Agriculture Reference
In-Depth Information
Figure 17.2. Cumulative number of
P
.
infestans
sporangia collected per week throughout
2004 in Viçosa, MG, Brazil, using a Burkard sampler.
17.4.3 Control measures
Management strategies are conveniently grouped into those that limit or reduce the
initial inoculum and those that retard pathogen growth rates.
A variety of techniques can limit or reduce the size of the pathogen population at
the beginning of the season. Elimination of infected potatoes can be carried out
whether they are in piles as individual tubers left in the field, or used as seed tubers.
Thus destruction of cull piles and destruction of volunteers are important
components of a comprehensive management system. Planting only healthy seed
tubers is also very important. If chemicals that can prevent pathogen growth in seed
tubers become available, these will be very beneficial. However, because sporangia
of
P. infestans
can be dispersed aerially, late blight is a community phenomenon
and, if there are many growers in a region, each of the members of the community
needs to take proper precautions to suppress late blight. If some growers do not take
these precautions, then their farms become potential sources of inoculum for their
neighbours.
Techniques that limit pathogen growth rates include utilization of cultivars with
field resistance, and periodic application of protectant or effective systemic
fungicides. Against sensitive isolates, the systemic fungicide metalaxyl could halt an
established epidemic. However, many populations throughout the world are no
longer sensitive to metalaxyl. Currently, many oomycete-specific fungicides such
as QoI compounds, dimethomorph, propamocarb, etc. (Köller, 1998) have been
