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- Author or Editor: John B. Masiunas x
Experiments determined the effectiveness of the bipyridinium herbicides paraquat and diquat and of the diphenyl ether herbicide lactofen to desiccate onion (Allium cepa L.) shoots without affecting bulb quality and storage life. Paraquat, applied once, desiccated 80% of onion shoots within 3 days. Diquat desiccated ≈ 60% of onion shoots within 10 days of treatment. Lactofen caused slight necrosis but did not adequately desiccate onion shoots. Diquat and paraquat reduced sprouting of `Red Wethersfield' more than of `White Portugal'. Chemical names used: 6,7-dihydrodipyrido[l,2 2',1'-c] pyrazinediium ion (diquat); (±)2-ethoxy-l-methyl-2-oxoethy1 5-[2chloro-4-(trifluoromethyl)phenoxyl] -2-nitrobenzoate (lactofen); 1,1'-dimethyl-4,4'-bipyridinium ion (paraquat).
In the past few years, leaf trichomes of tomato (Lycopersicon esculentum) and related wild species have received considerable attention due to their potential role in insect resistance. However, the last complete characterization of all 7 trichome types was by Luckwill in 1943, before the advent of scanning electron microscopy (SEM). Since that time, the taxonomic designations of the genus have been modified, expanding from 6 species to 9. The purpose of this work was to use SEM to observe and record trichome types from the presently accepted Lycopersicon species, and determin etheir species specific distribution. Studies have shown variation within trichome type due to number of cells per trichome, and base and surface characteristics.
A three-year study determined the effect of winter cover crops on weeds and vegetable crops in a vegetable production system. Winter rye and hairy vetch were interseeded in the fall of 1990, 1991 and 1992 at 112 and 34-kg ha-1, respectively. The cover crops were killed by ether applying glyphosate at 1.1 kg a.i ha-1 [reduced tillage(RT)] or mowing and disking the cover crop (Disked). The conventional tillage (CT) was bare ground with a preplant incorporated application of 0.84 kg a.i ha-1 of trifluralin. During the three years, the greatest snap bean yields were in the CT; total yields of cabbage and tomato varied between the years; and were not affected by management systems. Weed control was similar in the RT and CT treatments during the three years. Disked cover crop treatments tended to have greater weed numbers than either RT or CT treatments.
Black polyethylene mulch and weed control strategies were evaluated for potential use by small acreage herb producers. In both 1988 and 1989, the mulch greatly increased fresh and dry weight yields of basil (Ocimum basilicum L.) and rosemary (Rosmarinus officinalis L.). Parsley (Petroselinum crispum Nym.) yield did not respond to the mulch. Preplant application of napropamide provided weed control for 2 weeks, but was subsequently not effective on a heavy infestation of purslane (Portulaca oleracea L.). Hand-hoed and glyphosate-treated plots (both with and without plastic) produced equivalent yields. Chemical names used: N, N -diethyl-2(1-napthalenoxy)-propanamide (napropamide); N- (phosphonomethyl) glycine (glyphosate).
Winter-killed cover crops may protect the soil surface from erosion and reduce herbicide use in an early planted crop such as pea (Pisum sativum). Our objective was to determine the potential of winter-killed cover crops in a snap pea production system. White mustard (Brassica hirta) produced the most residue in the fall but retained only 37% of that residue into the spring. Barley (Hordeum vulgare) and oats (Avena sativa) produced less fall residue but had more residue and ground cover in the spring. Greater ground cover in the spring facilitated higher soil moisture, contributing to higher weed numbers and weight and lower pea yields for oat and barley compared with a bare ground treatment. White mustard had weed populations and pea yields similar to the bare ground treatment. Within the weed-free subplot, no differences in pea yields existed among cover crop treatments, indicating no direct interference with pea growth by the residues. In greenhouse experiments, field-grown oat and barley residue suppressed greater than 50% of the germination of common lambsquarters (Chenopodium album) and shepherd's-purse (Capsella bursapastoris), while in the field none of the cover crop provided better weed control than the fallow.
Winter-killed oats (Avena sativa) may have potential for use to suppress weeds in early seeded crops such as pea (Pisum sativum). Residue biomass and surface coverage are generally correlated with weed suppression. Oat residues also contain allelochemicals. Our objective was to determine if oat cultivars vary in residue production and allelopathy. Differences between oat cultivars were observed in residue production, and for effects on emergence of common lambsquarters (Chenopodium album) and shepherd's-purse (Capsella bursa-pastoris) in the greenhouse, and germination of pea and common lambsquarters in an infusion assay. Two of the oat cultivars producing the greatest biomass, `Blaze' (in the field) and `Classic' (in the greenhouse), interfered minimally with pea germination and were among the best cultivars in inhibiting common lambsquarters and shepherd's-purse. `Blaze' also greatly inhibited common lambsquarters germination in the infusion assay that measured allelopathy. Thus, `Blaze' and `Classic' possess suitable characteristics for use as a cover crop preceding peas.
