Hemp dogbane taxon

-Hemp dogbane Outline (1996)
-Hemp dogbane Bibliography (1996)
a. Apocynum cannabinum
b. taxon: intraspecific variation

4.26.96
Agronomy 517: Weed Biology and Ecology
Spring Semester, 1996

Hemp Dogbane (Apocynum cannabinum L.) Outline

Prepared by: Kari Jovaag

I. Taxonomy

A. Current

• Order: Gentianales
  
• Family: Apocynaceae
  
• Genus: Apocynum
  
• Species: cannabinum
  
• related species
  
  • A. androsaemifolium
    
    • spreading plant
      
    • relatively large, pinkish flowers
      
    • deflexed leaves
      
  • A. medium
    
    • Characteristics intermediate between A. cannabinum and A. androsaemifolium
      
  • others-confused, variable

B. History of the genus

• Very confused
  
• Apocynum comes from greek words meaning dog and away from
  
• Dates from 1st century Greece, uncertain exactly what plants it contained
  
• North American species included by 1669 (in Preludia Botanica)
  
• Linnaeus established the genus in Species Plantarum in 1753
  
• Many new species were added-most similar to A. cannabinum, A. androsaemifolium, or A. medium
  
• Non-North American species have been removed from the genus

C. Common names for A. cannabinum

• Hemp dogbane
  
• Dogbane
  
• Indian hemp
  
• dropsy root
  
• others

II. Description

A. Stem

• 1-5 ft. high
  
• Branching-main axis usually exceeded by the branches
  
• Contains a milky white juice
  
• Tough, smooth

B. Leaves

• 2-6 in. long
  
• Opposite, sessile or on short petioles
  
• Oblong, pointed at both ends
  
• Smooth to pubescent

C. Flowers

• Perfect, regular, mostly erect
  
• Terminal or axial
  
• In dense, flat-topped clusters
  
• Small(3 long), 5-lobed, greenish-white
  
• 5 stamens, inserted on the corolla
  
• Fillaments shorter than anthers
  
• Anthers arrow-shaped, convergent, slightly adhere to stigma
  
• 2 carpels, seperate except the 2 stigmas are fused
  
• Borne May-August

D. Seed pods

• Twin 4 in. long pods
  
• Round and smooth, diam. or less
  
• Dark reddish-brown when mature
  
• Conjoined (though easily seperated) at distal ends while maturing
  
• 0-60 pods/plant

E. Seeds

• Small, flat: About long, .75mm wide
  
• About 1.5 g per 1000 seeds
  
• Brownish with tuft of fine, white hairs
  
• Mature August-October
  
• 80-200 seeds/pod

F. Roots

• Much branched
  
• White or grey
  
• Primary lateral roots grow as radii about the primary vertical root at depths of 6-20 in.
  
• Secondary lateral roots develop along the primary lateral roots, growing perpendicularly away from the primary lateral roots 2-8 in. then growing away from the primary vertical root
  
• Tertiary roots develop from secondary roots in a similar manner
  
• Secondary vertical roots develop along the lateral roots

III. Distribution and Habitat

A. Geographical Distribution

• Temperate-30th parallel to 55th parallel
  
• Native to North America
  
• Widespread in United States

B. Habitat

• Common in fields, thickets, ditches, along streams
  
• Usually occurs in patches, somtimes very dense
  
• Prefers fertile, moist, medium to heavy textured soils
  
• Seldom found on sandy or low fertility soils

IV. Biology

A. Perennial

• Reproduces by seeds and rootstocks
  
• Seeds are dispersed by wind and water
  
• First flowering in May of 2nd year
  
• Established plants initiate spring growth from crown buds
  
• Buds are located at irregular intervals along lateral roots

B. Germination

• Light increases germination- 41%(Robison and Jeffery 1972)
  
• Scarification increases germination- 28-36%(Mitchel 1926)
  
• Temperature
  
  • Highest germination percent occured at 35*C
    
  • Will germinate between 10 and 40*C
    
• Very susceptible to moisture stress-did not germinate at 9.1 bars osmotic pressure or more (Evetts and Burnside 1972e)
  
• Depth
  
  • Seeds on the surface dry out-low germination
    
  • Highest germination at 0.5-1 cm, 60-70%
    
  • Germination at greater depths greatly reduced- no germination at or more (Evetts and Burnside 1972b)
    
• Length of burial (Evetts, Burnside, and Fenster 1972)
  
  • Nearly all seeds germinated initally (in alternating 20-30*C temps)
    
  • 3-10%germination after 9 months
    
  • No germination after 21 months

C. Rate of aboveground development (Shultz and Burnside 1979)

• Emergence to bud stage: 3-7 weeks
  
• Bud to early flower: 5-11 days
  
• Early flower to full bloom: 7-9 days except in a spoybean field where it was 23 days
  
