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Vegetable IPM Updates Archive
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When do Weed Seeds germinate? (Dec. 14, 2011)

The length of time it takes weed seeds to germinate can vary considerably even within the same field due to variations in soil and microclimatic conditions. Every year can be different. We conducted a test to determine how long it took for various weed seeds to germinate after they were exposed to moisture. Seven summer and winter annual weeds, two grasses and five broadleaf weeds were chosen for this test. Seeds for these weeds were placed in teabags and buried 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 8 locations at Roll, Bard, The Gila Valley, and the Yuma Valley. The tests began in August and were conducted each month until February. The time to germination appears in the following table. The time to germination for the summer annual grass (barnyardgrass) was 24 hours in august and September, became longer in October (48 hours) and still longer in December (96 hours). It did not germinate in January. The winter annual grass (cannarygrass) took 168 hours to germinate in September and dropped to 96 hours in December. The summer annual broadleaves took from 24 hours (Purslane) to 96 hours (Pigweed and Nightshade) to germinate. The winter annual broadleaf weeds (lambsquarters and Shepardspurse) took from 72 to 168 hours to germinate.

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

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For questions or comments on any of the topics please contact Marco Pena at the Yuma Agricultural Center.
College of Agriculture, The University of Arizona, Tucson, AZ.

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