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M.J. Else

In Integrated Pest Management (IPM), the costs of a control measure are compared to the potential for economic losses caused by a pest, with control measures being recommended only when expected costs of losses exceed costs of control. IPM models have been developed largely for insect pests, which multiply rapidly and for which timely population assessments are thus essential. Weed pests, on the other hand, multiply slowly. In the case of perennial crops, weeds may not reach populations sufficient to warrant control under conventional IPM criteria for many years. It is proposed that IPM concepts be adapted to weedy pests of perennial crops by creating models in which the long-term costs and consequences of both weeds and weed control measures are considered. These models would take into account expected increases in control costs and decreases in effectiveness of control measures over time and as a consequence consider some weeds to have effective thresholds at or near zero.

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Martin F. Quigley

Six durable but slow-to-establish groundcover species, and three fast-growing but short-lived groundcover species, were planted singly and in paired combinations under mature landscape trees to test for relative weed suppression. Installations were replicated on an urban site and a rural site, monitored for two growing seasons, and weeded periodically by hand. All weeds were dried and weighed, and subplot averages (160 observations) for each plant combination were tested by analysis of variance. Weeds were significantly fewer and smaller in the mixed species than in single species subplots. Weed biomass was also significantly less in monospecific groundcover subplots than in unplanted control plots. These results suggest that reduced maintenance cost (and input) for weed control, along with better initial coverage appeal of the paired plantings, may increase marketability of perennial groundcovers.

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Clauzell Stevens, Victor A. Khan, Theresa Okoronkwo, Ah-Yin Tang, Mack A. Wilson, John Lu and James E. Brown

Soil polarization for 98 days in 1985 resulted in a 91% reduction of weeds present in collard greens (Brassica oleracea acephafa L.) plots during 1986. Soil solarization was more effective in controlling weeds in collard green plots when compared to an application of Dacthal-75W herbicide in nonsolarized plots. Collard green plants grown in solarized soil showed an increase in yield and other growth responses. Soil samples from the rhizosphere of plants grown in solarized soil showed higher population levels of bacteria and thermotolerant fungi than from nonsolarized soil. There were significant negative responses in marketable yield and root growth of collard greens and in soil microflora in solarized soil in response to Dacthal-75W herbicide application. Chemical name used: dimethyltetrachloroterephthalate (Dacthal-75W).

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Bielinski M. Santos and James P. Gilreath

nutsedge and yellow nutsedge ( Cyperus esculentus ) are the most troublesome weeds to control in polyethylene-mulched vegetable crops and have the ability to emerge through the mulch, causing yield and quality losses ( Gilreath and Santos, 2005 ; Gilreath

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Robert H. Stamps and Daniel W. McColley

Five preemergence herbicides (prodiamine 0.5 G, prodiamine 65 WDG, dithiopyr 0.27 G, thiazopyr 2.5 G, and oxyfluorfen + pendimethalin 3 G) were evaluated for weed control and crop safety on 18 plants (Acer rubrum, Agapanthus africanus, Asparagus densiflorus, Camellia sasanqua, × Cupressocyparis leylandii, Cycas revoluta, Galphimia gracillis, Gelsemium sempervirens, Illicium parviflorum, Lantana camara, Loropetalum chinense, Myrtis communis, Ophiopogon jaburan, Plumbago, Quercus virginiana, Rhododendron, Viburnum suspensum, and Zamia floridana. Herbicides were applied at 1.7 kg a.i./ha, except for oxyfluorfern + pendimethalin, which was applied at 3.4 kg a.i./ha. Treatments were applied twice at 4-month intervals. Untreated and weed-free controls were used to determine herbicide effects on weeds and crops, respectively. All herbicide treatments reduced weed growth (dry-weight basis) and weeding times. Major weeds were dogfennel [Eupatorium capillifolium (Lam.) Small], southern crabgrass [Digitaria ciliaris (Retz.) Koeler], yellow woodsorrel (Oxalis stricta L.), tasselflower (Emilia spp.), and hairy crabweed [Fatoua villosa (Thumb.) Nakai]. Based on weed dry weights, overall weed control for the first 4 months was higher for diazopyr, thiazopyr, and prodiamine G than for the combination treatment. At 8 months, weed growth was similar for all herbicide treatments. The combination treatment was acutely phytotoxicity to more crops than the other treatments; however, phytotoxicity varied with crop, active ingredient, and formulation.

