19 



D'jscr i pt ion 



The leaf sheaths oF large crabgrass seedlings are tinged purple and are 

 covered witH long stiff hairs. The ligule is membranous, flat at the top, 

 and smooth (Fig. la). A ligule is a thin membrane or row of hairs at the 

 top of the junction of the leaf sheath and the leaf blade. Large crabgrass 

 3nd small crabgrass are the only species of the grass family which have a 

 membranous ligule. Auricles are absent. Auricles are the appendages pro- 

 jecting around the stem from both sides of the collar. The first leaf is 

 only about twice as long as it is wide. It is tinged light purple and has a 

 white strip running down the center. Both sides have silky, shiny hair. 



Biol ogy 



Large crabgrass, a summer annual, is a member of the grass family. It 

 is purplish or green and has very hairy leaves and sheaths. Leaves are 6 to 

 8 mm wide and 5 to 15 cm long. The stems are spreading and much branched. 

 Roots develop at nodes on the prostrate stems (Fig. 1). 



Large crabgrass reproduces by tillers and seeds. This weed has a pro- 

 lific tillering or branching habit. Just a few plants can spread rapidly 

 and cover considerable area. A single plant is capable of producing 150 to 

 700 tillers and 150,000 seeds. Plants can produce seeds at mowing heights 

 as low as 6 mm. If top growth is mowed, two or three seed crops may form in 

 a single growing season. 



Seeds germinate best from mid-spring to late summer. Large crabgrass 

 seeds are dormant for a short time after they shed. Large crabgrass con- 

 tinues to grow until mid-summer when days become shorter. Vegetative 

 growth slows down and plants enter their reproductive stage. Purplish seed 

 heads form until frost kills the plants. Plants that emerge early in the 

 season and have a long period of vegetative growth are much larger and more 

 competitive than plants that germinate late in the season. 



Large crabgrass is a serious weed of cultivated crops, lawns, nur- 

 series, orchards, and pastures. Once established, large crabgrass tolerates 

 both high temperatures and dry weather conditions. 



Cont r ol of Crabg r ass 



The basic principle of a large crabgrass control program is to prevent 

 rei nf estat ion by seed. Controlling seed production for several years will 

 help reduce the viable seed supply. 



Large crabgrass can not be controlled in one growing season because of 

 the great number of viable seeds that accumulate in the soil from years of 

 infestation. A good weed management program in a fruit orchard is one that 

 consists of both cultural and chemical methods of weed control. Satisfac- 

 tory control requires several years of conscientious adherence to a good 

 control program. 



