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Weeds and volunteer control in potatoes

Find out what are the resources available on weed control, including latest research project results and cost of application. 

Why are weeds a problem?

Can cause yield losses

Weeds are undesirable plant species that compete with cultivated crops for light, nutrients, water and growing room. Competition can lead to weak or poor performing potato crops, which under weed pressure can suffer yield losses of 14-80%. Potato skin finish can also suffer as a consequence of water competition. This subsequently affects marketability.

Can spread diseases and protect pests 

 Weed species can act as green bridges for pests and diseases to survive and proliferate on between cultivated crops, therefore providing a legacy effect.

  • Many nematodes are polyphagous and so parasitize numerous weed species in addition to potatoes, and potato volunteer weeds. These include economically important groups such as the root knot nematodes (RKN) (Meloidogyne) and root lesion nematodes (RLN) (Pratylenchus spp.). Volunteer potatoes can be particularly problematic by hosting potato cyst nematodes (PCN) (Globodera spp.) which are responsible for c.9% losses to the UK crop each year.
  • Weeds can also host diseases such as black dot (Colletotrichum coccodes). Black dot reduces potato quality by causing skin blemishes. Common arable weeds such as chickweed (Stellaria media), shepherds purse (Capsella bursa-pastoria), fat hen (Chenopodium album) and field bindweed (Convolvulus arvensis) can host black dot.

  • Large weeds such as fat hen can also obstruct effective pesticide applications during the season, such as blight protectants.

  • Weeds such as field bindweed or black bindweed (Fallopia convolvulus) might also prevent effective harvesting by binding harvesting equipment or preventing effective soil separation over harvester webbing.

Weed management strategies for potato crops

1. Non-chemical weed control 

Non-chemical weed management strategies include mechanical, hand or lazer weeding in-crop, or stale seedbed approaches between crops where broad-spectrum translocated herbicides, flame weeding or mechanical approaches could be used to reduce the seedbank of a field. These strategies are going to form an important component of growers weed management armoury going forwards.

  • There is a general decline in the number of approved herbicide active ingredients available for potato growers in the UK. This is largely in response to an EU pesticide Regulation (1107/2009), which altered the assessment criteria for approval of plant protection products over a decade ago.
  • Herbicide efficacy across the weed spectrum also appears to be in decline generally. This is a result of the new legislation selection criteria, and in-part, due to the development of resistance and tolerance to specific active ingredients in some weed species.
  • Weed maps could also become integral to weed management going forwards as a method of identifying areas for patch spraying or some other alternative or additional treatment to the rest of a field.
  • Alternative management practices may still require more research. Some will be more expensive in the long-term than current options. For example, current hand weeding in horticulture costs approximately £240 per acre (£600 per hectare).

2. Herbicides

The primary method of weed management in potatoes is to use a residual herbicide programme pre-emergence, usually containing a contact herbicide component, followed up by a post-emergence herbicide application where necessary.

  • Since the retraction of residual herbicide linuron (e.g. Afalon®, Adama) and contact herbicide diquat (e.g. Reglone®, Syngenta) from use in 2017 and 2019, two new herbicide options have come forwards; aclonifen (Emerger®, Bayer) and carfentrazone-ethyl (Shark®, FMC Ag.).
  • Emerger® containing programmes were investigated in trials at SPot West and SPot North in 2019 alongside or in combination with residual herbicides metribuzin (Shotput®, Adama), metobromuron (Praxim®, Belchim), pendimethalin (Stomp Aqua®, BASF), clomazone (Gamit 36 CS®, FMC Ag.) and prosulfocarb (Defy®, Syngenta). Shark® containing programmes were demonstrated at other SPot sites nationally.
  • Generally Emerger® was found to give good control of volunteer oilseed rape (Brassica napus), field bindweed, fat hen and knotgrass (Polygonum aviculare) in Maris Piper and Sunita crops. However, it was found to be improved as a partner product.
  • Shark® demonstrations indicated good weed control in Georgina and Lanorma crops although applications later than 10% emergence caused deformities in tubers and some reduction in vigour and yield so that timing of application is critical to success.
  • Aclonifen containing programmes ranged between £12.75 – 47.51 to the acre (£31.50 – 117.40 to the hectare). See Figures for SPot North residual herbicide efficacy and cost information:

Optimising herbicide efficacy

  • To make the best of herbicide products stick to label recommendations. Generally residual herbicide efficacy is aided by application to damp rather than dry soil.
  • Care should be taken to ensure sprayers are set-up appropriately and herbicides applied near to the soil surface at slow speeds.

The SnapCard APP can be used to assess spray deposition uniformity on farm to help ensure herbicide applications are optimal 

Find out what is the best practice when applying Shark or Emerger. 

Resources: