Leaf Damage
When plants have leaf damage, it can be divided into two different categories--it is either caused by living things or by non-living things. Living things includes pests, such as insects, rodents, mites, deer, birds, or rabbits, and diseases, such as fungi, viruses, bacteria or nematodes. These are the ones most gardeners expect to find when they investigate leaf damage. But there can be other non-living causes as well. For instance, these might include damage because of environmental, chemical or mechanical reasons.
Environmental leaf damage can mean conditions such as weather that is too dry or too wet, temperatures that are too cold or too hot, or storm or wind damage. Chemical reasons for leaf damage may mean too much or too little fertilizer, the wrong mixture of nutrients in fertilizer, or misuse of pesticides. Mechanical leaf damage could consist of something like hitting the tree with a lawnmower or injury from pruning. On fruit trees, it could consist of damaged caused by harvesting, either with machines or by hand.
When you are trying to determine what is causing leaf damage, the first thing to do is to examine the entire plant and see if you can find any patterns developing. Some of these might include checking the leaves for insects and looking for signs of chewing, like chewed edges or holes in the leaves. Check to see if other plants show signs of leaf damage or insects, especially if you have other plants in the same family.
If you have seen insects, the next step is identifying them and take appropriate measures to get rid of them. Leaf damage that is left unchecked will most likely kill the plant over time. If you have chewed leaves, the problem could be beetles, slugs, grasshoppers or caterpillars. Leafrollers literally cause the plant leaves to roll over. Leaf miners make tunnels that you can see between the layers of the leaf, while borers make holes in trunks, branches and stems.
A cut worm can cut through the plant at stem level or snap off leaves. Insects that suck can cause leaf damage by sucking on the leaves or by sending toxins into the leaves. If your leaves are curling, it could mean thrips or leafhoppers, but if leaves are turning yellow or they have stopped growing prematurely, check for aphids, mealybugs or whiteflies.
All diseases can affect the leaves of your plant in some manner. Fungi can cause wilting, yellowing, or leaf spots. Bacteria can cause leaf spots as well, followed by yellowing and dying leaves. Viruses can stop the whole process of photosynthesis, causing leaf damage in the form of mottling or yellowing. The damage will most likely affect one portion of the plant, causing it to die but will not kill the entire plant.