Management of Meloidogyne incognita with Chemicals and Cultivars in Cotton in a Semi-Arid Environment.

Management of Meloidogyne incognita (root-knot nematode) in cotton in the United States was substantially affected by the decision to stop production of aldicarb by its principle manufacturer in 2011. The remaining commercially available tools to manage M. incognita included soil fumigation, nematicide seed treatments, postemergence nematicide application, and cultivars partially resistant to M. incognita. Small plot field studies were conducted on a total of nine sites from 2011-2013 to examine the effects of each of these tools alone or in combinations, on early season galling, late-season nematode density in soil, yield, and value ($/ha = lint value minus chemical costs/ha). The use of a partially resistant cultivar resulted in fewer galls/root system at 35 d after planting in eight of nine tests, lower root-knot nematode density late in the growing season for all test sites, higher lint yield in eight of nine sites, and higher value/ha in six of nine sites. Galls per root were reduced by aldicarb in three of nine sites and by 1,3-dichloropropene (1,3-D) in two of eight sites, relative to the nontreated control (no insecticide or nematicide treatment). Soil fumigation reduced M. incognita density late in the season in three of nine sites. Value/ha was not affected by chemical treatment in four of nine sites, but there was a cultivar × chemical interaction in four of nine sites. When value/ha was affected by chemical treatment, the nontreated control had a similar value to the treatment with the highest value/ha in seven of eight cultivar-site combinations. The next "best" value/ha were associated with seed treatment insecticide (STI) + oxamyl and aldicarb (similar value to the highest value/ha in six of eight cultivar-site combinations). The lowest valued treatment was STI + 1,3-D. In a semi-arid region, where rainfall was low during the spring for all three years, cultivars with partial resistance to M. incognita was the most profitable method of managing root-knot nematode in cotton.

The relationship between environmental variables and response of cotton to nematicides.

Nematicide/irrigation rate trials were conducted in Texas (TX) in 2009 and 2010 in cotton grown at three irrigation rates, where irrigation rate (base (B), B - 33%, B + 33%) was the main plot and treatment (untreated check, aldicarb, and nematicide seed treatment (NST) and NST + aldicarb) were the subplots. Aldicarb improved cotton lint yield with the base (medium) irrigation rate over the untreated check, but not at the B - 33% and B + 33% irrigation rates. In a second evaluation, 20 tests conducted over 7 yr at the same field in TX and 12 tests conducted over 6 yr at the same field in Alabama (AL) were examined for impact of environmental variables (EV) on the response to NST (containing thiodicarb or abamectin), aldicarb, a nontreated check (CK), insecticide seed treatment (TX only), and a combination of NST + aldicarb + oxamyl (NST/A/O, AL only) on root galls (TX only), early season nematode eggs (AL only), and yield (both sites). Galls/root system were lower with aldicarb-treated plots, than for the CK- or NST-treated plots. As water (irrigation plus rain) in May increased, galls/root system increased for CK or insecticide-only-treated plots, and decreased for NST- and aldicarb-treated plots, suggesting efficacy of nematicides was strongly improved by adequate soil moisture. Nematode reproduction was not affected by EV in either location, though yield was negatively affected by root-knot nematode eggs in AL at 60 d. Yield in both AL and TX was negatively related to temperature parameters and positively related to water parameters. With the addition of EV in TX, chemical treatments went from not significantly different in the absence of EV to aldicarb-treated plots having higher yields than nonnematicide-treated plots in the presence of EV. In AL, NST/A/O-treated plots yielded similar to aldicarb and better than CK or NST in the absence of EV and had significantly higher yields than all other treatments in the presence of most EV.

Effects of Crop Rotation, Cultivar, and Irrigation and Nitrogen Rate on Verticillium Wilt in Cotton.

