University of Arizona a dot Cooperative Extension

Yuma County Farm Notes

Weed Seed Germination
arry Tickes, Area Agent/ANR, University of AZ; Dennis Monypeny;
Al Baber, The Gowan Company (retired)


The principal herbicides used on lettuce, Balan, Kerb and Prefar, are applied preemergence or preplant incorporated and work by inhibiting root growth in developing seedlings. Proper herbicide placement and time of application are critical for these herbicides to be effective. They must be in the right place at the right time. The right place is in the soil surrounding germinating weed seeds and the right time is when weed seeds are germinating. A test was conducted to help determine the proper time of application. Our specific objective was to determine how long it took for various weed seeds to germinate after they were exposed to moisture. The time to germination will vary considerably even within the same field due to variations in soil and microclimatic conditions. Every year could be different and this test was intended to provide a general indication of germination times for various common weed seeds.


Seven summer and winter annual weeds, 2 grasses and five broadleaf weeds, were chosen for this study. Seeds for these weeds were placed in teabags and buried 1/4 inch below the soil surface and in the seed row of newly planted lettuce fields prior to the germination irrigation. Teabags were pulled every 24 hours and evaluated for germination. This procedure was repeated in both sprinkler and furrow irrigated fields at eight locations in Roll, Bard, the Gila Valley and the Yuma Valley. The tests began in August and were conducted each month until February.

Hours to Germination

Weeds: Aug. Sept. Oct. Nov. Dec. Jan.
Barnyardgrass 24 24 48 72 96 NG
Canarygrass NG 168 96 96 96 NG
Lambsquarters 72 96 96 72 168 NG
Silverleaf Nightshade 96 96 72 96 NG NG
Pigweed 48 72 48 72 96 NG
Purslane 24 24 24 48 96 168
Shepardspurse NG NG 168 96 168 NG

NG = No germination

Full Disclaimers

Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, James A. Christenson, Director Cooperative Extension, College of Agriculture and Life Sciences, The University of Arizona.

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Information provided by:
Barry Tickes, Extension Agent, Yuma County
Dennis Monypeny, Ph.D.
Al Baber, the Gowan Company (retired)
University of Arizona, Tucson, Arizona.
Material written May 2002.

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