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What Works in Conservation 2020

William J. Sutherland
Lynn V. Dicks
Silviu O. Petrovan
et al.

11. Some aspects of enhancing natural pest control

11.3 Arable farming

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Combine trap and repellent crops in a push-pull system

1Parasitism: Two randomized, replicated, controlled studies from Kenya found that push-pull cropping systems increased parasitism of stem borer larvae. One of the studies found no effect on egg parasitism.

2Natural enemies: Two randomized, replicated, controlled studies from Kenya and South Africa found push-pull systems had more natural predators, both in overall totals and the abundance of different predator groups.

3Pests: Two of three studies (two randomized, replicated, controlled) in Ethiopia, Kenya and South Africa found fewer pests. One study found no effect on pest infestation, but pests were scarce throughout. Two replicated, controlled studies (one also randomized) found fewer witchweeds.

4Crop damage: Two of three replicated, controlled studies (one randomized) found less pest damage, but one study (where pest numbers were low) found effects varied between years and types of damage symptom.

5Yield: Four of five replicated, controlled studies (two also randomized) found higher yields and one found no effect.

6Profit and cost: Two studies in Kenya and a review found greater economic benefits. One study found higher production costs in the first year, but equal or lower costs in the following five years.

7Crops studied: maize and beans.

8Assessment: beneficial (effectiveness 70 %; certainty 68 %; harms 5 %).


Trade-off between benefit and harms

Use crop rotation in potato farming systems

10Pests: Nine studies from Canada and the USA and one review investigated the effect of crop rotation on pest or pathogen populations in potato. Three studies (including two replicated studies of which one randomized and one controlled) and a review found crop rotation reduced pest populations and crop diseases in at least one year or at least one site. One paired study found pest populations increased in crop rotation. Four studies (including one replicated, randomized, controlled trial) found increases and decreases in pest populations depending on rotation crops used and other treatments. One replicated, randomized, controlled study found no effect.

11Yield: Three out of five studies (all replicated, controlled, two also randomized) from Canada and the USA, found that crop rotation increased crop yield in some years or with certain rotation crops. The two other studies (both replicated, one also randomized and one replicated) found yield increases and decreases depending on rotation crops used.

12Profit: One replicated, controlled study found that crop rotation increased profit.

13Insecticides: Two studies (one replicated, controlled) found that fewer insecticide treatments were needed on rotated plots.

14Crops studied: alfalfa, barley, broccoli, brown mustard, buckwheat, cotton, lupins, maize, oats, pearl millet, peas, potato, rye, sorghum, soybean, sugar beet, timothy grass, wheat and yellow sweet clover.

15Assessment: trade-offs between benefits and harms (effectiveness 50 %; certainty 50 %; harms 25 %).


Unlikely to be beneficial

Create beetle banks

17Natural enemies in fields: Six studies from Canada, the UK and USA (three replicated, controlled, of which two were also randomized) examined the effects on predator numbers in adjacent crops. A review found that predators increased in adjacent crops, but one study found effects varied with time and another found no effect. Two studies found small or slow movements of predators from banks to crops. One study found greater beetle activity in fields but this did not improve pest predation.

18Natural enemies on banks: Four studies and a review found more invertebrate predators on beetle banks than in surrounding crops, but one of these found that effects varied with time.

19• Eight studies from the UK and USA (including two randomized, replicated, controlled trials and two reviews) compared numbers of predatory invertebrates on beetle banks with other refuge habitats. Two studies found more natural enemies on beetle banks, but one of these found only seasonal effects. One review found similar or higher numbers of predators on beetle banks and four studies found similar or lower numbers.

20Pests: A replicated, randomized, controlled study and a review found the largest pest reductions in areas closest to a beetle bank or on the beetle bank itself. One review found fewer pests in fields with than without a beetle bank.

21Economics: One replicated, randomized, controlled trial and a review showed that beetle banks could make economic savings if they prevented pests from reaching a spray threshold or causing 5 % yield loss.

22Beetle bank design: Two studies from the UK found certain grass species held higher numbers of predatory invertebrates than others.

23Crops studied: barley, field bean, maize, oats, pasture, pea, radish, rapeseed, soybean and wheat.

24Assessment: unlikely to be beneficial (effectiveness 25 %; certainty 60 %; harms 10 %).


Likely to be ineffective or harmful

Incorporate plant remains into the soil that produce weed-controlling chemicals

26Weeds: Six studies (including six randomized, replicated, controlled tests) from Asia, Europe and North America examined the effect of allelopathic plant residues on weeds by comparing amended soils with weeded controls. Three studies found a reduction in weed growth, and three found effects varied between years, weed groups, or type of weeding method in controls.

27• Four studies from Asia and North America examined the effect on weeds by comparing amended soils with unweeded controls. Two studies found a reduction in weed growth, but one found that residues applied too far in advance of crop planting had the reverse effect.

28• Two studies found that effects varied between trials, weed species or the type of residue used.

29Weed control: Two studies, including one randomized, replicated, controlled laboratory study, found that the decrease in weeds did not last beyond a few days or weeks after residue incorporation.

30Pests: One randomized, replicated, controlled study in the Philippines found mixed effects on pests.

31Crop growth: Two of three studies found that crop growth was inhibited by allelopathic residues, but these effects could be minimized by changing the timing of application. One study found effects varied between years.

32Yield: Three randomized, replicated, controlled studies compared crop yields in amended plots with weeded controls and found positive, negative and mixed effects. Three studies compared amended plots with unweeded controls, two found positive effects on yield and one found mixed effects (depending on crop type).

33Profit: One study found that amending soils increased profit compared to unweeded controls, but not compared to weeded controls.

34Crops studied: beans, cotton, maize, rice and wheat.

35Assessment: likely to be ineffective or harmful (effectiveness 39 %; certainty 47 %; harms 30 %).


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