Abstract
Various soil types were seeded with black locust and treated with different preemergent herbicides to determine their effect on germination, seedling survival, and growth. All treatments except oxadiazon and chloroxuron allowed acceptable survival and growth.
Millions of acres of new forest lands have been established in the United States using bare-root seedlings; however, only a small percentage was direct-seeded (1). In the southeast, southern pine has been direct-seeded with success in cut-over forest lands (5). On surface-mined lands, direct seeding of black locust (Robinia pseudoacacia) has been practiced extensively in the southeast with success (3, 4). However, direct seedling in natural loamy soils presents a greater challenge because of luxuriant weed populations. Weed control in tree nurseries is essential, but costs are high with hand-weeding methods. Herbicides are often cheaper and convenient if used properly (2). New herbicides need to be evaluated for damage to tree seed in addition to tree seedlings.
Previous greenhouse pot studies have evaluated the tolerance of black locust seed to various common herbicides in peat/sand and peat/ sand/soil mixtures (8, 9), suggesting that the use of herbicides in direct seeding might be feasible. However, the high germination rates in pot studies were not translated to field trials using seed from the same seed lot (7). Soil moisture problems, rodent pilferage, and/or herbicide activity may all have contributed to low survival. Further testing in soil under controlled greenhouse conditions is necessary in order to evaluate soil effects found in field conditions.
This report compares several trials of seedling survival and growth of black locust seed planted in different soil types, when treated with preemergent herbicides one day after sowing under controlled greenhouse conditions.
Materials and Methods
Seed were scarified with concentrated sulfuric acid for 60 minutes. Twenty-five seeds were planted in individual 3.8 liter plastic nursery containers at 0.6 cm depth in the following soil types:
* Eudora, silty-clay loam with a pH of 7.5, 2.0% organic matter, 146 kg available phosphorus (P), and 560 kg exchangeable potassium (K) per hectare.
* Shellabarger sandy loam with a pH of 6.1, 1.6% organic matter, 37 kg P, and 575 kg K per hectare.
* Cass loam/sandy loam with pH of 7.7, 1.2, organic matter, 22 kg P, and 336 kg K per hectare.
The following day, three replications of each of eight herbicide treatments were applied to the soil surface of randomly selected containers. Eight treatments (Table 1) using the best herbicide rates from our previous trials (6, 7) were prepared. Treatments were: alachlor, chloroxuron, DCPA, EPTC, napropamide, oxadiazon, pro-fluralin, and a control. A 1 ml aliquot stock solution was mixed with 232 ml of water to simulate a 1.3 cm irrigation per pot. Water and fertilizer were provided as needed throughout the experimental period. Seedling counts were made at 6-day intervals. Sixty days after seeding, plant height and final survival counts were recorded. Plants were cut at the soil surface and oven-dried at 65°0 C for 48 hours for dry weight measurements. Separate tests were conducted for each soil type, thus only ranking between herbicides should be compared.
Results and Discussion
Some herbicide treatments resulted in a significant survival reduction of black locust in some soil types (Table 1). Although grown at a different time, survival was less in soil than in peat/sand mixture as previously reported (6, 7), but usually herbicide comparisons within the different growing media were similar. Compared to the control, all plant measurements were significantly lower for oxadiazon in all three soil types (Tables 1, 2), which is contrary to previously reported results in both growth chamber (7) and peat/sand mixture studies (6). Significant survival differences (compared to control were found with chloroxuron, EPTC, profluralin, adn DCPA only in the loam/sandy loam soil.
Black locust seedlings were significantly shorter than the controls only in soil treated with oxadiazon (Table 2), while no difference was found in the earlier study with peat/sand. Generally, treatments did not cause individual dry weights to differ from the control (Table 2), except with oxadiazon, where survival was low. Survival with chloroxuron was low, but the few surviving seedlings, with little competition, grew to a large size.
Summary and Conclusions
Growth effects between herbicides within any given soil type did not generally differ from those found in the peat/sand mixtures. The one exception was oxadiazon, which severely reduced survival in soil, but not in peat/sand, indicating that high organic matter may be necessary to allow safe use of oxadiazon. Because most of the herbbicides used in this study did not decrease seedling survival or growth in soil, they could provide feasible alternatives to hand-weeding in tree nurseries and establishment of direct-seeded tree plantings.
Footnotes
- © 1987, International Society of Arboriculture. All rights reserved.
Literature Cited
- 1.↵Abbott, H. G. and S. D. Fitch. 1977. Forest nursery practices in the United States. J. For. 75:141–145.
- 2.↵Anderson, H. W. 1968. Two herbicides reduce weeding costs in Washington nursery trials. USFA Tree Planters’ Notes. 19:10–14.
- 3.↵Brown, J. H. and E. H. Tyron. 1960. Establishment of seeded black locust on spoil banks. West Va. Ag. Expt. Sta. Bull. 440.
- 4.↵Graves, D. H., S. B. Carpenter, and R. F. Wittwer. 1980. Direct seeding of commercial trees on surface-mine spoil. Interagency Energy/Environment R & D Program Report # EPA - 600/7-80-073.
- 5.↵Mann, W. F., Jr. and H. D. Burkhalter. 1961. The South’s largest successful direct-seeding. J. For. 59:83–87.
- 6.↵Warmund, M. R., C. E. Long and W. A. Geyer. 1980. Preemergent herbicides for seeded nursery crops. Hort. Sci. 15: 825–826.
- 7.↵Warmund, M. R., W. A. Geyer and C. E. Long. 1983. Preemergent herbicides for direct seeded Kentucky coffeetree, honeylocust, and black locust. USFS Tree Planters’ Notes. Summer, 24–25.
- 8.↵White, T. A. and G. L. Rolfe. 1982. Tolerance of direct-seeded black locust (Robinia pseudoacacia L.) to herbicides. Univ. of IL AES For. Res. Rep. 82-100. Urbana, IL 4 p.
- 9.↵White, T. A. and G. L. Rolfe. 1983. A test of tolerance: 1982 greenhouse herbicide trials with direct-seeded black locust. Univ. of IL AES. Urbana, IL 5 p.
