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Timothy N. Motis, Salvadore J. Locascio, and James P. Gilreath

Yellow nutsedge (Cyperus esculentus L.) interference with bell pepper (Capsicum annuum L.) has become an important concern because of the phase-out of methyl bromide as a soil fumigant. The critical period for yellow nutsedge control in pepper was determined in two adjacent experiments (removal and plant-back) conducted twice in separate fields each Spring and Fall 2000 in Gainesville, Fla. In the removal experiment, nutsedge was planted with pepper in all but the full-season (13 weeks) weed-free controls and removed at 1, 3, 5, and 7 weeks after pepper transplanting (WAPT). Full-season weedy control plots in the removal experiment were obtained by never removing nutsedge planted with pepper (0 WAPT). In the plant-back experiment, all but the full-season weed-free controls received nutsedge with nutsedge planted at 0 (full-season weedy control), 1, 3, 5, and 7 WAPT. Sprouted nutsedge tubers were planted at a density of 45 tubers/m2. Results indicated that a nutsedge-free period from 3 to 5 WAPT in spring and 1 to 7 WAPT would prevent >10% yield reductions of large and marketable peppers. Full-season nutsedge interference reduced pepper yields by >70%. When planted with pepper, nutsedge shoots grew taller than pepper plants with nutsedge heights at 5 WAPT up to two times greater in fall than spring. Results indicated that yellow nutsedge control practices should be initiated earlier and continue longer in fall than spring due to faster early-season nutsedge growth in fall than spring.

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Bielinski M. Santos, James P. Gilreath, and Timothy N. Motis

Two field trials were conducted in Bradenton, Fla., to determine the effect of reduced methyl bromide plus chloropicrin (MBr + Pic 67:33 v/v) rates applied under two types of virtually impermeable films (VIF) on nutsedges (Cyperus spp.) and stunt nematode (Tylenchorhynchus spp.) control, and `Capistrano' bell pepper (Capsicum annuum) crop yield. MBr + Pic rates were 0, 88, 175, and 350 lb/acre. Mulch types were low-density polyethylene (LDPE) mulch, Hytibar VIF, and Bromostop VIF. Results showed that there were no differences on weed and nematode control, and bell pepper fruit yield between the two types of VIF. Two exponential models characterized the nutsedge responses to MBr + Pic rates with LDPE mulch and VIF, with weed densities declining as MBr + Pic rates increased. Reducing MBr + Pic rates by one-half (175 lb/acre) under VIF provided similar nutsedge control as the full-rate (350 lb/acre) with LDPE mulch. Similar results were observed with stunt nematode, where the most effective control occurred with VIF. Bell pepper yield with LDPE mulch responded linearly to increased MBr + Pic rates. However, a logarithmic model described the response of pepper yields to the fumigant rates under VIF. The application rate of this fumigant could be effectively reduced to 25% of the commercial rate (350 lb/acre) under either VIF, without causing significant bell pepper yield losses.

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Bielinski M. Santos, James P. Gilreath, and Timothy N. Motis

Field trials were conducted from 1999 to 2003 to determine whether chloropicrin (Pic) stimulates nutsedge (Cyperus spp.) emergence through polyethylene mulch, and to examine at which Pic rate the stimulatory effect is maximized. Shank-injected Pic rates were 0, 50, 100, 150, 200, and 250 lb/acre. Application rates between 107 and 184 lb/acre of Pic stimulated nutsedge sprouting through polyethylene mulch by 60%, 400%, 58%, and 120% more than the nontreated control during four of the seasons. Rates above 250 lb/acre eliminated the stimulatory effect on nutsedge, reducing densities to the same levels as the nontreated control. The exact physiological mechanism of this stimulation is still unknown.

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James P. Gilreath, Bielinski M. Santos, and Timothy N. Motis

Field studies were conducted to compare the performance of several methyl bromide (MBr) alternative programs on sting nematode (Belonolaimus spp.) control and marketable yield of ‘Camarosa’ strawberry (Fragaria ×ananassa). The tested fumigation programs were 1) MBr + chloropicrin (Pic; 67:33 v/v) at 350 lb/acre, 2) Pic + metam sodium (MNa) at 300 lb/acre and 37.5 gal/acre, 3) 1,3-dichloropropene (1,3-D) + Pic at 35 gal/acre, 4) 1,3-D + Pic and dazomet at 35 gal/acre and 200 lb/acre, 5) propylene oxide at 45 gal/acre, 6) furfural + allyl isothiocyanate (AITC) at 600 lb/acre, 7) furfural and MNa at 56 and 50 gal/acre, 8) furfural + AITC at 400 lb/acre followed by four furfural applications of 6 gal/acre/injection, 9) furfural and MNa at 37 and 33 gal/acre followed by four furfural applications of 6 gal/acre/injection, 10) fosthiazate and Pic at 4.5 and 150 lb/acre, and 11) a nontreated control. The fumigation programs consisting of 1,3-D + Pic and dazomet, 1,3-D + Pic, Pic and MNa, and fosthiazate and Pic proved to be as valuable as the grower-standard MBr + Pic on strawberry plant vigor, sting nematode control, and early and total marketable yields.

