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Rural Diary
1 February 2020 Matthew Crampton

Perennial grass weed control of twitch

Perennial grass weeds are a problem on South Island farms and can build up over time, replacing higher producing grasses in your pastures. The one I come across a lot on-farm is the grass weed called twitch (Elytrigia repens), also known as couch.

Twitch spreads by its wiry creeping rhizomes and is commonly found as a problem throughout New Zealand’s home gardens, pastures and roadsides. Twitch is a problem because it isn’t productive compared to other pasture species, so as it dominates an area of pasture, the overall productivity drops. Like all weeds, it is also using valuable nutrients and moisture which are better utilised by desirable pasture species. 

Once identified, this weed requires a concerted effort and good timing to control it. But, let’s start with identification. From above ground, twitch looks similar to most pasture grasses, but give the leaf a pull and it shows its real colours by exposing the plant’s root system. The plant produces extensive rhizomes horizontally underground so as you pull up the grass plant some of the rhizomes come with it (you may have to gently dig out the root so it doesn’t snap off). The plant can be easily identified by its rhizomes which are bright white and grow horizontally about 10 cm below the surface. These rhizomes are a key characteristic of twitch (Image 1).

These rhizomes, which help with identification, are also the reason this weed is so successful. They provide a large reserve for the plant to bounce back after attempts at control, and also have the ability to survive being cut into pieces during cultivation, therefore dividing and producing a new plant from each piece. These two characteristics contribute to making this grass weed a problem on-farm, but by taking a few things into consideration control, is possible by depleting the rhizome’s reserves and eliminating each plant.

The best time to control any weed is when it has leaf area to take up the herbicide when actively growing, which for twitch is in the spring or autumn. Make sure you avoid the winter when twitch is dormant. In the South Island most pasture and crops are sown in spring and if there is a lot of twitch you can struggle to get control with this timing. In problem paddocks, alter your rotation so an autumn application of glyphosate is applied to actively growing twitch; this gives a great result. During your cropping phase, there is also the option of using a selective grass killer in some crops to help in the battle against this weed.

Consult with your local PGG Wrightson Technical Field Representative for advice around product selection and timing to ensure you get the result you are after and control twitch on your farm. Or for help identifying the weed, visit the PGG Wrightson YouTube channel and watch my ‘Grass Weeds: Twitch/Couch’ video.

Matthew Crampton

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Getting lime on early for next season's spring sown crops

01 February 2020

In New Zealand, our pastoral/cropping soils are usually slightly acidic. Over time, soils become more acidic due to a variety of factors including plant uptake of essential nutrients, leaching, decomposition of organic matter by microbes and the application of certain fertilisers such as elemental sulphur. 

When soils become too acidic, essential nutrients like phosphorus (P) and molybdenum (Mo) may become less available to plants. Conversely elements like aluminium (Al) become more available and toxic to plants. An excessively acidic soil can have a negative impact on the potential yield of the crop planted in it. This is where lime comes into a cropping programme and has a critical role to play in maintaining soil fertility. Adding the right amount of lime to a soil can neutralise high levels of Al and enable plants to use most essential nutrients more efficiently, and can stimulate microbial activity.  

The hydrogen ion (H+) concentration in soils, the sole cause of soil acidity, is measured in a pH scale ranging from 0.0 to 14.0 Depending on which end of the scale the pH is on, a soil can be either acidic or alkali. Acidic soils have a pH level between 0.0 and 7.0 and alkali soils have a pH value ranging from 7.0 to 14.0. The pH levels of most New Zealand soils generally falls within the range of 5.0 to 7.0, and most crops have an optimum soil pH between 5.8 to 6.4 (crop dependant). In simple terms, lime adds carbonate to the soil that reacts with water producing an alkali (OH-) and neutralising acid (H+). As acidity is neutralised, the pH increases, and the more carbonate added, the more acid is neutralised and the greater the pH increase.

A well-known, handy ‘rule of thumb’ is that 1 tonne per ha of good quality lime, for instance 80 percent calcium carbonate or better, raises the pH of a typical soil by 0.1 units. This rule of thumb is for pastoral soils that are soil tested to a depth of 7.5 cm. For crops that are sampled to a 15 cm depth, this ‘rule of thumb’ needs to be approximately doubled to 2 tonne per ha for a 0.1 unit change. 

Lime is sparingly soluble so it takes time (minimum of six and up to 24 months depending on climate and soil type) to dissolve and move down the soil profile. For this reason, it is best to apply lime to the soil at least six months prior to planting a spring-sown crop. The best way to evaluate the need for liming is to identify cropping paddocks early and have these soil tested (to 15 cm) to identify any potential pH issue. Then lime can be applied in a timely manner to rectify any issues with soil acidity. 

