Weed control strategies in sorghum

                   

Weed-free field for sowing 

Weed control need to be practiced in sorghum crop even before sowing so that the plants grow without any weed competition from germination onwards.That means the first weed control activity starts even before sowing sorghum.

         Weed-free environment in the early stages  

The weed seeds in the soil are allowed to germinate with the first rainfall and then the final harrowing or plowing is carried out.This practice will provide a weed free environment for vigorous and robust growth for the sorghum seedlings.

                      Weed-free crop 

Weeds are not allowed to grow during the first 45 days of growth of sorghum plants as this is the most critical weed competition period.

 Late weeding by farmers is due to many factors:

• Wait for weeds to become fodder to feed the cattle
• Erratic rainfall in black soil regions
• Unavailability of labor in peak periods
• Cost of labor etc.

 However, it should be remembered that delaying weeding will lower the yield proportionate to the delay.

 There are 3 methods of weed control practices:

• Control through crop cultural practices
• Manual or mechanical control
• Chemical control

 Efficient and effective weed control can be achieved by wisely combining the above methods of weed control practices.

Cultural practices:

A good crop cover by adopting right spacing between rows and within the row will smother the weed growth.For this adopt the recommended spacing of 45 cm between rows and 12 cm between the plants within the row.

Example of mulching with straw  

Mulching the soil surface in between rows with crop residue material like straw etc. may preventThe germination of weed seeds and at the same time smothers the established young weeds.This mulching practice also helps in conserving the soil moisture.Growing sorghum crop every year in the same field (monocropping) encourages injurious weeds to multiply like Striga and dominate in the field. Such weeds will reduce sorghum crop yields much more than the competition from a wide spectrum of weeds. So, adopting proper crop rotation practices will help in overcoming the domination of certain weeds and lessening the weed competition in sorghum crop.

Sorghum-Pigeonpea intercropping  

Intercropping practice in sorghum crop not only provide the monetary and land utilization advantages but also help in smothering the weeds with good crop cover over the land surface.

Manual weeding  

Manual weeding is a very common practice to control weeds in sorghum crop.Timely weeding is important than the frequency of weeding. It is necessary to keep the crop free during the first month of its growth through manual weeding.

Hand hoeing to control weeds  

Hand hoeing is an effective method adopted widely to control weeds in the inter - row spaces of line-sown crop. This method provides excellent physical condition to the crop growth by way of soil aeration through stirring of the soil .First hand weeding is done at about 20 - 25 days after sowing and should be repeated at fortnightly intervals up to 45 days of the crop.Manually operated implements like wheel push hoe are also used to control weeds in sorghum.

Mechanical weeding

Intercultivation using Blade harrowing in relatively dry and loose soil between the rows of sorghum, is a widely followed method for effective weed control as this operation cuts the root system of weeds resulting in desiccation of weeds.
Duck-foot harrows are also used for intercultivation in sorghum.  The first intercultivation is done about three weeks after sowing and the second and the third about a fortnight and a month later.No interculture would be possible when once the plants grow tall.

Chemical control:

The delay in manual weeding and intercultivation may be delayed due to the uncertain weather conditions.Therefore, chemical weed control has found a place in sorghum weed production. Chemical control or Herbicide application is advantageous in case of non-availability of labor and/or cost of labor for manual weeding is very high.Use of correct herbicides will provide completely weed-free situation to the crop where as manual or mechanical weeding can be done only after the emergence of weeds.Use of chemicals (herbicides) to control weeds should be based on their comparative advantage over the manual and mechanical control of weeds.

Herbicide application requires some knowledge about the use of such chemicals. Improper use of herbicides may lead to the complete loss of the crop.The farmers need to understand the proper use and application of herbicides before applying them to control weeds in sorghum crop.Satisfactory control can be obtained by combining timely cultivation, crop rotation and herbicide applications.However, efficient and cost-effective weed control can be achieved by using combination of herbicides or combining manual and herbicide control methods.

 Depending on the time of application, herbicides are grouped as:

• pre–planting (incorporated into the soil before sowing of the crop) herbicides,
• pre–emergence (after sowing but before emergence of seedling) herbicides,
• post–emergence (after emergence of weeds and the crop) herbicides.

Pre–sowing/planting (incorporated into the soil before sowing of the crop) application of herbicides.

Pre–emergence (after sowing but before emergence of seedling) application of herbicides.

Post–emergence (after emergence of weeds and the crop) application of herbicides.

Herbicides should be selected based on specific weed and grass problems encountered in each field and rotational crops to be planted following the sorghum harvest.It is very difficult to control grass-type weeds with post-emergence herbicides so plan to use a pre-emergent herbicide if grass-type weeds are expected.In general, herbicides like Atrazine, Propazine, Prometryne and Simazine are recommended for weed control in sorghum.Atrazine usually gives better control weeds than Propazine but Propazine was found to be safest.If the field is weedy with annual grasses and broad leaved weeds before sowing sorghum:Spray Praquat (Gramoxone) on the weeds at 0.5 to 1.5 liters per ha depending on the weed density. Consult the product label prior to use.

If the field is weedy with annual grasses and broad leaved weeds before sowing sorghum:

If sedges like Cyperus spp., Bermuda grass, Johnson grass,field bind weed dominate in the field, spray
Glyphosate (Roundup) at 0.5 to 1 liter. Direct the spray on the weeds as Glyphosate becomes inactive in the soil.Consult the product label prior to use.

Pre-emergence application:

• Atrazine or Propazine or Prometryne at 1.0 kg a.i./ha is recommended to control emerging weeds after the sowing of sorghum. There should be optimum soil moisture at the time of application of Atrazine.
• Application of Metalochlor 1 kg a.i./ha found to control the weeds effectively and increase the yield and net income of sorghum intercropped with pulses like Cowpea / Black gram / Green gram (mungbean).

Post-emergence application:

• Low rates of 2,4-D at 0.5 to 1.0 kg/ha may be applied when the plants are between 10 to 30 cm tall. Spraying later time affects yield by reducing seed set.
• Early treatment can also be injurious by damaging the root system.

Digera arvensis (Kundra)	Euphorbia hirta (Spurge)	Euphorbia purviflora	Borreria articularis (Button plant)
Celosia argentina (White cock's comb)	Alysicarpus sp.(One-leaf clover)	Portulaca oleracea (Common purslane)	Abutilon indicum (Indian mallow)
Corchorus olitorius (Jew's mallow)	Anagallis arvensis (Scarlet Pimpernel)	Xanthium strumarium (Cocklebur)	Cleome sp.(Wild spider flower)
Vernonia cinerea (Little iron weed)	Mollugo verticillata (Carpet-weed)	Bidense pilosa (Spanish needle)	Leucas aspera (Dronapushpi)
Amaranthus spp. (Pigweed)	Eclipta prostrata	Eclipta alba	Commelina spp. (Benghal dayflower)
Tridax procumbence (Tridax daisy, wild daisy)	Chloris barbata (Swollen Finger grass)	Chloris gayana (Feather Finger grass)	Ipomea spp. (Morning glory)
Paspalum distichum (Water couch)	Echinocloa spp. (Barnyard grass)	Dactyloctenium aegyptium (Crowfootgrass)	Digitaria sanguinalis (Crabgrass)
Cyperus rotundus (Purple nut sedge)	Setaria spp. (Foxtail)	Eragrostis spp. (Lovegrass)	Eleusine indica (Goose grass)
Cyperus defformis (Nut sedge)	Cyperus compressus( Nut sedge)	Cynadon dactylon (Bermuda grass)	Cyperus esculantus (Yellow nut sedge)