Header Image

Helping grow
the country

< Back to Blog
Rural Diary
1 April 2020 External Supplier

Standing the test of time

We all know that weeds in pastures are undesirable, but a recent study sponsored by the Ministry for Business, Innovation and Employment1 has reported that we have likely been underestimating their full cost to New Zealand agriculture. 

The study estimated that the total cost for just 10 common pasture weeds was likely to be over $1.3 billion a year in lost production, while Californian thistle alone takes over $700 million per annum 
from farmers. 

Farmers need to get on top of weeds to protect pasture yields, and fortunately they have some good tools at their disposal like Tropotox™ Ultra. Tropotox Ultra is a selective, grass and clover friendly herbicide that controls many broadleaf weeds in pasture, peas, clover and grass seed crops. It has a broad spectrum of activity with strength on thistles, buttercup, and seedling docks.

Tropotox Ultra contains 25 grams a litre MCPA and 375 grams a litre MCPB in a soluble concentrate formulation. It is a member of the phenoxy herbicide group, which were first discovered back in the 1930s, developed and commercialised in New Zealand in the 1980s, and still form the backbone of many of our pasture weed control programmes today.

Phenoxy herbicides mimic the natural plant growth regulator auxin in plants, causing abnormal growth, twisting of stems and cupping of leaves in susceptible species followed by plant death. However, monocots (for example grasses) are largely unaffected by the rates of phenoxy used, but many dicot plants (for instance broadleaves weeds) are highly susceptible. 

Tropotox Ultra is absorbed into foliage of growing plants where it moves to the growing points and interferes with key plant functions. Visible symptoms, such as twisting and curling of foliage, can be seen in a day or two but death of weeds can take several weeks. Clover, and some other legumes, lack the mechanisms that converts the product to the herbicidal active form, and once clover has at least two true trifoliate leaves it is tolerant to Tropotox Ultra.

Best use guides:

  • Apply Tropotox Ultra to small, actively growing weeds once clovers have passed two true tri-foliate leaves.
  • Do not apply to weeds under stress for example drought, water logging.
  • Use the higher rate where weeds are more advanced.
  • Avoid spraying where rainfall is expected within two hours of application.

For more information on how to get the best out of your pastures by using Tropotox Ultra, talk to your local PGG Wrightson Technical Field Representative.

Supplied by Agritrade
1Saunders JT, G. G. (2017). The economic costs of weeds on productive land in New Zealand. International Journal of Agricultural Sustainability.

External Supplier

Related Articles

Technical advice core to business relationship

01 April 2020

The business relationship between Nelson contractors Kevin and Andrew Fry (K & A Fry Contracting) and PGG Wrightson has grown so strong over the last five years, that both parties now promote and refer one another to new farmers in the district.

Established in 2002, K & A Fry Contracting are the biggest agri-contractors in the local area, offering hay silage, groundwork, feed conservation and spraying services. What started as a one-man business with a tractor and a seed drill, has grown to a sizeable partnership between Andrew and his father, Kevin. They now have a fleet of five tractors and a spray truck, operating with a team of six full-time staff. 

Andrew notes that spray contracting is the biggest part of their business and being able to rely on PGG Wrightson Technical Field Representative, Andrew Young, helps with inputs, advice and daily support in both their agri-contracting business and cropping ventures. 

“Andrew (Young) is outstanding for both his service and knowledge. We’re in constant communication with him for advice when we’re out on a job, and we talk to him daily about spraying.

“In many instances, we’re working for PGG Wrightson customers, but sometimes not. That doesn’t matter to Andrew, he’s always happy to help.

“He knows what he’s talking about and gives us sound advice. He’s quick to respond, and if there’s something he’s not sure about, he’s upfront in telling us that he needs to do some research first.”
The Fry’s also have 75 ha of crops under irrigation, growing maize for PGG Wrightson Seeds and Lucerne for baleage. They’ve recently added 11 ha hops, too. With the contracting business, Kevin and Andrew are not on the farm a lot of the time. Here, they rely heavily on Andrew Young to monitor the crops and regularly revise their crop management plans. 

 “Andrew is probably here at least three times a week checking on the crops and keeping things on track,” says Andrew Fry. “That gives us real peace of mind.”

He adds that they order everything through PGG Wrightson, “we find PGG Wrightson to be consistently reliable. We rarely have to wait for a product. Andrew normally delivers it too, unless it’s a big volume.

“We’re loyal to PGG Wrightson, but they’ve earned that loyalty. We consistently get good deals and Andrew’s support is invaluable in all areas of our business.”

Perennial weed control in new and established pastures

01 May 2020

Perennial weeds grow from one year to the next, usually from a large root system or root chip. New generations usually flower and seed in late summer and the parent plant normally shuts down over winter, lives off the energy reserves in its roots, then wakes up in the spring to continue growing.

