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William J. Sciarappa* and Gary C. Pavllis

Weeds are especially problematic in highbush blueberry which has a long establishment period, shallow-fibrous roots, and poor competitive ability in obtaining water, nutrients and sunlight. Commercial approaches in certified organic blueberry fields compared horticultural management methods in two New Jersey sites. The trials utilized both new and established blueberry blocks having trickle or overhead irrigation. Commercial methods investigated included rotary cultivation, mowing, propane flaming, cover crops, landscape fabric, and various mulches. Mulch comparisons included pine bark mulch, hardwood mulch, coffee grinds, cocoa grinds, municipal leaf mulch, and composted tea leaves. 3' × 12' plots were replicated 4 times in 4 adjoining rows. Applications of 3-4 inches of these mulches within the crop row to a new planting of Duke highbush blueberry have provided a combined weed control level of ca. 95% without landscape fabric and ≈98% with landscape fabric during 2003. Walkway weed suppression in new plantings was achieved with the establishment of two types of fine leafed turf fescues and monthly mowings. Bare ground percentage decreased from 80% to <2% within one year's time as these fine fescues gradually out-competed annual weeds for space. These fescue cover crops increased ground coverage from 8% to >95% over the seven month growing season. Such varieties were selected because they have good germination, require little water, use limited nitrogen and can squeeze out weeds through allelopathy. Applied research studies indicate that several suitable methods can be utilized for effective weed management in organic highbush blueberry production systems.

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Greg D. Hoyt and David W. Monks

Experiments were conducted to evaluate the effect of tillage systems and weed management on weed suppression and potato yield. Strip-tillage (ST) and conventional-tillage (CT) systems produced equal yields of Irish potato (Solanum tuberosum L.) or sweetpotato [Ipomoea batatas (L.) Lam.] when herbicide treatments were applied. Weeds in the nontreated control reduced yield of Irish potato and prevented storage root growth in sweetpotato. Excellent control of broadleaf signalgrass [Brachiaria platyphylla (Griseb.) Nash], henbit (Lamium amplexicaule L.), prickly sida (Sida spinosa L.), and common ragweed (Ambrosia artemisiifolia L.) was obtained with metribuzin + metolachlor applied preemergence at Irish potato planting, followed by sethoxydim + crop oil applied postemergence in ST and CT systems. Redroot pigweed (Amaranthus retroflexus L.) control was >98% at 4 weeks after treatment but was 73% to 84% at harvest across all herbicide treatments in both tillage systems. In sweetpotato, control of black mustard [Brassica nigra (L.) W.J.D. Koch], goosegrass [Eleusine indica (L.) Gaertn.], and fall panicum [Panicum dichotomiflorum Michx.] was >95% throughout the growing season for all herbicide treatments in both ST and CT.

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Shawn T. Steed, Allison Bechtloff, Andrew Koeser and Tom Yeager

Mulches have many positive benefits for the production of plants, ranging from weed suppression to water conservation. In this study, a novel method of using plastic film mulch for container-grown plants was evaluated. Plots of 25 japanese privet (Ligustrum japonicum) in #1 (2.5 qt) nonspaced containers were wrapped with 1.25-mil white or black plastic mulch over the top and sides of containers. Small plants were planted through the plastic and grown for 22 weeks with overhead irrigation. Water application amount was determined by moisture sensors placed in the substrate of each treatment. Plant growth, dry weights (DWs), weed fresh weights, weeding time, substrate electrical conductivity (EC), substrate temperature, total water applied, and mulch costs were determined. Black plastic (BP) and white plastic (WP) mulch reduced water applied by 82% and 91%, respectively, compared with the nontreated control (NT). Nontreated control plants grew faster and had greater DW at the end of the experiment. Mulched containers had fewer weeds and required less labor to remove weeds than the NT treatment. Substrate EC level was greater in BP and WP treatments than for the NT after 20 weeks, and plastic mulch did not result in different substrate temperatures. Plastic mulch added $4.94/1000 containers ($2.24 input cost and $2.70 removal cost) to production costs, not including disposal costs. This novel method of mulching nonspaced plants reduced irrigation water, herbicide applications, and weeding labor, but probably added 2–3 weeks to finish time.

