The response of pepper varieties to Egyptian broomrape and nodding broomrape was characterized in comparison with tomatoes grown in pots and in aqueous solution, according to two criteria: 1. germination of the parasite's seeds in the presence of the host roots; and 2. the number of parasites per host plant. More than 50% of Egyptian broomrape seeds germinated in the presence of all pepper variety roots except the sweet pepper Maor. However, only a few attached and developed. The two paprika varieties Lehava and Shani were hosts to more parasites than the sweet pepper varieties, and showed as many as 15 parasites per host plant. In contrast, tomato roots induced less then 10% seed germination but were highly susceptible to the parasite (30 parasites per host plant). Damage caused to pepper foliage and fruit was not significant, compared to the heavy damage caused to tomato. Pepper roots stimulated germination of 22 to 26% of nodding broomrape seeds but without the formation of parasitic attachments, whereas tomato roots stimulated germination of less than 10% of the seeds but the plants were then heavily damaged by the parasite. Interplanting of tomato with pepper in nutrient solution did not change the amount of Egyptian broomrape parasites on pepper, hut a fourfold increase in the number of nodding broomrape was observed on tomato roots, compared to the number of parasites on tomato roots when planted without pepper.

Laboratory experiments were carried out under aseptic conditions to study the effect of nitrogen applied as ammonium nitrate at 0, 20,40,60,80 and 100 ppm (wt per vol) in either distilled H2O or modified Hoagland's solution on germination and radicle length of branched broomrape in association with growing seedlings of different crops. As nitrogen rate increased, seed germination and radicle length of branched broomrape decreased linearly in flax, lentil, pepper, tomato, and wheat in modified Hoagland's solution. Similar responses to nitrogen application were found with distilled water. The parasite's seed germination was considerably lower in the media with wheat than with other crops, and lower still in the absence of crop seedings.

Herbicides were evaluated alone, in combinations, or as sequential treatments on direct-seeded tomato each year from 1982 through 1984. Diphenamid at 4.5 kg ai/ha or napropamide at 1.1 to 2.2 kg ai/ha alone are registered but frequently do not control weeds adequately, particularly when yellow nutsedge and/or Florida pusley is common. Combinations or sequential treatments are necessary to overcome these weed problems in cropping systems. Metolachlor at 0.8 to 3.4 kg ai/ha injured direct-seeded tomato in proportion to the rate applied. Pendimethalin at 0.6 kg ai/ha also injured tomatoes. Fluazifop at 0.3 to 0.6 kg ae/ha and sethoxydim at 0.2 to 0.5 kg ai/ha effectively controlled annual grasses without injuring tomato seedlings. These herbicides would reduce competition and would increase harvesting efficiency where grass weeds are a problem.

Tolerance of tomato cultivars to diphenyl ether herbicides applied postemergence was determined in greenhouse and field experiments. In greenhouse experiments, tomato cultivar tolerance differed, but acifluorfen injured all genotypes. ‘Carmen’, ‘PetoPride 2’ and ‘Heinz 1350’ tolerated acifluorfen while ‘Advantage’, and ‘Red Plum’ were susceptible. Growth habit and tolerance to 1.1 kg ae/ha acifluorfen was significantly correlated (r2 = 0.24). Field-planted tomato cultivars' tolerance to diphenyl ether herbicides applied postemergence differed. Heinz 1350 and ‘Veeroma’ tolerated diphenyl ethers, while Advantage and Red Plum were susceptible. Potency of diphenyl ethers also varied with oxyfluorfen the most injurious and acifluorfen and fomesafen the least injurious.

A surface-roller wiper that rotates by direct contact with the ground was developed to apply herbicides to broadleaf weeds in turf. The free-wheeling roller 1.8 m wide consists of a 30-cm diam PVC pipe covered with a 1.3-cm thick carpet The herbicide is delivered by gravity to the carpet through a pipe manifold. Broadleaf weeds in turf were effectively controlled with 2,4-D roller applied once as a 2% solution (2.2 kg ae/ha) or twice as a 1% solution (1.1 kg/ha). Herbicide drift was avoided with the roller applicator as indicated by lack of injury to tomato plants downwind from 2,4-D roller applied as a 5% (5.6 kg/ha) solution.

