Managing Pesky Weeds in Lawns

Transcription

1 Managing Pesky Weeds in Lawns SAM BAUER, EXTENSION EDUCATOR- TURFGRASS SCIENCE 2017 HENNEPIN CO. MASTER GARDENERS 1

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3 ON TONIGHT S MENU Refresher on lawn weeds Why do weeds occur Weed classifications Indicator weeds Resources to aid in weed control 10 steps in controlling weeds Herbicide options Problematic weeds 3

4 LAWN WEEDS Traditional weedy plants A grass with undesirable characteristics for the site Creeping bentgrass invasion in a stand of Kentucky bluegrass 4

5 LAWN WEEDS Can tolerate continuous mowing Disrupt lawn uniformity May have a rosette growth habit Leaves radiate from a central growing point and are flat along the surface of the ground Can be indicators of poor soil conditions or management issues 5

6 WEED INVASION TRIANGLE WEED INVASION ENVIRONMENT 6

7 HOW DOES SPACE OCCUR? poor establishment practices weakened turf improper species/variety selection damage from turf pests environmental conditions poor soil conditions improper lawn management physical damage (compaction or wear) all of the above 7

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9 IMPROPER MOWING Favors all weeds Mow at the maximum recommended height of the turfgrass species Avoid removing more than 1/3 of the leaf blade at once Sharp blades 9

10 Turfgrass Weed Classification Grasses or grasslike - monocots Broadleaves - dicots annual bluegrass broadleaf plantain yellow nutsedge 10

11 WEED CLASSIFICATION BY LIFE CYCLES Annuals Biennials Perennials 11

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13 Annual Annual Black medic White clover Large crabgrass Annual 13

14 Annual Annual Annual Prostrate knotweed Prostrate spurge Yellow woodsorrel 14

15 PROPER LAWN WEED CONTROL REQUIRES Good lawn maintenance Understanding of weed biology Understanding of conditions favoring specific weeds Diligence in executing mechanical controls New seedings, cool-season grassy weeds Understanding and proper use of herbicides Synthetic, organic 15

16 EXAMPLES OF INDICATOR WEEDS FOR POOR CONDITIONS AND MICROCLIMATES Compacted soils- annual bluegrass, prostrate knotweed, broadleaf plantain, pineapple weed Low nitrogen- white clover, black medic, trefoil Poor drainage- sedges, annual bluegrass High ph- plantains Surface moisture- moss, algae Low mowing, moist- chickweeds, annual bluegrass Dry areas- prostrate spurge, yarrow, black medic, yellow woodsorrel Shade- ground ivy, violets, chickweed New seeding- pigweed, lambsquarters, shepherd s purse 16

17 Weeds common to compacted soils Knotweed Pineapple weed Broadleaf plantain 17

18 Legumes as indicators of low soil nitrogen levels White clover Birdsfoot trefoil Black medic 18

19 Lambsquarters Early invaders of newly seeded areas Shepherd s purse Redroot Pigweed 19

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22 Dr. Aaron Patton, Purdue 22

23 STEPS TO CONTROLLING WEEDS 1) Know your turf: species/varieties, acreage 23

24 STEPS TO CONTROLLING WEEDS 1) Know your turf: species/varieties, acreage 2) Know your weed: life cycle, biology, growth 24

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26 STEPS TO CONTROLLING WEEDS 1) Know your turf: species/varieties, acreage 2) Know your weed: life cycle, biology, growth 3) Why is the weed there: turf stress, indicator weeds 26

27 STEPS TO CONTROLLING WEEDS 1) Know your turf: species/varieties, acreage 2) Know your weed: life cycle, biology, growth 3) Why is the weed here: turf stress, indicator weeds 4) Healthy turf = few weeds 27

28 STEPS TO CONTROLLING WEEDS 1) Know your turf: species/varieties, acreage 2) Know your weed: life cycle, biology, growth 3) Why is the weed here: turf stress, indicator weeds 4) Healthy turf = few weeds 5) Select the right herbicide safe to turf species, effective on weeds, environmental aspect, formulation, label restrictions (where can you use it?) 28

29 STEPS TO CONTROLLING WEEDS 6) Are the conditions right? time of year, weed status, weather conditions 7) Follow label directions 8) Make a uniform application blanket or spot-treat 9) Make follow up application(s) 10) Evaluate the results 29

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31 REDUCING HERBICIDE USE IN LAWNS Note indicator weeds and monitor invasion potentialremedy situations culturally Employ good cultural practices so as not to encourage weed invasion (e.g. higher mowing heights) Determine thresholds for weed acceptance (determine priority locations not treat everywhere) Spot treatment vs. blanket applications (treat by area not whole lawn, e.g. crabgrass along curb edges) 31

