Unit 2: Weed Control for Corn, SB, & Sorghum

1. Unit 2: Weed Control for Corn, SB, & Sorghum

2. Unit 2: Weed Control for Corn, SB, & Sorghum • Unit 2 Objectives: • Awareness of safety, proper use, and label warnings of pesticides • Understanding of herbicide application methods • Preemergence application • Postemergence application • Discussion of the effect of various tillage methods and its relationship to chemical efficacy

3. Unit 2: Weed Control for Corn, SB, & Sorghum • Precautions • Risks and benefits must be evaluated • Crops, people, & environment • Use should be restricted to minimize exposure • Current Label • Herbicides classified as Restricted Use Pesticides must be applied by a certified applicator • Chemical may be toxic or pose environmental concerns

4. Unit 2: Weed Control for Corn, SB, & Sorghum • Degree of toxicity indicated on the label by a Signal Word • Danger-Poison and Danger – high toxicity hazard • Warning – moderate toxicity • Always use personal protective equipment as recommended on the label for safety • Be aware of drift potential, especially near residential areas • Environmental Hazards • Groundwater advisories must be observed • Toxicity of fish/wildlife will be listed on the label

5. Unit 2: Weed Control for Corn, SB, & Sorghum • Proper Herbicide Use • Apply only to approved crops • Use proper rates • Apply at the proper time • Proper use will decrease risk of illegal residual, and environmental pollution • Be aware of proper harvesting or grazing withholdings

6. Unit 2: Weed Control for Corn, SB, & Sorghum • Proper Equipment Use • Spray tanks should be clean and free of other residues • Especially critical when spraying postemergence herbicides • Sprayer should be correctly calibrated and adjusted before adding herbicide to the tank • Follow recommendations on the label

7. Unit 2: Weed Control for Corn, SB, & Sorghum • Drift Precautions • Apply on calm or light wind days only • Be aware of wind direction and residential areas, ornamental crops, etc. • Some chemicals are very mobile, and effects can be observed far from the application site • Protecting the Crop • Do not apply to stressed crops

8. Unit 2: Weed Control for Corn, SB, & Sorghum • Understand crop sensitivities • Crop size • Climatic conditions • Previous injury from diseases, insects, or other chemicals • Proper Recropping Interval • Understand chemical carryover and how it can affect the next crop • Soil texture, organic matter, soil pH all may affect persistence

9. Unit 2: Weed Control for Corn, SB, & Sorghum • Proper Storage of Herbicides • Store in original, labeled containers in a secure place • Keep away from kids, livestock, etc. • Proper Disposal • Pressure wash, or triple rinse containers • Properly cleaned containers may be recycled, or be acceptable in some landfills • Mini-bulk returnable containers are desirable • Use caution if you are going to burn

10. Unit 2: Weed Control for Corn, SB, & Sorghum • Cultural and Mechanical Weed Control • Practices that aid in weed control • Adequate seedbed preparation • Adequate fertilization • Crop rotation • Proper planting date • Optimal row width • Optimal seeding rate

11. Unit 2: Weed Control for Corn, SB, & Sorghum • Planting in relatively warm soil helps the seed emerge quickly and compete with emerging weeds • 1st 3-5 wks. are critical for good weed control in corn and soybeans • Crops tend to compete very well after this point • Narrow rows can help • Squeezes out weeds • Puts more pressure on herbicides for weed control • If control is inadequate it is better to leave room for cultivation

12. Unit 2: Weed Control for Corn, SB, & Sorghum • Row cultivation • Can control when weeds are small • Smothers weeds • Careful adjustment to minimize crop injury • May not be necessary if herbicide controls weeds adequately, and no aeration is needed

13. Unit 2: Weed Control for Corn, SB, & Sorghum • Herbicide Incorporation • Reasons for incorporation • Minimizes depending on rainfall • May improve control of some weeds • Minimize surface losses • Distribute herbicide uniformly in the top 1-2” of soil • Suggested depth of operation for proper incorporation is 3-4”

