Crabgrass (Digitaria spp.) taxa

-Crabgrass Outline (1996)
-Crabgrass Bibliography (1996)
a. Large crabgrass (Digitaria sanguinalis)
b. Smooth crabgrass (Digitaria ischaemum)
c. taxa: complex of associated species or demography

4.18.96
Agronomy 517: Weed Biology and Ecology
Spring Semester, 1996
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The genus Digitaria Outline
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Prepared by: Dave Gardner
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The genus Digitaria
D. sanguinalis (L.) Scop.: Large Crabgrass
D. ischaemum (Schreb.) Muhl.: Smooth Crabgrass

Dave Gardner

I. History and overview of crabgrass (Mitich, 1988)
A. Crabgrasses were among the first cultivated grains.
B. Crabgrasses were grown for food thousands of years before considered weeds.
1. China in 2700 B.C.
2. Also in Switzerland, India, and Africa.
3. U.S. patent office introduced Large crabgrass as a forage crop in 1849
a. Large crabgrass is indigenous to Europe
b. No interest at first, but decades later southern ranchers found it ideal i. Affinity for hot, dry conditions
ii. Nutritious qualities as pasture and hay.
4. Central European immigrants brought crabgrasses in early 20th century.
a. The crabgrasses thrived as a forage crop
b. Immigrants later abandoned them in favor of corn and wheat
5. Smooth crabgrass most likely was introduced as a contaminate of turf seed
a. All cool season turfgrasses were introduced to the U.S. from Europe
b. Smooth crabgrass is a major turfgrass weed in Europe
6. Most species in the genus are still considered good forage grasses
a. Due to infestation of cultivated crops crabgrasses are presently considered to have little potential as a forage crop in the U.S. (Aiken et al., 1995)
C. Characters that made crabgrasses a good crop now make them good weeds
1. D. sanguinalis classified as 11th worst weed in the world (Holm et al, 1977)
2. 2nd most frequently reported weed in 1968 survey of farmers (USDA, 1968)
3. Reported as a weed in 36 crops in 56 countries (Mitich, 1988)
4. Large crabgrass:
a. One of three most serious weeds in peanuts
b. A principle weed of sugarcane, cotton, and sorghum
c. Most prevalent weed in N.E. U.S. spring alfalfa seedlings (Peters, 1979)
d. A major weed of turfgrass, particularly in the Southern U.S.
5. Smooth crabgrass is a major turfgrass weed throughout the U.S.
II. Classification of the genus (Mitich, 1988)
A. In 1759 Lorenz Heister named the genus Digitus (Latin for finger) in reference to the plants inflorescence
1. sanguinalis refers to blood-red or purple color
2. ischaemum refers to arrangement of seeds along spike midriff
B. Later classified by:
1. Scopoli in 1772 named large crabgrass Digitaria sanguinalis
2. Schreber in 1804 named smooth crabgrass Digitaria ischaemum
C. Overview of taxonomic classification (Woodland, 1991)
1. Class Liliopsida (Monocotyledons)
a. Subclass Commelinidae: Contains 7 orders and 16 families
i. Order Cyperales (Graminales): Contains 2 families
A) Family Cyperaceae (The sedges): 70-90 genera, 4000 species
B) Family Poaceae (Graminae, the grasses): 600 genera, 7500 species
1) Subfamily Panicoideae (The C-4 or Kranz anatomy grasses)
i) Digitaria spp.: The crabgrasses
ii) Closely related genera include Panicum, Paspalum, and Axonopus (Henrard, 1950)
2. Ancestry of Family Poaceae is unknown
a. Thought to have developed from primitive liliaceous stock
b. May have developed parallel to Family Cyperaceae (Datta, 1969)
D. Reported number of species in genus Digitaria varies widely by source
1. 60 Species (Mitich, 1988)
2. 325 Species (Henrard, 1950) -- Monograph of genus Digitaria, likely the most accurate number.
