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.
Disease conditions are usually caused by fungal spores being splashed onto foliage from contaminated soil, coupled with cool temperatures. They affect foliage and flowers.
Photo Credit: ©2000 Dolezal Publishing/Tim Butler
Distinguish disease from normal care problems as best you can – they often bear a superficial resemblance. Fungal disease damage mimics drought, and water allowed to stand on foliage in hot sun may brown plant leaves.
Photo Credit: ©2000 Dolezal Publishing/John M. Rickard
Brown leaf tips may result from underwatering, while too much water frequently causes yellowing of the entire plant’s foliage. Inspecting your plants on a regular basis and being aware of their needs, as well as any sudden changes, can help you distinguish what kind of problem you’re facing.
Photo Credit: ©2000 Dolezal Publishing/John M. Rickard
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.
Keep your plants evenly moist and properly fertilized and you’ll avoid a host of problems. Spider mites and thrips, for example, thrive on dry, stressed plants. On the other hand, you should allow soil to dry between irrigations or else you can create a hospitable environment for soilborne fungi.
Spray your plants with a stream of water early in the day to dislodge dust and pests. Promptly remove decayed or diseased plant matter from the garden to prevent it from infecting surrounding plants. Even debris that has fallen from healthy plants should be cleaned out, since slugs and snails and other pests find it a convenient shelter. Remove all weeds, which weaken plants through competition and provide another haven for pests and diseases. When the weather warms, bolster your anti-pest forces by inviting beneficial insects into your garden, such as green lacewings, ladybugs and parasitic, stingless wasps.
Inspect your garden regularly for signs of trouble. Look for discolored or spotted foliage, deformed leaves or flowers, stunted plants, chewed leaves, wilting, and sticky, sooty or powdery deposits. Take immediate action to find a solution.
If some of your plants show signs of disease, again take quick action to prevent them from infecting healthy companions by removing and destroying any with incurable viral diseases. If common fungal disease is the problem, use applications of soapy water every three days until the fungus subsides. Always make sure that treated foliage has a chance to dry thoroughly before sunset.
Insect pests are another matter. Insect damage can be tricky to diagnose unless you catch the culprit in the act. If you spot such damage, consider first how extensive it is and whether any action needs to be taken at all. Remember, the objective isn’t to rid your garden of every single pest, since the only way to even come close to that impossible task would also mean clearing your garden of helpful insects. The best action to take is to practice integrated pest management – or IPM, which always starts with the least environmentally-disruptive remedy. Step up to chemical pesticides only after all safe methods fail.
When pesticide use has become your very last resort, first try botanically derived products that break down quickly and limit harm to the environment. That said, do note that such products are not without their risks: Pyrethrin, for example, is derived from chrysanthemums, is harmless to humans and quickly kills certain pests. However, it’s also a broad-spectrum insecticide, which means it destroys helpful insects, as well as the harmful ones. Rotenone, another naturally-derived, broad-spectrum insecticide made from tropical tubers, is harmful to humans and (as with any chemical) should always be applied with great care.
Of course, if you have healthy plants and a clean planting bed from the start, combined with regular garden maintenance and routine plant inspection, you shouldn’t have to break out the chemicals at all!
