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The P&PDL Picture of the Week

Foliar Damage/Growth Regulator Injury from Herbicide Drift
"2,4-D Is in the Air!" Expect to See Symptoms on Landscape Plants

Gail Ruhl, Plant Disease Diagnostician

(Credits for Photos: top two photosgraphs taken by Karen Rane.)
Growth Regulator Damage to Crabapple Growth Regulator Damage to Caryopteris
Growth Regulator Foliar Damage to Sargent Crabapple Growth Regulator Stem Distortion Damage to Caryopteris
Growth regulatory injury to redbud

Growth Regulator
Foliar Damage to Redbud
Grown regulator injury to grape
Growth Regulator
Damage to Grape

(Click on the smaller image to view a larger image.)

Spring has finally sprung and so have the weeds! Growth-regulator type herbicides are being used to control weeds in lawns, fields, roadsides and pastures. This is the time of year that every dying plant part is wrongly blamed on the recent application of chemicals by a lawn service. If you have not yet received a phone call or a sample pertaining to suspected herbicide injury-just wait-they are coming!

Dieback of branches is not usually a typical symptom of damage from growth-regulator-type herbicide drift. Concentrate on the young foliage. Leaves of broad-leaved plants injured by growth regulator-type herbicide drift or volatilization will display symptoms of distortion, puckering and curling. Some species such as redbud, grape, rose, tomato and boxelder are more sensitive to injury and may be used as 'indicator' plants when looking for growth regulator-type damage. An 'episodic' event of injury, such as herbicide drift, is often easier to diagnose several weeks after the initial symptoms are observed since the newly emerging leaves will be normal in appearance.

If your client suspects herbicide injury and would like to submit a sample to the P&PDL, please encourage them to provide adequate information. We cannot accurately diagnose the possibility of herbicide damage without the names and dosage of all of the pesticides applied, date of application, date of symptom appearance and a complete description of the site and pattern of distribution. The P&PDL does not do chemical analysis of soil or plant tissue. Our weed science specialists provide a visual assessment of the symptoms on the sample as they relate to the herbicide information provided. Our response will indicate whether the symptoms seen are indicative or not indicative of the chemical or chemicals that were used. In most cases, this unbiased response is sufficient for the client's needs.

Although different herbicide groups usually show characteristic symptoms we always take great care in making a diagnosis based on symptoms since other causal factors such as late freeze damage, virus infection, mites and insects may also initiate herbicide look-alike symptoms on plant foliage.

Please refer to the publication ID-184, Diagnosing Herbicide Injury on Garden and Landscape Plants (pdf file), for additional information pertaining to diagnosing potential herbicide injury to ornamentals.

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Last updated: 17 May 2001/tlm.
The Plant & Pest Diagnostic Laboratory at Purdue University.