Presentation at the Conservation Garden Park by Dr. Ralph Whitesides, Utah State University on May 3, 2017. Livestream of the class available on the Conservation Garden Park Facebook page. https://facebook.com/ConservationGardenPark

1. RALPH WHITESIDES
UTAH STATE UNIVERSITY
PROFESSOR AND
EXTENSION WEED SPECIALIST ( E M E R I T U S )
What Do Weeds Think?

2. What is a Weed?
 Plant out of place
 Any plant growing where it is not desired
 Any plant someone will pay to remove or kill
 Any plant other than the crop/plant sown
 Plants that are competitive, persistent, and
pernicious. They interfere with human activities
and, as a result, are undesirable. (Ross & Lembi)

3. Common Approach
What is that plant?
How do I kill it?

4. Thoughtful Approach
What is that plant?
Why is it there?
Why is it there now?
How do I keep it from
being there in the future?

5. Life Cycles and Plant Families
 “ACEAE”
 Annual
 Winter annual
 Summer annual
 Biennial
 Perennial
 Simple perennial
 Creeping perennial

6. Plant Families
Asteraceae (sunflower)
Zygophyllaceae (caltrop)
Convolvulaceae (morninglory)
Brassicaceae (mustard)
Poaceae (grass)

7. Specimen Weeds
 Common dandelion
 Puncturevine
 Field bindweed
 Quackgrass
 Crabgrass
 Shepherd’s purse
 Dyer’s woad

8. Herbicide Nomenclature
Pre-emergence
Post-emergence
Contact
Systemic (translocated)

9. Cultural Control/Mechanical Control
Competition
Tillage
Fertilizer
Irrigation

10. Management Strategies
Annuals
Biennials
Perennials

11. Management Strategy for Annuals
Annuals on the list for today
Crabgrass
Puncturevine
Shepherd’s purse

12. Management Strategy for Crabgrass
Digitaria sanguinalis
Poaceae – native to USA, Caribbean
Summer Annual = germinate 55 F
Single Large plant = 150,000 seeds –
seed survive up to 15 years
Objective = prevent seeds

13. Forsythia in bloom

14. Large Crabgrass

15. Large Crabgrass

16. Mower Damage to Turf

17. Pre-emergence Herbicide Failure

18. Management Strategy for Puncturevine
 Tribulus terrestris
 Caltrop Family
 Summer Annual – native to Mediterranean Region
 One large plant in California produced 576,000 fruits.
Assuming 2 seeds per segment = 1,152,000 seeds/plant
 Germinates all season – lives in soil at least 4 years
 Susceptible to glyphosate, 2,4-D, dicamba
 Mechanical control = sweep seeds, vacuum seeds, roll
old pumpkins, or carpet

19. Puncturevine

20. Military Caltrops

21. Puncturevine Caltrops

22. Mechanical Control of Puncturevine

23. Shepherd’s Purse Management
 Capsella bursa-pastoris
 Winter annual mustard
 Member of mustard family
 Native of Europe
 Single plant produces several thousand seeds
 Remain viable for many years
 Seeds remain dormant in the dark - mulch

24. Shepherd’s Purse Flower

25. Shepherd’s Purse Seed Pods and Rosette

26. Management Strategy for Biennials
Biennial on the list for today
Dyer’s Woad

27. Dyer’s Woad
 Isatis tinctoria
 Native to Central and Western Asia
 Winter annual, biennial, or short-lived
perennial
 Plants produce 350-500 seeds
 Seed longevity under field conditions
unknown – some evidence for 8-10 years

28. Dyer’s Woad in Flower

29. Dyer’s Woad Seeds

30. Management Strategy for Perennials
Perennials on the list for today
Common dandelion – simple
Field Bindweed – creeping
Quackgrass – creeping

31. Common Dandelion
Taraxacum officinale
Native to Eurasia
Simple perennial with fleshy taproot
Spread by seed and new shoots from
roots
Dent-de-lion

32. Common Dandelion Inflorescence

33. Dent-de-lion

34. Simple Perennial

35. Lilac Bush

36. Lilac Bush

37. Field Bindweed
Convolvulus arvensis
Creeping Perennial
Native of Europe, North Africa,
Asia
Reproduces by seed and roots
Seed longevity > 50 years

