Weed Management in Horticultural Crops

CROPPING AND CULTURAL METHOD

Important cultural practices are:

a) Crop rotation: Many weeds thrive well and prove troublesome if the same crop is grown year after year. Crop rotation or changing the habitat interferes with the normal life cycle of many weeds. 3-5 years crop rotation should be practiced. e.g:

I. 1st year - Clean cultivated or tall crops- sugarcane and maize.
II. 2nd year - Grain crops like wheat, barley etc.
III. 3rd year- Grass land (used for pasture)

b) Crop competition: Simplest method of weed control. Weeds are strong competitors. They take the lion’s share of the plant nutrients. For every one kg of weed growth, soil produces about one pound less of crop. Thick crops strongly compete for nutrients by weeds. Most common smother crops are Sorghum (fodder), Clovers, Lucerne Soya bean and Sun hemps. Fodder crops are smothering as their frequent cuttings destroy the top growth of weeds before they set seeds. Smother crop weakens the underground parts of the weeds and they are easily killed by the cultivation that fellows.

c) Mulching: Straw mulching is practised to check weed growth. Paper mulch is used in pineapple (but is expensive).

d) Clean cultivation: It results in removal of the tops of perennial weeds and it gradually weakens and destroys their underground parts. Cultivation must be thorough and at short intervals so that surface growth of weeds is checked. The removal of surface growth results in non-manufacturing of food to replenish (feed) the roots.
Implements used for row cultivation:

• Spike tooth harrow: or drag harrow or peg tooth harrow uproot the germinating weed seedlings, break soil crust and stir the soil up to 1-5 cm depth. It is made of 23 cm long steel pegs (or spikes) fix on a frame. It is a commercial method of controlling weed seedlings in maize, cotton, soybeans, ground nut and grain sorghum,. It can be used any time after planting the crop till the crop plants are 7-10 cm tall. It does not injure crop seedlings.
• Spring-tine harrows: or spring tooth harrow has elliptical spring like tines with triangular and sharp free ends, used like spike tooth harrow but stir the soil up to 7.5 cm depth.
• Rotary hoe cultivator: is made up of two gang pairs/groups of hoe wheels or spiders one placed behind the other within each gang. There are row units with space within them to save the rows of crop seedlings. It is a tractor drawn implement for active soil movement to dislodge weeds. It is employed to destroy germinating weeds and grasses in the rows as well as those growing close to young crop plants.
• Wheel hoe: It comprises of wheel, two handle and a tine with reversible shovel or a three prong fork or rake as its cutting tool. It is manually operating weeding tool suitable for weeding small vegetable garden.
• Blade-harrow (Bak Khar): is bullock drawn, row cultivator implement. Its cutting tool is 30-95 cm long 5-6 cm wide sharp blades works like sweep of a cultivator. It cuts the weeds 7.5-10 cm below the ground and leaves them on soil surface as mulch. Used on heavy black soil.
• Cultivator (horse hoe): is efficient row weeding implement. These vary in size from single row five lined cultivators to multilined tractor drawn cultivators capable of weeding several crop grown at a time. This can cover several hectares area in a day with a bullock drawn five lined cultivator. Used for inter-row weeding in wide row crops. Its tines are fitted with shovels or sweeps as the cutting tool. They cut the roots up to 7-10 cm below the grounds. They control the established weeds. More effective at the time when weeds are in the seedling stage.
• Rice rotary weeders: is used for rice crop. They are single or double row weeders .It works manually. They can work both parallel and across the crop rows. In single row rotary rice weeder, one man can weed about one hectare of rice in 12 hours.

Implement for pre- plant control of weeds:

Weeds are controlled either before preparation of soil bed or continued suppression of weeds in the crop season. The objectives are achieved by proper pre-plant tillage in two stages, first a primary tillage of the field with a suitable soil inverting plough/disc and secondary tillage with light soil stirring implements like disc harrow, wooden ploughs, cultivators, spike-tooth harrow, weed mulcher and soil surgeon etc. The primary tillage buries the weedy vegetation and exposes their roots/rhizomes at the soil surface while the secondary tillage breaks the clods, exposes the vegetative propagules of weeds further for their subsequent collection by hook plankers or by manual labour. Corrugated rollers and other surface packing and smothering implements act against weed seedlings.