D. R. Smith, C. H. Gilliam, J. H. Edwards, and J. W. Olive

Controlling weed populations in container-grown nursery crops is essential for production of quality, marketable plants. A typical method of weed control is to broadcast granular herbicides with a cyclone spreader over the top of container-grown plants. Depending on growth habit and container spacing, non-target loss (herbicide falling between pots rather than in pots) can be as high as 86%. With most container nurseries making three to five applications of granular herbicide annually, this method of application results in significant non-target herbicide loss. Daily irrigation can further compound the problem by causing irrigation runoff. In many nurseries as much as 0.5-0.7 inches of water per day may be used during the growing season and this runoff water may contain herbicides, thereby threatening contamination of nearby water systems.

Two recently developed products with potential to reduce herbicide use in container nursery crop production are made from recycled waste paper. These products are pelletized recycled paper and crumbled recycled paper. Waste paper is ground with a hammer mill equipped with a series of three screens (the smallest about 0.25 inch), then compressed using pelletizing equipment to form pellets about 3/16 of an inch by 1 inch in size. To develop the crumble product, pellets are put through a granulator with variable pressure plates. Both recycled paper products are non-composted and have a C:N ratio of about 500:1.

Although using these recycled waste paper products may not be cost effective for every situation, there are situations where they could be of great value. Potential situations include large container production (10 gallons and larger) where increased pot spacing results in greater non-target herbicide loss, environmentally sensitive areas near surface water bodies, with plants that are difficult to weed due to thorns or spines, and in enclosed structures where herbicide use is restricted.

While recycled waste paper has demonstrated potential for a number of uses in the landscape, development of these recycled waste products into manageable forms may allow for use in container-grown crops. The objectives of this study were to evaluate these recycled paper products as non-chemical weed control alternatives for container production and to determine plant growth response to recycled waste paper used as a mulch on the surface of containers.

METHODS
Uniform liners of ‘Fashion’ azalea and ‘Girard’s Rose’ azalea were potted in trade gallon containers on August 9, 1995. The medium was a pine bark:peat (3:1 by volume) with 15 pounds Nutricote (18-6-8), 6 pounds lime, and 1.5 pounds Micromax added per cubic yard. Plants were grown in full sun and received daily overhead irrigation as needed.

Two paper products, recycled paper crumble and recycled paper pellets were surface applied at one of two depths, 0.5 or 1 inch. Phosphorus (P) was applied to the recycled waste paper products in the pots as triple superphosphate (0-46-0), at either 0 or 7.5 ppm, based on the dry weight of the paper products. Previous work had demonstrated sensitivity of some bedding plants to aluminum in the recycled paper and this was the reason for adding P. Other treatments included fabric disks, a fabric disk with Spin Out (a copper hydroxide root growth regulator), Rout 3G applied at 3 pounds active ingredient per acre, and a non-mulched control. With all mulch treatments 30 prostrate spurge seeds were placed either under the mulch or on top of the mulch. On May 7, 1996, azaleas were repotted into 3-gallon containers using the same medium, remulched with the recycled waste paper treatments, and the treatment of Rout 3G reapplied.

Data collected were prostrate spurge number per pot 30 and 75 days after treatment (DAT), and spurge fresh weight 75 DAT for ‘Fashion’ azalea pots only. In 1996, after repotting, spurge number was determined 30 and 60 DAT and spurge fresh weights were determined in pots of both azaleas 60 DAT (see table). Growth index (height + 2 perpendicular widths/3) was determined for both species 240 and 550 DAT. The pH of ‘Fashion’ containers was measured 7, 30, 90, 210, and 240 DAT.

RESULTS
WEED CONTROL. Recycled waste paper pellets applied to a depth of 1 inch suppressed spurge germination (0.0 spurge per pot 30 DAT; 0.3 spurge per pot 75 DAT), regardless of whether spurge seed were sown on top of the mulch or under the mulch. In contrast, recycled crumble provided poor spurge control at both depths and when spurge were sown on top of the mulch, there was increased spurge growth compared to when the seed were sown under the crumble mulch.

Better weed control from use of recycled pellets probably resulted from two factors. First, the pellets are three times the density of the crumble product, thus creating a greater barrier for weed seed germination under the mulch. Second, the recycled waste paper pellets absorb approximately three times their weight in water within a few days after application. As water is absorbed, the pellets swell, forming an interlocked mat of bonded pellets with a relatively smooth surface.

Results with the fabric disk showed limited spurge control with any treatment (data not shown). There was a seed placement effect 30 DAT with spurge number and 75 DAT with fresh weight with seed placement under the fabric resulting in less growth than seed placed on top of the fabric. Spurge also emerged around the container circumference and in the slit where the fabric disk fitted around the plant. There was a difference in the number of spurge if seed was placed under or on top of the fabric disk 30 DAT with spurge number being greater if seed were placed on top of the fabric disk. Spurge fresh weight at 75 DAT followed a similar trend.

