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Stem Rot

Phytophthora stem and root stem rot is a soil-borne fungal disease caused by Phytophthora sojae. This pathogen causes seed rots, pre- and post emergence damping off of seedlings and stem rot of plants at various growth stages. Disease development is favored by soil temperatures is above 60oF and high soil moisture. In young plants symptoms include rapid yellowing and wilting that is typically accompanied by a soft rot and collapse of the rot. Stem and root rot 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.

The stem shows dark discoloration of the stem that extends up from the root/soil line up the plant. Plumeria in early reproductive stages and beyond will have general yellowing of the lower leaves that progress upward on the plant and general overall wilting of the plumeria. As the disease progresses death of the plumeria typically occurs. Examination of the root system will show lateral and branch root discoloration and the tap root will also show a brown discoloration. Splitting of the root, crown and stem will show a tan to brown discoloration along the outside portion of the stem which extends up the plant . This brown discoloration that is observed when the plant is split is typically also evident on the outside of the stem.

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

Root and Stem rot can readily infect plumeria in their vegetative or flowering stages. The disease can survive up to FIVE YEARA in the soil. It is important to sterilize soil after a plumeria has had root or stem rot.

  • Root and Stem rot 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.
  • Fungicides can be used to manage the disease as well as burning the infected plants and sterilizing the soil.

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 plumeria 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 plumeria for the following symptoms:

Infected root and 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.

How to manage?

  • Burn straw and stubble or any crop residue or let the straw decompose.
  • Reduce watering and be sure adequate drainage is provided.
  • Balance the use of fertilizer or perform split application with high potash and lime to correct soil pH.
  • 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.