- Factors influencing herbicide choice and rate
- Time of herbicide application
- Restrictions related to herbicide use
- Current practice
- Past practice for post-planting cultivation
- Cultivations to enable growing and harvesting on heavier soils
- Potential problems with cultivation for weed control
Principles of weed control
Factors influencing herbicide choice and rate
- Soil type: heavier soils require higher herbicide rates. Organic soils have a limited choice of herbicides due to the high Kd factor of the soil.
- Period of weed control required: early or maincrop.
- Expected canopy size: large canopies quickly smother weeds and prevent late germinating species from competing with the crop.
- Use of polythene: check labels for recommended for use under polythene.
- Weed spectrum and time of emergence: difficult species include cleavers, fat hen, black nightshade, polygonums (black bindweed, redshank, pale persicaria), OSR, charlock, fumitory, cranesbill; the earlier after crop emergence weed competition begins, the greater the detrimental affect on the crop.
- Soil moisture at application: water insoluble herbicides are less active on dry soils. Contact herbicides or more water soluble products may be more effective under these conditions.
- Temperature and UV light: degradation in soil of residual herbicides is increased under high temperatures and high levels of UV light. Persistence is therefore reduced.
Time of herbicide application
- Pre-emergence herbicides should be applied before emergence of the crop. The latest time is when the soil begins to rise over emerging shoots.
- Post-emergence application of herbicides after emergence of potatoes can be detrimental to crop performance, particularly is applied during stolon tip swelling. Yield may be reduced without appearance of visible phytotoxic effects. This has been shown in experiments with rimsulfuron (“Titus”). More …
- If there is a high population of post-emergence weeds, effects of competition if a herbicide is not applied may be greater than detrimental effects of the herbicide.
- Weed competition can reduce the number of tubers formed and thus tuber yield. More …
Restrictions related to herbicide use
- Some cultivars are sensitive to pre-emergence herbicides; check the label restrictions.
- If a new cultivar is not listed on a herbicide label, check herbicide use with the plant breeder.
- Check labels for any restrictions to following crops.
- Check labels of herbicides used in preceding crops for any restrictions to following those herbicides with potatoes.
Weed control by cultivation
- On most potato soils cultivations are kept to the minimum necessary to produce a stone and clod free ridge or bed.
- Stone and clod separation severely limits the opportunities for post planting cultivation.
- Any inter-row cultivation will disturb the buried stones and clods.
Past practice for post-planting cultivation
- Ridges alternatively built up and harrowed down.
- Ridges harrowed down almost flat post planting, then gradually built up usually with a combination machine incorporating inter-row tines, over the ridge weeders and ridgers either disc or mouldboard.
Cultivations to enable growing and harvesting on heavier soils
- Stone and clod separation on heavier soils is a high risk strategy on these soils, as soil rarely dry out to sufficient depth, to allow the operation without serious structural damage.
- Old fashioned cultivation techniques are required, as follow.
- Plough early and level, subsoiled if required.
- Work seedbed down from the top, ideally Dutch harrow, wet clods must not be brought to the surface.
- Plant at mean soil level. Gradually build a ridge, again avoiding working below the level of dry soil.
- This may be with shallow tines and disc ridgers or mouldboard ridgers, or with powered interow cultivation.
- A clod free ridge can be built, which will allow harvesting, without excessive clods and thereby damage.
Potential problems with cultivation for weed control
- Ridging alone is insufficient to control weeds.
- Additional cultivation improves weed control but may result in damage to potato plants.
- Excessive cultivation or uncontrolled weeds can both result in loss of water from soil.
- In experiments weed control by cultivation has rarely been as effective as use of herbicides, though a combination of cultivation and reduced usage of herbicide may be effective.
Weed control with “burners”
Principles of flame weeding
- Uses propane in the liquid phase.
- Sprays out liquid through nozzles.
- Ignites away from the burner.
- Provides a hotter temperature where it is needed.
- Interchangeable boom with different burners for inter row weeding.
- Intense heat of >1000 oC is passed over the leaf of the plant.
- The liquid inside the leaf cells boils and then ruptures the cell.
- The plant can no longer photosynthesise and collapses and dies.
Potential problems with “burners”
- The method can be used only before crop emergence.
- There is concern about the energy consumption and production of greenhouse gases, which are not in accordance with environmental principles.
Other methods of weed control without herbicides
- Experiments have included incorporation of crop residues, inter-seeding between potato rows (e.g. with clover) and incorporation of a “green mulch” from oilseed rape sown in the autumn before potatoes.
- Results from these experiments have been poor or variable and such practices could increase slug populations.
- Mulching with polythene or paper is suggested to be effective but it is costly, labour-intensive and may interfere with early season foliar applications (particularly application of blight fungicides).
Notes on weed control
Weed control 2020 (Principles of weed control; aclonifen; influence of weeds on crop performance – results of experiment performed in 2019)
Weed control 2020 (Results from an experiment performed in 2019: relationships between weed and crop growth)
New developments in agrochemicals 2019 (Includes introduction to aclonifen)
Herbicides 2018 (Some options for weed control)
Non-chemical weed control 2015 (Potential for alternative control methods)
Use of rimsulfuron herbicide 2012 (Potential for making the best use of this product)
Herbicide updates 2011 (Includes use of adjuvant with prosulfocarb)
Weed control 2010 (Information now out of date)
Potato weed control 2008 (Includes discussion of some of the potential problems with weed control)
Weed control 2007 (Includes weed control with prosulfocarb)
Weed control in aquatic situations 2007 (Information now out of date)
Residual herbicides 2006 (Includes introduction to prosulfocarb)
Biostimulant experiments 2003 analysis (Includes an experiment showing some effects of post-emergence herbicide on crop performance)
Agrochemical product updates 2003 (Includes weed spectrum for flufenacet + metribuzin)
Weed control 2002 (Includes mechanical weed control)
Control of weeds 2001 (Introduction to flufenacet)
Herbicide principles 2001 (Influence of soil type, period of control required, etc)
Herbicide restrictions 2000 (Restrictions to the following crops)
Rimsulfuron herbicide 1999 (PRG experiment showed risk of application during stolon tip swelling)
Weed control 1998 (Effects of weed competition; effects of soil and crop condition on herbicide efficacy)
Rimsulfuron herbicide 1996 (Introduction to rimsulfuron and the weeds controlled)
Notes from an external source
Emerger herbicide 2020 – Bayer (Manufacturer’s information on aclonifen, including weed spectrum)