Preventing cucumber disease usually means understanding exactly what is happening to the plant and in the garden. There are three broad categories into which nearly all cucumber diseases fall, and each has a different approach for treatment and prevention. Pests and insects are a common cucumber disease that can be prevented with physical barriers, insecticides, companion plantings and beneficial insects. Bacterial infections occur when organisms enter the plant through damages leaves, vines or fruit and can be prevented with careful treatment of the cucumber vines and by keeping pests away from them. Fungal infections happen when airborne spores take root on the surface of the plant and can be prevented with attention to watering habits, pests and, eventually, fungicides.
No matter what cucumber disease might be prevalent in the area, one of the best ways to protect a plant is to use a variety that has been bred for resistance. Seeds and seedlings are usually marked as being disease resistant, and this resistance can go a long way. Certain diseases, such as pink root, brown spot and cucumber mosaic, really have no other form of prevention or treatment beyond the innate resistance inside the plant. This can be difficult for gardeners who are trying to grow heirloom varieties, however.
Another general way to help prevent cucumber disease from year to year is to remove all plant matter at the end of the growing season. This means removing all the leaves and vines and as much of the roots as possible. The ground should be tilled to a depth of at least 6 inches (about 15 centimeters). In addition, crops should be rotated to different locations each year so soil-borne diseases and pests, such as some beetles and nematodes, do not have a chance to infect the same variety of plants again the coming year.
Specific ways to prevent a fungal cucumber disease is to be aware of the amount and location of water. When watering, it is best to avoid making the leaves too moist and to use targeted watering methods such as watering cones, soaker hoses or thin irrigation tubes. Avoiding handling the plant too much also can help, because many fungal diseases enter plants through a breach in the plants' surface.
A bacterial cucumber disease can enter through the roots or be carried with insects. They can be airborne or soil-borne, and some are able to survive the winter in certain regions, making them a constant threat. Physical barriers, such as different types of garden cloth or sprays that coat the leaves, can be used. One of the best methods to prevent bacterial cucumber disease is to make sure that any signs of infection are removed from the garden as soon as possible, whether they are on the cucumbers themselves or on nearby plants.
Insects, including cucumber beetles, cannot only initially give the appearance of a cucumber disease but also are carriers for many diseases. The three largest pests for a cucumber plant are the spotted and striped cucumber beetle, aphids and slugs. Slugs are harmful to the plant but can be easily prevented by surrounding the plant with a special mixture of minerals that can dry out the slugs; sand and special traps that are filled with beer also work. Aphids are a more difficult, persistent problem that can sometimes be treated with insecticides or a gentle soap-and-water solution.
Cucumber beetles can quickly destroy plants and multiply. The best method to prevent them is either a physical barrier such as fine netting or companion plantings. Plants such as nasturtium, broccoli and marigolds all either repel or distract beetles from the cucumber plant. Once on the plant, they are best removed by hand or, in a worst-case scenario, insecticide, although cucumber plants are very sensitive to many chemicals in insecticides.