Lanbaichuan is a 77% copper hydroxide wettable powder registered for the control of citrus scab, applied as a foliar spray at a dilution of 500-600 times.
The product performance is described very directly:
This product works by releasing copper ions that interact with groups such as −SH, −NH2, −COOH, and −OH in fungal proteins, leading to the death of the pathogen.This product is a preventive fungicide.
"Preventive" is the entire essence of using this type of product.
After copper hydroxide is sprayed onto the crop surface, it slowly releases copper ions (Cu²⁺) under conditions where a water film is present (dew, rain, or high humidity).
After copper ions enter the pathogen, they bind to groups such as sulfhydryl (−SH), amino (−NH2), carboxyl (−COOH), and hydroxyl (−OH) in proteins, causing protein denaturation, inactivation of the enzyme system, and death of the pathogen.
This mechanism has three characteristics:
Multi-locus.Copper ions act on multiple groups on proteins rather than on a specific enzyme. For a pathogen to develop resistance, it would need to simultaneously mutate multiple resistance mechanisms — this isReasons why copper-based fungicides have hardly induced resistance to date.请提供需要翻译的中文段落。
Broad spectrum.It is effective against both fungi and bacteria. This is the unique value of copper-based formulations that distinguishes them from the vast majority of organic synthetic fungicides.
It must be covered in advance.Copper ions must be present on the surface before the pathogen contacts the crop. If sprayed after the pathogen has invaded the tissue, the copper ions cannot penetrate.
Citrus scab, caused by Elsinoë fawcettii, affects new shoots, young fruit, and tender leaves.
Typical symptomsLesions become suberized and raised, forming scab-like symptoms; leaves are distorted, and fruit surfaces become rough.
Infection patternsThe pathogen only infectsYoung tissues— When new shoots emerge but are not yet mature, and during the young fruit stage. Once the tissue matures (cuticle formation), the pathogen can no longer invade.
Three infection peaksSpring shoot stage, young fruit stage, and autumn shoot stage. During these three stages, the tissues are tender and constitute the key windows for control.
This pattern determinesPrevention and control must be carried out atNew shoot emergence stage, young fruit stageSpray in advance so that copper ions form a protective layer on the surface; if spraying is delayed until the tissue has matured, control efficacy drops substantially.
For comparison: systemic fungicides such as carbendazim can still act after the pathogen has penetrated (hyphae that have entered the tissue are inhibited), whereas copper-based formulations cannot — this is the fundamental difference between "preventive" and "curative" activity.
500-600 times dilution.
For a 30-jin (15 kg) sprayer, a 500-fold dilution requires 30 g of pesticide, and a 600-fold dilution requires 25 g.
Citrus trees have large canopies. In practice, high-volume sprayers or mechanical spraying are mostly used, and the water volume is adjusted according to the tree size. The key isAccurate concentrationDo not arbitrarily reduce the dilution ratio just because of the large water volume required.
The phytotoxicity risk of copper-based fungicides is relatively high among all fungicides and requires special attention:
Sensitive to young and tender tissues.Tender shoots, young fruit, and flowering stages are sensitive to copper, and symptoms such as fruit surface spotting and leaf burn may occur. In citrus, particular attention should be paid to the concentration during the young fruit stage; a 500-fold dilution carries a higher risk than a 600-fold dilution.
High temperature and high humidity exacerbate phytotoxicity.At high temperatures, copper ions are released rapidly and exhibit strong activity; combined with evaporative concentration, the risk of phytotoxicity increases. Application should be avoided during the midday high-temperature period.
Some varieties are sensitive.Peach, plum, and apricot are sensitive to copper and generally not recommended for use. Citrus is relatively tolerant, but differences also exist among varieties (such as certain pomelo types).
Mixing with certain agents will aggravate phytotoxicity.Copper-based fungicides should not be mixed with alkaline pesticides, and mixing with certain organophosphorus pesticides may increase the risk of phytotoxicity.
Recommended practicesFor first-time use or when switching to a new product variety, conduct a small-area trial spray first. Observe for 3–5 days to confirm no phytotoxicity before applying to a large area.
"The optimal timing for application is before disease onset or at the early stage of infection." "Apply once every 10-15 days."
For copper-based formulations,"Pre-onset" is more important than "early stage of onset.", because its therapeutic effect is very limited.
Relationship Between Rainfall and Pesticide ApplicationThe persistence of copper-based fungicides relies on the surface film of the spray deposit, which can be lost through rain washing. Therefore:
Apply pesticide before rain to establish a protective barrier.
Shorten the interval during the rainy season.
Consider re-spraying after heavy rain.
Copper ion release requires a water film.In a completely dry environment, the release of copper ions is slow. This may appear contradictory (copper is both susceptible to rain washing and dependent on water), but what it actually means is:Intermittent moisture (dew, light rain) is required, rather than continuous heavy rain washout.请提供需要翻译的中文段落内容。
Copper-based formulations are corrosive to metals.The sprayer should be thoroughly cleaned immediately after use, with particular attention to metal components such as nozzles, valves, and pump bodies.
Do not share sprayers with alkaline pesticides.(without thorough cleaning). Copper-based formulations react with alkaline substances and become ineffective.
Cleaning wastewater must not be discharged into rivers or ponds.Copper ions are toxic to aquatic organisms.
Copper-based fungicides rarely induce resistance, which is extremely valuable in resistance management.
Conversely, precisely because it "does not induce resistance," it is prone toOverreliance请提供需要翻译的中文段落。
Long-term high-frequency use may lead to copper accumulation in soil.
Has effects on non-target organisms (such as earthworms and some natural enemies).
Therefore, a reasonable approach is to schedule copper-based products during periods of moderate disease pressure and preventive-oriented applications, while reserving highly effective systemic fungicides for critical disease periods.