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J.P. Mitchell, W.T. Lanini, S.R. Temple, E.V. Herrero, E.M. Miyao, P. Brostrom, R. Morse and F. Thomas

Conservation tillage (CT) row crop production is currently not widely adopted in California. Recently, however, interest in evaluating the potential of CT systems to reduce production costs and improve soil quality is growing in many areas in the state. In 1997 and 1998, we evaluated four cover crop mulches (rye/vetch, triticale/vetch, Sava medic, and Sephi medic) in a CT-transplanted tomato system relative to the conventional winter fallow (CF) practice. In both years, yields were comparable to the CF under the triticale/vetch and rye/vetch mulches. Earthworm populations after 2 years of CT production were increased 2- to 5-fold under mulches relative to the CF system. Soil carbon was increased by 16% and 6% after 2 years of CT production under the triticale/vetch and rye/vetch mulches, respectively. Weed suppression under the triticale/vetch and rye/vetch was comparable to the CF with herbicide system early in the season in both years but was maintained through harvest in only one season. Soil water storage (0-90 cm) was similar at the beginning of the tomato season in triticale/vetch, rye/vetch, and fallow plots but was higher under the mulches during much of the last 45 days of the 1998 season. Further refinement of CT practices in California's vegetable production regions is needed before wider adoption is likely.

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John L. Maas, John M. Enns, Stan C. Hokanson and Richard L. Hellmich

Larvae of several insects injure and kill strawberry (Fragaria ×ananassa Duchesne) plants by burrowing into and hollowing out plant crowns. Occasionally, these infestations are serious enough to cause heavy economic losses to fruit producers and nursery plant growers. In 1997 in Beltsville, Md., we observed wilting and dying mature plants and unrooted runner plants in two experimental strawberry plantings. Injury by larvae was extensive; large cavities occurred in crowns, and the central pith tissues were removed from stolons and leaf petioles. Often, insect frass was seen at entrance holes. Larvae removed from hollowed-out parts of injured plants were identified as the European corn borer (Ostrinia nubilalis Hübner) in their fifth instar stage. Their presence in this instance also was associated with a cover crop of millet [Setaria italica (L.) P. Beauv., `German Strain R'] planted between the strawberry rows for weed suppression. This is the first published report of the European corn borer attacking strawberry. Although this insect may occur only sporadically in strawberry plantings, it may become important in the future. Growers and other professionals should become aware of this new strawberry pest and recognize that its management in strawberry will be different from management of other crown-boring insects.

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John R. Teasdale and Aref A. Abdul-Baki

Hairy vetch (Vicia villosa Roth), crimson clover (Trifolium incarnatum L.), and rye (Secale cereale L.) and mixtures of rye with hairy vetch and/or crimson clover were compared for no-tillage production of staked, fresh-market tomatoes (Lycopersicon esculentum Mill.) on raised beds. All cover crops were evaluated both with or without a postemergence application of metribuzin for weed control. Biomass of cover crop mixtures were higher than that of the hairy vetch monocrop. Cover crop nitrogen content varied little among legume monocrops and all mixtures but was lower in the rye monocrop. The C:N ratio of legume monocrops and all mixtures was <30 but that of the rye monocrop was >50, suggesting that nitrogen immobilization probably occurred only in the rye monocrop. Marketable fruit yield was similar in the legume monocrops and all mixtures but was lower in the rye monocrop when weeds were controlled by metribuzin. When no herbicide was applied, cover crop mixtures reduced weed emergence and biomass compared to the legume monocrops. Despite weed suppression by cover crop mixtures, tomatoes grown in the mixtures without herbicide yielded lower than the corresponding treatments with herbicide in 2 of 3 years. Chemical name used: [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one](metribuzin).

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Richard P. Buchner

California walnut farmers compete with pests and diseases to produce an economically viable crop. Current control strategies work reasonably well for most pest and diseases. However, the future of these techniques is a matter of speculation. This presentation describes current production practices and potential alternatives to “traditional” pest and disease control. Codling moth, walnut husk fly, mites, navel orangeworm, aphids, and scale are typical insect pests that have an impact on California walnut production. Spray decisions using Integrated Pest Management, beneficial insect releases, mating disruption, insect growth regulators, and orchard sanitation offer potential alternatives. Major diseases include: Phytophthora crown and root rot, crown gall, oak root fungus, and walnut blight. Control options include careful site selection and orchard management, resistant rootstocks, competitive bacteria for crown gall control, and copper compounds for walnut blight suppression. Weed growth is related to the amount of light reaching the orchard floor. Mature trees often shade the orchard floor, subsequently reducing the need for weed suppression. Herbicides are typically used for vegetation control. Choice of irrigation system, cultivation, mowing, cover crops, and flaming offer potential alternatives either alone or in combination with conventional herbicides.

