Cucumber Stem Rot

Gummy Stem Blight

• The fungus that causes gummy stem blight may be introduced to the garden through infected seeds, borne on the wind or spread from the debris of previously infected plants. Gummy stem blight affects both the stems and the leaves of cucumber vines and causes black rot of the fruit. Leaves develop brownish spots that spread -- and may merge into blotches that cover the entire leaf. The stems split, forming cankers that may exude a gummy brown substance. The infected stem and often the entire vine dies. The cucumbers may develop watery areas called black rot. No cucumber varieties are resistant to gummy stem blight.

  Remove or plow under any possibly infected plant debris from previous crops and plant only certified virus-free seeds. Remove weeds and infected plants and destroy them away from the garden to prevent the spread of the disease. Apply a fungicide while plants are young to help protect them from gummy stem blight. Clean gardening equipment in between uses.

Pythium Root Rot

• When Pythium aphanidermatum attacks cucumber plants, it first infects the roots of the plant, and quickly spreads to the plant's main stem closest to the roots. The stem becomes chlorotic (loses color) and then turns brownish-orange. The plant wilts suddenly and may collapse at the base of the stem. Infected stems look waterlogged and turn brown or black. Pythium prefers warm, moist conditions. The spores spread through splashing or standing water. Avoid wetting the cucumber vine's leaves. Remove weeds, plant debris and infected plants and destroy them away from the garden to avoid spreading the disease. Sanitize gardening tools between uses. Use a fungicide to control less severe infections.

Phytophthora Blight

• Caused by Phytophthora capsici, this blight causes damping-off of seedlings, root and crown rot, stem lesions and fruit rot. Spots appear first on the leaves, but the infection soon spreads through the plant, causing the plant to collapse and die. The vine looks watery and brown. Phytophthora fruit rot initially appears on the cucumber stem or the part of the fruit that touches the ground, causing softened areas that appear waterlogged. The fungus may be airborne or already present in the soil from a previous infection. Phytopthora spores may also be introduced to the garden when infected plant debris is nearby. If water stands for more than a few hours around the cucumber, the fungus produces zoospores that swim to the plant.

  Keep weeds and plant debris away from the cucumber plants and do not plant cucumbers in soil where infected plants formerly grew. Improve soil drainage if practical and water early in the day so excess moisture has time to evaporate. Fungicides may help, but do not provide complete control. It is generally better to remove infected plants and destroy them away from the garden.

Insect Vectors

• Cucumber beetles not only feed on cucumber plants and fruit, damaging or destroying the plant, but also transmit bacterial wilt. While the vines are young, use row covers to protect them from the beetles. Remove the covers once the plants begin to flower, so the bees can get to the blossoms. Beetle traps may help control infestations and eliminate the need for pesticide control.

  Aphids transmit cucumber mosaic virus, the most destructive cucumber disease in the world. Plants infected by cucumber mosaic alone may suffer partial wilt and poor or no fruit on the affected part of the vine. Cucumbers that also have fusarium or pythium fungal infections will collapse and die within about one week.

  Spray the garden with insecticides to control aphid populations and cucumber beetles. Use a product formulated for the type of insect that's attacking the cucumbers, and follow label instructions carefully. Reflective mulches made of aluminum confuses and repels aphids. Remove infested plants and destroy them away from the garden to kill the insects and any diseases they may have transmitted to the plant.