Regional Gardening Reports :: National Gardening Association

In the Garden:
Lower South
June, 2011
Regional Report

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This skeletonized leaf is the work of young caterpillars with mouth parts too small to eat the leaf veins.

Gardening Whodunit

I have written before about the importance of being able to identify pests and beneficial insects in their various stages of development, including eggs, larvae, and adults. Frequent visits to the garden do indeed help us stop a problem early on by catching the culprits before they do major damage.

This year I've spent a lot of time "apprehending" pests who are up to no good in my garden. In fact my youngest daughter is both fascinated and appalled at my unflinching ability to repeatedly smash caterpillars, harlequin and stink bugs between my thumb and forefinger!

It has indeed been a scene worthy of an entomological horror movie these past few weeks. My only concern is that I am getting less squeamish about the gross goo and in fact, growing kind of fond of the crunching sound, considering instead my intense disgust at the senseless vandalism these crawling marauders seem to revel in!

Sometimes however we see the damage caused by pests but the guilty party is not present. So it is also helpful to be able to identify the types of damage various pests cause to our plants. Here are some helpful clues for at least narrowing it down to groups of pests. What follows is a super simplified, down and dirty, quick guide to the gardening version of "whodunit?"

We can divide almost all pests of the garden and landscape into two groups: those with piercing/sucking mouthparts and those with chewing mouthparts. The true bugs, which include stink bugs, leaf footed bugs, harlequin bugs, and lace bugs, have piercing/sucking mouth parts. They feed by sticking their long narrow mouthparts into leaves or fruit and sucking the juices out. Sometimes they "spit" a caustic substance into the plant and then slurp up the dissolved contents! YUCK! Their damage is seen as small spots where the green color has been removed. Tomato fruit may have yellow areas at each pierced spot due to the effect of the bug's "spit". If the leaves or fruits are young when attacked, they will develop distorted growth or crinkled areas as the foliage grows. Fruit will have a pockmarked or deformed area that doesn't expand and grow normally.

Thrips and spider mites also feed on the juices in plants with mouthparts that are more like a jig saw blade, cutting the plant surface and lapping up the liquid. Damage occurs as small specks where the green color is instead left tan to brown. Mites can cause a bronzing color on the upper foliage when a lot of them are present.

Other piercing/sucking feeders include aphids, whiteflies, leafhoppers, mealybugs, and scale. These pests feed on the sap of the plant's leaf or stem rather than on the spongy mesophyll like the bugs mentioned above. So they have a lot of fluid flowing through them. Thus they have a lot of fluid flowing out of them. The result is the sticky honeydew substance that falls on surfaces below, often turning black as a sooty mold grows on the sugary honeydew. When you see this sticky stuff, one of the above mentioned pests is likely the cause.

Pests with chewing mouthparts actually eat away sections of the plant. Some common examples of chewing pests that we often encounter above ground are beetles, caterpillars, grasshoppers, leaf miners, and borers. Beetles very often eat holes in plant leaves but can also feed from the sides of foliage. Weevils are a type of beetle with small mouthparts at the end of a long snout, sort of like an elephant's trunk. They eat a hole in fruit, stems or roots. Their main damage is usually from their larvae that hatch out of eggs they lay in the plant.

Caterpillars can feed from the edges of leaves or start their holes in the interior of a leaf. Others cut off small tender stems. When caterpillars are young they are not able to eat the tougher veins and so their damage produces a skeleton network of veins or a lace-like appearance. As they molt and get larger mouthparts, they can eat even the small to medium sized veins. Grasshoppers eat away the leaf tissues like older caterpillars.

Leaf miners feed in between the top and bottom layers, leaving a winding white trail through the green leaf tissues. Borers feed inside the stems of plants or fruits, and some can even eat into woody tissues of a tree trunk. The evidence of their presence is holes into the stems or trunks and sometimes frass, which is like sawdust that has been through the borer!

Below ground chewing pests include grubs and wireworms, both of which are beetle larvae that feed on plant roots.

Do some investigating work in your garden and landscape this year. A small magnifying glass or loupe is helpful. As you observe and learn you'll be building your "whodunit" skills over time and will soon be the next botanical Sherlock Holmes!

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