Jiang Yongzheng: Master the two key timings for weeding, turn enemies into friends and reduce herbicide use

(Continued from previous article) Jiang Yongzheng, head of the Pesticide Application Division at the Agricultural Chemicals and Toxic Substances Research Institute, has delved into weeds for 40 years, and stepped down from her post in July this year, but her bond with weeds is not over yet. Throughout Jiang Yongzheng's research career, she has witnessed the entire process of weeds going from being utterly evil to being accepted. Farmers in the past all followed the practice of "eradicating weeds completely," but now they must learn how to "coexist with grass." Doing a good job of weed management is the real way.

Weed management must be a long-term war of resistance; master two key timings for weeding

There is a huge weed seed bank underground. How exactly should farmers deal with it? Jiang Yongzheng says that most farmers want to remove weeds as soon as they see them, frequently patrolling fields and cutting grass, but after weeding, fertilizing and watering will also once again stimulate the seed bank in the soil to sprout. Therefore, not long after weeding, the weeds become dense again. So for convenience, some farmers choose to use herbicides.

"Farmers often call and say: 'There is such-and-such weed in my field, how should I remove it now?' But in fact there is no ready-made miracle cure for weeding; with weeds, it is always a long-term war of resistance." Jiang Yongzheng says that most people cannot comprehend why there are so many weeds, which is why they hope for a one-time solution. But weed populations are enormous, so one must be patient and continuously keep them company.

Jiang Yongzheng calls weeding weed management, because to deal with weeds one must first understand their characteristics. "There are two key timings for weed management: the first month after crops are just planted, and before weeds flower." She explains that when crops have just sprouted, their growth rate cannot compare with weeds, so at this time weeds need to be cut to reduce competition. After crops grow taller, they will shade part of the sunlight, and the growth rate of weeds naturally cannot compare with crops. For example, weeds under fruit trees generally cannot grow tall because of the tree shade.

Jiang Yongzheng says that at this time these weeds close to the ground can just help preserve moisture on the surface, and next one only needs to ensure the weeds do not get too tall. The next weeding timing is before weeds flower and set seed. "No one knows exactly how many weed seeds are underground. I always tell farmers: 'Let these seeds grow out as much as possible.' Because for every 1 plant that grows out, there is 1 fewer seed underground." Then, by weeding before the weeds flower and set seed, future seeds are reduced, and management of the field area will become smoother and smoother.

Leaving appropriate grass makes crops grow better and also attracts natural enemies to help

Jiang Yongzheng believes that weeds are not harmful to agriculture. By fully understanding their characteristics, weeds can be good companions for field crops. "By making use of the characteristics of weeds and not letting weeds affect crops in number or growth, they can instead be a plus."

In recent decades, with the rise of organic and natural farming, sod culture that coexists with crops has gradually been accepted by farmers. Many orchards, such as those for dragon fruit and pomelo, plant grass under the fruit trees. Jiang Yongzheng says that the negative harm of weeds is mainly because they compete with crops for nutrients, or become habitats for pathogens, pests, rats and other harmful organisms, or, like Mikania micrantha, spread over large areas and damage native vegetation. But if one understands weeds well enough, leaving them in the field can make the soil healthier.

"With no grass at all, the soil is essentially unprotected. When violent winds and heavy rain come, topsoil is easily lost. And if it is cleared too cleanly, once seeds of other more dominant weeds blow in, because of the lack of competition it is even easier to accelerate their establishment and rooting, turning them into weeds that are difficult to control."

Jiang Yongzheng says that eradicating weeds completely lacks consideration of economic benefit, while only wanting to prevent the appearance of weeds fails to consider environmental protection. Leaving appropriate grass and carrying out integrated management of weeds is the sustainable and labor-saving approach.

"Farmers should first ask themselves why they do not want weeds." Jiang Yongzheng explains that, under conditions that do not affect crop growth, weeds can reduce wind and rain erosion of the soil, increase soil permeability, and can also form an impermeable layer in the soil, safeguarding soil ecology. For Taiwan, China, where the rainy season is concentrated in summer, weeds can reduce topsoil loss, also help reduce evaporation of surface moisture, and even shorten the time rainwater soaks the soil.

"If weeds are well controlled, they can actually help crops grow too!" Grass can intercept nutrients lost from the soil, and dense root systems can also absorb available nitrogen in the soil. Even after weeds die and decompose, the nutrients they contain are released and returned to the soil surface, providing crops with more nutrients. And appropriately retaining weeds can also provide a living environment for natural enemy organisms, allowing diverse natural enemies to control pests.