A field experiment was conducted under center-pivot irrigation in four wedges, with one wedge in continuous cotton (CC) and three wedges in a rotation (ROT) with 2 years cotton and 1 year in sorghum. Three irrigation rates (base = 1.0B, 1.5B, and 0.5B) were applied during 2007 to 2009 on a susceptible (ST) and partially resistant (PR) cultivar. Nitrogen applied during the season was proportional to irrigation rate. In the ROT wedges, 0.5B, 1.0B, and 1.5B irrigation and nitrogen rates averaged 1, 3, and 9% incidence of wilt, respectively. Disease incidence in the CC wedge averaged 6, 18, and 34% wilt incidence for 0.5B, 1.0B, and 1.5B irrigation and nitrogen rates. In the ROT wedges, the ST cultivar returned $143/ha more than the PR cultivars at the 0.5B irrigation and nitrogen rate whereas, at the 1.0B and 1.5B rates, the PR cultivars averaged $121 and $350/ha more than the ST cultivar. There was no significant irrigation and nitrogen or cultivar effect in the CC wedge on net value; however, trends were similar to the ROT wedge. Overall, ROT returned $285/ha more than CC, PR cultivars returned $123/ha more than the ST cultivar, and 1.0B returned $271 and $296/ha more than 0.5B and 1.5B rates, respectively. Microsclerotia density of V. dahliae averaged 2/cm3 of soil in the ROT wedges and 23/cm3 of soil in the CC wedge. Crop rotation, avoiding excessive irrigation, and using a partially resistant cultivar all reduced incidence of Verticillium wilt and improved net returns.

Irrigation Timing Impacts the Efficacy of Foliar-Applied Fungicides Toward Foliar and Soilborne Pathogens of Peanut.

Fungicides not reaching target organisms result in decreased disease control. In the southeastern United States, foliar-applied fungicides are routinely used to manage peanut (Arachis hypogaea) diseases. Irrigation is often applied to wash fungicides from treated foliage to obtain maximum control of diseases caused by soilborne pathogens. Administering irrigation before fungicide residues have dried may adversely impact foliar disease control. A microplot study was conducted in 2003, 2004, and 2005 to evaluate the redistribution of azoxystrobin, tebuconazole, and flutolanil plus chlorothalonil following different irrigation timings. Standard fungicide regimes were subjected to 1.3-cm of irrigation 0, 6, 12, 24, 48, or 96 h after application, and a nonirrigated control was included. Microplots not receiving irrigation were covered while irrigation treatments were administered. Irrigation timing was significant for the number of early leaf spot (Cercospora arachidicola) lesions per leaf. Leaf spot was more severe when irrigation was administered immediately following fungicide applications, and was significantly reduced with a 6- and 12-h delay prior to an irrigation event, whereas maximum control was obtained when irrigation was delayed for 24 h or later. To further quantify fungicide residue distribution, Sclerotium rolfsii was used to bioassay foliage and pods. Lesion development on leaflets, which was greater for earlier irrigation timings, did not differ for the 12-h and later timings and was generally similar to the nonirrigated controls. Pod colonization for all fungicides increased according to a quadratic function of irrigation timing, with the least colonization occurring at the 0-h timing. Colonization of pods treated with azoxystrobin was similar for all irrigation timings; whereas, suppression was greatest for tebuconazole at earlier irrigation timings. This study demonstrates that irrigation can be used to redistribute fungicides applied to peanut foliage to improve control of soilborne pathogens but administering irrigation within 24 h may decrease leaf spot control.

Field Evaluations of Leaf Spot Resistance and Yield in Peanut Genotypes in the United States and Bolivia.

Field experiments were conducted in 2002 to 2006 to characterize yield potential and disease resistance in the Bolivian landrace peanut (Arachis hypogaea) cv. Bayo Grande, and breeding lines developed from crosses of Bayo Grande and U.S. cv. Florida MDR-98. Diseases of interest included early leaf spot, caused by the fungus Cercospora arachidicola, and late leaf spot, caused by the fungus Cercosporidium personatum. Bayo Grande, MDR-98, and three breeding lines, along with U.S. cvs. C-99R and Georgia Green, were included in split-plot field experiments in six locations across the United States and Bolivia. Whole-plot treatments consisted of two tebuconazole applications and a nontreated control. Genotypes were the subplot treatments. Area under the disease progress curve (AUDPC) for percent defoliation due to leaf spot was lower for Bayo Grande and all breeding lines than for Georgia Green at all U.S. locations across years. AUDPC for disease incidence from one U.S. location indicated similar results. Severity of leaf spot epidemics and relative effects of the genotypes were less consistent in the Bolivian experiments. In Bolivia, there were no indications of greater levels of disease resistance in any of the breeding lines than in Bayo Grande. In the United States, yields of Bayo Grande and the breeding lines were greater than those of the other genotypes in 1 of 2 years. In Bolivia, low disease intensity resulted in the highest yields in Georgia Green, while high disease intensity resulted in comparable yields among the breeding lines, MDR-98, and C-99R. Leaf spot suppression by tebuconazole was greater in Bolivia than in the United States. This result indicates a possible higher level of fungicide resistance in the U.S. population of leaf spot pathogens. Overall, data from this study suggest that Bayo Grande and the breeding lines may be desirable germplasm for U.S. and Bolivian breeding programs or production.

