Agriculture Reference
In-Depth Information
disease, which is also vectored by psyllids. The
name “zebra chip” derives from the symptoms in
tubers, consisting of dark stripes in fried tissue,
and flecks and stripes in fresh tissue. Symptoms
can be absent in fresh tubers, but appear very
strongly when fried. Zebra chip also causes foliar
symptoms in plants very similar to psyllid yel-
lows and purple top, as mentioned above. Crop
damage from zebra chip can be intense despite
low psyllid population density. At times, zebra
chip is found in crops despite psyllids having
never been detected in the field. This difficult cir-
cumstance has resulted in extensive insecticide
use for psyllid control, and associated risk of in-
secticide resistance development. A thorough
review of zebra chip research and information
has been provided by Munyaneza (2012).
or beneficial insects that can be confused with
common pests can be seen in
Fig. 9.2 (b-d).
It is
important to remember that not all insects found
in potato are detrimental to crop development
and that the identification of insects is crucial
before taking curative measures.
9.4
Integrated Crop Management
The potato is a high-value crop with many
arthropod pests that can damage foliage, reduce
crop yield, and even feed on the tubers, thereby
rendering the crop unmarketable. As such, pests
that impact plant growth and damage tubers
should be managed to avoid economic loss. In
order to avoid crop damage, potato producers
should be good practitioners of integrated pest
management (IPM).
IPM programs aim to coordinate production
and pest management in a fashion that reduces
pest damage to the crop, with low hazards to
humans and the environment. There are four key
principles to IPM programs: pest identification,
monitoring, control action guidelines or economic
injury levels, and management of the pest. In order
to implement IPM, practitioners must be able to
characterize and assess the pest population accur-
ately and make sound management decisions.
Correct identification of the pest is the first
step in an IPM program for any crop; the other
three IPM principles are set in motion on the
pest's identification. Proper identification is also
important, because many insects benefit the
crop by preying on pest species. Insects that prey
on pest species are often referred to as “beneficial
insects”. Monitoring for pests can be species spe-
cific, as is the case with pheromone traps that
typically attract only one species. Economic
thresholds are almost always species specific.
The number of pests per sample unit that inflict
economic damage is dependent on the pest spe-
cies, since they consume different amounts of
foliage or affect the crop in different ways. Man-
agement tactics, particularly pesticide use, rely
on proper identification, as many insecticides
control only specific types of insects.
Once the pest has been identified, monitor-
ing should be conducted to determine the dens-
ity and life stages of the pest present in the crop.
Monitoring tactics will vary based on the species
monitored and can include: sweep net sampling,
Sampling and monitoring
Monitoring psyllid colonization and develop-
ment in potato fields has proven to be exception-
ally challenging since the advent of zebra chip.
This is due to the low populations required to
transmit damaging levels of zebra chip. In prac-
tice, a combination of techniques is used, in-
cluding yellow sticky traps deployed inside the
potato fields near edges, leaf sampling concen-
trating on field margins, and in some cases,
vacuum sampling machines of various designs.
Yellow sticky cards are most effective at detecting
early adult colonists, but very poor at assessing
resident populations in the field. Leaf samples
are used to detect and monitor levels of repro-
duction and nymphal development. A majority
of psyllid nymphs and eggs will be found in the
middle of the plant canopy.
9.3
Miscellaneous Pests
The potato can be colonized or can serve as a
temporary host for numerous insect species that
can impact the crop negatively. The insects de-
tailed above are the most common pests of po-
tato that have broad distribution, but numerous
pests are regionally important in various areas
where potatoes are grown.
Table 9.1
lists some
of these regionally important pests, with some
helpful references that can serve as a starting
point for further research on those species.
Additionally, some of these less common pests
