Stem Rot

Stem Rot is a disease that causes the decaying of the inner layers of the Plumeria. The plumeria stem becomes soft and squishy as the inside rots away.  Stem rot moves very quickly and is almost always fatal to cuttings. Stem Rot usually occurs while trying to root cuttings or during winter storage.

Cool temperatures and wet soil contribute to Stem Rot.  Rooting cuttings and newly rooted plumerias are at highest risk for developing stem rot.

Stem rot officially is a disease caused by a fungus infection in the stem. Fungus that causes stem rot are Rhizoctonia, Fusarium and Pythium. Stem rot can readily infect crops that are in their vegetative or flowering stages. The disease can survive up to five years in the soil. Symptoms of stem rot includes staining of infected area, reduced crop yield and crop failure.

  • The disease can be spread through the use of unfiltered water as well as unsterilized tools.
  • Also leaving previous dead roots in soil can increase the risk of stem rot. Spores can also enter the plant through injured stem tissue on the plant including from insect attacks. The fungus impedes stem functions like transporting nutrients. It can cause water to leak through the lesions of stem tissue.
  • An issue with maintaining this disease is the lack of management by crop producers. Producers of plumeria tend to not manage for the disease because it normally results in the loosing of the affected cuttings or newly rooting plants.
  • Fungicides can be used to manage the disease as well as burning the crop after harvest or letting it decompose.

What it does

Stem rot leads to formation of lesions and production of chalky grains and unfilled panicles.

Why and where it occurs

The infection bodies or sclerotia are found in the upper soil layer. They survive in air-dry soil, buried in moist soil, and in tap water. They can also survive on straw, which is buried in the soil. 

Infection is high on plants with wounds as a result of taking cutting with infected tools or rooting cuttings with infected soil. The panicle moisture content and nitrogen fertilizer also influence disease development.

How to identify?

Check the plant for the following symptoms:

Infected stem rots

  • visible numerous tiny white and black sclerotia and mycelium inside the infected culms
  • infected culm lodges and caused unfilled panicles and chalky grain
  • The stem becomes soft or mushy.
  • Initial symptoms are small, irregular black lesions on the outer leaf sheath near water level. Lesions expand as the disease advances.

Why is it important?

The infection is seen on the rice crop during early heading and grain filling. The leaf sheaths decay and cause lodging and lower grain filling. It can cause heavy losses in many countries.

For example, in Japan, there are 51,000−122,000 hectares infected and estimated annual losses of 16,000−35,000 due to this disease. In Vietnam, the Philippines, and India, losses from 30% to 80% were recorded.

How to manage?

  • Burn straw and stubble or any crop residue after harvest or let the straw decompose.
  • Drain the field to reduce sclerotia.
  • Balance the use of fertilizer or perform split application with high potash and lime to increase soil pH.
  • Chemicals such as fentin hydroxide sprayed at the mid-tillering stage, thiophanate-methyl sprayed at the time of disease initiation can reduce stem rot incidence in the rice field.
  • Other fungicides such as Ferimzone and validamycin A also show effectivity against the fungus.
  • Do not reuse soil know to to have had infected plants.
  • Root only in fresh sterilized soil.

Once a Plumeria has survived it’s first winter, Stem Rot is usually not a problem.

Plumeria Cuttings:  Infected cuttings typically fail to root. Instead they develop rot that gradually moves up the stem. Leaf wilt and leaf spotting may be evident. The rotted stem eventually becomes shriveled, turns dull dark brown to black in color, and falls over in its pot.

Mature Plumerias:  Although rare,  mature plants can lose a branch or two from stem rot and/or freeze damage.  Freeze damage looks almost the same as Stem Rot.  In either case, with mature plumeria just cut off the affected areas and a mature plumeria will bounce right back with new branches and leaves.

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