Rout provided excellent spurge control. Spurge germination was about 70% by 75 DAT as evidenced by 20.5 spurge in the control treatment.

Recycled pellets at a 1-inch depth continued to provide excellent spurge control after the plants were repotted in May 1996. There was a relationship between mulch type and the addition of P on two of three weed variables measured with both azaleas. When P was added to the recycled crumble, spurge growth (fresh weight) was increased at both depths. With ‘Girard’s Rose’ azalea 60 DAT, recycled pellets provided greater spurge control (spurge number per pot) than recycled crumble, and the 1-inch depth provided greater control than the 0.5 depth; data for ‘Fashion’ azalea followed a similar trend.

GROWTH INDICES. Both cultivars grown with recycled waste paper mulch were generally similar in size to non-treated control plants and Rout treated plants at 240 DAT. No treatment produced a negative effect on plant growth when comparing effects of recycled paper treatments on ‘Girard’s Rose’. At 550 DAT all recycled paper treatment effects on ‘Girard’s Rose’ were similar to the effects on plants grown with Rout and non-treated control plants.

‘Fashion’ azalea growth indices at 240 DAT exhibited a relationship between mulch type and depth. Crumble-grown plants were similar at 0.5-inch and 1-inch depths; however, plants grown with pellets were smaller at the 1-inch depth than those grown at 0.5 inch. The authors observed that the pelleted mulch appeared to retain more water than the crumble mulch. Since all treatments were watered similarly with overhead irrigation, the growth suppression with recycled pellets may be related to excess moisture.

At 550 DAT, ‘Fashion’ azalea growth indices were affected by mulch, depth, and P. Crumble-grown plants had larger growth indices compared to pellet-grown plants, and plants grown in the 0.5 depth were larger than those grown in 1 inch. Plants grown with P were larger than those without P.

pH. When P was added to recycled paper, medium solution pH was lower than for no P treatments. Initially (7 DAT), the crumble recycled paper medium solutions had higher pH levels than pelleted; however, by 30 DAT pellet medium solution had a higher pH level than crumble and maintained a higher level throughout the study. The higher pH for pellets is probably due to the density of the pellets themselves, being three times more dense than the crumble. The pH of the waste paper pellets is 6.8 and crumble 7.0. Generally, pH values of the paper treatments with no P were more similar to that of the control than those treatments with P. Medium solution pH gradually became more acidic with all treatments over the course of the study, ranging from 5.6 - 6.6 at 7 DAT to 4.9 - 6.0 at 240 DAT. These levels are within acceptable ranges for container grown nursery crops.

Previous work has shown the addition of P is necessary to alleviate Al toxicity with sensitive bedding plants. Our data show that with container-grown plants additional P was not beneficial for plant growth when recycled paper is used as a non-chemical weed control alternative. While plant quality was not rated, all plants had good foliar color. Repotting the trade gallon container-grown azaleas into 3-gallon containers and reapplying the mulch had no negative effect on azalea growth.

Our research shows that recycled waste paper in the pelleted form provides superior weed control compared to the crumble form and that the 1-inch depth is necessary to provide adequate weed control during a growing season. Additionally, two environmental issues are addressed with this product; a reduction in chemical use and an alternative application of a post-consumer by-product that would otherwise be disposed of in landfills.

Effects of Recycled Paper Mulches on Control of Prostrate Spurge Seed in Container-grown Azaleas After Repotting
			‘Girard's Rose’			‘Fashion’
Treatment	Depth (in)	P level (ppm)1	Spurge # 30 DAT2	Spurge # 60 DAT	Fresh wt.3 60 DAT	Spurge # 30 DAT	Spurge # 60 DAT	Fresh wt. 60 DAT
Pellet	0.5	0.0	0.25	2.3	3.1	0.29	2.1	3.5
Pellet	0.5	7.5	0.37	1.4	10.6	0.43	0.86	12.1
Pellet	1.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0
Pellet	1.0	7.5	0.0	0.25	0.03	0.0	0.14	0.01
Crumble	0.5	0.0	1.9	4.0	5.6	1.0	3.0	0.26
Crumble	0.5	7.5	5.0	5.0	23.0	6.2	5.9	26.3
Crumble	1.0	0.0	1.4	2.0	3.5	1.6	2.3	4.0
Crumble	1.0	7.5	2.5	3.6	56.2	2.0	3.1	46.0
Rout 3G4		0.0	0.25	1.6	9.5	0.29	1.9	10.9
Control5		0.0	5.3	8.1	59.1	5.7	8.9	57.6
1Phosphorus source was triple superphosphate: ppm based on weight of recycled paper per pot. 2Days after transplant. 3Measured in grams. 4Rout 3G herbicide applied at 3 pounds active ingredient per acre. 5No mulch applied.