Safe use methods of plant growth regulators in agriculture
Plant hormones are organic small-molecule substances synthesized within plants at extremely low concentrations that have significant effects on plant growth and development; they are also called natural plant hormones or endogenous plant hormones. Plant hormones can be divided into auxins, gibberellins, cytokinins, abscisic acid, and ethylene; plant hormones play an important regulatory and controlling role in plant growth and development, such as affecting plant germination, rooting, flowering and differentiation, and affecting plant germination, rooting, flowering, fruiting, dormancy, and abscission.
Because most hormones produced by plants themselves are easily decomposed, more than 95% of the hormones used in production are artificially synthesized; such substances are called growth regulators, and they are used not only in crop production but also for post-harvest preservation and ripening of fruits and vegetables.
As analogs of natural plant hormones, plant growth regulators are generally slightly toxic or low in toxicity. Although they are not intended to kill harmful organisms and can only regulate plant growth and germination, they are still managed uniformly as a category of pesticides.
The following mainly introduces the use of several plant growth regulators in our town.
1. 2,4-D is the abbreviation of 2,4-dichlorophenoxyacetic acid. It has low cost and is widely used. At low concentrations, farmers use it for seed soaking and sprout promotion, which can increase the germination rate; at medium concentrations (1-25 ml/L), spraying it on orange and pear trees at flowering can prevent flower and fruit drop and induce the production of seedless fruit; when oranges are ripe, it can also be used to soak citrus fruits for preservation; at higher concentrations, it can kill many broadleaf weeds, and glyphosate can also be added to increase efficacy in killing weeds.
2. Naphthaleneacetic acid mainly stimulates growth, rooting of cuttings, flower and fruit thinning, prevents flower and fruit drop, induces flowering, inhibits sprouting, and promotes early maturity and increased yield. Farmers in our town generally spray it on tomatoes and cucumbers to prevent flower drop and promote fruit set. It is more often used for cuttings of osmanthus seedlings and grape seedlings; before cutting, the base is soaked 2 cm and soaked for 2-3 hours before cutting. Some farmers use it as a rooting agent: 2.5 g of 20% naphthaleneacetic acid mixed with 20 jin of water, or applied as a drench to soak the roots, to promote early growth and more root growth of camphor trees and magnolia trees and improve the survival rate.
3. Gibberellin, also called 920, is a broad-spectrum plant growth regulator that can promote plant growth and development, increase yield, improve quality, promote germination, reduce fruit drop, and increase fruit set rate. The earliest contact farmers in our town had with 920 was spraying it at heading and flowering, which can bring full heading within two or three days and reduce the harm caused by cold dew wind. However, if the concentration is too high, it can increase internode length and easily cause lodging, so it was gradually replaced with safer grain-filling fertilizers such as Gulibao, which contains a small amount of 920 and also fertilizers such as potassium dihydrogen phosphate, and can similarly make rice seedlings head uniformly and improve the seed-setting rate.
4. Ethephon is a synthetic low-toxicity plant growth regulator that works by releasing ethylene. Ethephon promotes early coloring and ripening of fruits and vegetables, storage and preservation, and removal of astringency; it can also regulate the flowering period, promote early coloring and ripening of melon vegetables, shorten the crop growth period, and increase yield. Some farmers in our town use it by spraying it on melon crops and tomatoes, and it is also used a lot on fruit trees such as citrus. During the color-turning period of citrus, spraying about 150 mg/kg of ethephon on the canopy can make citrus mature 1-2 weeks earlier. Ethephon has strong physiological activity and must not be used indiscriminately, so as to avoid phytotoxicity.
5. Forchlorfenuron, as a swelling agent, is often used on melons, vegetables, and fruits. It has the strongest activity and can accelerate cell division, promote cell enlargement and differentiation, and prevent flower and fruit drop. Farmers in our town often spray it on watermelon, cucumber, citrus, and grapes. Spraying 1-2 times before and after flowering can bring earlier marketing and increase yield. When used on vegetables, it is generally sprayed on lettuce.
In recent years, Tianfengsu broadcast on the Yiyang rural channel also belongs to plant regulators. Its main component is brassinolide. It can be used for seed soaking and, during the rice seedling stage and tillering stage, heading and flowering stage, and grain-filling stage, mixed with pesticides and sprayed once a month. It can advance heading, improve the seed-setting rate, increase 1000-grain weight, and increase yield; it can make rice mature 4-7 days earlier and reduce the harm caused by cold dew wind. It can also be sprayed on vegetables, which can make vegetables come to market one week earlier.
Although plant growth regulators have low toxicity, they are still pesticides after all, and harmful incidents caused by excessive use occur from time to time, such as cracked watermelons in Jiangsu and cucumbers and loofahs growing thicker and longer in refrigerators. The residual amount should be minimized as much as possible, and plant growth regulators that decompose quickly, have a short residual period, and are low in toxicity should be selected. Under the premise of the same effect, regulators with a short residual effect period and low toxicity should be selected. For example, for rice seedling dwarfing agents, uniconazole can be used instead of paclobutrazol. The two have the same physiological function, but uniconazole has high activity, a short residual period, and is safe. Second, the correct use concentration, frequency, and timing must be mastered. Third, improve efficacy and reduce dosage, maximize the role of regulators, greatly increase crop yield and quality, and, more importantly, ensure the quality and safety of agricultural products.