Choose Disease and Insect Resistant Plants to cope with Pests

Disease-resistant plants are beneficial in gardens

Bill Sevier: Ask a Master Gardener

Saturday, March 12, 2016

Q: What is a disease-resistant plant, and how does one find them? Ann, Tulsa

A: Anyone who has gardened in any fashion has experienced problems with various pests, including diseases, insects and the like. Diseases of plants may be caused by either fungi, bacteria, viruses or nematodes, but most diseases are caused by various types of fungi.

Gardeners and farmers cope with fungal infections three ways. First is by eliminating conditions favorable to infections such as altering methods of watering, improving air circulation and other means.

Secondly, in situations where a specific fungus may be expected, such as in plants susceptible to powdery mildew, preventative fungicides may be used. These chemicals are only preventative, at best, and will not cure an existing infection.

The third way to cope with the problems is to select plants that have been shown to have some resistance to pests. In nature, disease-resistant plants are usually due to a spontaneous change of genes in the DNA, which protects the plant from a disease. This is nature’s way of coping with threats of survival. For this random spontaneous genetic change to occur, it usually takes many years and many, many generations of plants. Once changed, there is an increased likelihood that the plant species will survive.

This beneficial spontaneous genetic change in nature can now be done in the laboratory. New technology is making it easier and faster to make precise changes to genes that produce resistance to disease. This can be done rapidly as opposed to the years it takes to let nature produce the same changes. Plants altered in the laboratory are called genetically modified or GM plants. The process to producing a disease-resistant plant in the laboratory or in nature is different, but the results are similar.

There is no one good source for information about a plant’s disease resistance. The Purdue University Extension website has one of the best lists for annuals and perennials having disease resistance.

Nurserymen carefully collect and sell cultivars of plants that have been shown to have resistance to fungi and other pests. New varieties are being introduced every year, and the nurserymen’s information about disease resistance is usually the single best source.

One should remember that resistance means the plants are less likely to get a certain disease; it does not mean it is totally protected. It still is important to alter your care of plants to make an infection less likely. It is still important to eliminate conditions that promote disease, such as avoiding overhead watering to keep water off leaves and to space plants in such a way to improve air circulation. Mulch is also important for many plants to prevent soil-born fungi from infecting, splashing from soil to leaves.

So when you decide to purchase a plant, be it tree, shrub or ornamental, be aware of what diseases it may be prone to and see if the nursery has information about resistance.

For more information or to ask a question about gardening, contact the Master Gardeners at 918-746-3701 from 9 a.m.-4 p.m.

Garden tips

§  Remove flowers from spring-blooming bulbs after blooming is completed. This will allow the plant to direct its energy into its bulb for next year's blooms, rather than producing seeds.

§  Allow foliage of these bulb plants to die and turn brown naturally before removal. As long as the leaves are green, they are storing energy for the following year.

§  These bulb's root systems become inactive after blooming and cannot absorb fertilizer. It is best to fertilize them at the time of planting, in the fall or in the spring when their leaves first emerge from the soil.

§  Divide and replant overcrowded, summer- and fall-blooming perennials. Mow or cut back old liriope (monkey grass) and other ornamental grasses before new growth begins.