Crop protection in organic agriculture - Organic Agriculture: A Global Perspective - page 108

be done by focusing on organic matter build up over many years, and minimising applications
of additional organic fertilisers during crop growth.
The absence of fungicide use in organic cereal production has given rise to concerns about
grain moulds and mycotoxins on organic cereals. These concerns are not always justified.
Fusarium scab of wheat was less severe in organic than in conventional farms in the Nether-
lands (Tamis and van den Brink 1998). In several German studies, Fusarium contamination of
grains and concentrations of deoxynivalenol (DON) were also lower in organic than in con-
ventional farms (Birzele et al . 2002, Schollenberger 2002), while in some French studies
Fusarium head blight severity and mycotoxin levels were similar in organic and conventional
wheat production (Champeil et al . 2004). DON concentrations were also similar in organic
and conventional grains in a British study (Berlath et al . 1998), but were below the European
threshold level. Average levels of ochratoxin A contamination (from Penicillium and Aspergil-
lus ) were similar in rye and barley grains from organic and conventional farms, but signifi-
cantly lower in organic than in conventional wheat grains (Czerwiecki et al . 2002). Thus, there
is no reason to believe that mycotoxins would constitute a problem in organic cereal products
(Schollenberger et al . 1999). The main reason for lower contamination levels at some organic
farms may be the lower N contents and greater diversity of non-pathogenic fungi on the ears of
unsprayed plants (Lemmens et al . 2004). Moreover, mycotoxin production per unit mycelium
can be enhanced by the stress of certain fungicides (Felix D'Mello et al . 1998).
Insect pests can often be kept in check by a greater diversity of non-herbivorous arthro-
pods. Piorr and Hindorf (1986) noticed an increase in beneficial insects during the conversion
period on a biodynamic farm. Reddersen (1997) also observed a higher diversity of arthropods
in organic cereal fields, accompanied by a lower arthropod abundance compared to conven-
tional cereal fields. In many other studies, a relatively high arthropod abundance in organic
compared to conventional wheat fields was associated with a higher arthropod diversity in
organic wheat fields (Moreby et al . 1994, Basedow 1995, Pfiffner and Niggli 1996). Feber et al .
(1997) measured similar levels of pest butterf lies in organic versus conventional farmland, but
found significantly more non-pest butterf lies in organic farmland. Total numbers of epigeic
predatory arthropods were also highest in organic farming systems compared to pesticide
intensive agricultural production systems (Basedow 1991). Among epigeic predators, carabid
abundance and species richness were higher in organic cereal fields, while staphylinid and
spider abundance and species richness were generally similar in different management systems
(Booij and Noorlander 1992). The reasons for the frequently greater arthropod diversity in
organic farms can be found in the greater variety of food sources associated with greater plant
diversity within fields and in surrounding habitats (Booij and Noorlander 1992, Holland and
Fahrig 2000, Asteraki et al . 2004).
Greater plant diversity in the field can also have benefits for disease control in cereal crops.
Different cereal crops, for example barley and wheat, have sometimes been grown in mixtures
resulting in a reduction in barley powdery mildew by increasing the distance between suscep-
tible plants (Burdon and Whitbread 1979). However, mixtures of wheat and field beans resulted
in higher powdery mildew severity on the wheat crop as the bean density increased (Bulson et
al . 1997); this was probably as a result of the greater N content of the wheat plants. Cultivar
mixtures with different resistance genes have also been very effective in controlling different
barley powdery mildew pathotypes (Finckh et al . 2000). The use of cultivar mixtures was a
very effective and widespread practice in the former Eastern Germany (Finckh et al . 2000) and
is now practiced on a large scale in rice production in China. Unfortunately, organic growers
have not yet widely adopted this practice. Another form of mixed cropping, relay cropping of
clover between cereal plant rows, is gaining popularity in Europe. This practice helps control