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Crop Special - Potatoes

A guide to the timing and use of adjuvants in potatoes

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weeds

Problems

  • Weeds in potatoes, particularly vigorous species such as fat hen and polygonums, can cause severe yield losses. On black fen soils yields can be reduced by up to 40%, although on mineral soils this will be less.
  • Weeds compete for light, nutrients and water and can shade the crop, reducing photosynthesis affecting yields. Competition for water can indirectly exacerbate scab problems, leading to loss of quality.
  • Weeds can also adversely affect tuber size through early competition and without adequate weed control, tubers may not meet size or uniformity specifications for the chosen market.
  • They can also disrupt harvest, particularly tall species such as cleavers and bindweed which can get wrapped around the harvester.
  • Key potato weeds are cleavers, wild-oats, chickweed, knotgrass, fat hen, redshank, polygonums, fumitory and groundsel.

Solutions

  • The most common herbicide treatment in potatoes is a pre-emergence application of residual-acting linuron with the total herbicide diquat/paraquat. Other widely used pre-emergence herbicides include metribuzin, metribuzin + flufenacet and clomazone.
  • Some post-emergence herbicides are applied for specific weeds, with Titus (rimsulfuron) being used for cleaver, fathen, redshank and nettle control.

Independent trials show that Arma improves the performance of low-dose highly active sulphonyl-urea herbicides such as Titus. The SU’s low application rate gives little room for sufficient surfactant in the formulation for consistent results.

Weed Control
Titus and Adjuvants

The addition of Arma may well be adding as much as 50 times the amount of surfactant present in the spray solution.

Arma improves the effect of reduced rate applications, improves the speed of initial knockdown and improves the control of “difficult” or larger weed species.
Where specific graminicides such as cycloxydim (Laser) or propaquizafop (Falcon) are used in potatoes for the control of wild-oats, Toil adds to their effective performance. Being a 95% w/w methylated rapeseed oil, Toil is safe to the crop and to the environment.

diseases

Problems

Potato blight

  • Caused by the fungus Phytophthora infestans, this is the most devastating disease affecting potatoes throughout the world. It costs the industry millions of pounds in lost or spoilt produce.
  • It causes damage through destruction of the haulm, adversely reducing yield and quality and through tuber blight which affects marketable yield, quality and storing ability of the tubers.

Solutions

  • Potato blight must be controlled by a robust fungicide programme of 10 to 12 sprays starting from the rosette stage right through to desiccation. It is important to keep to tight spray intervals to ensure complete protection of foliage and tubers.
  • The blight market is crowded. Key products include cymoxanil + mancozeb, fluazinam, mancozeb, cyazofamid, zoxium + mancozeb and dimethomorph + mancozeb.

  • Work at Oak Park in Ireland shows that the addition of Banka to fluazinam (Shirlan) can delay blight from 12 to 19 days.
  • With mancozeb (Dithane NT) the delay was moved from 3 to 8 days.

Disease Control
Fungicides and Banka

 

  • In work from the West of Scotland College, after 18 days, fluazinam (Shirlan) treatments were showing 5% blight but with the addition of Banka this was reduced to only 1%.
  • The improved disease control also resulted in extra marketable yields of around 4 t/ha.

Disease Control
Shirlan and Banka

Disease Control
Electis and Banka

  • In independent trials, the addition of Banka to Electis in a programme increased yields by 5.5 t/ha.

Banka is widely compatible with a range of blight fungicides and has been successfully trialled with a number of new products including Electis (zoxium + mancozeb). However it is not recommended with Ranman, as this is twinpacked with its own organosilicone adjuvant.

pests

Problems

Aphids and Potato Virus

  • Aphids transmit the damaging viruses Potato Leaf Roll virus and Potato Virus Y (PVY). These are particularly important in seed crops.
  • Aphids in ware crops can cause yield loss and affect fry colour.

Solutions

  • Aphids and virus yellows are generally controlled by a foliar aphicide usually applied in June to July. Control is complicated by the widespread problem of resistance
  • In seed crops an aphicide programme starts early and should alternate products with different modes of action. Generally around 4-5 sprays are used with a 10-14 day interval.
  • In ware crops one application of pirimicarb or pymetrozine is only necessary when aphids are in high numbers (5 aphids per compound leaf).
  • Key aphicides in potatoes are pymetrozine, pirimicarb, cypermethrin, lamda-cyhalothrin or deltamethrin.

programme timings PDF Version (140k)

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