Pigeon peas as a supplement for lactating dairy cows fed corn silage-based diets.

Holstein rumen-cannulated cows [n=7; initial body weight (BW) 640.56±71.43 kg] were fed a corn silage basal diet with 1 of 3 concentrates (C=control; P10=10% pigeon peas; P20=20% pigeon peas). Cows were randomly assigned to treatments in a replicated 3×3 Latin square and individually fed using Calan gates. Each experimental period was 21 d with 7 d for adaption and 14 d for sample collection. Ruminal fluid samples were taken the last day of each experimental period and analyzed for pH, ammonia, long-chain fatty acids, and volatile fatty acids (VFA). Consecutive a.m. and p.m. milk samples were taken during the last 2 wk of the 21-d period and analyzed for fat, protein, long-chain fatty acids, and somatic cell count. Dry matter intake (kg/d) was reduced during the second period and was greater for P10 diets. Milk protein was greater for cows fed P20 compared with P10. Energy-corrected milk was greater for cows fed the control diet compared with P10. Treatment had no effect on milk yield. Ruminal fluid pH decreased over sampling times; however, pH remained at or above 5.5. Diets did not affect ruminal fluid pH; however, pH was different for sampling periods. Ruminal ammonia decreased until 8h postfeeding at which time it peaked consistent with changes in ammonia concentrations that usually peak 3 to 5h postfeeding on diets high in plant proteins. Dietary treatments altered ruminal fluid VFA with reduced concentrations of acetate and greater concentrations of propionate for control diet, resulting in reduced acetate:propionate ratio. Isobutyrate exhibited an hour by treatment interaction, in which isobutyrate decreased until 8h postfeeding and then tended to be greater for P10 than for other treatments. Animals fed the P10 diet had greater concentrations of ruminal isovalerate. Ruminal cis-9,trans-11 and trans-10,cis-12 conjugated linoleic acid (CLA) isomers were not affected by dietary treatments. The P10 diet had greatest ruminal synthesis of cis-9,trans-11, but control cows had greatest ruminal synthesis of trans-10,cis-12. Milk CLA isomers were similar among treatments. Trends were observed for greater cis-9,trans-11 and trans-10,cis-12 for the P10 diet. Pigeon peas may be used as a protein supplement in dairy diets without affecting milk production, dry matter intake, or ruminal environment when they replace corn and soybean meal.

Effect of Fumigation on Rotylenchulus reniformis Population Density Through Subsurface Drip Irrigation Located Every Other Furrow.

Plots naturally infested with Rotylenchulus reniformis were sampled in the spring of 2006 and 2007 at depths of 15 and 30 cm in the bed, furrow over the drip tape, and "dry" furrow, and at approximately 40 to 45 cm depth in the bed and dry furrow. Then, 1,3-dichloropropene (Telone EC) was injected into the subsurface drip irrigation at 46 kg a.i./ha, and 3 to 4 weeks later the plots were resampled and assayed for nematodes. The transformed values for nematode population density (IvLRr) before fumigation were higher at 30 and 40 cm depths than at a 15 cm depth. IvLRr before fumigation was higher in the soil over the drip lines than in the bed or dry furrow and was higher in the bed than the dry furrow. IvLRr was higher in the plots to be fumigated than the plots that were not to be fumigated for all depths and locations except at a 15 cm depth over the drip lines, where the values were similar. However, after fumigation, IvLRr was lower over the drip lines at a 30 cm depth in plots that were fumigated compared to samples in a similar location and depth that were not fumigated. There were no other location/depth combinations where the fumigation reduced IvLRr below that in the nonfumigated plots. Yield in 2006, which was a very hot and dry year, was predicted adequately (R(2) = 0.67) by a linear model based on the preplant population density of R. reniformis, with a very steep slope (-2.8 kg lint/ha per R. reniformis/100 cm(3) soil). However, no relationship between nematode density and yield was seen in 2007, which had cooler weather for most of the season. Yield was not significantly improved by fumigation through the drip irrigation system in either year compared to plots treated only with aldicarb (0.84 kg a.i./ha), indicating that the level of control with fumigation did not kill enough R. reniformis to be successful.

