In the registration technical requirements for Lanfeng Baihu, the very first item is an explicit prohibition:
Prevention and control of Fusarium head blight in wheat,It cannot be used after wheat flowering.It is only allowed to be used before or at the early stage of wheat flowering. Avoid using this product after flowering to reduce the risk of mycotoxin contamination. Ensure thorough spray coverage on the ears.
This prohibition is the part of this article that most needs to be clearly articulated.
1. Why can't it be used after flowering?
Fusarium head blight of wheat is caused by pathogens of the genus Fusarium. This pathogen has a dangerous characteristic:The toxin it produces (deoxynivalenol, DON) is an indicator of concern for food safety.
Fusarium head blight not only causes yield losses but, more critically, results in mycotoxin-contaminated grains. Wheat with excessive mycotoxin levels cannot be used for food processing and is even unsuitable for use as animal feed.
Why does applying pesticides after flowering increase the risk of mycotoxin contamination?
The pathogen infects the floral organs during the flowering stage and subsequently colonizes the grains and produces mycotoxins. When fungicides are applied after flowering, the chemicals come into contact with tissues that have already been infected — application at this stage may alter the metabolic state of the pathogen and, in some cases, even stimulate mycotoxin production. Meanwhile, post-flowering applications occur closer to harvest, resulting in a higher risk of combined fungicide residues and mycotoxin contamination.
It is prudent to register this as an explicit prohibition.Observing the time red line is more important than making an extra application.
II. The window for Fusarium head blight control: apply fungicide at flowering
The control window for wheat fusarium head blight is extremely narrow:
The ascospores of the pathogen are disseminated by wind and rain, and germinate and infect the floral organs during the flowering stage.Continuous rainy weather during the flowering stage is the decisive condition for the epidemic.
"Apply pesticides at flowering stage; take preventive measures before rain."These eight characters encapsulate all the key points for the prevention and control of this disease. Once wheat flowering is complete and the floral organs have withered, the infection window closes; any subsequent fungicide application is both ineffective and non-compliant (as described above).
Apply spray to the panicle thoroughly.Fusarium head blight occurs on the ears, so the spray must reach the ear parts. Spraying only the leaves is as good as not spraying at all.
III. Three Targets, Three Windows
Fusarium head blight of wheatSpray the panicle before or at the early stage of flowering. The application window is the narrowest.
Wheat rustApply as a uniform spray diluted with water before disease onset or at the early stage of infection; a second application may be made at an interval of 7–14 days depending on disease severity.
Rust diseases (stripe rust, leaf rust, and stem rust) are caused by rust fungi, whose spores are disseminated over long distances by air currents, resulting in explosive epidemics.Once a disease focus forms, it spreads extremely rapidly.Therefore, intervention should be initiated at the early stage of disease onset (when only sporadic diseased leaves first appear in the field).
Northern corn leaf blightFor conventional spraying at the early stage of disease onset, 2 applications can be made at an interval of 7-10 days.
Northern corn leaf blight is caused by Exserohilum turcicum and spreads from the lower leaves upward.At the early stage of disease onsetThis means when lesions first appear on the lower leaves — this judgment requires field inspection and cannot wait until the upper leaves also become diseased.
Three targets, with the window period extending from "before flowering" to "early stage of disease onset"—none of them is "after disease onset."The value of this group of pesticides lies in prevention and early control.
IV. Technical Positioning of the Two Components
EpoxiconazoleFluorinated triazole, systemic. Inhibits C-14 demethylase activity in the sterol biosynthesis of pathogenic fungi, blocking cell membrane formation; it also enhances chitinase activity in crops. It can be absorbed by stems and leaves.Transported upward and outward请提供需要翻译的中文段落内容。
PyraclostrobinMethoxyacrylates. The target is the cytochrome bc1 complex (Complex III) of the mitochondrial respiratory chain. In plantaStrong penetrability and certain systemic action.However, the degree of systemic translocation is not equivalent to that of triazoles.
Rationality of the combination: epoxiconazole provides systemic translocation and long-lasting efficacy, while pyraclostrobin provides rapid interception at the penetrative level; the different sites of action reduce the risk of a single mechanism being overcome by resistance.
Product performance: Adopts a novel synergistic mechanism to rapidly disrupt the nervous system of pests, causing immediate cessation of feeding and irreversible paralysis, ultimately leading to death."Pyraclostrobin... exhibits good protective and curative activity." Here "protective" precedes "curative," consistent with its penetrant positioning.
V. Dosage and Dilution Rate
Wheat: 45–65 mL/mu, diluted with 30–50 kg of water per mu.
Corn: 50–70 mL per mu, diluted with 45–60 kg of water per mu.
The dosage and water volume for corn are both higher than those for wheat. Reasons: Corn plants are tall (especially after the large trumpet stage), with large leaf area and plant height exceeding 2 meters, requiring more spray solution to achieve adequate coverage.
17% is the total content.(Pyraclostrobin + epoxiconazole), with the specific ratio as indicated on the product label. This determines its dosage: the absolute amount of active ingredient per milliliter of the formulation is not high, so the dosage is measured in milliliters rather than grams.
6. Resistance Management
Both components belong to high-resistance-risk categories: the strobilurin (QoI) class (strong within-class cross-resistance) and the triazole class (cross-resistance among azoles).
The mixture reduces the probability of a single site being overcome, but this does not mean it can be applied repeatedly at high frequency.
Recommendation: Position as a core fungicide for the critical disease period, with the number of applications per season controlled; rotate with fungicides of different modes of action (organosulfur protectants, copper-based formulations, microbial-derived agents); use in the "protectant-based framework" at the early stage of disease onset.
VII. Precautions for the Use of Triazoles
Epoxiconazole belongs to the triazole class and carries a risk of growth inhibition at high doses.Strictly follow the registered dosage; do not increase the dose arbitrarily.
Excessive use of triazole fungicides on wheat may cause delayed heading and plant dwarfing, thereby reducing yield — the very opposite of the original intent of "increasing the dosage to prevent disease."