Principles of pest control in the landscape

Pictured above is a marigold plant infested with spider mites.

Many times, that age old question comes up, “How do I get rid of those pesky insects eating my garden.” The best answer to that question is not control but prevention. With a few preventative practices the gardener can eliminate many of these insects and disease pests.

Plant breeders have developed plants that are resistant to many of the diseases and insects that would normally attack the older variety of plants. If certain pests are prevalent in the growing area, it is best to use pest-resistant varieties. A good example is the French marigolds are more resistant to spider mite than the African varieties. For soil borne diseases, tree seedlings are grafted onto another rootstock that can resist the soil-borne diseases that would otherwise affect a native root stock.

Environmental conditions can affect the habitat of many diseases and insects thus eliminating their desire to set up camp in the landscape. This environment includes planting plants where they have the proper temperature, light and humidity.

Warm and humid conditions often invite diseases to develop on plants that wouldn’t otherwise be infected. Plants should be properly spaced to allow good aeration to reduce the creation of this kind of conditions that invited the disease. Watering at the right time of day to allow excessive moisture to evaporate will also help.

Selecting the right plant for this climatic zone will create a healthy plant that is able to resist many diseases and insects that may attack the plant. Southwestern Oklahoma has a Hardiness Zone 7, which can withstand average minimum temperature from minus 10 ºF to 0ºF. When grown in the wrong regions, plants are unable to develop properly and are more likely to die from disease and insect infestations. A good example is blue spruce. Although it can grow here in protected, well-drained loamy soil, it does poorly in our growing conditions and should be avoid.

Planting seeds and transplants during the proper time will ensure healthy plants that can tolerate the diseases and insects that may attack weak plants. This applies especially to annuals, which complete their live cycles in one growing area.

Preparing the soil properly will grow healthier plants. Depending on the tillage operation desired, weeds must be controlled by either killing them chemically or plowing them under the soil. Tilling too deep, especially when planting turfgrass, can cause settling, compaction and bring weed seeds to the surface. A well-prepared growing bed should drain freely to avoid waterlogged conditions, which can cause poor plant development.

Dead plant material left on the soil surface can harbor diseases and insects, so, debris should be removed or buried in the soil. Similarly, diseased plant parts can spread the problem to healthy plant parts so remove them. Insect pests have been known to overwinter in the debris of plants close to where their food supply will be readily available in the spring.

Broken branches, wounds, cracks and insect holes can provide easy entry to disease organisms and insect larvae. When pruning, make cuts smooth and at the proper site. Cleaning up pruned debris will eliminate the site for diseases and insects to overwinter. Tools should be cleaned and disinfected periodically.

Weeds compete for nutrients and also harbor diseases and insect pest. Since weeds are volunteer plants, they have become adapted to that site and are capable of performing under existing conditions. They are thus more competitive than the landscape plant, which requires the grower’s care.

Healthy, properly fertilized plants will resist diseases and insects better than under-fertilized ones. Soil testing can reveal the nutritional status of the soil so that fertilizer amounts can be amended for adequate plant nutrition. Without a soil test, use a complete fertilizer such as 10-20-10 for a balance of nutrients.

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