Weed Control Topic 2044 Melissa M. Fowler

What is a Weed?  Any plant that is out of place  Any plant that grows where it isn’t wanted  Examples  A corn plant growing in a soybean field  A tulip growing in the middle of a yard

Detrimental Effects  Compete with crops for  Moisture  Light  Nutrients  Contaminate crops and their products  Off flavored milk  Weed seeds in a seed crop  Carry pathogens

Detrimental Effects Cont.  Poisonous to livestock  Loco Weed  Nightshade  Milkweed  Increased production costs  Cultivation  Chemicals  Seedbed preparation  Nuisance

Beneficial Effects  Prevent erosion  Provide food and cover for wildlife  Reduce leaching of minerals  Add organic matter

Eradication vs. Control  Eradication  Killing every existing plant  Destroying all reproductive organs  Dormant seeds  Below ground organs  Control  Reducing existing plants  Presence of some weeds does not seriously interfere with the area’s economic use.

Prevention  Use clean, weed-free seed  Use clean equipment  Grow weed-adapted crops  Watch for weed seeds in packing material or nursery stock

Methods of Control  Biological  Mechanical  Chemical

Biological Control  Caterpillars  Used to kill thorny shrubs  Fungus  Velvetleaf will wilt and die  No harm to crops or ornamentals  Fungal Spores  Sprayed on rice crop  Weeds controlled within 7 to 10 days  As effective as herbicides  No damage to rice

Biological Control Cont.  Allelopathy  Plants produce chemicals  Chemicals harmful to other plants  Chemicals exude through plant roots or will be washed from leaves by rain

Mechanical Control  Cultivation  Uproot and/or cut off roots  Mulches  Layer of plant or artificial material on soil surface  Work by cutting off light source  Burning (1800 o F)  Flame directed on weeds for short time  Done in cotton  Effective for killing small weeds

Mechanical Control Cont.  Flooding  Used on rice paddies  Kills non-aquatic weeds

Chemical Control  Herbicides  Depend on rain to wash them into soils  Types of Application  Preplant  Preplant incorporated  Preemergence  Postemergence

Herbicide Types  Contact  Kills the part of the plant that it touches (contacts)  Not carried throughout the plant  Will not kill perennial weeds  Example: Paraquat  Systematic  Blocks metabolic activity  Translocated throughout the plant  Necessary to kill perennial weeds  Example: Roundup

Herbicide Types Cont.  Selective  Kills one type of plant but not another  Some will kill broadleaves, but not grasses  Others will kill some grasses and some broadleaves, but not others  Example: Atrazine  All selective herbicides are systematic BUT not all systematic herbicides are selective.

Surfactants  Sticking agent added to help herbicides stick  Facilitate absorption of chemical  Also known as: Crop Oil Concentrate (COC)

Active Ingredient (a.i.)  Ingredient that actually kills the plant  Pounds/ acre  Ounces/ acre  Too little will not work sufficiently  Too much will harm the crop and cause pollution  Follow label directions