Compendium of Potato Diseases - (PDF, 101 mb) - USAID

Fig. 30. Calcium deficiency on potato sprouts: A, healthy sprout;
B, sprout treated with calcium sulfate; Cand 0, calcium-deficient
sprouts. Note necrosis of tips and tendency for lateral branching.
(Courtesy P.W. Dyson and J.Digby, and copyright permission of
Macaul,y Institute for Soil Research)
flecks form in the pith. Tubers may be extremely small. Internal
rust spot is more severe on dry soils with low Ca, a tendency
towards acidity, and amoderate to low base-exchange capacity.
(See also internal heat necrosis and phosphorus deficiency.)
Seed tubers in Ca-deficient soil remain hard and produce
relatively normal roots. Sprouts become necrotic immediately
behind the tip and fail to grow (Fig. 30). In storage, sprouts
become necrotic 3-5 mm below the tip due to collapse of outer
cortex and inner pith and, later, of vascular tissue. Multiple
lateral branches form below the sprout tips, and, with certain
cultivars, small tubers known as "little potato" form
prematurely before the development of aboveground sprouts.
Ca deficiency and internal sprouting show certain relationships.
Symptoms are most severe on sandy soils below pH 5.0,
where symptoms of Mn or Al toxicity may also be present.
Calcium treatment of sprouts reduces incidence of necrosis
below the tip. liming the soil above pH 5.2 should be avoided
because of potential Tranferof problems ld lave Ca with fom toyoun common levesand scab. romthe
Transfer of ('a from old leaves to young leaves and from the
top of the plant to the tubers is limited. Ca must therefore be
available during the entire growing period, particularly during
tuberization.
Selected References
BRAUN, H., and I). E. WILCKE. 1967. lodenprofile und ihre
Beziehungen zum standortbedingten Auftreten der Eisenfleckigkeit
bei Kartoffeln. Phytopathol. Z. 59:305-336.
DeKOCK, P. C., P. W. DYSON. A. HALL, and F.B.GRABOWSKA.
1975. Metabolic changes associated with calcium deficiency in
potato sprouts. Potato Res 18'57-5 I.
WALI.ACET.,and E.J.HEWITT. 1948. Effects of calciumdeficiency
on potato sets in acid soils. Nature 161:28.
Magnesium
Mg deficiency is one of the most commonly encountered
nutritional problems. Because Mg is highly mobile within the
plant, new growth appears essentially normal and symptoms
develop on older leaves. A pale, light green color--later, amore
definite necrosis begins at the leaf tips and margins and
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progresses between the veins, becoming most severe toward the
center of the leaf. l.eaves are usually thick and brittle and roll
upward, with tissue raised between tile veins (Plate 10). Necrotic
leaves either hang on the plant or abscise. Roots are stunted,
reducing the ability of the plant to absorb Mg.
Mg deficiency usually occurs on sandy acid soils that are
readily leached. but may occur on heavier soils. High rates of K
fertilizer or high K levels in soil accentuate Mg deficiency.
Solubility of Mg is increased b. acid-forming fertilizer.
Sym ptomis freq uenti'follow leaching after periods of heavy rain.
Exchangeable Mg should exceed 50 ppm for mineral soils and
higher (100 ppm) for muck soil.
Mg may be supplied as MgSO 4 in fertilizer or dolomitic
limestone or as a 2'i MgSO 4 foliage spray. Higher
concentrations usually may be applied to foliage without injury.
Selected References
BONI)E, R. 1934. Potato spraying -- lhe value of late applications and
magnesium-bordeaux. Am. Potato .1.11:152-156.
CH UCKA, J.A., and B.E.BROWN. 1938. Magnesium studies with the
potato. Am. Potato .. 38:301-312.
SAWYER. R.L.,and S.L.I)AI.t.YN. 1966. Magnesium fertiliation of
potatoes on Long Island. Am. Potato J. 43:249-252.
Sulfur
S deficiency, as reported in several locations in Wisconsin on
Planefield loamy sand, is a generai yellowing with a slight
upward rolling of leaflets. Symptoms vary from slight to
marked chlorosis over the entire plant. Beneficial responses
have been obtained with sulfur soil applications or with
fei ,;,'izers containing sulfur.
Aluminum
A Itoxicity causes roots to become short and stubby with few
branches. Leaves remain normal in color although plants are
small and spindly, with branches rising at acute angles. Potato;,
relatively tolerant to Al toxicity.
Al solubility is often high in soils below pH 5.0. Soil
conditions may be corrected by adding superphosphate
fertilizers, increasing soil pli to 5.5 or above with lime, or
increasing the organic content of the soil.
Selected References
BROWN, B.A.. A. H AWKINS, F.. J. RI)BI3NS. A. V. KING.and R.I.
MUNSEI.LI. 1950. Causes of very poor growth of crops on a
formerly productive soil. Soil Sci. Soc. Am. Proc. 15:240-243.
HAWKINS, A.. B.A. BROWN, and E..1. RUIBINS. 1951. Extreme
case of soi toxicity to potatoes on a forme rlyproductive soil. Am.
Potato .1.28:563-577.
Boron
In plants with B deficiency, growing points die; lateral buds
become active: internodes are shortened: leaves thicken and roll
upward: and tileplant assumes aI bushy appearance. Starch
accumulation in leaves is pronounced and may resemble virus
leafroll. Roots are short, thick, and stunted. Tubers are small.
showing surface cracking particularly at the stolon end and
localized brown areas under the skin near the stolon end or
brown vascular discoloration.
Some sandy soils, peat soils, and overlimed, acid, upland,
podzolized soils are inherently low in B or apparently fix B so
that it becomes unavailable to plants.
Applications of B should be made cautiously because B is
toxic to potatoes in relatively small amounts and deficiency is
rare.