Weed Ecology Seed This chapter should be important to all students. With annuals and biennials, if you manage the seed

1. Chapter 2 Weed Ecology Seed This chapter should be important to all students. With annuals and biennials, if you manage the seed and/or soil seed bank, you can manage the weed. Seed management is not an easy task.

2. Weed Ecology Understanding the biology/ecology of weeds is paramount to developing effective, sustainable control strategies. This understanding also allows one to have the ability and knowledge to understand why a control strategy may fail at times and be very successful at other times. It is the foundation to sound science and effective weed management.

3. Weed Ecology/Biology can be defined as: the understanding of the requirements or conditions necessary for germination, establishment, growth, and reproduction of weeds--long term survival of the species. Weed Ecology cont.

4. What are the weed growth requirements? What limits the weeds growth/germination? How do weeds grow (upright vs. prostrate)? Do they spread by seed or vegetative propagules? When does a seedling become a perennial? How many seed are produced? How long do they survive in the soil? Weed Ecology cont.

5. Weed Seeds Seeds are the principal means by which weed species perpetuate themselves and invade new areas. (Control the seed and you control the weed.) Seeds are tiny, encapsulated embryonic plants. Seeds enable embryonic life to exist in suspended animation for years---to preserve, protect, and ensure survival of the species. And we call this??????????

6. Resumption of Growth Germination can be defined as the resumption of growth of a seed or a vegetative part. Imbibition of water Increased respiration Mobilization of food reserves Digestion of reserved foods For our crops, this sequence begins promptly after planting and proceeds in an orderly fashion to the seedling emergence.

7. Why Study Dormancy Farmer – probably a waste of time Scientist – to study the weed, we must know how to grow it. To grow it, we must understand what is required to make it germinate and grow. Student – frequently their thesis topic and they need the information to graduate.

8. Dormancy The state of “suspended development” We (man) have selected our crops to not exhibit dormancy, “Mother Nature” has done the opposite to preserve the weeds. We try to understand this so we can better manage the weeds, but I am not sure that we have done much more than better understand “why we still have weeds”

9. Types of Dormancy Innate – imposed germination inhibition, these are all “genetically” controlled Impermeable seed coat Chemical inhibitors Immature embryo Seeds can undergo scarification, fire, stratification, and time to over come innate dormancy

10. Types of Dormancy Induced – sometimes referred to as “secondary dormancy” Seed being exposed to excessive environmental condition. Crabgrass “eagerly” emerges in the spring. If it turns off hot and dry, the seed may be put into induced dormancy. When conditions are “seemingly” favorable for germination the seed will still not germinate – must go through another winter or some other condition to remove this “induced state”

11. Types of Dormancy Enforced – imposed by conditions unfavorable for germination. The most easily understood type of dormancy. When conditions are “corrected” – germination will proceed. Light, water, oxygen, temperature, pH, soil depth, etc.

12. Seed vs Propagules Seed more resistant to loss of viability Seed more numerous Propagules emerge with greater vigor Propagules are more difficult to control because the control agent must kill the entire propagule Seeds are not killed by herbicides

13. Seed Characteristics that Contribute to Dormancy Hard or Impermeable seed coats to water and/or oxygen Immature embryo Germination inhibitors

14. Scarification Physically damaging the seed coat. This can be done chemically, physically, or even biologically. Chemically---H2SO4 Physically---sand paper, soil abrasion, harvest equipment. Biologically---microorganisms digesting the seed coat. Passing through a bird or animal.