32 KEYS TO EFFECTIVE HERBICIDE APPLICATIONS 1) Identify the weed correctly 2) Set threshold levels 3) Select the appropriate product 4) Calibrate equipment properly 5) Calculate and measure the herbicide accurately 6) Apply products uniformly over treatment area 7) Monitor results 32

33 WHEN HERBICIDES BECOME NECESSARY Considerations Safety to applicator and desirable turfgrass species Personal Protective Equipment required Environmental impact Effectiveness on target weed(s) Weed status: growth stage and development Range of weeds controlled Longevity of control Potential injury to off target plant material Equipment to apply properly 33

34 WHEN HERBICIDES BECOME NECESSARY Considerations cont d Economics Spot treat vs broadcast Timing of application Use of additives: surfactants or adjuvants Granular vs liquid Mode of action Amines vs esters Effects on future maintenance practices Weather patterns at time of application Read the Label 34

35 HERBICIDE SELECTION BASED ON TIMING OF APPLICATION Preplant (broadcast)- applied prior to seeding or sodding; directed at controlling all existing vegetation Preemergence (broadcast)- applied as a barrier prior to weed seedlings emerging from the ground; most effective with annual weeds Postemergence (broadcast or spot)- applied to weeds that have germinated and are actively growing; juvenile plants are generally easier to control than more mature plants 35

36 Common Preplant Herbicides General vegetation killers: Glyphosate- Roundup Glufosinate-ammonium- Finale Diquat- Reward Organic vegetation killers: Pelargonic acid Various formulations of citric and acetic acids combined with various plant oils 36

37 Common Perennial Grassy Weeds Best Controlled Non-Selectively Examples of perennial weedy grasses: Quackgrass Brome grass Tall fescue Creeping bentgrass Rough bluegrass (Note: sometimes this grass is intentionally seeded into moist shady areas as a desirable lawn grass.) Note that reseeding or resodding will be necessary following the application of these materials. 37

38 Common selective, preemergence herbicides available in homeowner formulations Primarily used for controlling annual weedy grasses: Pendimethalin Trifluralin Prodiamine Dithiopyr Corn gluten meal For use at seeding: Siduron Mesotrione 38

39 GDD TRACKER ( 39

40 POSTEMERGENCE HERBICIDES Control is best on younger weeds Apply only to actively growing turf Applications during hot, dry weather may increase turf injury and reduce weed control Selectivity is best with broadleaf weeds Consider the addition of a surfactants for improved control 40

41 APR MAY JUN JUL AUG SEP OCT NOV Cool Season Perennial Broadleaf Weeds Warm Season Broadleaf Weeds Period of active growth Optimal time for postemergence control Acceptable time for postemergence control

42 POST-EMERGENT HERBICIDES FOR BROADLEAF WEEDS AND JUVENILE WARM SEASON GRASSY WEEDS Broadleaf weeds: 2,4-D Dicamba Triclopyr Mecoprop Fluroxypyr Grassy weeds: Quinclorac Mesotrione Fenoxaprop 42

43 Weed and Feed Products Advantages Convenient Effective Disadvantages Timing differences May apply more herbicide than needed Issues with seeding 43

44 ORGANIC HERBICIDES 44

45 ORGANIC HERBICIDE OPTIONS Selective options: 1. Fiesta (iron chelate)- post-emergent 2. Adios (sodium chloride)- post-emergent 3. Halo (various oils)- post-emergent 4. Corn gluten meal- pre-emergent Non-selective options: 1. Various combinations of acid (citric and acetic) 2. Various oils (citric and clove) 45

46 CREEPING CHARLIE PROBLEMS? Creeping charlie (ground ivy) has a competitive advantage in the shade Overcome with shade tolerant turf species: fine fescue, tall fescue, rough bluegrass Consider pruning to improve sunlight penetration Reduce moisture, compaction Use post-emergent herbicides with the active ingredient triclopyr in fall Hand-pulling stolons can be effective at reducing the population 46

47 CRABGRASS QUACKGRASS Annual Crabgrass Warm-season Preemergent work best Postemergent are effective Quackgrass Perennial Cool-season Preemergent- no option Postemergent- no option (non-selective only) 47

48 MOSS Problem in: Shade, wet, compacted sites Closely mown turf Cultural control: Thick, healthy turf Reduce shade, moisture, compaction Consider breaking up moss by spiking and aerating Raise mowing height Shade tolerant grasses Chemical control: The active ingredient Carfentrazone Ferrous sulfate monohydrate, sulfuric acid based products 48

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50 Dense Shade Mixture 50

51 Weeds always find a way in the harshest environments 51

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54 ADDITIONAL INFORMATION UMN Turfgrass Science Website: UMN Extension Turfgrass Management Website: Sustainable Urban Landscape Information Series: Yard and Garden Info: Facebook: University of Minnesota Yard and Garden Blog: Smart Gardens Radio Show WCCO AM830, Saturdays 8-9am Sam contact: , twitter 54