14. Unit 2: Weed Control for Corn, SB, & Sorghum • May require two passes for best operation • Second pass should be at angle and no deeper than first pass • Proper application and incorporation minimizes crop injury and carryover problems • Uniform distribution depends on type of equipment, depth of operation, speed of operation, soil texture, soil moisture • Placement deeper than 1-2” may dilute the herbicide and reduce effectiveness

15. Unit 2: Weed Control for Corn, SB, & Sorghum • Field Cultivators • At least 3 rows w/ sweeps • 7” or less spacing between sweeps • Level and operate at 3-4” depth • Minimum 5 mph ground speed • Tandem Disks • Blade diameter of 20” or less • 7-9” blade spacing • 3-4” operating depth

16. Unit 2: Weed Control for Corn, SB, & Sorghum • 4-6 mph ground speed • Want to move soil full width of the blade space • Slower speed or lack of leveling device can cause streaking of herbicide • Combination Tools • Advantage is they can handle more surface residue • More uniform one-pass incorporation than disk or field cultivator • No better than two passes w/ one of the other tools

17. Unit 2: Weed Control for Corn, SB, & Sorghum • Chemical Weed Control • Several factors to consider when planning weed control: • Soil • Tillage program • Crops • Weed problems • Management operations

18. Unit 2: Weed Control for Corn, SB, & Sorghum • Herbicide performance depends on: • Weather • Proper selection • Application • Minimize crop injury by using proper timing, application rates, uniform spraying • Damaged crops are more prone to disease

19. Unit 2: Weed Control for Corn, SB, & Sorghum • Unfavorable conditions • Cool, wet weather • Delayed crop emergence • Deep planting • Seedling disease • Poor physical condition of soil • Poor quality seed

20. Unit 2: Weed Control for Corn, SB, & Sorghum • Next season’s plans must also be considered when selecting a herbicide program • Corn/SB herbicides may have restrictive recropping intervals • Check label for restrictions • Can vary depending on the number of applications, timing, weather, soil, pH, etc. • Ex. Atrazine restricts planting wheat after corn

21. Unit 2: Weed Control for Corn, SB, & Sorghum • Persistent corn herbicides of concern for SB • Atrazine • Clopyralid (Stinger) • Prosulfuron • Persistent SB herbicides of concern for corn • Imazaquin (Scepter) • Chlorimuron (Classic)

22. Unit 2: Weed Control for Corn, SB, & Sorghum • Weed Resistance to Herbicides • Like insects, weeds have the ability to become resistant • Weeds that have become resistant to different chemicals • Pigweed, waterhemp, lambquarters, ragweed, cocklebur, and many others • Management recommendations to help prevent herbicide resistance: • Scout fields regularly & identify resistant weeds, keep records of weed populations to monitor/restrict their spread

23. Unit 2: Weed Control for Corn, SB, & Sorghum • Rotate herbicides w/ different sites of action • No more than two applications of the same herbicide in the same or successive years on the same weed w/ same site of action • Use other strategies for weed control • Especially critical when using herbicide tolerant crops • Use multiple sites of action • Tank mix • Premix • Sequential applications

24. Unit 2: Weed Control for Corn, SB, & Sorghum • If practical use rotary hoeing and cultivation to control resistant weeds • Hand weeding may be needed • Herbicide resistant weeds can spread from nearby highways, railroads, utility areas etc. where total vegetation control may be used • Herbicide Combinations • In tank mixes, premixes, or sequential applications • Can control more weed, reduce carryover, reduce crop injury

25. Unit 2: Weed Control for Corn, SB, & Sorghum • May be able to split apply (same herbicide, two apps.) or sequential apply (two apps., different herbicides) • Many combinations sold as premixes • Harness Xtra • Lightning • Canopy XL • Alleviates some compatibility problems associated w/ tank mixing • Some are tank-mixed • Allows adjustment for local problems • Weed pressures • Soil conditions

