So you've worked hard keeping your garden looking its best, but what's this you see on the leaves of your beautiful plants - bugs! No matter how well you groom the garden, pests are inevitable. Here are the top 5 pests that are known to attack plants in the garden. 

1. Aphids - Aphids, tiny, pear-shaped bugs with long, slender mouthparts, aren't picky. They bother members of nearly every plant family in North America, including shade trees, flowers, vegetables, fruits and ornamentals. A healthy plant can withstand a few aphids, but a severe infestation can cause distorted foliage and dropped leaves as the pests siphon out the sweet juices. Aphids also excrete a sweet substance known as honeydew, which supports the growth of black sooty mold. According to Utah State University Extension, there are more than 1,300 aphid species in North America. Aphids are most often green, but depending on the species and the type of plants they eat, they may be brown, yellow, black or red. 

2. Scale insects - There are at least 200 species of scale insects. The miniscule, delicate-looking, flying male adults are rarely seen, but the tiny, crawling nymphs and the adult females manage to weaken plants as they suck out the juices. Most species of adult female scale insects are protected by hard or soft "shells," and are commonly found on plant stems. Hard-shelled, or armored scale, are more difficult deal with because the pests are so well protected. 

3. Whitefly - These annoying pests aren't actually flies. Unsurprisingly, they are related to other sap-sucking pests, including scale and aphids. Whiteflies lay tiny eggs on the underside of leaves. After hatching, the microscopic, crawling nymphs begin feeding in a few hours, increasing in size until they emerge as winged adults. The adults do little harm, but the nymphs suck plant juices at all stages of development. Like aphids, whiteflies leave sweet honeydew, which attracts black sooty mold. The honeydew also attracts ants, which may kill beneficial insects that help control whiteflies and other harmful pests. 

4. Spider mites - Difficult to see with the naked eye, speck-sized spider mites are usually easy to spot by the fine webbing they leave on plants. If you suspect spider mites, use a magnifying glass to look for mites and eggs on the underside of leaves. Mites often appear after pesticides are used to kill other insects, as the toxic chemicals destroy the mites' natural enemies. Mites are often more problematic in dry, dusty conditions or when plants are water stressed. 

5. Thrips - Yet another pest that damages plants by sucking out juices, thrips are tiny, flying insects with fringed wings. They tend to feed in large groups and are easy to spot because they fly away en masse when disturbed. There are at least 6,000 types of thrips, and some are actually beneficial. This is yet another good reason to avoid pesticides, as chemicals kill the good and the bad indiscriminately.

Tips on Controlling Sap-Sucking Insects

Chemicals should always be a last resort when plants are affected by sap-sucking insects, as pesticides are non-selective, killing beneficial insects that feed on harmful pests. As a result, unwanted pests come back stronger and more difficult to control. Always encourage the presence of natural enemies such as:

Insecticidal soap spray and horticultural oil sprays are often effective for severe infestations, and are less harmful to beneficial insects.

Mary H. Dyer

A Credentialed Garden Writer, Mary H. Dyer was with Gardening Know How in the very beginning, publishing articles as early as 2007.