During this time of the year, we visit fields and constantly receive plant samples with symptoms of what could be herbicide, disease, or insect injury. Our Plant Pathologist Dr. Bindu Poudel-Ward analyzes them for pathogens, Dr. John Palumbo checks for insect damage, and we also examine for possible herbicide injury.
As we all know IPM involves an interdisciplinary effort to identify and prevent problems we encounter in our industry.
Kerb, Balan, and Prefar are the major herbicides we have used in lettuce production in Arizona for the last 50 years. These herbicides work by inhibiting root growth in small weeds and under some specific conditions can injure lettuce.
Symptoms of injury could include stunting, leaf margin chlorosis, malformation of the cotyledons and first true leaves, inhibition of main root and lateral roots. Diagnostics sometimes can be challenging because some of the symptoms can also be produced by other factors such as the soil salinity, water management problems, environmental stress or cold, diseases, possible drift from chemical thinning operations and other factors.
It is common that growers send soil or tissue samples to laboratories to compare herbicide concentrations from a healthy section of the field with the affected injured area. If the concentration of the compound in question is significantly different between “healthy” and “bad” samples this could be an indication of herbicide injury. Most laboratories use gas chromatographs (GC) and liquid chromatographs (HPLC) for analysis. Standard extraction and detection methods are costly but accurate and precise3.
The following links will take you to publications that (1) could help you identify some of the symptoms of common lettuce herbicide injury and (2) interpret results reported by laboratories.
References:
- Lettuce Injury from Preplant and Preemergence Herbicides(ACIS) (arizona.edu)
- Quantitative Guidelines For (arizona.edu)
- Vegetable IPM Updates Archive (ACIS) (arizona.edu)
