Crop protection in organic agriculture - Organic Agriculture: A Global Perspective - page 104

Pest and disease management case studies in organic ersus
conentional agriculture
Relatively few replicated, on-farm studies compare the relative effectiveness of organic and
conventional crop protection practices. This is particularly true for vertebrate pests. Table 4.2
lists recent examples of field comparisons between organic and conventional agriculture in
different crops and location. These studies show that biodiversity is generally higher on organic
farms, that pests and pathogens are usually regulated by organic practices, but that there are
exceptions in either case. Few studies monitor pest levels and related yield losses. Even fewer
studies are integrative for crop protection, monitoring both pests and pathogens. We provide
two detailed, integrative case studies selected from European agriculture and commercial
operations in the western USA to illustrate some constraints and benefits of organic agricul-
ture practices. These examples and those listed in Table 4.2 illustrate many of the general
themes described above, including:

1 holistic approaches that characterise organic agriculture;
2 the kinds of pests and pathogens affected by different management practices;
3 the possibility of different, but equally successful, routes to crop protection; and
4 the importance of diversity in promoting ecosystem services for organic agriculture.

Table 4.2 Recent on-farm and field-experiment comparisons of pest or disease levels under
organic or ecological versus conventional management
Crop Management

practices in
organic crops

Crop protection consequences as
compared to conentional

Reference

Almond A mixed cover crop,

no fertilisers or
pesticides

Shot hole disease more severe, almond
scab on leaves and fruits similar; no
differences in fungal communities

Teviotdale and
Hendricks
(1994)

Apple Organic soil

amendments that
promote soil
microbial diversity

Higher growth scores and lower
colonisation by root pathogens
( Pythium sp., Rhizoctonia solani )

Manici et al .
(2003)

Organic soil
amendments that
promote soil
microbial diversity

Less Pythium root rot, more non-
pathogenic Pythium spp.

Mazzola et al .
(2002)

Sulfur sprays More severe apple scab ( Venturia

inaequalis ), similar orange tortrix
( Argyrotaenia citrana)

Vossen et al .
(1994)

Weed-, disease-,
nutrient
management

Lower abundances of predaceous
beetles, lower diversity of non-
predaceous beetles

Pearsall and
Walde (1995)

Carrot Biological pest

control, soil
management

Higher diversity of predaceous
arthropods

Berry et al .
(1996)

Cereals
(wheat,
barley,
triticale,
rye)

Organic practices
(lower fertility, no
pesticides)

No difference in epigeic collembolan
composition

Alvarez et al .
(2001)

No difference in species richness of
butterflies, rove beetles, spiders, lower
richness of carabids

Weibull et al .
(2003)