Paraquat for citrus

Citrus fruit make-up a vast family including not only oranges, lemons, limes and grapefruit, but also calamondins, citrons, pomelos and ugli fruit.

Integrated pest management (IPM) systems have been introduced to minimize the impact of citrus growing on soil, water, air and biodiversity.  Paraquat has a key role in sustainable citrus production by controlling weeds that would otherwise seriously reduce productivity.  It can be used in conjunction with other techniques to manage soil erosion, particularly the use of strips of grass or legume cover crops between trees.

Paraquat can be safely sprayed to manage the weed flora along the crop rows between the grass or legume strips without fear of damaging the citrus trees.  Paraquat is immobile in soil and cannot move to the roots and up into the shoots.  Tree bark cannot be penetrated by paraquat meaning that it can be sprayed right up to the base of the trees.  Even if paraquat drifts onto citrus leaves there is little or no damage because paraquat does not move through plants like glyphosate does.

Citrus fact file

  • 1:  Brazil is the leading citrus growing country
  • 8.7 million ha of citrus are grown worldwide
  • 48% are oranges, 25% mandarin types, 12% lemons and limes, 3% grapefruit
  • 33% of crops are grown for juice
  • 10 years for a tree to bear a full harvest

Traditionally, and in poorer farming communities, citrus groves are hoed by hand to remove weeds.  This is labor-intensive and time-consuming, and, therefore, can limit opportunities for other activities, including education.  Effective use of herbicides can very significantly reduce the resources needed to control weeds.  The most commonly used herbicides include paraquat and glyphosate which have no activity in the soil, and the class of herbicides known as ‘residuals’ which remain active in the soil and prevent the germination of weed seeds.

Intensive use of glyphosate and residuals has led to changes in weed flora (‘weed shifts’) as species more tolerant to their particular modes of action become more dominant.  ‘Soft’ weeds, typically prostrate annual grasses which are easily controlled, are replaced by re-invasion of cleared land by more aggressive, pernicious weeds, which reduce crop yields.  These compete with citrus trees to reduce yield and quality and may make harvesting difficult.

Grass or cover crop strips between tree lines reduce soil erosionUsing paraquat, however, to manage the weed flora rather than eliminate it, can help to maintain a balanced flora, which precludes the dominance of aggressive species.  Paraquat only removes the top growth of well-established weeds, and does not affect the germination of new seedlings allowing vegetation to re-establish after 1-2 months.  A controlled presence of soft weeds maintains the balance of the weed flora and prevents weed shifts to more competitive species simply because bare ground for them to colonize is less available.  The presence of non-competitive vegetative cover also provides habitats to encourage biodiversity.  The wildlife encouraged will include predators of insect pests, which would otherwise have to be controlled chemically.