Agriculture Reference
In-Depth Information
and destruction and disposal of infected trees. However, PPV was detected again in 2004,
leading to a new campaign of survey and eradication (Ramel
et al.,
2006).
If a pathogen requires two hosts to complete its life cycle, control is possible by eradi-
cation of the less important host. The wheat stem rust fungus,
Puccinia graminis
f. sp.
tritici
, is a case in point. It requires two hosts, wheat and barberry, to complete its life
cycle and until the 1950s was the most important pathogen of wheat in the United States
(Leonard, 2001). Since the 1950s, however, stem rust has declined in importance in the
United States, due in part to the successful eradication of its alternate host, common bar-
berry (Campbell & Long, 2001).
2.2.2
Sanitation
Sanitation refers to eliminating or reducing the amount of inoculum present by various
means, including removal of infected plant parts and plant debris. Destroying crop resi-
dues is an important practice, but how it is performed depends upon the type of crop
and the type of pathogen. Burying crop debris (see Section 2.3.1) can destroy certain
pathogens, particularly if the residues are ploughed in deeply enough, while burning crop
residue is a common practice for cereal crops in some parts of the world and will destroy
many pathogens. However, burning has some drawbacks, particularly, loss of nutrients
and increased soil erosion.
Removal of infected plant parts by pruning has been recommended for the control
of fungal pathogens of perennial crops, for example, black Sigatoka disease during the
establishment phase of plantains (Emebiri & Obiefuna, 1992), while pruning of infected
plant parts and removal and destruction of plant debris form an integral part of the man-
agement of
Botrytis
in greenhouses (Hausbeck & Moorman, 1996).
Field sanitation is
also recommended for control of late blight in potatoes (Sherf & Macnab, 1986; Cohen,
1987). Removal of plant debris by burning was shown to reduce severity of tan spot
(
Pyrenophora tritici-repentis
) in wheat and to increase yields (Carignano
et al.,
2008),
while burning of chickpea stubble minimised stubble-borne inoculum of
Ascochyta rabei
(Gan
et al.,
2006). However, some workers consider that burning has limited utility for
plant disease control, since elevated soil temperatures are unlikely to be uniformly intense
enough at the soil surface and throughout the upper soil profi le where pathogen survival
structures are found (Felton
et al.,
1987). Thus, burning crop residue in Saskatchewan
was shown to increase the incidence of plants infected with the common root rot patho-
gen,
Cochliobolus sativus
(Ledingham
et al.,
1960)
and although burning wheat residue
in Brazil reduced the population of
C. sativus,
disease severity was not reduced (Reis &
Abrao, 1983; Reis
et al.,
1990).
2.2.3
Crop rotation
Crop rotation is an ancient cultural practice and a form of crop rotation is described in
Leviticus
25:3-5, whereby fi elds were not to be sown and vineyards not to be pruned once
every seven years, as a means of providing complete rest for the land (Howard, 1996).
Indeed, the benefi ts of crop rotation include maintenance of soil structure and organic
matter, and a reduction in soil erosion that is often associated with continuous row crops
(Janvier
et al.,
2007). The main purpose of rotating crops in conventional arable rotations