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Kirk D. Larson

Southern California strawberry growers use clear polyethylene mulch to increase soil warming and promote plant growth and fruiting, but use of clear poly mulch is only feasible when effective preplant soil fumigation controls weeds. In the absence of methyl bromide fumigation, the use of wave-length selective (WLS) or black polyethylene bed mulches may be required for adequate weed suppression, but the influence of these materials on strawberry plant growth and productivity in southern California is not well-documented. We conducted experiments in 1994–95 and 1995–96 to determine the influence of various mulch formulations on soil temperature and growth and productivity of `Chandler' strawberry in Irvine, Calif. Clear poly and a green WLS material (IRT76, AEP Plastics) were compared in both trials; in addition, the 1995–96 trial included a brown WLS material (ALOR, PolyWest, Inc.) and a black poly mulch. For both trials, freshly dug runner plants were established in premulched beds in early October, and soil temperatures were continuously monitored at a 10-cm depth using thermocouples and a recording datalogger. Fruit harvest commenced in December and continued through June. In both years, clear poly mulch resulted in significantly greater soil temperatures, greater December plant diameters, and greater early and total fruit yields than other mulches. In both years, use of clear poly resulted in 12% greater fruit yields than the other three materials. No growth or productivity differences were observed among the WLS and black mulches, although differences were observed in mean soil temperatures.

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Joseph DeFrank

Azolla (Azolla filiculoides) is a floating fern that maintains a symbiotic relationship with an N-fixing blue-green algae. In many parts of Asia, azolla is used as a green manure in flooded rice cultivation. Taro (Colocasia esculenta) grown under flooded conditions is used to produce a traditional Hawaiian staple, poi. Azolla has been present in Hawaii for many years, but is not used in a controlled way for either nutrient augmentation of production sites or weed suppression. In this experiment, azolla was removed from a stream on the island of Kauai and multiplied in a nursery pond. Phosphoric acid was added to the nursery pond as a nutrient (P = 5 ppm) at 5-day intervals to accelerate azolla growth. Azolla was moved from the nursery pond and added to taro production plots at a seeding rate of 488 kg·m–2. Phosphoric acid was used in production plots to hasten coverage of the water surface by azolla. Ten days after azolla inoculation, production plots were covered and taro seed pieces were planted. Weed dry weights from conventional and azolla covered plots were recorded 91 days after taro planting. Taro corms were harvested 315 days after planting. Weed dry weight in azolla plots was 86% less than conventional plots. Azolla delayed taro maturity, causing a 41% reduction in marketable corm yield.

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Marvin P. Pritts and Mary Jo Kelly

Competition from weeds and an interplanted sudangrass [Sorghum bicolor (L.) Moensch, formerly S. sudanense (Piper) Stapf.] cover crop was allowed to occur in newly-planted strawberries (Fragaria ×ananassa Duch.) for varying lengths of time, and at different times during the growing season. Newly planted strawberries were most susceptible to weed and cover crop competition during the first 2 months after planting, as both runnering (stolon formation) and subsequent yield were impacted. In 1994-95, 1 month of weed competition in June reduced yield by 20%, whereas 2 months of weed competition reduced yield by 65%. However, 1 month of uncontrolled weed growth later in the growing season had little to no impact on yield, although weed biomass was much less then. Herbicide (napropamide) use alone was insufficient to prevent weed competition and yield reduction. In our study, yield was reduced 0.67 t·ha-1 or 5.5% for each 100 g·m-2 of weed biomass. The data suggest that it is critical for growers to minimize weed competition early in the planting year when weed growth is greatest. Since an interplanted sudangrass cover crop displaced a portion of the weeds, it could be seeded later in the year to provide some weed suppression without a negative impact on yield. Chemical names used: N, N, Diethyl-2-(1-naphthalenyloxy)-propionamide (napropamide); N-(phosphonomethyl)glycine (glyphosate).