E. Digitaria spp. are primarily of temperate and tropical origin.
F. Digitaria spp. are of various habit and very deviating character (Henrard, 1950)
III. 13 weedy species of genus Digitaria infest the U.S., 8 of which are significant
A. Digitaria bicornis (Lam.) Roem. & Shult. ex Loud.(Hafliger and Scholz, 1980)
1. Found from gulf coastal plain to Texas
B. Digitaria ciliaris (Retz.) Koel.
1. Found in southeast, south central, western U.S.
2. Inhabits waste places, rotation crops, aquatic biotypes
3. This would probably be considered the 3rd most serious weedy species
C. Digitaria filiformis (L.) Koel.
1. Found in northern, southeast, south central U.S.
2. Inhabits waste places, rotation crops, perennial crops
D. Digitaria horizontalis Willd.
1. Found in southeast U.S.
2. Inhabits waste places, rotation crops
E. Digitaria ischaemum (Schreb.) Muhl.: Small crabgrass
1. Also called fingergrass (Hanson and Juska, 1971)
2. Found in all regions of U.S.
3. Inhabits waste places, rotation crops, perennial crops, turfgrass
F. Digitaria longifolia (Retz.) Pers.
1. Found in south central U.S.
2. Inhabits waste places, rotation crops, perennial crops
G. Digitaria sanguinalis (L.) Scop.: Large Crabgrass
1. Also called hairy crabgrass or fingergrass (Hanson and Juska, 1971)
2. Found in all regions of U.S.
3. Inhabits waste places, rotation crops, turfgrass
H. Digitaria violascens Lk.
1. Found in southeast, south central U.S.
2. Inhabits waste places, rotation crops, grass land
I. Digitaria sanguinalis and D. ischaemum are the most important weedy species
IV. General characteristics of Digitaria sanguinalis and D. ischaemum
A. Taxonomic differentiation between the species
1. Seedling comparative characteristics (King, 1955)
a. Digitaria sanguinalis (Large crabgrass)
i. Lighter green, spreading form, conspicuously hairy
ii. Not well adapted to survival in turfgrass
iii. Severely damaged by early frosts
b. Digitaria ischaemum (Smooth crabgrass)
i. Dark green, tall, devoid of hairs
ii. Well adapted to survival in turfgrass
iii. Not harmed by early frosts
2. Mature plant comparative characteristics (King, 1955)
a. D. sanguinalis
i. Height to 1 meter
ii. Profusely branched
iii. Stalks are more robust, blades and sheaths are hairy
iv. Extensive rooting at nodes
b. D. ischaemum
i. Height 15-40 cm
ii. Not extensively branched
iii. Hairy on collar only
iv. Rooting at nodes not as extensive
3. Characteristics shared by both species (Hanson and Juska, 1971)
a. Both have finger-like racemes
b. Both have minute first empty glume and hyaline margins
c. Both have fibrous root systems
B. Geographic distribution of the species
1. Both are widely distributed throughout the world (King, 1955)
2. Both are observed in all regions of the U.S.
a. Both are widespread in warmer and temperate Eastern North America
b. Also locally abundant in other warm regions.
4. D. ischaemum
a. More common in Northeast U.S.
b. Locally in warm, moist areas.
5. D. sanguinalis
a. Most abundant in Southeast and mid-Atlantic
b. Also in warmer areas of the humid temperate zone
6. Both are serious turfgrass weeds in the transition zone because neither cool nor warm season turfgrass grow well there (Callahan and High, 1990)
