10/22/2008. AGRN 1003/1004 Dr. Weaver

Transcription

1 AGRN 1003/1004 Dr. Weaver Weeds Disease pathogens (fungi, bacteria, viruses, nematodes) Insects and related organisms Birds Mammals (deer, rabbits, rodents) Discussion of specific pest problems will occur in sections on specific crops Weeds are defined as any plant out of place, but particularly any plant that competes with crop plants and decreases yield or crop quality. Crops were originally planted in rows to allow for easier weed removal Some present-day crops evolved from plants that were originally weeds Cost of weed control is high (> $5 billion/year for herbicides alone) Weeds have extremely efficient survival mechanisms Plants introduced from foreign countries for economic purposes often become weeds, or invasive species (kudzu, privet) 1

2 Weed problems in peanut (above) and cotton (below). Cotton is so severely infested with nutsedge it will not be harvestable. Lower crop quality when included with harvest Decrease yields by direct competition with crops Harbor insects and diseases Can cause livestock injury Decrease land values Weeds are classified botanically, just like crop plants Also classified according to life cycle, as perennials (ex. Johnsongrass) or annuals (such as crabgrass), and Broadleaf weeds (morningglory) or grasses (foxtail) Usually a combination of terms are used when herbicide recommendations are being made, such as annual broadleaf or annual grass 2

3 johnsongrass crabgrass foxtail sicklepod Preventative if you can prevent a field from becoming infested with weeds, there is no need for control measures Clean up weedy roadsides, ditches, irrigation canals, and fallow fields Don t plant crop seeds that are contaminated with weeds Sanitize cultivation and other tillage equipment when moving from field to field Cultural- practice good crop production practices that provide for a healthy crop canopy and weeds will have less chance to compete Optimize row spacings and plant populations Fertilize the crop Optimize planting dates Biological introducing pathogens or insects that feed upon the weed Not widely practiced in crops, some in rangeland and other areas 3

4 Mechanical the oldest and most familiar form of weed control Hand-pulling and hoeing Cultivation Chemical herbicides account for more sales than any other pesticide Based on selectivity Selective herbicides kill certain plants but not others Examples are 2,4-D, which kills broadleaf weeds but not grasses, and trifluralin (Treflan ), which kills grasses in soybean and cotton Nonselective herbicides will kill all plants Best example is glyphosate (Roundup ), for which some major row-crops (soybean, corn, cotton) have been genetically engineered to have tolerance Other examples include paraquat (Gramoxone ) and trichlopyr (brush-killer) Based on mode of action Contact herbicides kill on contact with plant tissue Example is paraquat, a herbicide which is not translocated Works best on annual weeds Systemic herbicides are translocated throughout the plant, and kill from within Best example is glyphosate (Roundup ) Other examples include trichlopyr (brush-killer) Works best on perennial weeds, because it kills the roots, tubers and other underground parts from which perennial weeds regenerate 4

5 Based on time of application Herbicides can be applied at any stage of plant or weed growth, but this is usually specific to the particular herbicide Pre-plant herbicides are applied to soil prior to planting of the crop They are usually incorporated via tillage immediately after application, but not necessarily so Pre-emergence herbicides are applied to soil after planting, but prior to crop or weed emergence Post-emergence herbicides are applied to the plants after they have emerged, glyphosate is an example Getting satisfactory results from an application of herbicide means controlling the target weed 100%, with no injury to the crop Three major factors contribute to satisfactory results Application rate control and selectivity are often dependent upon applying the chemical at the correct rate Stage of growth of target weed or crop apply when weeds are most susceptible and crop is most tolerant. For weeds, they are often most susceptible when in early growth stages. Environmental conditions at time of application Soil moisture Air temperature Time of day Precipitation All these can impact a herbicide s effectiveness to a varying degree Water-stressed plants are less susceptible to herbicide damage Some herbicides are more effective in high intensity light, while others may be broken down by light and should be applied late in the day 5

6 There are at least 66 known diseases of rice alone Defined as the harmful alteration of normal biochemical and physiological development of plants Fungi these cause more diseases in plants than any other organism Rusts, smuts, mildews, blights, wilts are all caused by fungi Bacteria Cause crowngall, fireblight, some wilts Viruses Cause mosaics, leaf distortion Nematodes Cause root-knot, cyst, lance, reniform Exclusion Keep the disease out of a field, state or other geographic area Plant quarantines and certification programs Eradication Cultural sanitation Destruction of crop debris Elimination of alternate host Eradicant chemicals Therapy Heat, surgery, chemicals 6

7 Resistance Genetic control Best in terms of environmental effects, cost to producer Protection Chemical sprays Seed treatments, soil treatments Avoidance Choice of geographic area Planting site in local area Planting date Insects have plagued man since the beginnings of agriculture Insects were recognized as a plant pest long before the causes of disease were known In addition to attacking plants directly, they also transmit disease Biological control Certain insect predators are used to help manage pest populations Ladybird beetles love to feed on aphids Spiders, mites, assassin bugs and others feed on pests Fungi and bacteria can also harm damaging insects Bacillus thuringensis is an insect pathogenic bacterium 7

8 Bacillus thuringensis Produces proteins (Bt proteins) that are toxic to certain Lepidopterans (moths) Plants have been genetically engineered to produce Bt proteins on their own, and thus kill insects that feed upon them Commercially grown cultivars of cotton, corn, potato and other crops are engineered to resist attack by moth larva and other insects, such as the corn earworm and corn borers Genetic resistance Growing insect-resistant or tolerant cultivars is a viable alternative for some crops Wheat resistance to Hessian fly Cotton, corn resistance to insects via Bt technology Chemical pesticides Chief method of insect management in many crops Use is declining due to increased biological, genetic resistance usage Chlorinated hydrocarbons Examples are DDT, toxophene Most such chemicals are now banned in the US Organophophates Examples are Malathion, Methyl parathion Highly toxic to mammals and non-target insects Carbamates Examples are Sevin, Temik, Furadan Toxicity varies by chemical, Temik is often used as a nematicide Synthetic pyrethoids Synthesized derivatives of naturally occurring plant compounds Examples are Ambush, permethrin Low mammalian toxicity 8

9 IPM, an ecological approach using a combination of mechanical, physical, biological, legal, genetic, cultural, and chemical management techniques Main goal is to reduce or eliminate the use of chemical pesticides Occurs in three stages Prevention Observation Intervention Acceptable pest levels: The emphasis is on control, not eradication. It is better to decide on what constitutes acceptable pest levels, and apply controls if those levels ('action thresholds') are exceeded. Preventive cultural practices: Maintaining healthy crops is the first line of defense, together th with plant quarantine and cultural techniques such as crop sanitation (e.g. removal of diseased plants to prevent spread of infection). Monitoring: Regular observation is the cornerstone of IPM. Visual inspection, insect and spore traps, and other measurement methods are used to monitor pest levels. Mechanical controls: Includes simple handpicking, erecting insect barriers, using traps, vacuuming, and tillage to disrupt breeding. Biological controls: The main focus here is on promoting beneficial insects that eat target pests. Biological insecticides, derived from naturally occurring organisms (e.g.: Bt), also fit in this category. Chemical controls: Synthetic pesticides are generally only used as required and often only at specific times in a pests life cycle. 9

10 There are several steps in any IPM program, but only the first two essential steps are listed here Identification of pest species and any beneficial insects present know for sure what you are dealing with, and the potential for future damage Determine economic thresholds some crops can tolerate quite a bit of insect damage before dollars are lost 10