Agriculture Reference
In-Depth Information
The first two approaches tend to be prophylactic control measures and the latter involves the
substitution of synthetic chemical inputs used in conventional crops once pest or disease levels
begin to rise. Because prophylactic crop protection in organic systems is based on ecological
processes, the crop is seen as a host, the crop field and surroundings as a biotic community
with its abiotic conditions, and the pest or pathogen as an invader that colonises the crop
habitat, establishes and erupts. Barriers to pest outbreaks include various means of isolating
the crop from pest/pathogen source pools and regulating pest and pathogen populations once
established through community resistance (Table 4.1). Community resistance comprises those
factors that cause the habitat to be unsuitable for proliferation of invaders, such as resource
limitation, competition, and predation. Community resistance compensates for synthetic pes-
ticides in conventional agriculture (Drinkwater
et
al
. 1995, Lampkin 1999). Above-ground,
community resistance involves the conservation and enhancement of beneficial fauna, either
directly or via diversified vegetation. In soil, community resistance can be enhanced by activa-
tion of the soil food web through amendment with slowly decomposing organic materials.
Enhancement of biodiversity is the key element in these efforts. Curative measures, taken as
pest or pathogen populations begin to rise, include application of organically approved biocides
or behaviour-modifying compounds derived from natural sources or inundative releases of
other organisms (competitors, predators, or parasites). Curative measures may substitute for
synthetic pesticides in conventional agriculture (Guthman 2000), and can complement other
tactics, such as biodiversity enhancement. Successful crop protection in organic systems relies
on prophylactic measures that prevent pest and pathogen colonisation, establishment or build
up sometimes in combination with curative measures when needed.
Prevention of colonisation or establishment of pests and pathogens in organic agriculture
Colonisation of the crop field, orchard, vineyard, storage facility or other agricultural environ-
ment by pests and pathogens is prevented through sanitation, source isolation, and other pro-
tective measures. Practices to prevent colonisation and establishment of pests and pathogens,
namely sanitation, clean seeds or vegetative propagating materials, crop rotation, adjustment
of planting time, removal of certain weeds, fencing or netting against vertebrates, sealing or
repelling against storage pests, hold for both organic and conventional agriculture. However,
they are even more important for organic farming, because curative measures are restricted
here. The use of various crop protection practices to prevent colonisation of the crop by pests
and pathogens are at least as common in organic agriculture as in conventional agriculture
(Table 4.1). To illustrate some of the particular problems facing organic growers, we consider
seed sanitation and crop rotation.
EU regulation 2092/91 for organic farming requires that all inputs in organic agriculture,
including seeds and vegetative materials, must originate from the organic production chain
when available (Lammerts van Bueren
et
al
. 2003). Officially registered seeds and vegetative
material must be true to type, pure and healthy (in terms of percentage germination and
freedom from plant pathogens and pests). It is sometimes assumed that seed produced under
organic conditions would have a greater 'vitality' than conventionally produced seed, but there
is no scientific evidence for this assumption. It is more likely that the germination and emer-
gence capacity of seeds is primarily determined by the pathogens that become associated with
the seeds in the seed production phase and during seed storage. In conventional seed produc-
tion firms, seed samples are tested for pathogen infection, and infected seed batches are culled
so that seeds can be marketed as certified disease-free, but organic seeds are (still) frequently
produced in small companies that lack those facilities. Thus, organic growers may face
problems with seed-borne diseases as long as inspection of organic seed is less stringent than
that in conventional seed production (see
Chapter 5
).
