Diseases of Cucumbers
by George Giltner, Master Gardener
As the temperatures and bug populations continue to rise to their summertime highs, so rises the problems with diseases of the Cucurbitaceae family, including cucumbers. However preventative measures go a long way in extending the growing season and overall health of your cucs.
To begin with, plant disease resistant varieties and try new varieties to determine their ability to survive the onslaught of the challenges of nature. Also, just like the coach tells you in sports – first focus on the basics, like water, plant spacing, pH, porosity of the soil, weeds, and fertility issues. Healthy plants are more disease resistant – no doubt – no discussion necessary. Focus on these basics to reduce plant stress factors which affect natural defensive chemistry and mechanical resistance.
Water issues rank first and foremost, and it is the easiest issue to correct. If you plant bush cucumbers on bare, flat soil, they will be exposed to continuous splatters of fungi and bacteria with rain and watering. That bare soil will dry in the hot summer temperatures, exposing the plant to extreme water and heat stress variations which invite disease and insects.
A better planting plan would be to plant bush cucumbers in raised hills at least three feet apart with 1 foot spacing between plants on that hill. Mulch the hills with three inches of loose pine straw that has not been compressed or shredded. Air can easily flow around this type of mulch and rain splatter is eliminated while the soil underneath remains about 20 degrees cooler than bare soil. The tannins in the pine straw are a naturally antagonistic to many pests. The depth of composted organic matter in the mound should extend to two feet deep to optimally retain moisture and nutrients. Worms will inhabit the mound providing nutrient rich, air exchange tunnels which allows roots to grow deep and extensively.
Check your water source for pH, chlorine, sodium, and other minerals that can affect plant growth. Rain water reservoirs are an excellent alternative to tap water. Always use a moisture meter to determine the correct amount of watering necessary. Guessing leads to problems.
Avoid planting any member of the cucurbit family in the same soil location for at least three years. Squash, melons, and pumpkins can leave accumulated pathogens in the soil. Also this family, as others, will deplete the soil of specific minerals. Therefore crop rotation is paramount. Mineral depletions may appear as a biological disease, but soil testing or leaf analysis will detect the deficiency problem.
The worst and most common biological disease with cucumbers is the cucumber mosaic virus (CMV). The developing young leaves become yellow and wilt, while older leaves have yellow green or dark green mottling. CMV also infects clovers, nightshades, dandelions, and other plants. Insects like aphids and cucumber beetles can easily spread CMV. Remember that broad range insecticides will kill target the bad bugs, but also destroy nature’s balance by eliminating 95% of other beneficial and nondestructive life. Always use the least destructive insecticide. Remove infected plants to a distance of 100 yards for control. Use repellants like garlic and pepper spays religiously.
Research and become familiar with the following cucumber diseases:
Fungal diseases – Anthracnose, belly rot, downy mildew, fusarium wilt, gummy stem blight, scab, target leafspot.
Bacterial diseases – Angular leafspot and bacterial wilt
Viral diseases – Cucumber Mosiac Virus (CMW), Papaya Ringspot Virus (PRSV), Watermelon Mosiac Virus (WMV), and Zucchini Yellow Mosaic Virus (ZYMV)
Nematodes – Root Knot
Moisture on leaves, wet soil, and insect vectors are your enemies of a successful and long term cucumber crop. Therefore assure that your plants have an optimal growing environment (basic), plenty of beneficial insects are present in your garden and harmful bugs are under control. Also remove and dispose of diseased plants. Then healthy cucumbers can supply their complete healthy nutrient complement to your diet.