26. Unit 2: Weed Control for Corn, SB, & Sorghum • Read and follow all restrictions when tank mixing • Problems may occur when mixing emulsifiable concentrates w/ suspendible herbicides (liquid-flowable, dry-flowable) • Proper mixing can minimize the difficulties (agitation, carriers, etc.) • Must be cautious of accumulations in tank – thoroughly clean after application

27. Unit 2: Weed Control for Corn, SB, & Sorghum • Herbicide Rates • Rates vary • Time & method of application • Soil conditions • Tillage system • Weed pressure • Rates of herbicides in combination often are lower than the same chemical used alone

28. Unit 2: Weed Control for Corn, SB, & Sorghum • Soil-applied herbicides • Texture of the soil • Amount of organic matter • Specific recommendations for sandy soils • Postemergence rates • Size of the weed • Species of weed • Rates listed are broadcast rates • Adjustment will be needed if a different method is used • Formulations w/ different combinations may vary amount of active ingredient

29. Unit 2: Weed Control for Corn, SB, & Sorghum • Postemergence Herbicide Principles • Efficacy relies on foliar activity more than soil action • Some may have both modes of action • Rates and timing based on: • Weed size • The smaller the weed, the lower the rate • Weather • Penetration & action is higher in warmer weather and higher humidity • Rainfall within 30 min to 6 hrs. can reduce effect

30. Unit 2: Weed Control for Corn, SB, & Sorghum • Contact herbicides require more complete coverage • Coverage increases as water volume and spray pressure are increased • Nozzles that produce small droplets also increase coverage • Usually 10-40g of water/ac. for ground application • 30-60 psi suggested • Flat-fan • Hollow-cone nozzles • May be more drift risk

31. Unit 2: Weed Control for Corn, SB, & Sorghum • Crop size limitations often indicated on the label • Minimize crop injury • Maximize weed control • Weeds smaller than the crop • Basal-directed sprays may help minimize crop injury • Place more herbicide on the weed • Weeds taller than the crop • Rope-wick • Sponge app. • Place herbicide on weed instead of crop

32. Unit 2: Weed Control for Corn, SB, & Sorghum • Herbicide Adjuvants • Crop-oil concentrate (COC) • Spread herbicide across foliar surface • Keep surface moist longer • Aid penetration to the cuticle • Increases mixing ability w/ water • Petroleum or vegetable origin • 1-3 pints/ac, or 1% by volume • Better effect on postemergence app. compared to surfactants (both on weed and crop)

33. Unit 2: Weed Control for Corn, SB, & Sorghum • Nonionic Surfactants (NIS) • Cause spreading & wetting action by decreasing surface tension of water • Mixes and spreads over waxy/hairy surfaces rather than form droplets • Increase herbicide absorption into the weed • .25 – 1 pint/ac., or 1/8 to ½ % volume • Should contain 75-85% active ingredient • Ammonium Fertilizers • Increase herbicide activity on weeds like velvetleaf • Usually ammonium sulfate or Urea-ammonium nitrate (28%)

34. Unit 2: Weed Control for Corn, SB, & Sorghum • 28 – 2-4 quarts/ac. • Care should be used to reduce drift • Drift-reduction agents/retardants • Make sure you read the labels • Conservation Tillage & Weed Control • Minimum/ reduced till = any tillage system intentionally leaving crop residue on the soil surface • Mulch tillage = leave at least 30% of the soil covered w/ crop residue

35. Unit 2: Weed Control for Corn, SB, & Sorghum • Ridge & Zero tillage = no major tillage prior to planting • Ridge till ideal for banding preemergence herbicides because cultivation is part of the plan • No-Till • Conserves soil moisture • Conserves soil • Saves fuel • Increase timeliness of planting

36. Unit 2: Weed Control for Corn, SB, & Sorghum • If tillage eliminated before planting, must control existing weeds either before, at, or after planting • Greater reliance on chemical control of weeds • Preplant or postplant soil-applied not incorporated • Contact herbicides • Soil-residual herbicides may eliminate need for “knockdown” at planting • Early Preplant application may lead to more applications later in the season, or cultivation

