AGR 3102 Principles of Weed Science Unit 5: Methods of Weed Control Mechanical and Cultural Muhammad Saiful Ahmad Hamdani

Methods of Weed Control

Objective: to injure/kill weed plants physically and use physical barrier to impede weed growth. Consists of: 1.Hand pulling and hoeing: can be expensive (labour cost). Good for garden & small areas. 2.Tillage: burial, exposing weed seeds, pull-out de- rooting. 3.Mowing and slashing: more effective for tall-growing weeds; repetition may prevent seed production. More effective on broadleaf weeds than on grasses.

Tine harrowing-remove weed seedlings Ploughing Slashing Hand-hoeing

4. Weed seed destroyer – in Australia. Designed to destroy weed seeds during harvest and thereby reducing the potential for weed growth. Towed behind a harvester. Used in grain crop areas.

5.Burning and heat: -Steam sterilization of potting media for nursery operations; kills weed propagules (veg. parts), insects, pathogens. -Kill most emerged weeds and seeds. -However, lose benefit of allelopathy from straw; also eliminates potential for organic matter.

Windrow burning in Australia Rice straw burning in Malaysia

6. Mulching Reduced/blocked light and air penetration into soil: impede/prevent weed seed germination and growth. Materials used: hay, woodchips, rocks, sawdust, plastic mulch used in horticultural crops.

Disadvantages of Mechanical Control Not completely eradicate weeds. Not a long lasting control methods. High cost is needed (labor, machineries). High time and energy consuming. Need high efficacy esp. for control method using hoe and machineries. If not careful, might also destroy crops.

Methods of Weed Control

Objective: provides conditions more favourable for crop growth, less favourable for weeds. Involves agronomic practices and crop management. Consists of: 1) Grow Healthy & Competitive Crops:  Select competitive & resistant varieties  Provide optimal growing conditions for crops – suitable soil type, pH crops – suitable soil type, pH

 Irrigate and fertilize crop, not weeds  Early/delay sowing date – e.g. in rice farming  Intercropping – using empty space between crop rows

 Crop rotation: Crop rotation can disrupt weed life cycles. Crop rotation: diversity in herbicides use.

 High seeding rate - higher seeding rates increase planting density and planting uniformity: no space for weeds.HOWEVER!!! - not to be so high that yields are reduced (intraspecific competition, high humidity, lodging, disease potential)

2) Cover Crops: Used to compete with the weeds infesting an area. Prevent weed emergence and/or reduces growth of weeds. Can exclude light, provide a physical barrier to weed emergence, modify soil temperature and moisture, increase N 2 fixation, become fertilizer to crops. Allelopathic chemicals from the cover crop residue may also inhibit germination/growth of weeds.

3) Water Management: Flooding used in rice production for weed control. Many weeds are not tolerant to anaerobic conditions: death. Rice can survive flooding. Less suitable for aquatic weeds. Water deprivation can be a weed control method in orchard or plantation.

Disadvantages of Cultural Control Some methods consume large amount of natural resource (e.g. water). Weeds are even more aggressive than the latest variety. Crop rotation, not applicable in plantation and perennials. Cover crops is not suitable for some crops. Need high efficacy esp. for control method using precise irrigation and fertilizers, not practical in rice field.