Movement mechanisms and working principles of systemic plant protection products

How a systemic preparation is distributed within a plant

The main difference between systemic agents and contact ones is their ability to penetrate tissues and move through the vascular system. A contact preparation works exclusively on the surface where a drop of the working solution has landed. A systemic preparation is distributed throughout the crop organism and protects not only the treated leaf but also the new growth that appears after spraying, as well as organs hidden from direct contact.

To understand how systemic active ingredients work, a plant should be viewed as a hydraulic network with two main highways — the xylem and the phloem. It is through these transport corridors that chemical compounds move along with plant sap. The speed and direction of protection directly depend on which flow the substance enters.

• Xylem (wood): provides the upward flow of water and mineral salts from the roots to the leaves. Movement here goes in one direction — from bottom to top (acropetal), due to moisture evaporation through stomata. A preparation applied to the lower tier or applied to the soil rises to the top as transpiration occurs. If a pathogen or pest has attacked an upper shoot, it will inevitably encounter the pesticide accumulated there. However, the substance does not return down to the roots via the xylem.
• Phloem (bast): is responsible for transporting the products of photosynthesis from mature leaves to growth points, fruits, and the root system. This flow works in both directions, but primarily from top to bottom (basipetal). Preparations with phloem mobility are less common, but it is they that are capable of descending from the leaf apparatus to underground organs. This is critically important when protecting a crop from soil pests or root rots.

Separately, we highlight the translaminar properties of certain active ingredients. Such preparations do not move throughout the entire plant, but easily penetrate through the leaf blade from the upper side to the lower one. This allows for the successful destruction of targets hiding on the underside of the leaf, where sprayer drops do not reach directly.

Why the systemic effect decreases in field conditions

The effectiveness of systemic protection is directly tied to the physiological state of the plantings. The movement of the preparation occurs only when the processes of photosynthesis, transpiration, and active sap flow are taking place in the plant. In a stressed state, the crop's metabolism slows down, and the transport of the active ingredient is suspended.

In field conditions, the systemic properties of preparations are limited by three main factors:

• Temperature regime: at too low temperatures, biochemical processes are slowed down. The preparation cannot enter the vascular system and remains "locked" at the application site.
• Soil and air humidity: in case of moisture deficit, the plant closes its stomata to conserve water. The transpiration flow through the xylem stops, and the acropetal transport of the preparation ceases.
• Crop development stage: during the period of intensive growth, tissues rapidly pump nutrients, ensuring fast and uniform distribution of the pesticide. In the dormant phase or during suppression, one should not expect full-fledged systemic protection.

When planning chemical treatments, always compare the application regulations for a specific active ingredient with the current state of the field. A competent assessment of the weather and the activity of the growing season ensures that the systemic preparation will work against the target object at full strength.