leaves originating from the stem above ground level. As with many weeds, spending time to get to know them helps with identification. I suggest if you would like some help identifying weeds, contact your local PGG Wrightson Technical Field Representative.

Weeds in pasture often show up where the gaps are. If you have used weed control and left open areas, use some more seed to fill in those gaps and prevent the weeds establishing. This can sometimes happen, even in new pastures where something has gone wrong during establishment.

If your new pastures are patchy with large gaps, consider using the drill to fill in those gaps because weeds do not provide much in the way of value feed for your stock compared to modern productive grass species. Contact your local PGG Wrightson Technical Field Representative who can help.

Foliar nutrition as a management tool

01 December 2019

What is the most important nutrient that a plant needs? The answer to this question is: the one that is the most limiting, also known as the ‘law of the minimum’. This law states that growth is dictated not by total quantity of nutrients that are available, but by the scarcest nutrient.

Crops require 16 essential nutrients to complete their life cycle. Essential plant nutrients are divided into macro and micronutrient groups. Macronutrients are carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sulphur (S). 

Micronutrients include zinc (Zn), copper (Cu), iron (Fe), manganese (Mn), boron (B), molybdenum (Mo) and chlorine (Cl).

Plants require macronutrients in greater amounts compared to micronutrients, although all nutrients are important for plant growth. The first three macronutrients (C, H, and O) are supplied to plants majority by air so their supply to plants is not usually a problem. Ideally, the remaining 13 nutrients should be present in the soil in adequate amounts and proportion for optimum plant growth. 

Nutrient deficiency can occur for a number of reasons: when there is insufficient nutrient in the soil, where pH is significantly high or low, where a significant nutrient imbalance exists, or when they cannot be absorbed and utilised by plants as the result of unfavourable environmental conditions. The impacts of nutrient deficiency can cause many side effects, such as reducing a plant’s ability to fight pests and diseases and interfering with the conversion of nutrients into the proteins that are required for plant growth. 

Crop nutritional needs are supplied via the soil by applying capital and maintenance fertiliser. The quantity of solid fertilisers applied is usually based on soil test results, but these are mainly useful for macronutrients (soil testing for micronutrients is unreliable) and only report what is available for the growing 

crop instead of what the crop has actually taken up. There may be a need to look at complementary alternatives, such as foliar nutrition, to remedy nutrient deficiencies. Foliar nutrition is mainly based on plant tissue tests, which identifies nutrient deficiencies in the crop at the time of testing.

The purpose of foliar nutrition is not to replace soil fertiliser, as this is the most effective and economical means of supplying a plant’s macronutrient needs. The benefit of foliar nutrition is that it is an excellent method of supplying plant requirements of micronutrients (such as Mn and Mo), while supplementing any N, P and K needs for short-term growth. It is also a quick and effective management tool to favourably influence the growth of plants that have been compromised by environmentally induced stresses, such as adverse growing conditions and/or poor nutrient availability. Some of the main benefits of foliar nutrition are: 

  • Rapid correction of nutrient deficiency with immediate uptake of applied nutrients.
  • Accurate and even application of small amounts of key elements.  
  • Providing plants with certain micronutrients that may not be readily available in the soil.
  • Can be combined with other foliar chemicals, minimising application expenses.

Contact your local PGG Wrightson Technical Field Representative for advice or help with foliar nutrition.

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