16. Requirements for Germination Water – the solvent for food reserves Some weeds can germinate in nearly dry soil Oxygen – required for respiration Some weeds (aquatic) can germinate in flooded soil Temperature – enzyme activity, cell division Very species specific Light A requirement for some Favorable pH ALL factors MUST be met or germination will not occur

18. Depth of Burial – the most consistent Light Light intensity Spectral composition – red vs. far-red/near infrared Phytochrome interactions with light quality Red light promotes germination Far-red light inhibits germination Duration Environmental Factors that Impact Germination

19. Depth of Burial – the most consistent Light Environmental Factors that Impact Germination

20. Depth of Burial – the most consistent Light Temperature Both duration and extreme A cold period is required by some spp. – pecans A specific variation between hot and cold temperature Why have weeds evolved to use temperature as a germination requirement? Environmental Factors that Impact Germination

22. Depth of Burial – the most consistent Light Temperature Water Varies by species A certain level may need to be maintained Only a rainfall event required Too much may cause dormancy (induced) Rice production Environmental Factors that Impact Germination

23. Depth of Burial – the most consistent Light Temperature Water Soil Crust on soil surface Impacts emergence more than germination Compaction Goosegrass does well in compacted soil Soil Structure Environmental Factors that Impact Germination

24. Depth of Burial – the most consistent Light Temperature Water Soil Chemicals Contained in soil or in seed/fruit High levels of nitrate will stimulate germination Gibberellic acid – stimulates inactive form of phytochrome (but species dependent) Ethylene – stimulates germination Has been used on field scale to stimulate witchweed germ. Herbicide – EPTC, Vernam, Zorial – can stimulate germination Abscissic acid – (plant hormone) - promotes dormancy in seed Environmental Factors that Impact Germination

25. Depth of Burial – the most consistent Light Temperature Water Soil Chemicals Gas exchange Oxygen – restriction of oxygen from seed will inhibit germination Environmental Factors that Impact Germination

27. Soil Seed Bank “one year’s seeding--10 years’ weeding” The soil seed bank refers to seeds and fruits containing seeds on or in the soil.

28. PIGWEED POPULATIONS - (a hypothetical situation) Year 1 1 pigweed every 100 feet of row. 145 pigweeds/acre 100,000 seeds per plant = 14,500,000 seed 333 pigweed seed per square foot

29. PIGWEED POPULATIONS(a hypothetical situation) Year 2 1% of seeds germinate and emerge (145,000 plants) a herbicide controlled 99% of the pigweed. 1,450 plants survived the herbicide treatment these 1,450 plants produced 145,000,000 seed 3,329 seeds per square foot.

30. PIGWEED POPULATIONS(a hypothetical situation) Year 3 1% of seed germinate and emerge--1,450,000 plants treated with a herbicide and controlled 99% left 14,500 plants (1 every 3 square feet) treated with a second herbicide and again controlled 99% of remaining population left 145 plants--the original number we started with. 333 pigweed seed per square foot

31. PIGWEED SEED BANK(a hypothetical situation) Year 1 14,500,000 seed less the 1% which germinated 14,355,000 seeds left in the soil Year 2 14,355,000 from year one plus 14,355,000,000 seeds from the 145,000 uncontrolled plants during year 2. Year 3 we start off the year with 14,355,000 seeds from year 1 plus 14,355,000,000 from year 2 for a grand total of 14,369,355,000 pigweed seeds in the soil bank.

32. Seed Maturity Cutting of weeds to prevent seed production is a common recommendation. Turf, pastures, hay crops, roadsides, noncrop land. Mostly used for annual and biennial plants. Mowing must be timely. Several weeds can have their flowers, pods, or berries separated from the plant and still make mature and viable seed.

33. Seed Survival Seed can remain viable in fresh water. Field bindweed--55% germination after 54 months (4.5 years) in fresh water. Redroot pigweed--9% germinated after 33 months (2.75 years) in fresh water. Barnyardgrass--1% germinated after less than 3 months in fresh water.

