What Is Begonia Pythium Rot – Managing Begonia Stem And Root Rot

by johnah on November 27, 2020

What Is Begonia Pythium Rot?

Begonia Pythium (or Ptychotrya) is a fungal disease caused by a fungus called Phytophthora ramorum. It affects all types of plants including annuals, perennials, bulbs and trees. It causes stem and root rot which results in plant death within 2-3 years after symptoms appear.


Stems and roots are yellowish brown or blackened with necrotic spots. Leaves may turn pale green, then die back completely. The affected plant will not grow new shoots and leaves will wilt.

The disease is most common in warm climates where soil temperatures reach 50°F (10°C). It occurs naturally only when soil temperature reaches these levels but it can spread from one part of the garden to another if conditions are right.

When to see symptoms:

In cool climates, the disease usually appears between March and June. However, it can occur at any time during the year. Symptoms do not appear until late summer or fall in temperate zones such as North America and Europe. If you live in a hot climate, you might never experience symptoms because they don’t develop until later into the season.

What Causes Begonia Pythium?

The disease is caused by a fungus called either beigonia pithium or pythium. It is spread through the soil and also on infected plant material. The pathogen is most active during cool, wet conditions which allow it to survive in the soil. This is why rainy springs and fall are times when you are most likely to see this disease.

How Do You Prevent Begonia Pithium?

isolate new plants: This disease can spread through the soil and on infected plant material. When purchasing new begonias, make sure to purchase them from a reputable dealer and inspect them before adding them to your collection. If you bring home a new plant or piece of root, be sure to thoroughly disinfect any tools that come into contact with it. Always wash your hands after working with infected plants.

Don’t over water: This plant prefers to grow in consistently moist soil rather than wet soil. Make sure to only water your begonias when the soil is dry 1 inch deep. If the soil is kept damp, the begonias will be more susceptible to root diseases.

Add fresh compost: This plant grows best in a loose, well-draining potting mix. Add a 4-inch layer of fresh compost on top of the existing soil every spring. This will help improve the soil’s structure and boost its natural ability to drain.

Plant in raised beds: If you have sandy or clay soil, plant your begonias in raised beds filled with a good, loamy garden soil. This will help improve drainage and keep water from pooling around the roots.

Plant in afternoon: If you water your plants in the morning, water them in the afternoon if the temperatures are above 60°F (16°C). Watering begonias early in the day can cause their leaves to begin transpiring water before nightfall. If there is no nightfall, this can lead to disease and pest problems.

Remove and replace top 2 inches of soil every year: This helps remove any diseased plant material that has accumulated in the soil. It helps keep the soil healthy and prevents some diseases.

Cultivars and species known to be resistant: ‘Ellie’s Choice’ (Ellie is the breeder, not me!), ‘Sunset’, ‘Little Ruby’, ‘Red Sun’.

Cultivars and species known to be susceptible: ‘Bubblegum’, ‘Painted Lady’, ‘Red Robin’, ‘Avanti Superbells’, ‘Carnival’.

Begonia tuberous blights

What Is Begonia Pythium Rot – Managing Begonia Stem And Root Rot - igrowplants.net


The begonia tuberous blights are two fungal diseases that cause dark, leathery spots to develop on the stems and leaves of the plant.

Sources & references used in this article:

Suppression of Botrytis Blight of Begonia by Trichoderma hamatum 382 in Peat and Compost-Amended Potting Mixes by LE Horst, J Locke, CR Krause, RW McMahon… – … disease, 2005 – Am Phytopath Society

First report of Lasiodiplodia theobromae causing stem rot disease of begonia (Begonia x elatior hort.) in Brazil by MF Fujinawa, N de Carvalho Pontes… – … Plant Disease Notes, 2012 – Springer

Heat therapy for control of Pythium storage rot of begonia tubers by RD Raabe, KF Baker – I International Symposium on Flowerbulbs 23, 1970 – actahort.org

Wilt and root rot of poinsettia caused by three high-temperature-tolerant Pythium species in ebb-and-flow irrigation systems by N Miyake, H Nagai, K Kageyama – Journal of general plant pathology, 2014 – Springer

Identification and Characterization of Pythium Species Associated with Greenhouse Floral Crops in Pennsylvania by AR Chase – Western connection. Turf and ornamentals, 1998

Induced resistance in bean plants against root rot and Alternaria leaf spot diseases using biotic and abiotic inducers under field conditions by HMB Roth, B Mazuik – Quality Test and Inspection, 2003



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