Maui Association of Landscape Professionals

Efficacy of Granular Preemergent Herbicide

From the: Summer 2010 MALP Newsletter
By: Norman Nagata
University of Hawaii Extension Agent,
University of Hawaii, Cooperative Extension Service

This article "summarizes" a 6-month granular pre-emergent herbicide test that was conducted with Pendulum, Freehand, Ronstar, Barricade, Snapshot, Preen 9-17-9 with trifluralin, Amaze with benefin + oryzalin, and corn gluten to control garden spurge (Chamaesyce hirta), prostrate spurge (Chamaesyce prostrate), graceful spurge (Chamaesyce hypericifolia), emilia (Emilia sonchifolia), coat buttons (Tridax procumbens), goosegrass (Eleusine indica), and lovegrass (Eragrostis tenella); which are weeds commonly found in Hawaiian landscapes.

The test was conducted at the Cooperative Extension Service in Kahului, consisting of 4 replicated, 6' x 6' plots arranged in randomized complete blocks. Weed seeds and herbicides were applied to each plot and were irrigated daily for 25 minutes. Weed counts were taken every 2 weeks for 6 months. The table below summarizes the number of months that these herbicides provided >90% control.

Acknowledgements. This test was supported in part by the County of Maui and BASF Corporation

Longevity of granular preemergent herbicides on weed control

Herbicide

Rate per
1,000 ft (lb)

Weed Control: Months After Treatment¹

Garden Spurge

Prostrate Spurge

Graceful Spurge

Emilia

Coat Buttons

Goosegrass

Lovegrass

Barricade

7.1 lb

< 3.5 months

< 5.0

> 6.0

< 1.0

< 1.5

> 6.0

Ronstar

4.6

< 4.0

< 4.5

< 5.5

< 1.5

> 6.0

Snapshot

4.6

< 2.0

< 2.5

< 1.5

< 6.0

> 6.0

< 1.5

Freehand²

3.5

< 2.5

< 3.0

< 1.5

< 2.0

< 3.5

< 3.0

Freehand

4.6

< 3.5

< 3.0

< 2.0

< 4.0

< 3.0

Amaze

4.5

< 3.0

< 2.5

< 1.0

< 2.5

< 5.5

< 3.0

Pendulum

2.3

< 3.0

< 2.5

< 1.0

< 1.5

< 3.5

Preen

6.3

< 1.0

< 1.5

< 1.0

Corn Gluten

< 1.0

--⁴

< 1.0

< 1.5

< 1.0

Untreated Control³

< 0.5

< 1.0

< 0.5

¹Number of months herbicides provided >90% control (note: data was taken every 2 weeks and test was terminated after 6 months).
²Freehand was evaluated at 2 rates as requested by BASF Corporation, a sponsor of this test.
³Germination of Weed Seeds (months after planting.)
⁴(--)No control; germination time was similar to untreated controls.