Talk to your local PGG Wrightson Technical Field Representative today about soil testing potential cropping paddocks and suitable liming products. 

Getting the spray-out done right

01 March 2020

When planning to plant a new crop or re-grass, at least one spray-out of the old crop or pasture should be undertaken. This means spraying the paddock to kill all remaining foliage of the old crop and weeds to allow the establishment of the new crop without having to compete with large established weeds already in-situ.

Spraying out the old crop with a well-timed glyphosate based product, for example Roundup, can help reduce the number of cultivation passes and better prepare the paddock for direct drilling or minimal tillage. It also eliminates grass or crop regrowth and reduces turf clods on the seedbed surface, enhancing both the performance of residual chemicals used for weed control and seed-to-soil contact for the new crop or pasture. Lastly, removing residue from the previous crop or pasture reduces the risk of damage from some pests that continue to feed in the thatch and green matter of the old crop until a new seedling emerges. 

Regardless of the brand of glyphosate used, all are designed to kill grass weeds and struggle to effectively and quickly kill many broadleaf weed species, increasing the time to turn the paddock around into a new crop or pasture.

To overcome this issue, other herbicides can be added to the glyphosate at spray-out to aid the speed of “brown down” or help kill a number of broadleaf weeds not normally well controlled by the glyphosate. This is called a spike or companion herbicide. Careful consideration should be given as to product choice because they all have their strengths and weaknesses across the weed spectrum. Weeds should always be identified to help select the most suitable product to be used as a spike. 

The other important factor to remember is that whilst glyphosate on its own does not have any residual effects on the following crops, some of the spike herbicides do (up to two years with some products and some susceptible crops). Care must be taken when choosing the appropriate broadleaf spike so that following crop or pasture is not affected.

The addition of a broadleaf weed spike may reduce the effectiveness of the glyphosate on some other weeds.

Always take a paddock walk and make a pre-spray assessment of the weed species present to help you decide which product to use as a spike.

There are many different strength glyphosates and so the appropriate rate for the weed must be selected as per label. To increase efficacy for more difficult weeds, then the premium brands are far more reliable as their surfactant system is superior. The addition of the correct adjuvant to reduce drift and/or penetration through the canopy or leaf cuticle also helps efficacy. 

To get the desired effect from spray-out without affecting the following crop, seek advice from your local PGG Wrightson Technical Field Representative (TFR) who can help with weed identification and product choice, rate and timing. Contact your local TFR or PGG Wrightson store today.


Cropping programme and partnership delivers

01 March 2020

Wairarapa Arable Farmer, Richard Kershaw has worked alongside PGG Wrightson for the last 20 years, growing and selling multiple crops for seed and feed. 

The Kershaw family owns Moiki Farm on the East Coast, in the flat country between Martinborough and Greytown. The homeblock is 260 ha, with another 200 ha lease block. Different members of the family manage various aspects of the farm. 

The bulk of the business is cropping for seed production. They grow approximately 20 ha of ryegrass for seed, 20 ha of red clover for seed, 35 ha of hybrid maize seed and 12 ha of Milton oats. They also produce around 50 ha of barley and 110 ha of  maize for feed grain. In addition to this, the Kershaw’s fatten lambs and graze beef cattle.

Richard notes that their challenges are much the same as everyone else operating in the dry East Coast conditions. The farm is fully irrigated, and production has risen accordingly. He adds that there’s occasional but devastating biosecurity issues to contend with, such as the introduction of pea weevil into the Wairarapa about four years ago. Not growing the crop has been the only way to eradicate the pest.  

Working alongside Richard for the past two decades has been PGG Wrightson Technical Field Representative, Geoff Horrobin. In fact, Geoff has been with PGG Wrightson for approximately 40 years, servicing Masterton south to Martinborough for all that time, bar three years in the South Island.

“Geoff is our agronomist and we have relied on his expertise for many years” confirms Richard. “His knowledge of the area is second to none, plus he knows our business so well. 

“We count him very much part of our team and our cropping success. Annually, we sit down together to review our cropping programme. Geoff then takes responsibility for organising all our seed, fertiliser and ag-chem requirements as we need them.

“Crop monitoring is Geoff’s area of expertise, I’d say he is probably on farm two or three times a week in the height of the season, checking on each of our crops and reviewing our weed spray and fungicide programmes."

Due to the nature of their business, the Kershaws work with a group of people from PGG Wrightson, including the Rural Supplies store team, as well as PGG Wrightson Seed and Corson Maize. 
“We find PGG Wrightson exceptionally supportive of our business” concludes Richard. “Not only do we rely on them for quality inputs and advice, they bring us new contracts regularly.

“I’d say a fair chunk of our income has been a result of working with PGG Wrightson.”

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