Crabgrass

Scientific name: Digitaria spp.



Smooth crabgrass
Photo courtesy of Randall Prostak
University of Massachusetts

Habitat

Cultivated and uncultivated areas

Affected crops

Most agricultural crops

Distribution

Africa, Asia, Europe, South America, USA

Description

Large crabgrass (D. sanguinalis)

Synonym: Finger grass

The stem has a spreading, branching structure, bending abruptly at a sharp angle. It roots at its nodes. The leaves are linear, hairy, and turn dark-red or maroon as they mature. There are plenty of leaves near the base of the plant and scattered loosely along the stem. The flower head is finger-like and is composed of 4-6 thin spikes. It can produce as many as 150,000 seeds.

Smooth crabgrass (D. ischaemum)

The weed is very similar to large crabgrass except that the node does not have roots and the leaves do not have hairs. The flower head is composed of 2-6 spikes.

Effects and impacts

Large crabgrass competes directly for soil nutrients and moisture. It can reduce corn yield by 20%. It is an alternate host for leaf blast, mosaic virus, and nematodes. The infected weed becomes the source of infestation in the following cropping season (Rice IPM, 2001).

Studies show that the weed is found to be resistant to Fluazifop-p-butyl, Haloxyfop-methyl, and Imazethapyr on onion and vegetables growing in some parts of Australia; to Atrazine on corn fields and orchards in some parts of France and Poland; and to Fluazifop-p-butyl, and Sethoxydim on carrot and onion farms in some parts of Wisconsin, USA (Weed Science, 2005).

Methods of control

1. Proper selection of seeds
2. Thorough land preparation by plowing and harrowing twice to expose and/or bury the seeds
3. Closer spacing
4. Hand weeding or hoeing
5. Regular field monitoring

External links

• FAO. Digitaria ciliaris. http://www.fao.org/ag/AGP/AGPC/doc/Gbase/data/pf000219.htm
• The University of Vermont. Field corn weeds. http://pss.uvm.edu/pd/vtnapiapx/corn/cornweeds.htm#Crabgrass
• UC IPM. Identification of grasses. http://www.ipm.ucdavis.edu/PMG/FIG/weed_grass.html
• Virginia Tech. Large crabgrass. http://www.ppws.vt.edu/scott/weed_id/digsa.htm
• Virginia Tech. Smooth crabgrass. http://www.ppws.vt.edu/scott/weed_id/digis.htm
• University of Massachusetts. Weed herbarium. http://www.umassgreeninfo.org/fact_sheets/weed_herbarium/pages/digis.html

References

• CABI. (2001): Crop protection compendium. Global module, 3rd edition. CAB International Publishing. Wallingford, UK.
• CABI. (2000): Crop protection compendium. Global module, 2nd edition. CABI Publishing, Wallingford, UK.
• IRRI & Queensland University. (2001): Rice IPM. An interactive information and identification system for integrated pest management in rice. University of Queensland and IRRI.
• Moody, K.; Munroe, C.; Lubigan, R.; Paller , E. (1984): Major weeds of the Philippines. University of the Philippines, Los Baños. Laguna, Philippines.