V. Population biology of Digitaria sanguinalis and D. ischaemum
A. Evolution and selection
1. Wild races still found in old world habitats invading agriculture land.
2. These races evolved into present forms (Radosevich, 1984)
B. Genetic polymorphism
1. D. sanguinalis is very variable (Henrard, 1950)
a. Inflorescence and spiklets are particularly variable
b. Species is subdivided into many subspecies and varieties
2. Henrard does not mention polymorphism in D. ischaemum
C. Somatic polymorphism: no information located
D. Both have summer annual life cycles in temperate U.S. (Hanson and Juska, 1971)
1. Both grow from seed and are killed by frost each year in temperate regions
a. Seedhead appear midsummer
i. Short day for flowering (Radosevich, 1984)
b. Growth continues until frost kills (Hanson and Juska, 1971)
i. Purple color develops in foliage and on seedheads during cool weather of late summer and fall (more pronounced on large crabgrass)
ii. Quickly deteriorates into gray, bare area after dying in fall.
2. D. sanguinalis may over winter in subtropical climates.
a. In bermudagrass mowed to 2.5 inches w/33-35º F Min. Annual Temp.
i. Crabgrass observed to over winter, flower in April, May
ii. Caryopses matured by June (Youngner, 1960)
iii. Plants found year-round, heavy germination in Jan. and Feb.
E. Stage 1 Pioneer Weed (2-5 years) (Aldrich, 1984)
1. Crabgrass is a principle weed of reestablishing prairie
a. Prolific seed production (Discussed in seed biology section)
b. Allelopathy (Discussed in plant biology section)
VI. The seed biology of Digitaria sanguinalis and D. ischaemum
A. Seed strategies
1. Seed numbers
a. Large crabgrass plant can produce 700 tillers and 150,000 seeds in temperate areas (Mitich, 1988)
b. Larger numbers in tropical areas (where grows and sets seed year round) c. In many areas, large crabgrass becomes predominate weed species after 2 years where no herbicides used due primarily to seed production (Johnson and Coble, 1982)
2. Seed dispersal
a. Seeds are easily dispersed by mowers and other equipment and on shoes, especially if moist (Turgeon, 1994)
b. Seeds lodge in hairs of pasture animals (Radosevich, 1984)
B. Seed development
1. Decumbent growth habit of D. ischaemum allows seed production in a mowed situation
C. Seed dormancy and germinability
1. Dormancy
a. Fresh seed is dormant
i. Dormancy can be broken by puncturing or scarifying (Gianfanga and Pridham, 1951)
ii. Fresh seed remains dormant for several weeks under ideal conditions for germination (Toole and Toole, 1941)
iii. Normal dormancy period 2.5 to 6 months (Laudien and Koch, 1972)
b. Temperature requirements and germination rates change as seed ages
i. Minimum 196 days required for all freshly harvested seed to germinate
ii. 1 year old seed germinated in 7-14 days (Toole and Toole, 1941)
iii. 16 months in dry storage or 2 months in moist sand removes dormancy
c. Studies described above suggest that current year seed is not responsible for late season germination.
2. After-ripening: no information located
3. Mechanisms of developmental arrest
a. Cold soil temperatures enforce dormancy (Turgeon, 1994)
D. The soil seed bank
1. Replenished annually in the fall
2. Current year seeds do not contribute to late season germination
a. Continued germination may be caused by steady replenishment in germination zone due to eroding of soil (Gianfagna and Pridham, 1951).
b. Alternate wetting and drying through season also promotes germination.
E. Seed germination, seedling emergence
1. Annual period of Crabgrass germination ‰ 5 months (King, 1955)
a. D. ischaemum, in Iowa, from late April until August
b. D. sanguinalis in late May until October
c. Both have initial flush, then declining rate of germination
2. Temperature
a. Warm soil promotes germination
i. First flush of D. ischaemum germination when soil temp. ‰ 58º F.
