Bronzing your baby shoes is one thing; bronzing in the garden indicates a problem.
What is bronzing?
Bronzing refers to the way some leaves or fruit turn purplish or bronze-colored as a result of mineral imbalances, pest feeding, chemicals, environmental conditions, or disease. Bronzed leaves tend to be smaller than normal and the damaged areas are unable to perform photosynthesis. Bronzing damage may look similar to sunburn damage, except that sunburned leaves tend to turn grey, rather than bronze. Bronzed fruit has a dry, rough texture.
Too much (or too little) of certain minerals can cause bronzing. Mineral imbalances can generally be avoided by regularly adding organic material to your garden soil. It’s a good idea to know what to look for when scouting your foodscape:
Did you know that rice farmers rate plant varieties using leaf bronzing scores (LBS)?
Apparently, rice varieties are scored on their ability to tolerate excessive iron in the soil.
There are many pests whose feeding habits can lead to leaf and fruit bronzing. Most of them are sap-sucking pests:
Chemical damage can occur when herbicides, pesticides, and fungicides, such as sulfur, are applied incorrectly. Also, the wind can carry herbicides and other chemicals from neighboring gardens and yards that may cause leaf bronzing. If you see bronzing, necrosis, interveinal chlorosis, desiccation, and distorted growth, it may be chemical misuse or overspray.
Air pollution often causes high levels of ozone (O3) in the atmosphere. Ozone, combined with high temperatures and bright sunlight, can cause purple-brown discoloration, or bronzing, on the upper surface of leaves. This is particularly common, in the Bay Area, on bean plants.
Use bronzing as a clue when you walk through your garden. The brownish or purplish discoloration of bronzing is a clear sign that something is amiss.
You can grow a surprising amount of food in your own yard. Ask me how!