Weed Science
BP-10-4
COOPERATIVE EXTENSION SERVICE • PURDUE UNIVERSITY • DEPARTMENT OF BOTANY AND PLANT PATHOLOGY LILLY HALL OF LIFE SCIENCES • WEST LAFAYETTE, INDIANA 47907	PATHOLOGY

DIAGNOSING HERBICIDE INJURY T. N. Jordan, Extension Weed Specialist

When diagnosing herbicide injury, consider all possible causes including environmental and mechanical factors, as well as diseases and insects. Observe the condition of the whole plant. Also, look for the effectiveness of the herbicide on weeds in the treated area. Herbicide injury will usually occur in definite patterns within a field. Look for —

1)	drift patterns across a field.
2)	overapplied rates at the end of
rows.
3)	uniformly injured strips caused
by application equipment.
4)	differential injury across soil
types (injury on light soils such as sandy knolls and/or lack of weed control on heavy soils such as in low spots in the field).

Primary Sites of Action and Injury of Some Commonly Used Herbicides
Most herbicides can be grouped ac-cording to their mode of action (the type of injury symptoms they express).
knowing a few characteristics of each group of herbicides, the injury caused jn a particular field can be identified through a process of elimination. The specific herbicide may not be readily determined, but all herbicides that do not produce the characteristic injury symptoms can be eliminated. This leaves a much smaller group of herbicides to consider. By checking records of the fields in question or by determining what was applied in adjacent fields, the herbicide which caused the injury can be identified.

1)	Photosynthetic Inhibitors
Action: These herbicides are most
often applied to the soil and are absorbed by plant roots. The herbicide moves with the flow of water into the foliage by the xylem system (systemic) but does not translocate back down into the roots by the phloem system. When photosynthetic inhibitor herbicides are used postemergence, their action is contact and requires thorough wetting of the foliage, usually with the aid of an adjuvant. Injury occurs on leaves and above ground stems. No damage is caused to the root system. Plants must germinate and turn green before they die.

Injury: Plants turn yellow then die back from the bottom to the top. Leaves turn yellow between the veins then begin dying from the tip toward the base and from the outer edges toward the center.
Specific Herbicides:	Atrazine,
Bladex, Tenoran, Sinbar, Lorox, Princep, Milogard, Sencor/Lexon, Basagran.

2)	Cell Growth Inhibitors
Action: Herbicides work on the germinating seedlings and stop growth of the roots and/or shoots before they emerge.

Injury: Symptoms may be expressed in the roots and/or shoots, but mostly in one or the other. Those herbicides that affect the root system usually do not cause any visible damage to the above ground stem other than stunting.

Root injury symptoms -- Injury may appear as root pruning and the inhibition of secondary roots. Roots may be swelled or club-shaped. The lower stems
Cooperative Extension Work in Agriculture and Home Economics, State of Indiana, Purdue University and U.S. Department of Agriculture Cooperating. H.G. Diesslin Directo, West Lafayette- IN. Issued in furtherance of the Acts of May 8 and June 30,1914. It is the policy of the Cooperative Extension Service of Purdue University that all persons shall have equal opportunity and access to its programs and facilities without regard to race, religion, color, sex or national origin.