Cow and calf performance on Coastal or Tifton 85 Bermudagrass pastures with aeschynomene creep-grazing paddocks.

Cow and calf performance was determined in a 2-yr, 2 x 2 factorial, grazing experiment using Coastal or Tifton 85 (T85) replicated Bermudagrass pastures (4 pastures each; each pasture 4.86 ha), without or with aeschynomene creep-grazing paddocks (n = 4, 0.202 ha each, planted in May of each year, 13.44 kg/ha). On June 10, 2004, and June 8, 2005, 96 winter-calving beef "tester" cows and their calves were grouped by cow breed (9 Angus and 3 Polled Hereford/group), initial cow BW (592.9 +/- 70.1 kg, 2-yr mean), age of dam, calf breed (Angus, Polled Hereford, or Angus x Polled Hereford), calf sex, initial calf age (117 +/- 20.1 d, 2-yr mean), and initial calf BW (161.3 +/- 30.4 kg) and were randomly assigned to pastures. Additional cow-calf pairs and open cows were added as the forage increased during the season. Forage mass was similar for all treatment pastures (P > 0.70; 2-yr mean, 6,939 vs. 6,628 kg/ha, Coastal vs. T85; 6,664 vs. 6,896 kg/ha, no creep grazing vs. creep grazing). Main effect interactions did not occur for performance variables (P > 0.10; 2-yr means), and year affected only the initial and final BW of the calves and cows. The 91-d tester calf ADG was greater for calves grazing T85 than Coastal (0.94 vs. 0.79 kg; P < 0.01), and for calves creep grazing aeschynomene compared with calves without creep grazing (0.90 vs. 0.82 kg; P < 0.03). Calf 205-d adjusted weaning weights were increased for calves grazing T85 compared with Coastal (252.9 vs. 240.3 kg; P < 0.01) and for calves with access to creep grazing (249.9 vs. 243.3 kg; P < 0.05). The IVDMD of esophageal masticate from pastures had a forage x creep grazing interaction (P < 0.05; Coastal, no creep grazing = 57.4%; Coastal, creep grazing = 52.1%; T85, no creep grazing = 59.1%; T85, creep grazing = 60.0%), and IVDMD was greater (P < 0.05) for T85 than for Coastal pastures. Cows were milked in August 2004, and in June and August 2005, with variable milk yields on treatments, but increased milk protein (P < 0.05) for cows grazing T85 compared with Coastal pastures in August each year, contributing to increased calf gains on T85 pastures. These results complement previous research with T85 and indicate increased forage quality and performance of cattle grazing T85 pastures. Calf gains on T85 pastures and for calves on creep-grazed aeschynomene paddocks were high enough to influence the efficiency of cow-calf operations.

Effects of Row Pattern, Seeding Rate, and Inoculation Date on Fungicide Efficacy and Development of Peanut Stem Rot.

Two field studies were conducted in 2000, 2001, and 2002 to determine the effects of row pattern (91.4-cm single or 20.3-cm twin) and seeding rate (single: 12.5, 17.4, or 22.6 seed m-1or twin: 6.2, 8.9, or 11.5 seed m-1) on peanut stem rot (Sclerotium rolfsii) development. The first study was conducted in a naturally infested field and relative efficacy of azoxystrobin (Abound 2.08 F, applied at a rate of 0.3 kg a.i. ha-1 at 60 and 90 days after planting [DAP]) also was evaluated. In this study, stem rot incidence was significantly greater (P < 0.05) in single rows planted at high seeding rates than in twin rows planted at any of the seeding rates. Row pattern did not affect azoxystrobin efficacy, and disease incidence was nearly half as much in twin rows treated with fungicide than incidence in single rows treated with fungicide. In the second field study, individual peanut plants in fumigated plots were inoculated once with S. rolfsii at 50, 70, or 90 DAP. Stem rot incidence at harvest was significantly greater on plants inoculated 50 DAP than plants inoculated 70 or 90 DAP. The incidence of spread to adjacent rows was higher in plots where plants were inoculated at 50 than at 90 DAP. Plants inoculated 90 DAP had less disease at harvest, but often developed more severe symptoms within the first week after inoculation compared with plants inoculated 50 or 70 DAP. Symptoms were more severe in single than in twin rows, and at the higher seeding rates. Data from these studies suggest that the physical spacing between plants is a critical factor in stem rot development both on individual plants and in plant populations.