37. Unit 2: Weed Control for Corn, SB, & Sorghum • Today’s equipment much better suited for reduced-till systems • If done properly, crop residue should not effect herbicide distribution • Early preplant app. or postemergence herbicides often provide adequate control • Existing vegetation in corn and SB stubble is often annual weeds • If small, easily controlled w/ contact herbicide that has some soil-residual activity

38. Unit 2: Weed Control for Corn, SB, & Sorghum • Broadleaves • 2,4-D or dicamba (Clarity) may be used prior to corn or no-till SB • Observe planting delay recommendations • Using Cover Crops • What are people in IL using? • What is the advantage of a cover crop? • Hairy vetch • Controlled w/ 2,4-D or dicamba before planting

39. Unit 2: Weed Control for Corn, SB, & Sorghum • Winter rye or wheat • Controlled by glyphosate(ex. Touchdown) prior to planting corn or SB • How early should you spray? • Varies depending on the season • Dry – late control can dry out soil too much for the crop • Wet – late control can help to dry out the soil • Too much decomposing residue can inhibit the emergence/viability of the corn seedling

40. Unit 2: Weed Control for Corn, SB, & Sorghum • Control of Perennial Sods • Pasture land or CRP returning to production • Perennial Grass Sods • Glyphosate is most effective • Fall application is best • Mow in late summer • Allow 6-8” growth before application • Springtime application • Must wait for 6-10” new growth • Paraquat + atrazine (Gramoxone Max) also very effective

41. Unit 2: Weed Control for Corn, SB, & Sorghum • Perennial Legume Sods • Need 6-8” growth • Do not take a spring cutting (will delay corn planting too much) • When planting corn can follow with: • 2,4-D • Dicamba • Glyphosate • May apply glyphosate in the fall after the last cutting taken

42. Unit 2: Weed Control for Corn, SB, & Sorghum • Fall Herbicide Applications • Increasing in popularity in IL • Two approaches: • First approach • Use soil-applied grass control herbicide to control annual grasses the following season • Usually in very northern IL • Helps to reduce workload in the spring • Disadvantage • Higher application rates

43. Unit 2: Weed Control for Corn, SB, & Sorghum • Grass control may not last throughout following season • Second approach • Control winter annuals and perennials in no-till corn & SB • Used by those who have problems w/ control in the spring • Problem weeds • Marestail, chickweed, purple deadnettle • Form dense mat that makes burndown control difficult

44. Unit 2: Weed Control for Corn, SB, & Sorghum • Insufficient spray coverage • Fluctuation in spring temperature • Timeliness of application • Potential benefits: • Prevent those mats that can interfere w/ planting and tillage • Reduce vegetation where insects may harbor • May allow earlier planting as soil may warm & dry sooner • Prevents these weeds from producing seed, reduces future weed problems

45. Unit 2: Weed Control for Corn, SB, & Sorghum • Fall application of chemical takes the chemical w/ the food to roots, so you get complete root control as well • Can use higher application rates, if needed (some herbicides) • Three approaches to controlling winter annuals with fall herbicide app. • Apply a herbicide w/ residual soil activity before most winter annual weeds germinate • Use a nonresidual (glyphosate, 2,4-D, paraquat) to emerged while they are small • Combination of these two strategies

46. Unit 2: Weed Control for Corn, SB, & Sorghum • Goal is to reduce the detrimental vegetation pressuring the crop at planting • Possibly eliminate need for spring burndown control • May or may not be effective • Herbicide selection • App. Rate • Weather • Time of planting

47. Unit 2: Weed Control for Corn, SB, & Sorghum • How should you decide if this is a good tool for your operation? • If you’ve had a control problem in the past • Things to remember: • May not need fall application, if spring app. Provide satisfactory control • Spring burndown may still be needed even if you spray in the fall