• Full bloom to pod initiation: 6-13 days

D. Rate of Root Development

• Root systems can sperad laterally to 11.6 ft. and vertically to 7 ft. in the first season after germination (Frazier 1944)
  
• Root systems can spread laterally to 19.5 ft. and vertically to 13.6 ft. 2 years after germination (Frazier 1945)
  
• One lateral root was traced 29 ft. without finding the end (Hitchcock and Clothier 1898)

E. Dormancy

• 50%of seeds are dormant when released from seed pod
  
• Seed dormancy an be broken by scarification and light
  
• Crown root dormancy likely broken by warmer temperatures in spring
  
• Crown root dormancy can be broken by long daylength photoperiod

F. Leaf feeding Insects (Shultz and Burnside 1976)

• Species
  
  • Woolly bear moth (Arctiadae Ammalo tenera)
    
  • Pyralidae Pyrausta futialis
    
  • Leaf roller moth (Tortricidae Aphelia pallorana)
    
  • Milkweed tiger moth (Euchaetras egle)
    
• The first two caused the most damage
  
• Defoliation was about 80%in Nebraska in 1976, decreased in 1977 and 1978
  
• Insects would probably not be able to control dogbane

V. Reproduction

A. Sexual Reproduction

• Mostly self-sterile
  
• Outbreeding
  
• Hybridization
  
  • A. medium is a hybrid of A. cannabinum and A. androsaemifolium
    
    • Variable progeny
      
    • Low fertility
      
    • Usually found where populations of A. cannabinum and A. androsaemifolium intersect
      
  • Hybridization may be responsible for much of the confusion in classifying species of Apocynum

B. Vegetative Reproduction

• Stems developing from adventious buds can become independent plants when the lateral root conecting it decays
  
• Tillage can drag portions of roots to other locations where they may become established
  
• Regenerative capacity of roots (Shultz and Burnside 1979)
  
  • Cyclic pattern
    
  • Highest in February-April
    
  • Lowest in September-November
    
  • Abnormal peaks after considerable damage from insects or hail
    
• Regrowth after clipping
  
  • Evetts and Burnside 1972(d)
    
    • 5%of 10 day old greenhouse-grown seedlings are capable of regrowth from root buds, but it took 21 days for the first to emerge
      
    • Percent capable of regrowth increased to 80%and days to first emergence decreased to 8 by the time seedlings were 46 days old
      
  • Robison and Jeffery 1972
    
    • No regrowth observed until 41 days
      
    • By 65 days plants were producing more than one shoot after clipping

VI. Economic Importance

A. Benificial Uses

• American Indians used it for thread and cord
  
• Some glycosides and resins which are heart stimulants and diuretics can be extracted from the roots
  
• Source of nectar for honeybees
  
• Source of rubber

B. As a Weed

• Unsightly
  
• Considered poisonous to livestock by many authors
  
• Noxious weed
  
  • Competes better with sorghum and soybeans than with corn
    
  • Can become a significant problem in no-tillage systems
    
  • Dogbane populations higher in irrigated fields
• Can cause yield loss (Shultz and Burnside 1979)
  
  • Dryland sorghum: 30-45%reduction
    
  • Dryland soybeans: 28-32%reduction
    
  • Irrigated soybeans: not significant
    
  • Dryland corn: none to 15%reduction
    
  • Irrigated corn: none to 10%reduction
• Allelopathic effects
  
  • Found to cause a 33%decrease in 20-day sorghum growth (Wyrill and Burnside 1976a)
    
  • Reductions in corn, soybean and sorghum growth were not significant, but possibly masked (Shultz and Burnside 1978g)

VII. Management

A. Chemical control

• PRE
  
  • Generally do not provide satisfactory control of established plants
    
  • Can provide satisfactory control of seedlings
    
    • Butylate
      
    • EPTC
      
    • Atrizine
• POST
  
  • Control is eratic
    
  • September treatment better than June
    
  • Glyphosate (Roundup)
    
    • generally better than 2,4-D
      
    • effectiveness increased with lanolin ring
      
    • Impurities in water (i.e. high Ca++, Zn++) may decrease effectiveness
      
  • Dicamba + 2,4-D amine
    
  • Dowco 433

B. Mechanical Control

• Intensive tillage doesn't control established populations (Becker 1982)
  
• In continuous corn dogbane densities tend to be lower with greater tillage
  
• Tillage may tend to spread dogbane rather than control it

C. Cultural Control

• Corn/soybean rotations with glyphosate selectively applied in the soybean phase were found to have lower densities than continuous corn (Buhler et al. 1994)
  
• Rotations containing alfalfa
  
  • Alfalfa competes effectively with dogbane
    
  • Frequent cutting may reduce the root reserves of dogbane

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