Arable News

  • Written by: Farmers Guide
  • Posted:

Getting the most from pre-em potato herbicides

Weed control and early blight management are at the top of potato growers’ to-do lists

Weed control and early blight management are at the top of potato growers’ to-do lists, says Agrovista agronomist Craig Green.

Given the very limited post-emergence herbicide armoury, getting the best from pre-emergence applications in potatoes is vital to maintain a clean crop. It’s not just about choosing the right products – it means applying them correctly, too, Craig Green (above) advises.
“Most growers will know what suits their soils, weed spectrum and varieties best,” he points out. “There is a decent range of products available, some of which can be mixed and matched to suit.” 
A good all-round recommendation that can be used on most varieties on medium soils is Sencorex Flow (metribuzin) at 0.5-litres/ha plus Afalon (linuron) at 1.1-litres/ha. Craig often adds 1.5 litres of diquat to burn down establishing weeds.
“This mix will take out most problem weeds and has good persistence. On very light soils and sands I’ll replace Sencorex with Defy (prosulfocarb) at 4-litres/ha.”
This season a new active from Belchim, metobromuron, is available as Praxim. Its key advantage, says Craig, is excellent safety in all soils, including very light soils and sands. It also has no buffer restrictions.
“We see it replacing linuron. I’ll be recommending it at 2-litres/ha on soils with body and add Artist, which contains metribuzin and flufenacet, at 1.5-litres/ha to boost control of weeds like black bindweed, cleavers and field pansy. On very light soils I’ll up the Praxim to 3-litres/ha and use Sencorex Flow at 0.25-litres/ha to deliver a lower dose of metribuzin.”
Artist (flufenacet + metribuzin) also has activity against black-grass, helping to maintain pressure on the weed throughout the rotation, says Craig.
He will add Remix, a paraffinic oil that reduces spray drift, to all his pre-emergence recommendations. “You only need a slight breeze growing across the baulks to create a spray shadow on the sheltered side, which reduces the protective barrier. Using Remix ensures even distribution of chemical across the baulks. Many of our growers are convinced of the benefits,” says Craig. 
Anyone missing the pre-emergence herbicide slot can use Shark (carfentrazone-ethyl) plus diquat as a fall-back at peri-emergence, at 0.25- and 2-litres/ha respectively. This is contact-only so will increase reliance on subsequent post-emergence treatments, he points out.
These are limited to Basagran (bentazone) for very small weeds, or Titus (rimsulfuron) at 50g/ha (except on potatoes grown for seed). 
Blight protection will begin with Ranman Top (cyazofamid) at 0.5-litres/ha at the rosette stage. “This gives excellent control of foliar blight and also early zoospore activity in the soil,” he notes. “If there’s any risk that blight is already present, add Option (cymoxanil) at 0.15kg/ha and reduce the Ranman dose to 0.375-litres/ha.”
From then on it’s a question of ringing the changes to reduce selection for resistance, using a sequence of Consento (fenamidone + propamocarb), Zampro (ametoctradin + dimethomorph) and Ranman during rapid canopy development and introducing Shirlan (fluazinam) as necessary as growth tails off.
“Aim to keep spray intervals tight to avoid problems if bad weather delays spraying, and add Option any time where kickback is needed,” says Craig. “If you think you’ve travelled through a blighted patch, disinfect the sprayer before moving onto the next field.
“First time out with the sprayer be sure to note awkward areas around telegraph poles or tight corners, where the sprayer can’t reach, and burn these off. They only act as reservoirs for infection, as will volunteers in other crops – these will need controlling too.”
*Craig Green is an agronomist with Agrovista, based at Great Ellingham, Norfolk ([email protected]).

Nitrogen boost for maize
Maize drilling is well underway and pre-em herbicides will soon be applied. Growers, especially those on light soils, should consider spraying N-Lock, a nitrogen stabiliser from Dow AgroSciences, just before final seedbed cultivation so it can be worked into the soil, says Craig. 
Applied at 2.5-litres/ha it can be tank-mixed with glyphosate, he adds. “N-Lock slows down the conversion of ammonium into nitrite, reducing losses and ensuring more nutrient is available later when the plants really need it but when spreaders can no longer travel due to crop height.”
The average yield response in trials is 6.6t/ha, he notes. “You only need 1t/ha to pay for it, so it really is worth trying.”


  • Written by: Farmers Guide
  • Posted:
Prev Story:Growers of dynamic wheatsNext Story:Agronomy Update – June 2015