POTATO
DIEASE AND THEIR CONTROLS
There are many
diseases that affect potato tubers, so as you sort through your potato harvest
each year, take a moment to check for disease
symptoms.
The are many types of
diseases in potato
Septoria leaf spot
Less
vigorous plants are usually affected. Small, round to
irregular spots with a grey center and dark margin on
leaves. Spots usually start on lower leaves and gradually advance
upwards. At later stage spots coalesce and leaves are blighted.
Controls : Maintain wide spacing, roted with unrelated crops, resistant varieties.
Late blight(Phytophthora infestans)
Late blight affects potato
foliage and tubers. Foliar symptoms start with brown to black, water soaked
lesions on leaves and stems which produce visible white sporulation at the
lesion margins under humid conditions. Whole plants and fields may collapse
rapidly. Tuber infection is initiated by sporangia from foliage being washed
down into the soil and usually begins in wounds, eyes, or lenticels.
Controls : Resistant
varieties; early planting, wide spacing to help keep leaves dry.
Early
blight (Alternaria solani)
Early blight usually affects
potato foliage but tuber infections can also occur. Tuber lesions are dark, sunken,
and circular often bordered by purple to gray raised tissue. The underlying
flesh is dry, leathery, and brown. Lesions can increase in size during storage
and tubers become shrieked.
Controls : Maintain
wide spacing and use drip irrigation to keep leaves dry. Harvest plants before
the disease becomes severe.
Black scurf/ canker
(Rhizoctonia solani)
Black scurf is purely
cosmetic and does not reduce yield, even in storage. Irregular, black hard
masses on the tuber surface are overwintering structures (sclerotia)
of the fungus. Presence of these sclerotia may be
minimized by harvesting tubers soon after vine-kill and skin set. While the sclerotia themselves do not cause damage, they allow the
pathogen to survive in the soil and serve as evidence of its presence. In cool,
wet soils, R. solani can cause dark, sunken lesions
on underground sprouts and stolons. Cankers can
also form on the tubers themselves, usually at the stolon or in lenticels. Cankers on tubers which can be small and superficial but may be
large, sunken and necrotic.
Controls : The
use of resistant varieties in soils where the problem recurs is the only
economical means of long-term control.
Potato Virus Y
Potato Virus Y (PVY) can
cause necrotic ring spots on tubers, depending on which strain of the virus is
present, which potato variety is grown, and the time of infection. Affected
tubers have roughened rings of darker brown or reddened skin.
Controls : Maintain
wide spacing, early planting, resistant varieties.
Fusarium
Dry Rot (Fusarium spp.)
Fusarium dry rot
causes internal light to dark brown or black dry rot of the potato tuber. The
rot may develop at an injury site such as a bruise or cut. The pathogen
penetrates the tuber, often rotting out the center. Extensive
rotting causes the tissue to shrink and collapse, usually leaving a dark sunken
area on the outside of the tuber and internal cavities.
Controls : Resistant
varieties; early planting, wide spacing to help keep leaves dry.
Pink rot(Phytophthora erythroseptica)
Pink rot infections start at
the stolon end and result in rotten and discolored periderm with a clear delineation between healthy and
diseased tissue. When exposed to air, tuber flesh turns pink and then
brown-black.
Controls : The use of resistant
varieties in soils where the problem recurs is the only economical means of
long-term control. Eliminate
infection sources by early roguing of diseased
plants. Minimising cultivation damage to plants will prevent contact
infection.
Black
heart- disease
Black Heart is caused by lack of oxygen during storage which causes the tissue to die from the inside out and turn black. The condition is not reversible but if you notice it quickly and correct your storage conditions you can prevent the whole crop from being affected.
Common Scab (Streptomyces spp.)
Common
scab produces tan to dark brown, circular or irregular lesions which are rough
in texture. The type of lesion is dependent on potato cultivar, tuber maturity
at infection, organic matter content of soil, strain of the pathogen, and the
environment. Common scab is controlled or greatly suppressed at soil pH levels
of 5.2 or lower, though a closely related but less common species of
Streptomyces known as acid scab can survive down to 4.0.
Controls : The
use of resistant varieties in soils where the problem recurs is the only
economical means of long-term control.
Tobacco Necrosis Virus (TNV)
TNV is a rare tuber blemish
disease with no haulm symptoms. The disease is also known as ‘ABC’ disease
named after three symptom categories first described in the Netherlands. The ‘ABC’ name refers to (A) dark brown raised
patches, (B) dark sunken lesions, sometimes in rings or horseshoe shapes, and
(C) light brown cracked patches. Any combination of these symptoms may occur
but look for dark coalescing rings, very dark patches, and mild light tan
patches. All are often associated with distinctive small corky lesions that
crack through the skin and superficially resemble elephant hide (see Rhizoctonia). The blemishing can be very severe.
Controls : Elimination of alternative host plants will help
reduce the risk of disease. Take care to prevent potentially contaminated soil
from infecting clean fields.