HPIPM:Bronzing
From BugwoodWiki
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Author: Howard F. Schwartz, David H. Gent, Gary D. Franc and Robert M. Harveson
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Contents |
Identification and Life Cycle
Bronzing is related to the presence of ozone in the atmosphere, and damage can be proportional to the concentration and period of exposure to that air pollutant. High concentrations of ozone are moved downward from the upper atmosphere during severe thunderstorms, or are produced during lightning strikes. Ozone is also produced by a photochemical reaction on bright clear days with temperatures above 80°F in the presence of ambient air pollutants such as nitrite and sulfite. High soil moisture favors ozone bronzing because stomates remain open, whereas wilted plants with closed stomates are less sensitive. Plants grown at optimum soil fertility may be more sensitive than those grown at too high or too low fertility. Bronzing is widespread in areas that recently had severe thunderstorms. A glaze-like bronzing on bean leaves may also be caused by another air pollutant, PAN (peroxyacetyl nitrate), but this symptom appears on the lower leaf surface. Certain foliar pesticides, e.g., copper and sulfur products, applied during hot weather may also cause upper leaf surface burning similar to bronzing.
Plant Response and Damage
Bronzing is restricted to the upper leaf surface and appears as a reddish-brown flecking that may uniformly cover the entire leaf surface or parts of it. Bronzing may occur on one or more leaves of any given plant. Affected leaves may eventually turn yellow and drop. Damage varies considerably throughout and between fields. Bronzing is similar in color to rust, but rust spores are readily rubbed off of leaves and can be present on lower as well as upper leaf surfaces.
Management Approaches
Biological Control
No biological control strategies have been developed for bronzing.
Cultural Control
Use tolerant varieties if bronzing has been a problem. Certain varieties are susceptible to bronzing, but little is known about resistance in commercially grown varieties.
Chemical Control
No chemical controls are available for bronzing.
The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality.
