Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
We are seeing problems with melon leaf yellowing again this year. This is a common problem in muskmelons and specialty melons. There are several potential causes.
If the yellowing is on leaf edges it most commonly is due to salt effects and fungicides. Copper fungicides are often the culprit in this leaf yellowing, causing a phytotoxic reaction. Foliar fertilizer applications can often worsen the yellowing by increasing salt levels on the leaves.
Each year there are some fields of cantaloupes that are affected by manganese toxicities. This occurs when bed pH drops below 5.4 which affects soil chemistry so that plant available manganese increases greatly and plants take up quantities that become toxic. As a micronutrient, manganese is needed in only small amounts and the sufficiency range is between 20-100 ppm. Symptoms of manganese toxicity are pin hole yellow spots clustered between the veins of older leaves
Marginal yellowing on cantaloupes due to excess salts (Dan Egel, Extension Vegetable Pathologist, SWPAC, Purdue University)
Leaf bleaching due to reaction to copper fungicides
Magnesium deficiencies also can occur at low pH and older leaves will show interveinal chlorosis. These symptoms can be confused with mite damage so check for mites in the diagnostic process.
Air pollution is another cause of yellowing of cantaloupe leaves. This yellowing is usually confined to older crown leaves.
Air pollution damage to melons