Integrated Disease Management of Leaf Spot and Spotted Wilt of Peanut.

Field experiments were carried out to evaluate the effects of integrated management of early leaf spot, caused by Cercospora arachidicola, and spotted wilt, caused by Tomato spotted wilt virus (TSWV), on peanut (Arachis hypogaea) using host resistance, two tillage systems, and varying fungicide programs. Effects on pod yield and economic return were assessed. Genotypes C-11-2-39 and Tifrunner demonstrated the best field resistance to TSWV, whereas cvs. DP-1 and GA-01R and line C-28-305 were among the genotypes with the best leaf spot resistance. Epidemics of both diseases were comparable or suppressed in strip-tilled plots compared with conventionally tilled plots. Leaf spot intensity decreased with increased fungicide applications, but to a lesser degree with use of resistance and strip tillage. Yields and net returns were similar between tillage treatments in 2002 and lower in strip tillage in 2003. Genotypes with the greatest yields and returns were C-11-2-39, C-99R, and GA-01R. Returns were comparable among the four-, five-, and seven-spray programs in both years, despite differences in yield. The standard production system, Georgia Green in conventional tillage with seven sprays, resulted in lower returns than half the integrated systems tested in 2002, but had comparable or higher returns than nearly all systems in 2003. When significant, yields and returns were correlated with spotted wilt intensity to a greater degree than leaf spot intensity.

Effects of Plant Spacing, Inoculation Date, and Peanut Cultivar on Epidemics of Peanut Stem Rot and Tomato Spotted Wilt.

Two microplot studies were conducted with peanut (Arachis hypogaea L.) in 2000, 2001, and 2002 to determine the effects of plant spacing, inoculation date, and cultivar on stem rot development caused by Sclerotium rolfsii Sacc., tomato spotted wilt incidence, and microclimate (temperature and relative humidity). Stem rot severity and incidence decreased as plant spacings were increased in 5-cm increments from 5 to 30 cm. Two cultivars with similar susceptibility but different growth habits were compared. Perhaps due to heavy irrigation and extensive vegetative growth, stem rot was similar for 'Florida MDR-98' and 'Georgia Browne'. Plants inoculated later in the year (90 days after planting [DAP]) had less disease at harvest, but often developed more severe symptoms within the first week of inoculation than plants inoculated at 50 or 70 DAP. Canopy microclimate was different than ambient conditions for all treatments; however, differences among treatments were inconsistent and did not explain differences in disease among spacings. Generally, as plant spacing decreased and plant population increased, stem rot increased and tomato spotted wilt was reduced. These data demonstrate that the physical spacing between plants is a critical factor in disease development.

Influence of herbicide tolerant soybean production systems on insect pest populations and pest-induced crop damage.

Conventional soybean weed management and transgenic herbicide-tolerant management were examined to assess their effects on soybean insect pest populations in south Georgia in 1997 and 1998. Soybean variety had very little impact on the insect species observed, except that maturity group effects were observed for stink bug, primarily Nezara viridula (L.), population densities on some sampling dates. Stink bugs were more abundant on the early maturing varieties in mid-season. Velvetbean caterpillar, Anticarsia gemmatalis Hübner, potato leafhopper, Empoasca fabae (Harris), and grasshoppers Melanoplus spp. were more numerous on either conventional or herbicide-tolerant varieties on certain dates, although these differences were not consistent throughout the season. Soybean looper, Pseudoplusia includens (Walker), threecornered alfalfa hopper, Spissistilus festinus (Say), and whitefringed beetles, Graphognathus spp , demonstrated no varietal preference in this study. Few weed treatment differences were observed, but if present on certain sampling dates, then pest numbers were higher in plots where weeds were reduced (either postemergence herbicides or preplant herbicide plus postemergence herbicide). The exception to this weed treatment effect was grasshoppers, which were more numerous in weedy plots when differences were present. In post emergence herbicide plots, there were no differences in insect pest densities between the conventional herbicides (e.g., Classic, Select, Cobra, and Storm) compared with specific gene-inserted herbicide-tolerant materials (i.e., Roundup and Liberty). Defoliation, primarily by velvetbean caterpillar, was different between soybean varieties at some test sites but not different between herbicide treatments. We did not observe differences in seasonal abundance of arthropod pests between conventional and transgenic herbicide-tolerant soybean.

Effects of hot, humid weather on milk temperature, dry matter intake, and milk yield of lactating dairy cows.