The study was undertaken to compare the level of total phenolics and the allelopathic potential of Pluchea lanceolata in soils cultivated once or twice a year. Thirty-five cultivated fields were sampled from seven sites in three different seasons. The leaf area, leaf weight, height, and density of P. lanceolata plants were measured. Leaves of P. lanceolata were analyzed for nine chemical characteristics: leaf ash, total phenolics, phosphate, Cu, Zn, Na, K, Mg, and Ca. Weed-infested topsoil and subsoil were analyzed for pH, electrical conductivity, organic carbon, chloride, bicarbonate, total carbonate, phosphate, total phenolics, Zn, Na, K, Mg, and Ca. Fields cultivated twice a year were designated as Group I, while those cultivated once a year were designated as Group II. Biotic and chemical characteristics of plants of Group I and II were not different. Topsoil and subsoil of Group II had higher values for Ca, while topsoil of Group I had higher values for total phenolics. The higher phenolic content of Group I topsoil was probably due to greater incorporation of weed plant parts into the soils as compared to Group II fields. Seedling growth of crop plants such as radish, carrot, maize, mustard, tomato, turnip, and wheat was affected more by soil from P. lanceolata-infested fields that were cultivated twice a year than those cultivated only once. A correlation between higher total phenolic content of P. lanceolata-infested topsoil with two cultivations, and growth response of crop plants was recorded.

Additive series experiments were conducted under greenhouse conditions to determine the effect of season-long interference of different initial population densities of purple nutsedge on the shoot dry weight and fruit yield of tomato and bell pepper. Purple nutsedge densities up to 200 plants/m2 linearly reduced shoot dry weight at flowering and fruit yield of both crops as weed density increased. Both variables were directly correlated, and for each percentage unit of tomato shoot dry weight loss at flowering, fruit yield was reduced 1.24 units, whereas for bell pepper this relationship was 1 to 2.01. Total shoot and tuber biomass of purple nutsedge increased as density increased. The presence of either crop caused a decline in the total shoot dry weight accumulation of purple nutsedge, with tomato producing a higher degree of loss than bell pepper to the weed. Fruit yield losses due to purple nutsedge interference reached 44% for tomato and 32% for bell pepper.

Black nightshade was selectively controlled along with other annual weeds in direct-seeded tomatoes by BAY SMY 1500 applied preemergence. BAY SMY 1500 was also found selective for transplanted tomatoes when applied prior to transplanting or soon after planting prior to black nightshade emergence. Black nightshade control and crop selectivity were obtained with BAY SMY 1500 at 0.75 and 1.25 kg ai ha-1 applied on sandy loam and clay loam soils, respectively.

Studies quantifying weed seed production as a function of weed density are expensive and difficult, and lack of these data is a common limitation in modeling weed population dynamics over time. Observed empirical and theoretical relationships between crop yield loss curves and weed seed production curves led us to the hypothesis that there should be a strong relationship between the shapes of these two curves. Data from literature sources were evaluated to test this hypothesis for hyperbolic curves and to determine if the data describing the crop yield loss caused by weeds could provide estimates of the shape parameter of a hyperbolic equation for describing density dependence in weed reproduction. For each of 162 data sets, a shape parameter (N50) and a scale parameter (U) were estimated for an increasing hyperbolic model both for absolute crop yield loss as a function of weed density (N50YL, UYL) and for weed yield (either total biomass yield or seed yield) as a function of weed density (N50WY, UWY). N50YL was strongly correlated with N50WY across all data sets, with an apparent 1:1 relationship between the two. This relationship suggests that the shape parameter of the yield loss model may substitute for the shape parameter of a hyperbolic model describing the density-dependence of weed seed production. This substitution will be most useful in weed population modeling situations where data describing crop yield loss as a function of weed density are already available, but data describing weed seed production as a function of weed density are not available.

