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.

​​Click image to enlarge