Lactating cows were exposed to moderate and hot, humid weather to determine the effect of increasing ambient temperature, relative humidity, or temperature-humidity index (THI) on intake, milk yield, and milk temperature. Minimum and maximum temperatures averaged 17.9 and 29.5 degrees C (cool period) and 22.5 and 34.4 degrees C (hot period), and minimum and maximum THI averaged 63.8 and 76.6 (cool period) and 72.1 and 83.6 (hot period). Environmental conditions had minor effects on intake and milk yield during the cool period. During the hot period, the THI 2 d earlier and mean air temperature 2 d earlier had the greatest impact on milk yield and DMI, respectively. Both breeds maintained milk temperature within normal ranges during the cool period, but Holstein and Jersey p.m. milk temperatures averaged 39.6 and 39.2 degrees C during the hot period. Current day mean air temperature during the hot period had the greatest impact on cow p.m. milk temperature, and minimum air temperature had the greatest influence on a.m. milk temperature. Dry matter intake and milk yield declined linearly with respective increases in air temperature or THI during the hot period and milk temperature increased linearly with increasing air temperature. Dry matter intake and milk yield both exhibited a curvilinear relationship with milk temperature. Environmental modifications should target the effects of high temperatures on cow body temperature and should modify the environment at critical times during the day when cows are stressed, including morning hours when ambient temperatures are typically cooler and cows are not assumed to be stressed.

Determination of Whole-Cell Fatty Acid Profiles for the Characterization and Differentiation of Isolates of Rhizoctonia solani AG-4 And AG-7.

Fatty acid methyl esters (FAMEs) of isolates of Rhizoctonia solani AG-4 and AG-7 were characterized by gas chromatography and analyzed with Microbial Identification System software. Palmitic, stearic, and oleic acids were common in all isolates from both anastomosis groups (AGs) and accounted for 95% of the C14 to C18 fatty acids present. Oleic acid, most common in both R. solani AG-4 and AG-7 isolates, accounted for the greatest percentages of total FAMEs. The presence, quantities, or absence of individual fatty acids could not be used for distinguishing AG-4 and AG-7 isolates. Anteisopentadecanoic and 9-heptadecanoic acids, however, were specific to all three AG-7 isolates from Japan but absent in other AG-7 isolates and all AG-4 isolates. Pentadecanoic acid occurred in only two of the R. solani AG-4 isolates, but was not found in any of the AG-7 isolates. The AG-4 isolates could be distinguished from AG-7 isolates when quantities of FAMEs and key FAME ratios were analyzed with cluster analysis and principle components were plotted. Isolates of AG-7 from Arkansas, Indiana, and Georgia appeared to be more closely related to each other than to AG-7 isolates from Japan and Mexico. These differences in FAMEs were sufficiently distinct that isolate geographical variability could be determined. A dendrogram analysis cluster constructed from the FAMEs data showed results similar to that of the principal component analysis. Euclidean distances of total AG-4 isolates were distinct from total AG-7 isolates. The Arkansas and Indiana AG-7 isolates had a similar Euclidean distance to each another but the percentages were different for the AG-7 isolates from Japan and Mexico. In conclusion, variability of the FAMEs identified in this study would not be suitable as the main diagnostic tool for distinguishing individual isolates of R. solaniAG-4 from AG-7.

Polymeric microcapsules of alachlor and metolachlor: preparation and evaluation of controlled-release properties.

The microencapsulation of alachlor and metolachlor in the polymers cellulose acetate butyrate, ethyl cellulose, poly(methyl methacrylate), and poly(alpha-methylstyrene) with different emulsifiers is described. The controlled-release properties of these formulations were measured under greenhouse conditions on barnyardgrass, crowfootgrass, smallflower morningglory, and Palmer amaranth. The emulsifiers had little effect on the activity of the herbicides. The herbicidal activities of the poly(methyl methacrylate) and poly(alpha-methylstyrene) formulations were consistently lower on all weed species when compared to the activities of the cellulose acetate butyrate, ethyl cellulose, and commercial formulations. The ethyl cellulose formulation of alachlor exhibited controlled-release properties. The results with metolachlor were similar to those with alachlor except that none of the metolachlor formulations exhibited efficacy superior to that of the commercial formulation or controlled release properties.

Effects of dietary fiber on intake, milk yield, and digestion by lactating dairy cows during cool or hot, humid weather.

