If you have an unhappy plant the first things you should look at are the amount of sun and water it is getting and how much sun and water the plant wants.
If that is fine, check the nutrients in the soil. You can send a soil test off to the state or use one of the many kits available.
If all is still well and you don’t see critters, consider a fungal or bacterial problem. Especially with the high humidity in Houston, fungus can be a problem. Virus problems are rare in the home garden.
So how do you tell a fungus from a bacteria problem?
|Random plants are affected||Usually cluster of plants is affected|
|Leaf spots on either new leaves or old leaves, but not both||Usually affects all leaves equally|
|Leaf spots are random on leaves||Leaf spots usually on the tips, edges, or between veins. There is usually a recognizable pattern|
|Symptoms develop slowly||Plant can be effected overnight|
|Leaf spots can be dry or wet, may have yellow ring around them and vary in size||Leaf spots usually uniform in size and don’t have a halo|
|—||Plant has been overwatered|
|Spots are dry and papery||Spots are slimy|
|No odor||Rotten smell|
|Spots are mostly circular, cross over leaf veins||Spots have straight edges and follow between leaf veins|
|Small pits with raised edges appear on leaves||—|
To prevent damping off fungus in seeds you are germinating use sterile pots and soil. You can sterilize your soil by placing it in a glass bowl and putting a potato in the middle of the bowl under soil. Bake until the potato is done. Or you can just buy it. If you do get a damping off fungus in your seedlings try spraying them with a fungicide containing copper.
To kill fusarium and verticillium wilt first remove plants. Then till and moisten your soil. Cover with clear plastic and seal the edges. After about two weeks the heat will have killed the wilt. To identify the wilt split a plant stem vertically and look from brown rotten lines in the stem.
Viral infections are not often seen in the home garden. They appear different than fungus and bacteria problems. Viral infections often show as mottled yellow spots on leaves, you may see thin rings on leaves, spots on leaves are very tiny. Viruses are usually spread by insects. Once your plant has a virus it has it for life. There is no fixing it, you must remove the plant to protect other plants.
Plant names followed by VFNT have resistance to several diseases. V – resistance to Verticillium wilt, F – resistance to Fusarium wilt, N – resistance to root-knot nematodes, and T – resistance to Tobacco Mosaic Virus. So if you’ve had problems with any of these, consider buying resistant plants.
‘Immunox’ or ‘Neem Oil’ are often good choices for treatment of fungal problems. Nurseries have several products for fungal problems, many specific to specific fungi or plants.
There are also products for bacterial problems but your best option in that case is to wipe down the effected area with alcohol, take a clean sharp instrument and remove the bacteria affected area plus a buffer area. Fungicides with copper sometimes help with bacterial infections.
Mulching around your plants helps keep down fungal infections. Fungal infections are spread when rain or sprinklers kick up soil and fungus from soil lands on plants.