ii. D. sanguinalis germinates better in warmer soil ‰ 74º F
b. Lab studies (Hanson and Juska, 1971)
i. 20-40º C temp alternations gives good germination
ii. 15-25º C is also effective, especially if older seed
iii. Best germination in lab tests at 20-30 and 20-35º C temp alterations
c. Field studies with D. sanguinalis (King and Oliver, 1994)
i. Maximum emergence at 25º C and -30 kPa soil water potential
ii. Greatest emergence rate at 30º C
iii. Germination % lower if temp increased or decreased or if soil water potential decreases
iv. Germination occurs at all temperatures above 15º C and at soil water potentials ranging from -30 kPa to -100 kPa
3. Moisture
a. If germinated in minimal moisture conditions, subsequent dry weather will check growth or destroy seedlings.
b. Moist seeds at 3º C. break dormancy rapidly 25-26 days before germination starts in the spring. (Toole and Toole, 1941)
c. Increased fluctuations in soil moisture causes increased germination of crabgrass in drier sandy soils due to hydration-dehydration cycle.
(Leck et. al., 1989)
d. Moisture accumulation occurs in 3 distinct phases (King and Oliver, 1994)
i. Rapid water uptake during imbibition
ii. A lag phase of little water uptake
iii. Subsequent water uptake associated with growth
4. Light
a. Light aids germination if conditions are less than optimal
b. A dense stand of turfgrass will effectively shade out crabgrass
5. Depth of emergence
a. 0.5-2 cm is normal depth for germination (Laudien and Koch, 1972)
b. Seeds can emerge from 3.5 cm in some soils (Hanson and Juska, 1971)
6. Seedlings grow rapidly if moisture, fertility, warmth, and light are abundant
VII. The plant population biology of Digitaria sanguinalis and D. ischaemum
A. Weedy adaptation for survival
1. Crop mimicry
a. Prostrate growth habit of smooth crabgrass
i. Allows seed set
ii. Allows plant to avoid the mower
2. Herbicide resistance
a. Crabgrass is generally susceptible to control with herbicides
i. Large crabgrass once was, but now fall panicum is dominate annual grass in N. Carolina due to atrazine use. (Johnson and Coble, 1982)
b. Glutathione conjugation
i. Crabgrass is more tolerant to chloro-s-triazines than most other annual weeds (Robinson et al., 1976)
A) Control with atrazine and simazine can be variable
B) Crabgrass can convert atrazine to H2O soluble metabolites more rapidly than most weeds via glutathione-s-transferase.
ii. Crabgrass is not tolerant of many other herbicides classes
A) Fenoxaprop-ethyl (An aryloxyphenoxy) is effective because crabgrass can't convert to water soluble metabolites (Tal et al., 1993)
B) Herbicide resistance is not a serious problem in turfgrass management
3. Stress adaptation
a. Digitaria spp. are C-4 plants adapted to hot and dry weather
i. They are photosynthetically efficient (Waddington et. al., 1992)
A) D. sanguinalis and D. ischaemum
1) Use C-4 photosynthesis
2) CO compensation concentration point is 1 ul/L.
3) Light saturation @ 5000 ft. candles
4) Assimilates 50-80 mg CO2 dm-2 hr-1
5) Stomata can close to conserve water
B) Compared with cool season turfgrasses:
1) Use C-3 photosynthesis
2) CO2 compensation concentration points
i) Poa pratensis: 55 ul/L
ii) Agrostis palustris: 47 ul/L,
iii) Lolium perenne: 60 ul/L
iv) Festuca arundinacea: 45-69 ul/L
3) Light saturation @ 1000-3000 ft. candles
4) Assimilates 15-35 mg CO2 dm-2 hr-1
b. Adaptation to hot weather gives Digitaria spp. a major competitive advantage over cool season turfgrass during the summer months
B. Intra- and inter-specific competition
1. Competitiveness due to root system characteristics
a. Crabgrass produces a disproportionately large root profile that aids in its competitive ability (Davis et al, 1967)
i. Roots grow 2 meters deep and 2.5 meters away from plants
ii. Many plants (e.g. Kochia) with similar root profiles grow much larger
b. Crabgrass root development is rapid
i. Aids in competitive ability with other plants during establishment
2. Allelopathy
a. Crabgrass is only plant in prairie that is toxic both to stage 1 plants and Triple-awned grasses (Stage 2) (Aldrich, 1984)
b. Extracts from crabgrass shoots inhibits germination of crown vetch (Bieber and Hoveland, 1968).