Field experiments were conducted in 1998 and 1999 at Five Points, CA, in the San Joaquin Valley under irrigated conditions to study competition between four commonly grown tomato cultivars and velvetleaf and to identify cultivar characteristics associated with greater tolerance to velvetleaf. The effect of velvetleaf competition varied with both year and tomato cultivar. When grown with 5 velvetleaf plants m−1 of row, marketable yield of tomato was reduced 8% in 1998 and 60% in 1999 for cultivar H8892 and 58% in 1998 and 80% in 1999 for cultivar H9661, compared to cultivars grown in monoculture. Across velvetleaf densities, height of tomato cultivars was not reduced compared to that of cultivars grown in monoculture. However in 1999, canopy width of tomato cultivars grown with velvetleaf was less than that of cultivars grown in monoculture. At early stages of growth, the leaf area index of tomato cultivars grown with velvetleaf was less than that of cultivars grown in monoculture. Crop growth rate and aboveground dry biomass of tomato cultivars grown with velvetleaf were generally less than those of cultivars grown in monoculture. Yield loss at high weed density was similar among cultivars, whereas yield loss at low weed density varied among cultivars. Cultivar tolerance to velvetleaf varied with year. However, cultivar H8892 had low yield loss and cultivar H9661 high yield loss at low weed density in 1998 and 1999. For cultivar H8892, leaf area expansion rate was also among the greatest for both years.

Isoxaflutole, a preemergence herbicide for use in corn, causes bleaching of plant tissue and plant death at low rates. A concern regarding widespread use of isoxaflutole is the unintentional exposure of high-value, minor hectareage crops that may be sensitive. Unintentional exposure could occur because of carryover from a previous application, spray drift, or contamination of irrigation water. The objective of this study was to determine the potential for injury to nine minor hectareage Michigan crops. Crops evaluated were: adzuki bean, alfalfa, carrot, cucumber, dry bean (navy and black beans), onion, sugar beet, and tomato. Experiments were conducted in the greenhouse to evaluate injury from low rates of isoxaflutole applied to soil to simulate carryover as well as low concentrations of isoxaflutole in 2.54 cm of irrigation water applied over the course of 1 h to 15-cm-tall plants. Isoxaflutole rates and concentrations that cause 20% injury (I20) were calculated using Seefeldt's log-logistic dose–response model. Regardless of application type, onion was always the least sensitive plant to isoxaflutole (I20 = 37 g/ha applied to soil and 194 μg/L in irrigation water), whereas navy bean and black bean were the most sensitive (I20 = 9 g/ha applied to soil and 5 μg/ L in irrigation water). The remaining plants exhibited intermediate sensitivity. All of the rates that resulted in injury were substantially less than the rates used for weed control in corn. Carryover from isoxaflutole applications in corn production may require plant back restrictions for certain sensitive crops.

Rice by-products were evaluated in the greenhouse for herbicidal activity on various weeds and crops. Rice by-products and corn gluten meal (CG) were applied at 0, 125, 250, 500, and 750 g m−2 preemergence (PRE) and preplant incorporated (PPI). The efficacy of rice by-products and CG in reducing weed emergence and shoot weight of broadleaf species was in the order of medium-grain fatty rice bran (MF) > long-grain fatty rice bran (LF) > CG > defatted rice bran (DF) > long-grain hull (LH) > medium-grain hull (MH). For reducing grass emergence, MF = CG > LF > DF > LH > MH, and for shoot weight reduction, CG > MF > LF > LH > DF = MH. Palmer amaranth and ivyleaf morningglory were the most susceptible weeds (91 and 82%) followed by sicklepod, hemp sesbania, and prickly sida (65 to 70%). Velvetleaf was the most tolerant broadleaf weed. Grasses were not as susceptible to rice bran as broadleaf weeds. In general, MF was the best material for reducing weed emergence and its efficacy was not affected by application method. Cotton and corn were the most tolerant direct-seeded crops to MF (6% reduction in plant stand), and soybean, Italian ryegrass, tomato, and rice had intermediate tolerances (30 to 86% stand reduction). Mustard, cucumber, and lettuce were the most susceptible crops (71 to 98% reduction in plant survival). The minimum effective rate was 250 g m−2 MF PPI or PRE.