34. Seed Longevity Seed size has very little to do with the ability of the seed to remain in the soil for extended periods of time and still remain viable. Some of the longest lived seeds in soil are also some of the smallest seed. GENERALLY, grass seeds do not survive in the soil as long as broadleaf weeds

35. Effect of Soil Tillage on Weed Seed Soil tillage is beneficial for weed seed germination. If you don’t have weeds and are not preparing a seedbed---don’t till the soil. (exception – sometimes will help with water infiltration and wind erosion). The improvement of weed seed germination following tillage is generally due to weed seed being exposed to light (just a flash is needed) or bringing the seed closer to the soil surface so that it can emerge.

36. Weed Population Shifts Rotational crops to monoculture Tillage alone or tillage with herbicides Wide row-spacing to narrow row-spacing Conventional tillage to reduced tillage Herbicide selection THERE IS NO ORDER OF IMPORTANCE--ALL OF THE FACTORS CAUSE SHIFTS

37. Weeds and Herbicides We must now contend and try to manage herbicide resistant weeds. 1945-55 – the use of 2,4-D reduced broadleaf weed problem... Then the grasses invaded… 1965-70 – trifluralin controlled most annual grasses and many small-seeded broadleaf weeds Herbicides are sometimes very specific and their use has caused some weed problems to become more serious VERY IMPORTANT!!! Herbicides do not kill weed seeds! The seed must begin germination or germinate and grow before herbicide will kill the weed.

38. Seed Production

39. Soil Seed Bank A Weed’s mechanism for long-term survival Lupinus arcticus (Legume) collected beneath permafrost in Yukon Terr. Estimated age 10,000 years – some seed germinated! Seeds from a British Museum herbarium that were 237 years old germinated Several other accounts can be given The “sleeping state” of a plant’s life cycle

40. Weed Density The number of weeds in a given area It should be obvious that the higher the weed number the greater the interference Some species have the capability to develop very high populations in a very short time

41. Beal, Duvel & Turner Studies Beal, 1879 Buried seed, 3 out of 100 species germinated after 100 yr Duvel, 1904 27 out of 48 still germinated after 39 years of burial Turner, 1933 After 81 to 90 years of burial, 7 species germinated (all legumes)

42. Importance of soil-seed germination Not the level or magnitude, but the fact that it does occur. Evidence exists that tillage hastens depletion of the seed bank. Now we promote reduced tillage Seed longevity is increased if seed are mixed in the soil rather than left on the surface. Seems to conflict with statement above.

43. Depletion of the soil-seed bank Natural ageing, respiration, enzyme activity Germination Microorganisms Other soil organisms Birds and animals Climate/environment Fire

44. Recovery of the Soil Seed Bank Little definitive data on this subject Difficult to do and takes many years Scientists are impatient, must publish One year seeding, seven years weeding One year seeding, ten years weeding Very likely “species specific”

45. Factors Affecting Seed Production Quickness that this can occur Produce seed when flower is severed Nutrients Water Light Even under the most adverse conditions some seed is produced (likewise w/crops)

46. Annuals Weed Sci. 1988. 36:787-791 Weed Sci. 1979. 27:290-293 Weed Technol. 1996. 10:727-731 Weed Sci. 1979. 27:73-76 Weed Sci. 1988. 36:787-791. Weed Technol. 1990. 4:31-34 Weed Technol. 1996. 10:727-731

48. Balloonvine/Soybean Seed

50. Acid Scarification & Balloonvine Germination

51. Effects of Oxygen on Balloonvine Germination

54. Effect of Temperature and Light on Eclipta Seed Germination

59. Devil’s-claw Germination

60. Rhizomes vs Creeping Roots Perennial broadleaf weeds “generally” have creeping roots NOT rhizomes Johnsongrass has rhizomes Field bindweed has creeping roots Horsenettle has creeping roots Silverleaf nightshade has creeping roots Bermudagrass has stolons

61. Vegetative Reproduction Capacity

62. Perennials Weed Sci. 1981. 29:625-628 Weed Sci. 1982. 30:158-163 Weed Sci. 1982. 30:238-243 Weed Sci. 1987. 35:360-363

65. Silverleaf Nightshade: Seedling to Perennial