What is causing a mum plant to develop red leaves is a common late-season question? We will explore the multiple possibilities that result in red leaves.
Red leaves on garden mums can develop due to several possible factors. Root Rot. Pythium root rot and cold temperatures can result in an uptick of anthocyanin production in the leaves, causing red foliage of the overall plant (Fig. 1). Usually this occurs on a single plant or isolated plants around the mum field. Inspecting the roots for rot will help diagnose the problem.
Stem Cracks
Single stems or sides of the plant that develop red leaves are usually a result of stem cracks (Fig. 2). Usually the crack occurs at the base of the stem where it attaches to the central stem.
Stem cracks can result from mechanical damage from brushing against the plant, wind damage, weak stems, or heavy stems that break. These cracks are often challenging to observe when inspecting the plant which makes diagnosing the situation difficult.
Phosphorus Deficiency, Type 1 Cool Season
The typical symptomology of a phosphorus (P) deficiency is lower leaf purpling or reddening (Fig. 3). Red coloration is enhanced by cool temperatures too. Low P concentrations, cold temperatures, and wet substrate conditions can all play a part in the development of symptoms.
Read the full e-GRO Alert at e-gro.org