PPDL Picture of the Week
July 31, 2017
Manganese toxicity on cantaloupes
Wenjing Guan, Assistant Professor, Department of Horticulture and Landscape Architecture, Purdue University
Manganese toxicity is a
common problem for cantaloupes growing in sandy soils across southwestern
Indiana. This is a pH related plant nutrient disorder. It often occurres
in the fields or sections of the fields with soil pH ≤5.5. Manganese exists in
soil solution as either Mn2+ or Mn3+. Plants take up manganese in the form of Mn2+. The proportion of exchangeable Mn2+ increases dramatically as soil pH decreases,
and waterlogged soils can promote the reaction.
Manganese toxicity develops
on both cantaloupes and watermelons. But the symptom is more often observed on
cantaloupes. The symptom first noticed when light green to yellow color shows
between the veins on older leaves. Look at the leaves toward the sun
and you will notice the chlorosis is formed by numerous tiny light green
to yellow pin-hole type spots growing together. As the affected tissue dies,
yellow areas become necrosis. Because symptom of manganese toxicity can easily
be confused with foliar diseases, growers may misdiagnose the problem and waste
fungicides by spraying for nonexistent diseases.