Among the plants that are good at using "chemical weapons", the role of sonchus oleraceus is very powerful. Although it is a small wild weed, its appearance is not amazing, but it must not be underestimated. It often dominates the fields and dares to bully sorghum and corn, which are much taller than it. Many farmers in the north know that if there are groups of chicory in sorghum fields or corn fields, sorghum and corn will be killed by this plant bully before long. However, the "chemical weapon" of sonchus oleraceus is different from narcissus. It secretes a toxin at the root instead of the fragrance of flowers, which spreads around the soil and kills the surrounding plants.
If elms are planted around vineyards, grapes will suffer. Among them, elm is strong and grapes are weak. As long as the two sides touch each other, the arrogant elm will attack the grapes with its "chemical weapons". The closer the distance between the two sides, the greater the lethality of elm secretions, and finally the leaves of the grapes will wither, and the fruits will be sparse or even completely dead. You can observe for yourself if you are interested. Grapes growing near elms always have long branches on their backs, so try to stay away from them.
Walnut trees and apple trees in the orchard are also a pair of "enemies". Walnut leaves constantly secrete "walnut quinone", which flows into the soil with rainwater, causing great damage to the root system of apple trees and making the apple trees nearby unable to grow normally.
Chemical warfare between plants also happened on vegetables. Celery and Chinese cabbage, for example, are close relatives and their roots secrete special substances. If planted together, they tend to wither. Also, the root exudate of bitter celery is not directly toxic to other plants, but it can promote the propagation of a fungus, which can cause potato wilt. In addition to bitter celery, tomatoes, pumpkins, cucumbers, apples, cherries and sunflowers are also natural enemies of potatoes, which are easy to make potatoes sick and reduce production.
Wheat has obvious inhibitory effect on hemp, sesame and celery, so it is not suitable for cohabitation. Don't plant corn in the field where buckwheat has been planted, and don't plant sesame near sorghum. Tobacco and mulberry are sworn enemies, which is almost devastating to mulberry.
In the vast forest, enemies between plants abound. Pine and elderberry can't live in peace. Elderberry not only strongly inhibits the growth of pine, but also prevents the seeds of pine falling in front of it from sprouting. Pine trees also directly fight ash, spruce, oak and birch, but the result is always unfortunate, and pine trees are often squeezed out by them.
It can be seen from so many examples that the "war" between plants is the use of "chemical weapons", that is, their unique chemical secretions. Recently, scientists have carefully studied plant secretions and applied them to agricultural production practice. They began to use phytochemicals to control pests and diseases, eliminate weeds in the field, and make all kinds of plants reasonably match together, learn from each other's strengths, help each other and benefit each other, so as to achieve the effect of increasing production.
In this regard, the most common examples are corn and soybeans, which are a pair of "in-laws" with good relations. Because corn needs nitrogen fertilizer, and soybean rhizobia is a small nitrogen fertilizer plant, which fixes nitrogen in the air in the soil and absorbs as much as corn needs. They live together, without a life-and-death struggle, but they are good neighbors who take care of each other.
Vegetable experts have found through long-term production practice that some plants' "chemical weapons" are very effective against pests. As long as it is used reasonably, the effect is much stronger than spraying pesticides. For example, Pieris rapae is afraid of the taste of tomatoes and lettuce, so people plant them with Chinese cabbage, so that Pieris rapae will not dare to approach it rashly and Chinese cabbage will be protected from its harm. Plant some castor in the soybean field. The smell of castor will keep the beetles that harm soybeans away. In addition, Chinese cabbage is prone to root rot, and the bactericide secreted by the root of Chinese chives can just kill the root rot bacteria and make it grow next to Chinese cabbage and act as a "healthy doctor" of Chinese cabbage, which is perfect.
Camellia oleifera is an important oil crop in southern China, which is prone to bituminous coal disease and seriously affects oil production. But if I grew up with litsea cubeba, I wouldn't get this disease. Where's the secret? It turns out that the leaves and fruits of Litsea cubeba often emit aromatic oil, and citral in aromatic oil has the ability to kill bituminous coal germs. So litsea cubeba became a doctor specializing in driving out rape.
The above examples show that the relationship between plant neighbors is subtle and complex, and it is a regular expression in natural selection. As long as human beings thoroughly understand the mystery between them, it is of great significance for developing agricultural and forestry production, rationally selecting plants, reducing pesticide consumption and protecting environmental sanitation.