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Bielinski M. Santos, James P. Gilreath, and Timothy N. Motis

Two field trials were conducted to determine the effect of reduced methyl bromide plus chloropicrin (MBr + Pic 67:33 v/v) rates applied under two types of virtually impermeable films (VIF) on nutsedges (Cyperus spp.) and stunt nematode (Tylenchorhynchus spp.) control, and bell pepper (Capsicum annuum) crop yield. A split-plot design with six replications was established, with MBr + Pic rates in the main plots and mulch types as subplots. MBr + Pic rates were 0, 88, 175, and 350 lb/acre. Mulch types were low-density polyethylene (LDPE) mulch, Hytibar VIF, and Bromostop VIF. Results showed that there were no differences on weed and nematode control, and bell pepper fruit yield between the two types of VIF. Two exponential models characterized the nutsedge responses to MBr + Pic rates with LDPE mulch and VIF, with weed densities declining as MBr + Pic rates increased. Reducing MBr + Pic rates by one-half (175 lb/acre) under VIF provided similar nutsedge control as the full-rate (350 lb/acre) with LDPE mulch. Similar results were observed with stunt nematode, where the most effective control occurred with VIF. Bell pepper yield with LDPE mulch responded linearly to increased MBr + Pic rates. However, a logarithmic model described the response of pepper yields to the fumigant rates under VIF. The application rate of this fumigant could be effectively reduced to 25% of the commercial rate (350 lb/acre) under either VIF, without causing significant bell pepper yield losses.

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Bielinski M. Santos, James P. Gilreath, Timothy N. Motis, Marcel von Hulten, and Myriam N. Siham

Field trials were conducted to: 1) determine the effect of mulch types and applied concentrations of 1,3-dichloropropene + chloropicrin (1,3-D + Pic) on fumigant retention; and 2) examine the influence of mulch films and 1,3-D + Pic concentrations on purple nutsedge (Cyperus rotundus) control. 1,3-D + Pic concentrations were 0, 600, 1000, and 1400 ppm, and mulch types were white on black high-density polyethylene mulch (HDPE), white on black virtually impermeable film (VIF-WB), silver on white metalized mulch, and green VIF (VIF-G). Regardless of the initial 1,3-D + Pic concentrations and mulch types, fumigant retention exponentially decreased over time. When 1400 ppm of 1,3-D + Pic were injected into the soil, 1,3-D + Pic dissipation reached 200 ppm at 3.2, 2.9, 2.2, and 1.5 days after treatment (DAT) under VIF-G, VIF-WB, metalized, and HDPE mulches, respectively. At 5 weeks after treatment (WAT), HDPE mulch had the highest purple nutsedge densities among all films. The treatments covered with VIF-G had purple nutsedge densities <5 plants/ft2, regardless of the applied fumigant concentration, while VIF-WB and metalized mulch reached this weed density with 696 ppm of the fumigant. In contrast, 1186 ppm of 1,3-D + Pic were needed to reach this weed density with HDPE mulch. Correlation analysis showed that mulch fumigant retention readings at 3 DAT effectively predict purple nutsedge densities at 5 WAT (r ≤ –0.94). These findings proved that 1,3-D + Pic activity on purple nutsedge can be improved with the use of more retentive films, which cause longer fumigant retention, thus improving efficacy. Growers might elect reducing 1,3-D + Pic rates to compensate for the relatively higher cost of fumigant-retentive mulches, without losing herbicidal activity.

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James P. Gilreath, Timothy N. Motis, Bielinski M. Santos, Joseph W. Noling, Salvadore J. Locascio, and Daniel O. Chellemi

Field studies were conducted during four consecutive tomato (Lycopersicon esculentum) -cucumber (Cucumis sativus) rotations to examine the longterm residual effects of tomato methyl bromide (MBr) alternatives on soilborne pests in double-cropped cucumber. Four treatments were established in tomato fields: a) nontreated control; b) MBr + chloropicrin (Pic) (67:33 by weight) at a rate of 350 lb/acre; c) tank-mixed pebulate + napropamide at 4 and 2 lb/acre, respectively, followed by 1,3-dichloropropene (1,3-D) + Pic (83:17 by volume) at 40 gal/acre; and d) napropamide at 2 lb/acre followed by soil solarization for 7 to 8 weeks. Each of the following seasons, cucumber was planted in the same tomato plots without removing mulch films. For nutsedge [purple nutsedge (Cyperus rotundus) and yellow nutsedge (C. esculentus)] densities, napropamide followed by solarization plots had equal control (≤15 plants/m2) as MBr + Pic during all four cropping seasons. However, nematode control with solarization was inconsistent. Marketable yield data proved that fumigation in tomato fields with either MBr + Pic or pebulate + napropamide followed by 1,3-D + Pic had a long-term effect on double-cropped cucumber.