Studies established the critical period for eastern black nightshade (nightshade) (Solanum ptycanthum Dun.) competition in pea (Pisum sativum L.) and determined the effect of N fertility on pea and nightshade growth. In 1992, pea yields were most affected when nightshade was established at planting and remained for 4 or 6 weeks, while in 1993, competition for 6 weeks caused the greatest reduction in pea yields. In a sand culture study, pea biomass and N content were not affected by three N levels (2.1, 21, and 210 mg·L-1). Nightshade plants were five to six times larger in the highest N treatment than at lower N levels. Nitrogen content of nightshade was 0.76% at 2.1 ppm N and 3.22% at 210 ppm N. Choosing soils with low N levels or reducing the N rates used in pea may decrease nightshade interference and berry contamination of pea.
Greenhouse hydroponics and field experiments were conducted to determine how nitrogen (N) fertilizer treatments affect tomato (Lycopersicon esculentum Mill.) growth, yield, and partitioning of N in an effort to develop more sustainable fertilization strategies. In a hydroponics study, after 4 weeks in nitrate treatments, shoot dry weight was five times greater at 10.0 than at 0.2 mm nitrate. An exponential growth model was strongly correlated with tomato root growth at all but 0.2 mm nitrate and shoot growth in 10 mm nitrate. Root dry weight was only 15% of shoot biomass. In field studies with different population densities and N rates, height in the 4.2 plants/m2 was similar, but shoot weight was less than in the 3.2 plants/m2. At 12 weeks after planting, shoot fresh weight averaged 3.59 and 2.67 kg/plant in treatments with 3.2 and 4.2 plants/m2, respectively. In 1998, final tomato yield did not respond to N rate. In 1999, there was a substantial increase in fruit yield when plants were fertilized with 168 kg·ha-1 N but little change in yield with additional N. Nitrogen content of the leaves and the portion of N from applied fertilizer decreased as the plants grew, and as N was remobilized for fruit production. Both studies indicate that decreasing N as a way to reduce N loss to the environment would also reduce tomato growth.
Two experiments were conducted to evaluate processing pumpkin and processing squash tolerance to preemergence herbicides. The experiments were randomized complete block designs with three or four replications. The herbicides were applied after seeding the crop using a CO2-pressurized sprayer delivering 233 L/ha. We evaluated clomazone alone, and in combination with either halosulfuron or sulfentrazone. The first experiment was conducted in Morton, Ill., using `Libby's Select' processing pumpkin (Cucurbita moschata). None of the treatments caused any significant pumpkin phytotoxicity. On 7 July all treatments reduced the number of grass weeds compared to the untreated control. There were no differences in grass control between the herbicide treatments. Broadleaf control was best in sulfentrazone at 0.56 kg/ha or clomazone + halosulfuron at 0.56 + 0.13 kg/ha and worst in the untreated control. Weed control decreased by the 29 July rating; grass and broadleaf weed control was unacceptable in all treatments due to infestation with perennial weeds. Sulfentrazone alone or with clomazone was safe for use on pumpkins in heavier soils. The second experiment, conducted in Champaign, Ill., used `NK530' processing squash (Cucurbita maxima). None of the treatments caused any squash phytotoxicity. The best control on 14 July was with combinations of clomazone and sulfentrazone. On 10 Aug., all herbicide treatments were similar in their control of broadleaf weeds. Sulfentrazone and halosulfuron do not injure processing pumpkin or squash when applied either alone or in combination with clomazone.
In some years, the emerging leaves of white oak and, to a lesser extent, of red oak in the Midwest have developed abnormally. This abnormality is referred to as leaf tatters. Reports to state foresters and Extension specialists associated tatters with herbicide applications. In 2005, white and red oak seedlings were treated in a spray chamber delivering 187 L/ha, with seven herbicides at three concentrations, 1/4×, 1/10×, and 1/100× of the standard field use rate. These herbicides and their standard field use rate of the active ingredients included atrazine at 2.3 kg/ha and chloroacetanilide herbicides: acetochlor at 2.0 kg/ha, metolachlor at 2.1 kg/ha, and dimethenamid at 0.8 kg/ha alone or mixed with atrazine at 2.3 kg/ha, at the leaves unfolding stage. After treatment, oaks were placed outdoors in a randomized complete-block design. Leaf symptoms in our study were similar to those seen in the landscape. In chloroacetanilide-treated white and red oak seedlings, browning of interveinal leaf tissues was noticed 5–6 days after treatment. The dried leaf tissues then dropped off, leaving only the main vein with little interveinal leaf area. In few seedlings treated with atrazine, the leaf tissues turned yellow to brown, while in few others, interveinal tissue damage was restricted, leaving small holes in the leaf. When chloroacetanilide herbicides were applied with atrazine, the dominant symptoms were those of leaf tatters. A few seedlings treated with dimethenamid and atrazine had predominately atrazine symptoms. Although new growth later in the season was not injured, the leaves with tatters remained on the plant until the end of the growing season. The study will be repeated in 2006.