9. Keep an eye on your bugs

Insect damage to plants is much more than cos­metic. Viruses and bacteria often can only enter a plant through some sort of opening, and bug damage provides that. Some insects actually act as a transport for viruses, spreading them from one plant to the next. Aphids are one of the most common carriers, and thrips spread impatiens necrotic spot virus, which has become a serious problem for commercial producers over the past 10 years. Aster yellows (photo, right) is a disease carried by leaf­hoppers and has a huge range of host plants. Insect attacks are another way to put a plant under stress, rendering it less likely to fend off disease.