Biology Reference
In-Depth Information
environments and selection pressures. Genetic diversity in kochia as estimated by
simple sequence repeat markers was high (Mengistu and Messersmith 2001), with
90% of the variation occurring within populations. Genetic diversity within and
among resistant and susceptible populations was similar. This result suggests that
despite generations of herbicide selection, kochia maintains high genetic diversity
through substantial levels of gene flow within and among populations. High levels
of genetic variation, and the accompanying increased ability to respond to selection
pressures, natural or artificial, are expected to affect the spread or success of an
invasive species (Lee 2002; Sakai et al. 2001). Little is known about genetic diver-
sity of Canadian kochia populations, and high levels of genetic diversity may well
be an important factor contributing to their spread.
8.9
True Integrated Pest Management
It has been suggested, and appears to be true, that many integrated pest manage-
ment (IPM) programs can be more accurately described as “integrated pesticide
management” or as the “other IPM” (Ehler 2006). Clearly, to effectively manage
invasive weed species over the long term, we have to look beyond herbicides alone.
Indeed, true integrated weed management not only requires that tools other than
herbicide be employed, but that management practices are multi-disciplinary, and
are compatible (O'Donovan et al. 2007).
It is not easy to make pest management strategies compatible. For example, early
weed removal is desirable for optimum canola yield, but can cause greater root maggot
(
Delia
spp.) (Diptera: Anthomyiidae) damage in canola (Dosdall et al. 2003). In a recent
popular press article describing this study, the following result was highlighted: ' . . . up
to 70% of root maggots are eaten by predators and 40% of the survivors are killed by
parasites' (McMenamin 2006). Therefore, when insect pests are below economic
thresholds and sprayed unnecessarily, beneficial insects may also be killed. In the
Prairies, economic thresholds for major insect pests are known, updated annually, and
rapidly adopted by producers. Similarly, Diadegma wasp (
Diadegma
spp.) parasitize
and can almost totally neutralize outbreak of a diamondback moth (
Plutella xylostella
L.)
pest. However, '…Diadegma produce more eggs when they can feed on wild mustard
or yellow rocket (
Barbarea vulgaris
Ait. f.) early in the year and survive longer on
lamb's-quarters and perennial sowthistle (
Sonchus arvensis
L.)' (McMenamin 2006).
Thus, weed control can negatively impact management of other crop pests; the relative
risks of yield loss due to weed competition or insect damage must be balanced.
8.10 Conclusions
Although some would take issue with the classification of our most common and
economically important Prairie weeds as invasive aliens, most of these species are
true aliens that have immediate and verifiable impact on crop producer income and
