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Down the Garden Path

Weird Growths, Holes and Exudate

Insects are very interesting to watch as they go about their lives in nature from early spring through fall. We notice them when something goes wrong or missing on our valuable landscape plants and flowers, especially when those insects are considered detrimental to growing our prized flowers or being able to harvest that perfect vegetable.

When we see missing plant parts, holes in leaves or flower buds and the flowers themselves missing, we can be pretty sure that is being caused by a chewing insect. Lots of times we never see the culprit, but they leave behind their droppings that confirm they were there under the cover of darkness. A second group of insects feed on plant sap and are a little harder to spot. They will be the same or similar color to the plant they are feeding on or hiding in plain sight, looking like they are part of the plant. Good clues that they are there will be shiny clear spots on the leaves as they expel digested plant juices. On that exudate grows sooty mold, a dark black mold, the other visual clue.

Insects known as leaf miners give us another kind of feeding and damage to leaves. Eggs are laid on young developing leaves where the larvae hatch and disappear under the surface of the leaf. From there on, they feed between the upper and lower epidermis of the leaf, consuming the cells that produce the green color. Evidence of their feeding is easily seen by holding up a leaf to the sun, the damage is translucent and early enough you will see the actual insect moving around. Later the insect may be gone via a very small emergence hole leaving behind its droppings between the layers of the leaf.

There is yet another group of insects that are with us every year that we never see, yet provide clear evidence in early summer that they have visited our yards. We are beginning to see them now. Gall forming insects have yet another distinctive feeding habit. Just about all plant gall forming insects start out their life cycle very early in the year when the buds of their host plants are just beginning to swell, before we see any leaves. Those insects arrive just in time to insert eggs into those tiny tender leaves as they begin to emerge from the protective overwintering bud scales. The egg stimulates the quickly growing tissue to grow additional leaf tissue around the egg and becomes a weird looking growth called a gall.

Back to the feeding part. As the egg hatches the extremely small larvae begin to feed on the interior of the gall, rich in nutrition. So while the larvae are actually feeding on the tissue, we do not see any evidence of that, just the gall being there. As the insect increases in size, more is eaten and often times the gall changes color. Eventually, the nearly adult insect will create a hole from within and emerge to finish off their life cycle elsewhere. Next time you are out walking the yard and enjoying the beauty, see if you can spot those less obvious insects that have visited your backyard.