When controlling any plant pest you need to know the type of insect to give the right control. Knowing the difference between nocturnal (night feeding) and diurnal (day feeding) insects will help you solve many problems.
For example. when a plant’s leaves get more ragged every day, but you can’t see anything on the leaves causing the troubles… suspect a night chewer. There are lots of them.
Snails, slugs, earwigs and cutworms – notorious garden enemies – all night feeders. To double-check the diagnosis, take a flashlight and inspect the plant at night after 10 PM if possible.
Look carefully through the plant, on the ground beneath it, under and over leaves. You’ll probably find the culprits.
Chewing and Sucking Insects
You probably know of two kinds of insects in terms of the way they feed on plants:
- Chewing insects that cut holes in leaves – caterpillars, grasshoppers, beetles, earwigs, snails and slugs (which aren’t insects but might as well be).
- Sucking insects that push their pointed snout mouth parts into plant tissue and suck out juices – aphids, scale insects, white flies, mites.
It’s easy to get the impression that all sucking insects are small like aphids and mites and that all chewing insects are large like caterpillars and earwigs.
But this is not necessarily so. The squash bug, chinch bug, and some of the stink bugs are the size of your little fingernail – large as insects go – yet they are sucking insects.
Their mouth parts work the same as the much smaller aphids, white fly, and mites. On the other hand, some chewers are quite small; the black flea beetle that chews leaves is less than 1/4 inch in diameter.
The leaf that is rolled, puckered, or twisted out of its normal shape is a plant doctor’s delight.
With few exceptions, you are almost sure to find the cause if you examine it carefully.
Some caterpillars make it and art form and their specialty of leaf rolling. When you unroll a leaf, expect first to find a little, green, hairless caterpillar on the inside.
This is a leaf roller. You have to blast the leaves with a spray application in order to get it inside where the worms are.
If there are just a few such rolled leaves pick them off, throw them in the garbage, and be done with it.
You may find certain kinds of aphids inside a rolled leaf.
No matter what the color, aphids are always identifiable by their soft, almost transparent bodies, big abdomens (the round, rear section of the body) with tiny prong-like things on the back end, and six legs.
The leaf rolling aphid can be controlled with specific sprays but it takes a strong jet of spray. ln order to prevent re-infestation (outdoors), mark your calendar to spray during the late dormant season.
Do the leaves contain transparent window-like sections or etched trails through the green?
The etched trails are caused by leaf miner, a small worm that tunnels inside the leaves just under the surface. Hold such a leaf to the light and you might even see one of the worms inside the trails.
Lack of Vitality
In the case of trees or large shrubs, a general lack of vitality can be caused by borers in the trunk and branches.
Examine the bark closely. You may find little holes, perhaps with sap oozing out. Those are the signs of borers, little larvae that bore their way into the wood.
For control spray the whole tree and the soil surface around the tree. With so many new chemicals on the market… check with your county agent for the best treatment options for your area.
Mildew and Other Diseases
The most frequent plant disease you will find is powdery mildew. It’s gray, has a powdery and mealy feeling under your thumb.
Other diseases are generally limited to just a few kinds of plants. You will find descriptions and controls for the serious ones with a quick search of the web.
Poor Plant Care
Leaves that are discolored but reveal absolutely no small insects on the undersides when examined closely with a magnifying lens and show none of the symptoms mentioned above are probably suffering from a physiological trouble.
This is the time to ask yourself about the plant`s environment and care. Any of these causes are possible:
- Too much or too little sun
- Too much or too little water
- Too much or too little fertilizer
- Wrong kind of fertilizer (the plant may need more nitrogen and less phosphorus and potassium, or some other adjustment in the nitrogen | phosphorus | potassium balance)
- The plant may need iron (ask locally about this — it’s usually a general neighborhood problem)
Sometimes a plant will become wilty and appears ready to die but shows none of the symptoms mentioned up to this point.
If that’s the way things are, you have only one place left to suspect – the roots.
Gophers could be eating the roots, moles could have dislodged the plants, or any of a number of soil insects could be feeding in the roots.
Dig into the soil and look at the roots, using a hand lens if necessary. Of all possible disorders of plants the initial cause is most often poor drainage.
Waterlogged soil reduces air in soil, encourages mold, rotting, decreases beneficial bacterial activity. Poor drainage may cause build-up of toxic salts from fertilizers and water.