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Photo Credit: ©2000 Dolezal Publishing/Tim Butler

Disease conditions are usually caused by fungal spores being splashed onto foliage from contaminated soil, coupled with cool temperatures. They affect foliage and flowers.

Just as someone with a weakened immune system can develop pneumonia after a common cold, plants in poor health are susceptible to pests and diseases. Annuals that are underwatered, undernourished or stressed in any way can succumb to afflictions that likely wouldn’t phase a stronger plant.

The best way to defend against insects and ailments, even before you plant, is to choose disease-resistant varieties, adaptable species and a diverse assortment of plants that encourage beneficial insects to stay in your garden.

If you’re shopping for transplants, check them for signs of diseases and pests, and make sure that your planting site suits the species you’ve chosen (sun-loving plants for a full-sun garden, for example). Rotate annuals through your beds from season to season since soil tends to harbor diseases that destroy repeat plantings. Help eliminate lingering insects and disease-causing organisms by cultivating the soil prior to planting and periodically thereafter. (Cultivating exposes organisms to the sun, killing them or limiting their growth.)

As you’re digging, add enough compost or other organic matter to provide adequate drainage and aeration. This helps eliminate insect hiding places and destroys fungus that causes damping off, rust and downy mildew. Avoid overcrowding your plants when planting, which causes poor air circulation and can result in powdery mildew or other diseases. A floating row cover helps protect new seedlings from insects, as well as from temperature changes that can stress and weaken young plants.