BP-15
$1.00

DIAGNOSIS AND CONTROL OF MUSKMELON DISEASES

Richard X. Latin, Extension Plant Pathologist
Department of Botany and Plant Pathology

Accurate diagnosis is a necessary first step for effective disease control programs. Early recognition of characteristic symptoms can save valuable time and result in more efficient and effective disease management. Familiarity with the stage of crop development at which symptoms are most likely to occur also is important. Fusarium wilt and bacterial wilt, for instance, most often appear soon after plants begin to vine. Gummy stem blight symptoms also can appear when plants are relatively young. The foliage diseases anthrac-nose, Alternaria leaf blight, powdery mildew, and downy mildew are associated with closed crop canopies.

This publication describes and illustrates the key diagnostic features for seven common muskmelon diseases, explains the disease development, and discusses methods for disease control.

Fusarium Wilt

Fusarium wilt is caused by the soil-borne fungus Fusarium oxysporum f. sp. melonis. Race 2 of the Fusarium wilt fungus is most common in the Midwest. The pathogen may infest organic debris in the root zone of other crops, but only muskmelon roots are infected and colonized. Plants infected early in the season produce little or no fruit, and late season infections prevent maturation of fruit.

Symptoms

Among the first symptoms of the disease is wilting of older leaves during the heat of the day followed by partial recovery at night. Because the wilting and recovery can continue for a week or more, the affected foliage becomes chlorotic (Figure 1). Close inspection

Figure 1. Wilted, chlorotic foliage is an early symptom of Fusarium wilt.

of wilted vines reveals brown, necrotic streaks along the stem. A red or brown exudate (Figure 2) is often associated with necrotic streaks. A cross-section of infected stems shows distinct vascular necrosis (Figure 3).

Figure 2. Necrotic streaks and red-brown exudate appear on stems infected with Fusarium wilt.

Figure 3. Vascular necrosis is part of the Fusarium wilt syndrome.

Disease Cycle

The Fusarium wilt fungus overwinters in midwestern soils as thick-walled chlamydo-spores associated with crop residue. Roots are infected at any time during the growing season; however, wilt is most noticeable soon after the plants begin to vine. The fungus colonizes root tissues and multiplies throughout the vascular tissue. Chlamydo-spores form within the roots as plants die.

Disease Control

Use of resistant cultivars is the only reliable way to keep infested fields in muskmelon production. Several commercially acceptable resistant cultivars exist, but their resistance

Cooperative Extension Service • Purdue University • West Lafayette, Indiana