Phloem mobility of crop protection products

Abstract

Phloem mobility of a crop protectant is an attribute that contributes positively to its efficacy. Herbicides, insecticides and fungicides, generally organic molecules of small molecular weight, are applied foliarly and often must move to remote plant parts (such as meristems, emerging leaves, roots and fruits) via the phloem to achieve economically useful activity. In addition, insecticides must move within the phloem to be effective against piercing and sucking insects. Conversely, phloem mobility of crop protectants and their metabolites can also contribute to detectable residues in raw agricultural commodities. This is especially true of compounds that are biologically stable and applied during fruit development or seed set. Thus, the knowledge of phloem mobility allows an understanding of potential benefits (efficacy) and potential risks (dietary exposure) of a crop protection chemical. The customers for this knowledge range from the discovery chemist and biologist (who participate in the design of the chemical), through to the regulatory official (who grants permission to sell) and the farmer, the ultimate beneficiary of the technology. One can estimate or predict phloem mobility (based on physical/chemical properties and molecular structure) using a number of models, or measure it directly (in whole plants or explants) with a variety of techniques. In the future, crop protection and crop production technology will increasingly rely on effective transport of macro-molecules, such as protein toxins for insect control and mRNA for signal initiation and coordination of growth and development processes. Phloem mobility will be equally important for these macromolecules and for the small molecules that currently control pests and influence plant growth and development. Understanding the processes that control macromolecular transport in the phloem will lay the foundation for effective use of this technology in the decades to come.