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1 November 2019 Matthew Crampton

Weed control in new pastures

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.

Matthew Crampton

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Controlling yellow bristle grass

01 November 2019

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.


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.

Don't let disease rob your maize crop

01 December 2019

Maize gets a number of diseases and they can all affect the final yield, but one of the most damaging is Northern Leaf Blight (NLB) caused by the fungus Exserohilium turcicum. 
NLB overwinters in infected maize leaves, husks and trash from the previous crop. The NLB fungal spores are produced when environmental conditions are favourable in the spring and early summer; then with the aid of rain splash and wind, NLB infects the new plant growing in the same or neighbouring paddock.

New developing leaves that are exposed to periods exceeding 12 hours of wet or damp conditions and temperatures between 18 to 27 degrees are susceptible to infection from NLB if the fungal spores are present. Then heavy dews and warm humid conditions spread the disease rapidly and move the infection to the lower leaves and cob. The most common and most damaging time for infection in New Zealand is December to January.

Yield loss from NLB is driven by the loss of leaf area. With weather conditions favouring infection from the early tassel stage in the crop, yield can be impacted by as much as 30 percent. With an infection later than this stage, the impact is considerably less and there is an increased risk of lodging.

So what can you do to manage the risk?

  1. Crop rotation
    Growing maize crops back-to-back in the same paddock increases the amount of inoculum passed from one crop to the next, so try to avoid this.
  2. Maize grain
    Crops of maize grown after a maize grain crop are more susceptible to infection than after a silage maize crop because more stova is left after harvest.
  3. Cultivation
    If you fully cultivate after harvesting the maize, burying all of the residue, then there is less plant material to infect. Direct drilling, minimal cultivation and strip tilling leave trash on the surface can lead to an infection risk to the next crop.
  4. Hybrid selection
    All major seed breeders publish the susceptibility of each hybrid to NLB, so when choosing your hybrid, make sure you take this into account.
  5. Planting date
    Late planted crops are at higher risk from developing NLB as there is more inoculum around in the environment from earlier planted and infected crops. The later planted crops are more likely to be at an earlier growth stage when infected.
  6. Fungicides
    There are a few products with activity on NLB but they have to be sprayed either before or at early infection, protecting the plant from infection rather than trying to cure it. The best time to prevent the worst impact of disease is at early tassel stage; usually this has to be done by an aircraft because of the crop height.
  7. Monitor 
    Ensure you monitor the crop through the high risk infection period and growth stage.

For more advice on how to manage and control NLB, contact your local PGG Wrightson Technical Field Representative.


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