3. Yield losses and loss of turfgrass quality
a. Crabgrass infestations lower turf quality in P. pratensis grown under low fertility (Waddington et.al., 1992)
b. Silage maize yields may be reduced 40% if crabgrass allowed to compete for whole season (Vengris, 1975)
C. Plant density, cropping systems
1. Crabgrass numbers increased as row spacing increased (Aldrich, 1984)
2. Crabgrass yield is at least double when grown between corn rows than within.
3. Crabgrass reduced corn yields if planted between rows and K levels were high.
a. might be due to ability to tiller and root at nodes, that produces a more extended and denser root system. (Shea and Peters, 1977)
D. Mechanisms of interaction between species: No information located
E. Specific conditions which favor or limit adaptation
1. Conditions that favor adaptation of crabgrasses
a. In weak turf, spreads over large area by prostrate stems that root at nodes
i. Crabgrass is opportunistic and invades turf mown to close
A) Increased stress to turf (Waddington et.al., 1992)
B) Increased light penetration to soil surface
b. The question of soil pH
i. Crabgrass favored by liming (Westover, 1926), crabgrass decreased by liming (Monteith and Bengston, 1939)
ii. Crabgrass is tolerant of low soil pH (4.7-6.3) (Buchanan et al, 1975)
iii. Crabgrass infestation thus is more likely decreased by liming
c. Maximal growth in wet soil (Zimdahl, 1980)
d. Crabgrass most serious in tall fescue (and other turfgrasses) that are fertilized during summer months (Waddington et.al., 1992)
e. High available P promotes crabgrass germination
f. Soil preference (Laudien and Koch, 1972)
i. sandy loam > sand > loamy sand > peaty soil > peat > clay
2. Conditions that limit adaptation
a. Soil compaction reduces stands (Hanson and Juska, 1971)
b. 50% shade reduces crabgrass dry matter 56% (Bantilan et al., 1974)
VIII. Control Strategies
A. Preventing seed set for several years is required for control
B. Specific strategies in crops
1. Crabgrass discouraged by tillage (Aldrich, 1984)
2. D. ischaemum infestation reduced 98% using grain sorghum residue
3. Crabgrass encroachment into coastal bermudagrass stands can be controlled through defoliation management-- Infrequent 1 in. cuttings (Aiken et al., 1995)
4. Crabgrass is suppressed by crop rotations that allow herbicide use.(Johnson and Coble, 1982)
5. Avoid summer N application to pasture (Kim, 1983)
C. Specific strategies in turfgrass
1. A dense stand of turf will reduce germination (Hanson and Juska, 1971)
2. Fertility
a. Increased N levels increase P. pratensis growth and competitive ability, decrease crabgrass cover (Waddington et.al., 1992)
b. Phosphorus
i. Increased phosphorus decreases crabgrass encroachment into turfgrass
(Turner et al., 1979)
ii. Crabgrass seedlings already present are very responsive to and rapidly assimilates phosphorus (Vengris et al., 1955)
iii. Better to avoid phosphorus application in spring
1) This limits availability to germinating crabgrass seedlings
2) Turfgrass requires relatively less phosphorus and has an adequate root system to locate required quantity
3. In non-herbicide treated areas, smooth crabgrass increases as mowing height decreases (Dernoeden et al. 1993)
a. Tall fescue mowed at 8.8 cm will effectively manage crabgrass
b. Herbicides required annually if mowed shorter than 8.8 cm
c. Herbicide use more effective than N fertility in short mowed tall fescue
D. Labeled herbicides
1. Preemergent herbicides are favored
2. Postemergent products for turf are very limited in selection and effectiveness