Chrysanthemum nematode

The chrysanthemum nematode (Aphelenchoides ritzemabosi) belongs to the order Aphelenchida and family Aphelenchoididae. It is a microscopic eelworm, typically measuring 0.5 to 1.2 mm in length.

This species is an endoparasite that lives inside the leaves, stems, and buds of the host plant, moving through water films.

The life cycle is rapid, often completing within 10 to 14 days under warm and humid conditions, which allows populations to explode quickly.

These nematodes can survive in a dormant state within dried plant tissue or soil for several months, awaiting favorable conditions for reactivation.

Identifying this pest in the field relies entirely on observation of characteristic symptoms, as individual nematodes are invisible to the naked eye.

The nematode infects a wide array of host plants, most notably chrysanthemums, but also strawberries, dahlias, phlox, and various weeds.

They enter the leaf tissue through stomata and feed on the mesophyll cells, injecting enzymes that break down cellular structures.

The damage caused by feeding leads to tissue death, reducing the plant's photosynthetic capacity and overall health.

Severe infestations cause stunted growth, flower malformation, and may lead to the total collapse of the plant during the growing season.

Nematodes are primarily spread through infested cuttings, nursery stock, and contaminated soil, making sanitation a top priority.

The most common symptom is the development of angular, interveinal chlorotic spots on the leaves, which eventually turn brown or black.

Because the nematode movement is physically restricted by the leaf veins, the necrotic lesions appear block-shaped or angular.

As the infestation progresses, lower leaves wilt, wither, and eventually fall off, while the infection moves upward toward the growing points.

Inflorescences may become deformed or fail to open, and the overall plant vigor is significantly diminished over time.

In wet weather, the nematodes migrate from the soil or lower leaves up the exterior of the stem to reach new, healthy foliage.

The most effective strategy is to avoid introducing the nematode into your garden by inspecting all new plants thoroughly before planting.

Hot water treatment (soaking cuttings in water at 45–46°C for 5 minutes) is a standard effective method for disinfecting chrysanthemum stock.

Avoid overhead irrigation or watering that splashes water from the soil onto the foliage, as this facilitates the spread of the worms.

• Promptly remove and dispose of any plant parts showing symptoms of infection to limit the population.
• Sanitize all pruning tools and gardening equipment using a disinfectant solution to prevent cross-contamination.
• Implement crop rotation and soil sterilization practices in greenhouse environments to eliminate overwintering populations.

Utilizing certified pest-free planting material remains the best defense against this persistent and challenging plant pest.