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What Works in Conservation 2017

 | 
William J. Sutherland
, 
Lynn V. Dicks
, 
Nancy Ockendon
, 
et al.

7. SOME ASPECTS OF ENHANCING NATURAL PEST CONTROL

7.1 Reducing agricultural pollution

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Based on the collated evidence, what is the current assessment of the effectiveness of interventions that reduce agricultural pollution for enhancing natural pest regulation?

Unknown effectiveness (limited evidence)

● Alter the timing of insecticide use
● Delay herbicide use
● Incorporate parasitism rates when setting thresholds for insecticide use
● Use pesticides only when pests or crop damage reach threshold levels

Evidence not assessed

● Convert to organic farming

Unknown effectiveness (limited evidence)

Alter the timing of insecticide use

  • Natural enemies: One controlled study from the UK reported more natural enemies when insecticides were sprayed earlier rather than later in the growing season.

  • Pests: Two of four studies from Mozambique, the UK and the USA found fewer pests or less disease damage when insecticides were applied early rather than late. Effects on a disease-carrying pest varied with insecticide type. Two studies (including one randomized, replicated, controlled test) found no effect on pests or pest damage.

  • Yield: Four studies (including one randomized, replicated, controlled test) from Mozambique, the Philippines, the UK and the USA measured yields. Two studies found mixed effects and one study found no effect on yield when insecticides were applied early. One study found higher yields when insecticides were applied at times of suspected crop susceptibility.

  • Profit and costs: One controlled study from the Philippines found higher profits and similar costs when insecticides were only applied at times of suspected crop susceptibility.

  • Crops studied: aubergine, barley, maize, pear, stringbean.

  • Assessment: unknown effectiveness (effectiveness 40%; certainty 28%; harms 13%).
    http://www.conservationevidence.com/​actions/​723

Delay herbicide use

  • Natural enemies: Two randomized, replicated, controlled trials from Australia and Denmark found more natural enemies when herbicide treatments were delayed. One of the studies found some but not all natural enemy groups benefited and fewer groups benefitted early in the season.

  • Weeds: One randomized, replicated, controlled study found more weeds when herbicide treatments were delayed.

  • Insect pests and damage: One of two randomized, replicated, controlled studies from Canada and Denmark found more insect pests, but only for some pest groups, and one study found fewer pests in one of two experiments and for one of two crop varieties. One study found lower crop damage in some but not all varieties and study years.

  • Yield: One randomized, replicated, controlled study found lower yields.

  • Crops studied: beet and oilseed.

  • Assessment: unknown effectiveness (effectiveness 20%; certainty 25%; harms 50%).
    http://www.conservationevidence.com/​actions/​774

Incorporate parasitism rates when setting thresholds for insecticide use

  • Pest damage: One controlled study from New Zealand found using parasitism rates to inform spraying decisions resulted in acceptable levels of crop damage from pests. Effects on natural enemy populations were not monitored.

  • The crop studied was tomato.

  • Assessment: unknown effectiveness (effectiveness 50%; certainty 10%; harms 5%).
    http://www.conservationevidence.com/​actions/​726

Use pesticides only when pests or crop damage reach threshold levels

  • Natural enemies: One randomized, replicated, controlled study from Finland found that threshold-based spraying regimes increased numbers of natural enemies in two of three years but effects lasted for as little as three weeks.

  • Pests and disease: Two of four studies from France, Malaysia and the USA reported that pests were satisfactorily controlled. One randomized, replicated, controlled study found pest numbers were similar under threshold-based and conventional spraying regimes and one study reported that pest control was inadequate. A randomized, replicated, controlled study found mixed effects on disease severity.

  • Crop damage: Four of five randomized, replicated, controlled studies from New Zealand, the Philippines and the USA found similar crop damage under threshold-based and conventional, preventative spraying regimes, but one study found damage increased. Another study found slightly less crop damage compared to unsprayed controls.

  • Yield: Two of four randomized, replicated, controlled studies found similar yields under threshold-based and conventional spraying regimes. Two studies found mixed effects depending on site, year, pest stage/type or control treatment.

  • Profit: Two of three randomized, replicated, controlled studies found similar profits using threshold-based and conventional spraying regimes. One study found effects varied between sites and years.

  • Costs: Nine studies found fewer pesticide applications were needed and three studies found or predicted lower production costs.

  • Crops studied: barley, broccoli, cabbages, cauliflower, celery, cocoa, cotton, grape, peanut, potato, rice, tomato, and wheat.

  • Assessment: unknown effectiveness (effectiveness 39%; certainty 30%; harms 20%).
    http://www.conservationevidence.com/​actions/​750

Evidence not assessed

Convert to organic farming

  • Parasitism and mortality (caused by natural enemies): One of five studies (three replicated, controlled tests and two also randomized) from Europe, North America, Asia and Australasia found that organic farming increased parasitism or natural enemy-induced mortality of pests. Two studies found mixed effects of organic farming and two randomized, replicated, controlled studies found no effect.

  • Natural enemies: Eight of 12 studies (including six randomized, replicated, controlled tests) from Europe, North America Asia and Australasia found more natural enemies under organic farming, although seven of these found effects varied over time or between natural enemy species or groups and/or crops or management practices. Three studies (one randomized, replicated, controlled) found no or inconsistent effects on natural enemies and one study found a negative effect.

  • Pests and diseases: One of eight studies (including five randomized, replicated, controlled tests) found that organic farming reduced pests or disease, but two studies found more pests. Three studies found mixed effects and two studies found no effect.

  • Crop damage: One of seven studies (including five randomized, replicated, controlled tests) found less crop damage in organic fields but two studies found more. One study found a mixed response and three studies found no or inconsistent effects.

  • Weed seed predation and weed abundance: One randomized, replicated, controlled study from the USA found mixed effects of organic farming on weed seed predation by natural enemies. Two of three randomized, replicated, controlled studies from the USA found more weeds in organically farmed fields, but in one of these studies this effect varied between crops and years. One study found no effect.

  • Yield and profit: Six randomized, replicated, controlled studies measured yields and found one positive effect, one negative effect and one mixed effect, plus no or inconsistent effects in three studies. One study found net profit increased if produce received a premium, but otherwise profit decreased. Another study found a negative or no effect on profit.

  • Crops studied: apple, barley, beans, cabbage, carrot, gourd, maize, mixed vegetables, pea, pepper, safflower, soybean, tomato and wheat.
    http://www.conservationevidence.com/​actions/​717

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