Features Production Research
End-of-season checklist for managing late blight

October 25, 2011 – An
Alberta Agriculture specialist says that now is a good time to ensure that late
blight is not a problem next year.

October 25, 2011 – An
Alberta Agriculture specialist says that now is a good time to ensure that late
blight is not a problem next year.

“Despite the suitable
conditions, late blight disease levels were not as severe in 2011 as last
year,” says Robert Spencer, commercial horticulture specialist with Alberta
Agriculture and Rural Development, based in Stettler, Alta. “Increased
awareness in both the industry and the public led to a greater effort to
monitor fields, gardens and greenhouses in order to protect crops from late
blight, as well as a quicker response to any perceived infections.

“Despite the potentially
lower levels of disease, it is recommended that all growers of potato or tomato
(commercial or home garden) take specific steps to prevent the carryover of
disease into future years, as a number of valuable crop industries in Alberta
could be impacted by repeated outbreaks.”

At the end of the growing
season, growers should dispose of all above ground plant materials (stems and
foliage), whether infected or not, either by burial, freezing or composting.
This ensures that living tissues do not survive the winter and will break down
completely, thus preventing carryover of the late blight pathogen.

“Avoid placing infected
materials in uncovered compost piles as spores may be produced and spread the
disease to nearby plantings of susceptible crops,” says Spencer. “Piles may be
covered with a tarp until the materials have frozen and are completely dead.”

Since tubers represent the
primary method of disease carryover in potatoes in Alberta, every effort should
be made to prevent the survival of infected tubers. Carefully grade and sort
harvested potato tubers in an effort to remove any infected tubers. Commercial
seed growers should be prepared to further grade seed tubers in the spring, and
mancozeb-based seed treatments should be applied to try and protect developing
crops from seed-borne late blight.

“Culled tubers should be
disposed of in such as way at to encourage them to break down over winter,”
notes Spencer. “Culled tubers can be fed to livestock or may be chopped,
incorporated and buried, or can be placed in covered piles until they freeze
completely.”

The late blight pathogen
normally cannot survive away from living tissues. While the disease can survive
for a time on tomato fruit, spores will not carry over on tomato seed. The
disease can be introduced on living tomato transplants that are brought in from
areas where late blight survives the winter.

In Alberta, the late
blight pathogen does not survive or over winter in the soil, so growers should
not worry about re-infection by planting in or adjacent to a field where late
blight has occurred, provided there are no surviving tubers that could
reintroduce the disease through infected volunteer plants. However, rotating
between locations is always recommended, whenever possible, to prevent the
build-up of other diseases.

“All growers should take
the time to assess the past growing season and the level of risk of late blight
infection or re-infection that they will face for the next growing season,”
adds Spencer. “Determine where disease might have come from and put
preventative measures in place to protect against infection. It is in
everyone’s best interest to manage late blight as it is a community disease.”