Perennial weeds in new pasture become yield-taking because they are already established and compete with the small seedlings of a new pasture from the start. Their head start in establishment ensures the domination battle for space, light and nutrients is already won, and the seedlings of the new pasture plant species lose. This partial or total domination of the pasture leads to poor feed yields, quality and sometimes animal health issues.

Some examples of perennial weeds include Californian thistle, couch, dock and buttercup. Both perennial and annual weeds establish themselves in the pasture where there are gaps either caused by insect or grazing damage. Once there is an area of bare soil, weed seeds can colonise and grow, so over-sowing or under-sowing more pasture seed can help fill these gaps. Where there are perennial weeds already growing from roots or shoots, these bare areas are colonised quickly, and over-sowing or under-sowing won’t help.

Most clover safe selective herbicides can be quite unreliable at controlling perennial weeds and often require repeat applications to reduce the root biomass, which is the energy source of the perennial weed. A combination of grazing, mowing and spraying may keep the leaf area small on the weed, which will suppress the amount of growth below ground. In many situations, the only real alternative is to start again by spraying with glyphosate and reseeding.

It is critical that you use an appropriate dose rate of good quality glyphosate sprayed when the weed is actively growing and there is enough green leaf area to take up sufficient chemical. Leave cultivations for at least three to five days to allow translocation of the glyphosate to the roots of the perennial weeds.

For advice controlling perennial weeds, contact your local PGG Wrightson Technical Field Representative.


Top Tips:

  • Know what weeds you are dealing with and their life  cycle to time your best control strategy.
  • Avoid damage to pasture, gaps allow weeds to establish. Over-sow or under-sow pasture to fill gaps before perennial weeds colonise.
  • Mowing and grazing, as well as well-timed selective herbicide, remove aerial growth and reduce the weed's ability to grow a bigger root system.
  • Selective herbicides often require more than one application.
  • If all else fails, spray-out and start again.
  • For spray-out use, an appropriate dose of a quality glyphosate and spray the weed when it is actively growing with enough green leaf area, for instance around 10 cm, to ensure good coverage and uptake.
  • Do not cultivate for at least three to five days.

The right approach to sulphur for grazed pasture

01 May 2020

Sulphur (S) is present in all plants and is involved in photosynthesis, overall energy metabolism and carbohydrate production. It is part of an enzyme required for Nitrogen (N) uptake, so a lack of S can hamper N’s influence on plant growth. 

Together with N, S enables the formations of amino acids needed for protein synthesis. S also has a role in certain oil compounds which impact the flavour and smell of crops such as onions, 
garlic and brassicas.

Deficiency symptoms are similar to N deficiency, pale green leaves. However, the deficiency affects the new or younger leaves, unlike N where deficiency shows up on the older leaves. 

S is added to the soil through irrigation, rainfall and S fertilisers. It’s removed from the soil through the uptake of plants, leaching from the soil and animal and crop production. 

There are two different pools of S found in soils, these are 'plant available' and 'plant unavailable'. Sulphate-S is an anion (it carries a negative charge) and is the only form of S which can be taken up by the plant root system (plant available). However, it is found in the soil in relativity small amounts, and is typically held weakly by the soil’s anion exchange complex, known as Anion Storage Capacity (ASC), which means it is prone to leaching. The other pool of S is organic-S which is found in the greatest quantity in the soil but is unavailable to plants in the short term and does not leach. However, organic-S is very important as it does slowly supply sulphate-S (plant available) to the soil over the growing season. The potential amount of organic-S in soil varies with soil type, so knowing your soil type is important for fertiliser selection.

Soil testing for sulphate-S can be unreliable. The sulphate-S test is only at a point of time whereas the organic-S test is longer term, so they complement each other. Including an organic-S test in your soil sample results every few years overcomes some of the problems of testing for only the sulphate-S and you can check your reserve S levels. 

There are two common forms of S found in fertilisers. The first form is sulphate-S; it can be especially prone to leaching over winter but is easily absorbed by plant roots during a period of rapid growth.The second type is elemental-S which does not leach and is slowly available to plants (the same way organic-S is). Elemental-S is slowly available to plants because it needs to be oxidised to sulphate-S by soil microbes which takes time and requires warm soil temperatures. What form of S fertiliser you need will be very dependant on soil type and season.

Many fertilisers which contain S also contain N. Examples of sulphate-S fertiliser products are SOA and most YaraBela N+S products. Super10, although not containing N, does supply sulphate-S. Products containing elemental-S includes PhasedN and SulphurGain products. PhasedN Quick Start has both elemental and sulphate-S.

The key message for S application is little and often is usually best. This avoids issues caused by applications of high rates of quickly available S at one time of the year, such as leaching. Applying, some elemental-S during autumn means it will be oxidised in the spring when soil temperatures are warmer. In the spring, a top-up with some fast release S from products such as SOA, YaraBela N+S products and phosphate products containing sulphate-S might also be considered.

For more information on which type of S is suitable for your farm this autumn, contact your local PGG Wrightson Technical Field Representative.


Share this page