Chapter 17: MOA Part 3: Growth Regulators (Auxinic Herbicides)
17.6 Summary
Growth regulators are often referred to as auxins since this class of herbicides will mimic the action of auxins within the plant, causing rapid and or uncontrolled growth. Auxinic herbicides have been around since World War II and were the first selective herbicides developed. They continue to be an extremely important class of herbicides. These herbicides are crucial agrochemicals for selective weed management in grass and cereal crops and are generally phytotoxic to broadleaf plants, causing little or no damage to monocots. Monocot crops are tolerant, in general, because of restricted translocation, enhanced metabolism, and the lack of a vascular cambium in their phloem tissue. Broadleaf species can be tolerant because they metabolize the herbicide to a less toxic form. More recently genetically engineered soybeans are now able to tolerate 2,4-D and dicamba. In addition certain engineered corn hybrids are better able to tolerate 2,4-D.*
Key Takeaways
Key takeaways for this chapter include:
- Auxins are plant hormones crucial for cell elongation.
- Growth Regulators include synthetic auxins (Group 4) and Auxin Transport Inhibitors (Group 19).
- Injury symptoms for these herbicides include cupping and stunting of leaves, brittleness, stunting and twisting of stems, epinasty, poor root development and general abnormal growth.
- Biotechnology advances have resulted in crops that are able to tolerate applications of 2,4-D or dicamba including: Enlist corn, Enlist E3™soybeans, and Roundup Ready Plus Xtend soybeans.
*Check with your county extension agent for licensing information in your area