Possible Causes

• Brown spots on green bean leaves may be the result of wet leaves that become sunburned. The pests known as borers sometimes leave brown spots on spinach and beet leaves. Tomato blight sometimes features brown spots. Diseases that affect a cross-section of vegetables and may include brown spots as a symptom include downy mildew, target spot, cercospora leaf spot, gummy stem blight and black rot.
  
  

Resolving the Issue

• If you suspect sun scorch from wet leaves, switch your watering schedule to very early morning or the evening, allowing time for the leaves to dry before the sun comes out. If you suspect tomato blight, remove the affected leaves on a daily basis. Other diseases or infestations may be resolved by sprays devoted to the particular disease or pest.
  
  

What to Rule Out

• Brown leaves sometimes indicate a plant has been underwatered. But this sign usually shows itself on the edges or tip of leaves, or as brown, withered foliage, rather than as individual brown spots. Underfeeding or overfeeding may show itself in yellowing leaves or weak stems, but rarely as spots.