38. Field Bindweed Seed

39. Field Bindweed Flowers

40. Field Bindweed Roots

41. Quackgrass
Agropyron repens (Elymus repens)
Creeping perennial
Native to Europe and Western Asia
Reproduces by seed and rootstock
(rhizomes and roots)
Seed longevity 2-4 years

42. Quackgrass Seed and Leaves

43. Quackgrass Rootstock

44. What are Annuals Thinking?
Seed production
Not necessary to develop huge root
reserve, plan to die after they
produce seed anyway
Seed dispersal

45. What are Biennials Thinking?
Rosettes
Vernalization
Seed Production
Short-lived perennial

46. What are Perennials Thinking?
OK to produce seed, but not necessary
Establish significant root reserves
Develop brittleness as an ecological
advantage
Send progeny elsewhere and rebuild
root reserve

47. Field Bindweed Roots

48. Brittleness

49. Saltcedar (tamarisk)

50. Salt Cedar on the Freeway

51. Salt Cedar on the Freeway

52. Salt cedar

53. What Should Humans be Thinking About Weeds?
Stop annuals & biennials from seeding
Recognize apical dominance in
perennials
Understand “Source to Sink” in
perennials
When using herbicides understand
“selective” vs “non-selective”

54. Apical Dominance

55. Herbicide Selectivity

56. Herbicide Selectivity

57. Herbicide Selectivity

58. Herbicide Selectivity
 Source to Sink Translocation

59. Selective Grass Control in the Landscape

60. Selective Grass Control in the Landscape

61. Selective Grass Control in the Landscape

62. Selective Grass Control in the Landscape
Sethoxydim – Poast, Segment, others
Fluazifop – Fusilade II
Clethodim – Clethodim 2EC

63. Lawn Violet

64. Lawn Violet

65. Vinca major – Big Periwinkle

66. Lawn Violet (Viola sororia) and Vinca
Triclopyr – Garlon 3A (violets are
on the label)
Carfentrazone – Quicksilver
Triclopyr + clopyralid – Confront

67. Pillars of Weed Management, Prevention, Physical,
Mechanical, Cultural, Biological, Chemical, IWM

68. Methods of Weed Control
•Prevention
•Physical/Mechanical
•Cultural
•Biological
•Chemical
•IWM – Integrated Weed
Management

69. Weed Prevention
•Prevent arrival
•Prevent establishment
•Prevent Spread

70. Preventive Weed Control
1. Clean equipment
2. Irrigation water/canals/ditches
3. Soil
4. Organic Matter/Compost
5. Weed seed/seed quality
6. Spot treat/hand pull/herbicide
resistance
7. Neighborhood cooperation

71. 1. Clean Equipment

72. 2. Irrigation Water/Canals/Ditches

73. Lack of weed control
on canals and ditches.

74. 3. Soil

76. Virgin River St. George – Dec 21, 2010

77. 4. Organic Matter/Compost

79. Temperature 140 F or more

80. Estimatedhours requiredto kill 90% of
seeds (afterDahlquistet.al., 2007)
Temperature (°F)
140 122 115 108
time required to kill 90% of seeds (hours)
Annual
sowthistle
<1.0 2.1 13.3 46.5
Barnyardgrass <1.0 5.4 12.6 unaffected
London rocket <1.0 4.0 21.4 83.1
Common
purslane
1.3 18.8 unaffected unaffected
Black
nightshade
2.9 62.0 196.6 340.6
Tumble
pigweed
1.1 107.0 268.5 unaffected

81. 5. Weed Seed/Seed Quality

82. Seed Certification

83. 6. Chemical – Spot treatment/selectivity

88. 7. Neighborhood Cooperation

89. Neighborhood Cooperation

90. Neighborhood Cooperation

91. Neighborhood Cooperation

92. One year’s
seeding
equals seven
years
weeding!

93. Those who say
“Work well done
never needs redoing”
never weeded a garden

94. Summary
• Weed defined
• Plant Life Cycle
• Annual (winter or summer)
• Biennial
• Perennial (simple or creeping)
• Methods of Control – prevention,
physical/mechanical, cultural, biological, chemical, IWM
• What is that Plant?
• Why is it There?