An important goal for many gardeners is to maintain a pest- and disease-free landscape. Although it is impossible to eliminate all nuisances, reducing the number of pests is certainly achievable.

The most effective way to reduce pests in the garden is to begin before you have even selected any plants. 

First, start with a design that groups plants with similar needs together. Cluster plants that have comparable requirements for water, nutrients, exposure (sun or shade) and drainage.

Then choose plants that are suited to your site. Make sure you have enough room for the plant when it reaches full size. Consider using California native plants or plants from other parts of the world that enjoy a Mediterranean-type climate. Evaluate the light, seasonal high and low temperatures and wind at the site and choose plants that can tolerate those conditions.

Choose pest- and disease-resistant varieties when available. For example, the crepe myrtle is susceptible to mildew but nurseries now offer several resistant varieties, including ‘Zuni’, ‘Comanche’ and ‘Natchez’. Many roses, such as ‘Simplicity’ and ‘Meidiland’, are also now resistant to powdery mildew. If you have existing plants in your garden that are highly susceptible to disease, consider removing them.

At the nursery, always select the healthiest looking plants. Check the roots and avoid plants whose roots are kinked or circled. Stay away from any plants with signs of insects or disease.

Choose plants that can tolerate your existing soil conditions. To improve the soil,  amend it with organic matter such as compost. Doing so will improve the soil’s ability to retain water. Compacted soils should be aerated periodically.

Choose plants that will thrive within your site’s water limitations. Remember that most drought-tolerant plants will need water for their first several dry seasons but will need less as they become established. Consider your water quality. Many wells have high mineral levels that can affect plant health. Install a water-efficient drip-irrigation system and schedule it for infrequent deep watering in the early morning hours.

Too much or too little water can kill plants. Drought conditions often stress plants and make them susceptible to pests and pathogens. Mites and leaf-suckers are more damaging to plants that are not receiving enough water. Wood-boring insects primarily attack plants that are water stressed. 

Overwatering can also cause problems, such as root and crown diseases. Splashing water from overhead irrigation can spread fungal diseases. Our native oaks are particularly sensitive to overwatering. Too much water in the summer can predispose them to infection and disease.

Keep your garden area clean by regularly removing diseased plants, and crush all unwanted insects. Encourage beneficial insects by incorporating plants that attract natural predators and parasites. Provide water and shelter for birds, which also eat garden pests. Use garden barriers such as sticky bands and copper bands to keep pests away from your plants. Apply several inches of mulch to planted areas to reduce weeds, maintain soil temperature and reduce evaporation.

When pest problems do arise, address them immediately. Get professional advice by bringing a sample to the Napa County Master Gardener help desk (details below) or contact us by phone or email. The sooner you identify and arrest the problem, the less likely it will spread. In severe cases, you may need to remove the affected part of the plant or even the entire plant.

When you must use a pesticide, choose the least toxic solution. Low-toxicity pesticides include horticultural oils, insecticidal soap and botanicals. Remember that even pesticides labeled organic can be toxic. Follow label instructions and wear protective clothing as required.

A healthy, balanced and thriving garden is the best defense against pests and diseases. With a little planning, research and proper preparation and maintenance, you can prevent your garden from becoming a haven for unwanted pests and pathogens.

Napa County Master Gardeners ( http://cenapa.ucdavis.edu) answer gardening questions Monday, Wednesday and Friday, 9 a.m. to noon, at the UC Cooperative Extension office, 1710 Soscol Ave., Suite 4, Napa, 253-4221, or (877) 279-3065.