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Milton E. McGiffne Jr. and Chad Hutchinson

A 2-year field project was conducted in Thermal, Calif., on cowpea (Vigna unguiculata) mulch as an alternative weed control option in pepper (Capsicum annuum) production. Treatments included a bare ground production system with hand weeding, bare ground with no weeding, a cowpea mulch production system with hand weeding, and cowpea mulch with no weeding. Cowpea was seeded in July in 76-cm beds and irrigated with a buried drip line. In September, irrigation water was turned off to dry cowpea plants. The cowpea plants then were cut at the soil-line to form mulch. Pepper plants were transplanted into mulch and fertilized through the drip line. Every 2 weeks, the number of weeds emerged and pepper plant heights were recorded. In December, fruit production, pepper plant dry weight, and weed dry weight were recorded. Fewer weeds emerged in the cowpea mulch than the conventional bare ground system. At harvest, weed populations in nonweeded cowpea mulch were reduced 80% and 90% compared to nonweeded bare ground for 1997 and 1998, respectively. Weed dry weights in nonweeded treatments were 67% and 90% less than weed dry weights in nonweeded bare ground over the same period. Pepper plants in cowpea mulch produced 202% and 156% more dry weight than on bare ground in 1997 and 1998, respectively. Pepper plants in cowpea mulch produced more fruit weight than in bare ground with similar fruit size. Cowpea mulch provided season-long weed control without herbicides while promoting plant growth and fruit production.

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Craig A. Dilley, Gail R. Nonnecke and Nick E. Christians

The number of herbicides available for use in strawberry (Fragaria×ananassa Duch.) production is limited. Corn gluten hydrolysate (CGH) is a water-soluble extract of corn gluten meal (CGM), a by-product of corn wet-milling. Both CGH and CGM have been shown to inhibit root development of seedlings and can provide nitrogen (N). Four weed control and/or N- containing products were studied: CGH, CGM, urea (46N-0P-0K), and urea applied with DCPA at 8.4 kg·ha-1 a.i. Treatments were applied at N rates of 0, 9.8, 19.5, and 29.3 g·m-2. The 0 g·m-2 of N treatment served as the control. During the 1995 establishment season, all treatments were applied in June, July, and August. Treatments were applied in July and August during the 1996, 1997, and 1998 growing seasons. Dicot and monocot weed number and weed shoot dry weights were determined ≈30 days after both July and August treatments. Strawberry yield data were collected in June. Leaf N data were collected during the first week of July, before renovation. When CGH was applied in July, dicot weed number in August decreased in one of four years, but CGH never affected the number of monocot weeds. CGM application in July, reduced the number of dicot weeds found in plots in Aug. 1995 and 1998. Urea had no effect on dicot weed number from 1995 to 1997. However, in 1998, dicot weed number was reduced by as much as 79% as the rate of urea increased. In all study years, dicot weed number was reduced between 86% and 97%, for the high rate of DCPA + urea, compared with control plots. With few exceptions, rate of N had no effect on leaf N or yield. CGH exhibited limited potential as a natural weed control product; it reduced dicot weed number in one year, but did not affect the number of monocot weeds in any year. Strawberry yield in plots receiving CGH showed a linear increase in one year (1998), but did not show an increase in the other 2 years. Chemical name used: dimethyl tetrachloroterephthalate (DCPA)

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Stephen Reiners and Olga Wickerhauser

The possibility of using annual grain rye (Secale cereale L.) as a living mulch between rows of black plastic mulch was investigated. Rye was seeded immediately after plastic was laid and ≈30 days before transplanting bell pepper (Capsicum annuum L.) seedlings. Rye growth was controlled by postemergence herbicides and mowing or was left unmowed. These treatments were compared to a weedy control, cultivation, and standard preemergence herbicides for their effect on weed control and bell pepper yield. Within the rye treatments, the unmowed rye provided the best weed control and significantly decreased the number and size of weeds between crop rows. The rye cover crop also significantly reduced the yield of peppers. In both the mowed and unmowed rye treatments, total marketable yield was reduced 50% compared to clean cultivated and herbicide-treated plots. Further work is needed to minimize the competition between the living mulch and the crop.

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Dennis N. Portz and Gail R. Nonnecke

Continuous strawberry production on the same site causes proliferation of weeds and accumulation of pathogens in the soil and subsequently decreases strawberry yield ( LaMondia et al., 2002 ; Pritts and Handley, 1998 ). Continuous tillage to remove

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John Masiunas, Elizabeth Wahle, Laurel Barmore and Albert Morgan

A foam mulch system was developed that can be applied as an aqueous mixture of cotton and cellulose fibers, gums, starches, surfactants and saponins and dries to an one inch thick mat. This mulch may overcome the difficulty in applying and lack of persistence with natural mulches. Foam mulch also has the advantage of being able to be incorporated into the soil without requiring disposal like some plastic mulches. The objective of our study was to determine the effect of foam mulch and its color on weed control within the crop row and on yields of basil (Ocimum basilicum) and tomatoes (Lycopersicon esculentum). The foam mulch maintained its integrity for the entire growing season and provided weed control within the crop row comparable to black plastic mulch. The only weeds that emerged in the crop row were through holes in either the black or foam mulch. Foam mulch color did not affect weed control because regardless of color it did not allow light penetration andserved as a physical barrier impeding weed emergence. Basil shoot biomass was not affected by mulch treatment. Mulch color affected early, ripe fruit, and total yield of tomato. Tomato yields in the blue foam were greater than other treatments. Yields in the black foam mulch were similar to those in black plastic mulch. Further research is needed to characterize the effects of foam mulch on crop microenvironment. Currently foam mulch is being commercialized for use in the home landscape and other highvalue situations.