Photosystem II Inhibition and Weed Spectrum
Metribuzin binds to the D1 protein of Photosystem II in plant chloroplast thylakoid membranes, blocking photosynthetic electron transport. This causes excessive singlet oxygen accumulation, resulting in rapid chlorosis, leaf tip scorching, and complete weed desiccation upon sunlight exposure.
It is absorbed by both weed roots and foliage, providing both contact action on emerged weeds and residual soil barrier suppression against newly germinating weed seeds.
- Broadleaf weeds: Chenopodium album (bathua), Amaranthus viridis, Melilotus alba, Portulaca oleracea, and Trianthema portulacastrum.
- Grassy weeds: Phalaris minor, Digitaria sanguinalis, and Echinochloa colona.
- Major labeled crops: Sugarcane (pre- and early post-emergence), potato (pre-emergence), soybean, and wheat.
- Residual soil activity: Provides weeks of weed-free soil barrier when applied to a moist, clod-free seedbed.
Application Guidelines and Soil Texture Precautions
Metribuzin activity and crop safety are strongly influenced by soil organic matter and clay content.
Growers must adjust application rates according to soil texture to avoid crop phytotoxicity in light sandy soils.
- Soil texture caution: Reduce dosage in light sandy soils; do not use on coarse sand low in organic matter due to rapid leaching.
- Potato application: Apply pre-emergence within 0 to 5 days after planting before potato sprouts emerge through the ridges.
- Sugarcane application: Apply pre-emergence after sett planting or early post-emergence before tillering.
- Use flat fan nozzles to ensure an even, overlapping chemical barrier across the soil surface.
Official source
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Central Insecticides Board & Registration Committee ↗Related on KisanPe
Common questions
What chemical group does Metribuzin 70% WP belong to?
Metribuzin belongs to the triazinone chemical family (HRAC Group 5), functioning as a Photosystem II inhibitor.
When should Metribuzin be applied in potato fields?
Apply pre-emergence to moist soil after planting potato tubers but before potato sprouts emerge above ground.
Why is Metribuzin dosage adjusted based on soil type?
In light sandy soils with low organic matter, Metribuzin moves rapidly into the root zone, increasing the risk of crop phytotoxicity.
General guidance, not personal advice. For your farm, ask your local Krishi Vigyan Kendra or agriculture officer.
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