Since trees and weeds belong to higher plants, herbicides must have special selectivity in order to be safely and effectively used on seedlings, and the type and variety of herbicides can be varied to form multiple modes of selectivity. Some herbicides are not selective in nature, but they can achieve safe and effective weeding through proper use.

1. Morphological choice:

Seedlings and weeds tend to be different in morphology, and can be selectively used to obtain selectivity, such as Pinus sylvestris var. mongolica. The leaves are needle-shaped and have a waxy layer, which is almost perpendicular to the stem. When the herbicide is sprayed, the drops are easily rolled off the needles and are not easily damaged; the weeds and shrubs have larger leaves, no waxy layer, and have fluff, which is almost horizontally born on the stem. It is easy to contact and trap the liquid, so that the victim will die.

2. Time difference selectivity:

Some herbicides that are more toxic to young trees can also be safely and effectively weeded by selecting the appropriate application time, but not harmful to seedling growth. For example, paraquat or glyphosate, used for pre-emergence or pre-forestation, can kill weeds that are already growing or growing, but they can be quickly passivated in the soil without any effect on later seedlings and afforestation.

3. Displacement selectivity:

Soil treatment herbicides have different levels of toxicity to plants at different depths below the surface. The difference can be used to kill weeds in the topsoil and to protect young trees with deep roots.

4. Physiological selectivity:

The choice obtained by stems or roots of different plants on the difference in herbicide absorption and transport is called physiological selectivity. If the herbicide is easily absorbed and transported by the plant, the plant appears to be sensitive, whereas the plant appears to be insensitive.

5. Biochemical selectivity:

The selectivity of different plants through a series of biochemical changes. If the herbicide itself is not toxic to plants, but is toxic by absorption and metabolism, it is killed; or the herbicide itself is toxic to plants, but it is survived by absorption and metabolism, and it is called biochemical selectivity. .

6. Use protective substances to gain selectivity:

Selective herbicides can be selectively protected by protecting substances, such as larch seeds, which can be treated with activated carbon with strong adsorption properties to avoid or reduce the phytotoxicity of herbicides such as trifluralin.

7. Get the choice with proper application techniques:

Some herbicides that are toxic to seedlings can be used in the production period by directional spray method, protective equipment, and smear method, so that the liquid can not reach the seedlings and achieve the purpose of drug safety.

8. Use biotechnology to gain selectivity:

The herbicide-tolerant gene introduction can make the seedlings have the ability to be free from herbicides, thereby obtaining selectivity.