Weeds compete with coffee plants for water, light and mineral nutrients. If weeds are allowed to grow during late post-monsoon period, they use the soil moisture which coffee needs in the following dry weather. Free growth of weeds reduces the yield of coffee and plants assume a sickly appearance. In young clearings, weeds are a serious problem particularly during the first three years. The pruned fields where the ground is exposed are also prone to weeds.
Methods of weed control
Typically new clearings are hand-weeded 3 to 4 times and established coffee fields 2 to 3 times a year. During the monsoon season, weeds are slashed back (slash weeding) with the help of a matchete. Clean weeding is generally done during post-monsoon period. It is a labor intensive and time consuming operation in coffee estates.
In new clearings, the field is given a thorough digging (cover digging) to a depth of about 37 to 45 cm towards the end of monsoon. All weeds and vegetative debris are completely turned over and buried in the soil.
In young clearings, coffee at normal spacing covers only a small portion of the soil surface and there is room for prolific weed growth. Inter-planning of green manure crops, cover crops and annual crops such as grain legumes, cassava, beans, pigeon pea, yam, sweet potatoes, vegetables, pineapples help suppress weeds to large extent. Intercropping has been successful in Robusta coffee plantations in Wayanad region of Kerala. In established plantations, scuffling and mulching at the end of monsoon can be effective in controlling weeds.
Chemical Weed Control
Chemical weed control methods (weedicides) are employed where labour is scarce or expensive or when labour has to be diverted to other important cultural operations like manuring and spraying. Weedicides can be classified based on time of application (pre-emergent and post-emergent), mode of action (contact and systemic) etc.
Pre-emergent weedicides are applied before the emergence of weeds to moist soil. These are taken up through the germinating roots of weed seeds and remain in surface layers of the soil long enough to kill the weed seeds. These weedicides have a long residual effect and growth of coffee and cause phytotoxicity. Pre-emergent weedicides (simazine, Atrazine) are not usually advocated in coffee plantations. Post-emergent weedicides are applied when the weeds are applied when the weeds are actively growing. Unlike pre-emergent weedicides, the post-emergent weedicides become inactivated on coming into contact with soils and are thus unavailable to root system of plants. Hence they have no residual effect (paraquat- dichloride/gramoxone) kill only those plant parts which come into contact with them. They are quick acting and control a wide range of weeds. Care should be taken to target only the weed growth.
Systematic weedicides are absorbed through roots or aerial parts and are then translocated within the plants tissue and kill the entire plants system (Glyphosate/Glycel or Round up). The efficiency of weedicides can be increased by adding surfactants (wetting agents) facilitate uniform spreading of spray surface. These help spray droplets adhere to the plant and prevent droplets adhere to the plant and prevent droplets from bouncing off (Tween-20, Vettoplants).
Selection of Sprayers and Nozzles
Knap-sack or back-pak sprayers (low pressure, high volume) fitted with plastic container are preferred for application of weedicides in coffee. For blanket application, WFN 062 or WFN 040 flood jet nozzles are commonly used. When systemic weedicides are to be sprayed, ULV 50 nozzles is preferred. For spot applications, WFN 024 flood jet nozzles are used. The sprayers used for weedicide application should be properly labeled and thoroughly washed after each application. It is advisable not to use these sprayers for spraying pesticides on the coffee bushes.
Time of Application
Weedicides should be applied on a bright sunny day when there is sufficient moisture is soil and the weeds are actively growing but before their flowering and seed set. The first round of blanket application should be taken up by the end of April or at beginning of May when the weeds are about 10 to 15 cm high. If weeds are taller than this they should be slashed back and sprayed a week or 10 days later. Scattered patches of weed growth should be controlled by spot spraying 15 to 20 days after the blanket application may be necessary towards the end of monsoon i.e. September/October, which has to be followed by one or two spot applications. Generally, 450 1 of spray solution is needed per hectare for each blanket spray to achieve effective control of weeds.
Recommended Weedicides for Coffee
- Paraquat-di-chloride 24% EC at 0.067% a.i.(Gramoxone 500 ml per barrel).
- Glyphosate 41% EC at 0.27% a.i. (round up or Glycel at 1200 ml per Barrel).
The cost of chemical weeding could be brought down by nearly 50% by addition of urea @ 1% in spray solution. The dosage of gramophone could be brought down to 250 ml per barrel and that of round up or glycel to 600 ml per barrel when urea is added to the spray solution @ 2 kg per barrel without any reduction in their weed killing efficiency.
Experimental evidences indicate that continuous application of recommended weedicides did not affect the soil characteristics like organic matter content, pH, available ‘P’, ‘K’ etc., but significantly lowered the population of soil micro flora.
Mechanical Weed Control
Mechanization of weeding operation in coffee estates has been attracting attention of researchers and also coffee farmers in recent years. Many companies have come with manufacturing/import of machineries such as weed/brush cutters, rotary weeder that can be used in agriculture. Based on this background, studies were carried out at Central Coffee Research Institute; CRSS, Chettallli; RCRS, Thandigudi basis to evaluate various types of mechanical weed/brush cutters available in the market for controlling the weeds and also to assess their suitability in the sloppy terrains of coffee estates in terms of improving efficacy of farm operations, cost reduction and reducing drudgery of human labor.
The result of these studies indicated that controlling weeds by using hand held mechanical weed/brush cutters would be more economical compared to manual method and chemical method of weeding which would be also ensure saving of precious man days for other important cultural operations during critical periods.
The details on mechanical weed control are discussed in chapter 9 (Mechanization of coffee farm operations).