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Plantwise Factsheets for Farmers

Herbicides against weeds in soybeans

Zambia

Recognize the problem

Weeds compete with soybean for light, space, water and nutrients. Soybean plants are quickly overgrown. If weeds are not controlled on time, soybean yield will be very low.

Background

Most weeds can be controlled mechanically by pulling out, harrowing, or tillage. Some serious weeds can be chemically controlled. Be careful, some chemicals can only be sprayed before soybean germinates.
Glyphosate kills any plant, also soybean. Thus, spray before sowing, or after sowing but before soybean germination. Trade names: Cycat, Round up, Muscle up, Springbok, Scat, Erase, and others. It is of WHO toxicity class III, thus slightly toxic to you.
Chlorimuron-ethyl kills broad leaf weeds. Apply according to the label for not killing the beans.  Spry when soybean and weeds have emerged, but before weeds exceed 5 cm. Trade names: Classic or Bean weed killer.  It is of WHO class III, thus slightly toxic to you. Pre-harvest interval 45 days.
Quizalofop-p-tefurylare only kills grassy weeds including kapinga. Trade names Pantera or Quizate. It is of WHO class II thus moderately toxic. If a field has grassy and broad leaf weeds, you can mix chlorimuron and quizalofop in one sprayer or drum.

Management

For spraying glyphosate
  • Use a small hole fan-jet nozzle (orange), that makes a fine spray.
  • Mix 700 ml or 500gm in a 16-litre sprayer. The usual rate is 4 litres product / hectare. But double-check label as the products differ.
  • When spraying, the soil may be dry or moist; weed leaves should be young and fresh but not wet.  Spray at dry weather or at least 4 hours before rains. Do not enter the field for ½ a day at least.
  • Never spray when soybean has emerged, because it kills beans.

For spraying chlorimuron or quizalofop

  • Use a blue fan-jet nozzle which has a bigger hole.
  • Mix 3.5gm chlorimuron sachet in a 16-litre sprayer;  or 300gm sachet in a 200-litre drum of water per hectare
  • Or mix 130ml quizalofop in a 16-litre backpack sprayer;   or 1.5 litres in 200 litre drum of water per ha. But double-check label. When spraying, weeds should be fresh but not wet, soil can be dry or wet. 
  • When spraying hold the nozzle 1/2m high from the ground along planting lines walking 50 meters in 45 seconds. Do not enter the field after spray for ½ a day at least.

When using a pesticide, always wear protective clothing and follow the instructions on the product label, such as dosage, timing of application, and pre-harvest interval.

The recommendations in this factsheet are relevant to: Zambia

Authors: Conwell Chilala
Ministry of Agriculture and Livestock
tel: +260 977 598 505 email: chilalaconwell@yahoo.com
©CAB International. Published under a CC-BY-SA 4.0 licence.

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