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Potato leafroll
virus is a major limiting factor in potato production throughout
the United States. Infection by this virus can cause severe plant
symptoms accompanied by yield reductions, sometimes reaching 40-70
percent. In addition, in many potato varieties potato leafroll virus
causes a diffuse net necrosis in infected tubers, rendering them
unmarketable. Virus inoculum originates primarily from infected
seed, and spread in the field is only accomplished by aphid vectors,
the most important being the green peach aphid. Therefore, management
of the green peach aphid and its interaction with potato leafroll
virus is of paramount importance in all potato production areas
of Idaho and is crucial to controlling the spread of the virus in
the field.
Research is
currently being conducted to address several areas of aphid-virus
interactions that, when exploited, will aid in controlling the spread
of potato leafroll virus. These areas include:
| establishing
action thresholds for making insecticide application decisions
for reducing green peach aphid populations; |
| determining
seasonal inoculation dates that result in the highest levels
of potato leafroll virus infection and tuber net necrosis; |
| assessing
the effects of repeated insecticide applications on seasonal
green peach aphid population development and insecticide resistance.
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Appropriate
action thresholds allow growers to initiate aphid control measures
prior to significant virus spread in the field. Early season infection
by potato leafroll virus is unlikely to cause net necrosis in tubers
from infected plants, so knowing the relationship between the time
of infection and the development of net necrosis is critical for
optimizing aphid control strategies later in the season. There are
increasing reports that certain insecticides are not providing timely
and effective aphid control in potatoes. This, and the fact that
some insecticides are especially detrimental to aphid natural enemies,
means that growers must know whether or not repeated insecticide
use will result in increasing aphid numbers in the field.
Finally, the
recent introduction of late blight into Idaho coincided with a potato
leafroll virus epidemic in 1996. In other areas of the United States,
frequent use of fungicides for late blight control has resulted
in exploding green peach aphid populations because the fungicides
also kill fungi that attacks aphids. Research to examine this phenomenon
in Idaho will soon be initiated with a view to providing growers
with an integrated approach to late blight and potato virus control.
For more information
contact: Thomas M.
Mowry
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