LEAFLET 101

LMARCH 1982

Evaluation of Alachior for Weed Control in Container Grown Ornamentals
CHARLES H. GILLIAM and D. JAMES CROCKETT 1

requirement of most container grown nursery operations. Several studies have shown alachlor [2-chloro-2'-6'-diethyl-N (methoxymethyl)-acetanilide] 15 G to be an effective herbicide for container grown

W EED

CONTROL is a major labor

nursery stock2 ,3 ,

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T he research reported here was conducted by the Alabama Agricultural Experiment Station in cooperation with the LR-4 program, a project designed to improve registration ofpesticides for minor use crops such as ornamentals. Evaluations were made of (1) the efficacy of alachlor for weed control in selected container grown ornamentals, (2) phytotoxicity of alachior, and (3) effects of 'Assistant Professor and Research Associate, respectively, Department of Horticulture. 2

GLAZE, N.C., MEGH SINGH, AND S.C. PHATAK. 1980. Response of Pampasgrass and Two Azalea Cultivars to Alachlor, Oxadiazon, and Oxyfluorfen. Abstr. 89, Proc. Weed Sci. Soc. Amer. p. 41. 3 . RYAN. G. F. 1976. Control of Bittercress, Common Groundsel and Barnyardgrass in Two

alachlor on the growth of container grown plants. Plant species used were Aucubajaponica, Cleyera japonica, Gardenia Jasminoides, Liriope muscari, Photiniafraseri, and Pittosporum tobira. Rooted cuttings were potted into -gallon plastic containers in a pine bark-sand medium (4:1 ratio, volume basis). Medium amendments included gypsum, 2 pounds per cubic yard; triple superphosphate, 2 pounds per cubic yard; dolomitic limestone, 6 pounds per cubic yard; Aqua gro, 1 pound per cubic yard; and Esmagran minor elements, 4 pounds per cubic yard. Treatments of 15 G alachlor were surface applied at the rates of 4, 8, and 16 pounds active ingredient per acre 14 days after potting (May 14). A second application was made 60 days later. All treatments were replicated four times with four containers per replication in a randomized block
design.

Nursery Container Media. Proc. West. Soc. Weed Sci. 29:156-168. 4 RYAN, G. F. 1978. Timing of Alachlor-simazine

Applications in Container-grown Azaleas. Abstr.
35,5 Proc. Weed Sci. Soc. Amer. WEATHE]RSPOON, D.M. AND W.L. CURREY. 1978. Herbicide Phytotoxicity Evaluations for Woody Ornamentals. H ortScience 13:357.

The major weeds in the containers were common ragweed (Ambrosia atremisiifoia), bermudagrass (Cynodon dactylon), pigweed (Amiaranthus sp.), and crabgrass (Digitariasanguinalis). These four weed species were sown prior to herbicide application. AULuIJO and Pittospurumn species were grown in a shade house with 41 percent

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AUBURN UNIVERSITY Auburn University, Alabama

ALABAMA AGRICULTURAL EXPERIMENT STATION Gale A. Buchanan, Director

TABLE 1. EFFECTS OF ALACHLOR ON PERCENT WEED CONTROL IN SIX CONTAINER GROWN ORNAMENTAL PLANTS, 19801

Treatment

Weed control on three dates Pittosporum Photinia Liriope Gardenia Cleyera Aucuba 8/6 10/23 6/20 8/6 10/23 6/20 8/6 10/23 6/20 8/6 10/23 6/20 8/6 10/23 6/20 8/6 10/23 6/20 Pct. Pct. Pet. Pct. Pct. Pet. Pct. Pet. Pct. Pet. Pet. Pet. Pet. Pet. Pet. Pct. Pct. Pet. 95a 99a 97a 100a 98a 88a 89a 98a 100a 100a 100a 99a 100a 99a 100a 100a 98a 88a 91b 6b 74c 75b 86b Ob Oc Ob Od Oc Od Ob Multiple Range Test, 5 percent level. 99a 99a 99a Ob Ob 83a 88a 90a 68b Oc 92a 96a 100a 77b Oc 82b 93a 97a Oc Oc 83b 84b 94a 69c Oc 93b 96ab 99a 93b Od 100a 100a 100a 53b 30b 93b 98a 100a 65c Od 100a 99a 100a 93b Oc

Alachlor 99a 4 lb.................. 100a 94a 99a 8 lb. ................. 100a 96a 16 lb.................. 00a 99a 100a 90b Hand weed ............. 20b 45b Oc Oc No weeding ............. 20b 'Mean separation within columns by Duncan's 2 Active ingredient per acre.

2

TABLE 2. EFFECTS OF ALACHLOR ON GROWTH OF SIX CONTAINER GROWN ORNAMENTAL PLANTS'

Aucuba Height Width In. In.
2

Cleyera Height Width In. In.

Gardenia Height Width In. In. 24a 22a 26a 24a 20b 19ab 18ab 20a 20a 17b

Liriope Height Width In. In. 9b 10a 10a 9b 5c 17ab 19a 19a 16b 10c

Photinia Height Width In. In. 25a 21a 26a 25a 15b 14a 14a 13a 13a 7b

Pittosporum Height Width In. In. 9a 9a 9a 8ab 7b l la 10Oab 9b 9b 9b

Alachlor 3 15a 10Obc 8a 7b 4 lb................... lib 9a 14a 9a .................. 8 lb. 13a 16a 8a 8ab 16 lb................... lb 1 15a 7ab 8a Hand weed .............. 8c 5b lb 5c No weeding ............. 'Data collected November 1, 1980. 2 Active ingredient per acre. 3 Mean separation within columns by Duncan's Multiple Range Test,

5 percent level.

saran shading. Germination of the sown weed species was slowed under shade compared to full sun treatments. All other species were grown in full sun conditions. Plants were fertilized weekly with 150 p.p.m. N, 125 p.p.m. K, and 65 p.p.m. P in the form of Peters 20-20-20 commercial fertilizer (Peters Fertilizer Company, Fogelsville, Pennsylvania). All rates of alachlor equaled or increased the percent weed control in comparison to the hand weeded check treatments, table 1. No difference in percent weed control was observed when the three rates of alachlor were compared. All rates of alachlor provided 80-100 percent weed control. The final evaluation of percent weed control was conducted 90 days after the last application of alachlor. Shoot growth (height and width) was not

suppressed with alachlor at any rate, table 2. Hand weeded liriope and unweeded check treatments exhibited reduced shoot growth as compared to the alachlor treatments. No phytotoxicity was observed with any rate of alachlor on any tested species. However, both Photinia and Cleyera exhibited foliar chlorosis within 4 weeks of alachlor application. Evaluation of the data indicated no phytotoxicity occurred as a result of alachlor treatments. This is in contrast to earlier research in which Photinia exhibited phytotoxicity when treated with alachlor. In this study, treatment of both species with sesquestrene Fe corrected the foliar chlorosis symptoms. In summary, these data show alachlor to be an effective herbicide on the six container grown, ornamental species tested. Excellent weed control and no phytotoxicity were observed with any rate of alachlor applied.

Information contained herein is available to all without regard to race, color, sex, or national origin.

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