Lactating cows were offered diets with increasing neutral detergent fiber concentrations to determine the effects on intake, milk yield and composition, blood hormones, and nutrient digestion during cool or hot weather conditions. Tifton 85 bermudagrass hay was substituted for corn silage so that the forage portion of diets were: 1) 40% corn silage (control), 2) 32.4% corn silage, 7.6% bermudagrass, 3) 24.8% corn silage, 15.2% bermudagrass, or 4) 17.2% corn silage, 22.8% bermudagrass (dry basis). Dietary neutral detergent fiber concentrations (% dry matter) were 30.2, 33.8, 37.7, and 42.0, respectively. Intake of dry matter declined with increasing dietary neutral detergent fiber during cool and hot periods, but intake adjusted for cool weather treatment differences did not change further during hot weather. Milk yield declined linearly with increasing neutral detergent fiber during cool weather and changed quadratically during hot weather. Milk temperature declined with increasing dietary neutral detergent fiber for the p.m. milking during the cool period and declined with increasing dietary neutral detergent fiber for the a.m. and p.m. milkings during the hot period. Digestibility of neutral detergent fiber improved and ruminal turnover of particulate digesta was increased with greater dietary neutral detergent fiber content. No dietary fiber level by hot weather interaction was observed, suggesting that total energy intake may have and a greater effect on milk yield than dietary fiber content during hot, humid weather.

Comparison of Tifton 85 and Coastal bermudagrasses for yield, nutrient traits, intake, and digestion by growing beef steers.

A study was undertaken to compare Tifton 85 (T85) and Coastal (CBG) bermudagrasses for effects of cultivar and age at harvest on yields of DM and digestible DM, in vitro digestion, nutrient content, cell wall composition, in situ digestion kinetics, and feed intake and digestion by growing beef steers. In Exp. 1, T85 and CBG forages staged for growth in May or July of 1993 were harvested at 3, 4, 5, 6, 7, and 8 wk from subplots. Tifton 85 bermudagrass had 7.1% greater DM yield, 18.2% higher (P < .05) digestible DM yield, and 7.1% greater IVDMD than CBG, and, after 5 wk of forage growth, IVDMD of both T85 and CBG decreased with increased age at harvest (P < .05). In Exp. 2, T85 and CBG forages staged for growth in July 1997 were harvested at 2, 3, 4, 5, 6, and 7 wk from subplots. Even though T85 had higher concentrations of NDF and ADF than CBG, T85 had 34.1% higher DM yield, 47.9% higher digestible DM, 55.0% higher digestible NDF, 91.7% higher digestible ADF, greater IVDMD, in vitro NDF and ADF disappearances, and higher in situ DM and NDF digestion (P < .05). Coastal bermudagrass had higher concentrations of lignin and lower concentrations of total neutral sugars, arabinose, glucose, and xylose than T85 (P < .05). In vitro digestibilities of DM, NDF, and ADF were lower and concentrations of ADF and lignin were greater for 7- vs 6-wk harvests of both T85 and CBG (P < .05). In Exp. 3, T85 and CBG forages staged for growth in July 1997 were harvested as hay at 3, 5, and 7 wk from .8-ha pastures and fed to 36 individually penned growing beef steers (initial BW = 244 kg) to quantify ad libitum intake without supplementation. Tifton 85 bermudagrass had lower concentrations of lignin and ether-linked ferulic acid and greater concentrations of NDF, ADF, hemicellulose, and cellulose than CBG (P < .05). Steers fed T85 had higher (P < .05) digestion of DM, OM, NDF, ADF, hemicellulose, and cellulose than steers fed CBG. Digestion of NDF, ADF, hemicellulose, and cellulose decreased (P < .05) with increased age at harvest for both cultivars. In conclusion, T85 produced more DM and had more digestible nutrients in vitro, in situ, and in vivo than CBG, and 3 and 5 wk of growth would be recommended ages to harvest either cultivar.

Effects of dietary forage source and amount of forage addition on intake, milk yield, and digestion for lactating dairy cows.

Lactating cows were used to determine the effects of increasing forage content from alfalfa (Medicago sativa L.) hay or Tifton 85 bermudagrass (Cynodon sp.) hay or Tifton 85 bermudagrass (Cynodon sp.) hay on dry matter intake (DMI), milk yield, and nutrient digestion. Forage proportions and neutral detergent fiber (NDF) content of diets were (dry basis) 1) 45% corn (Zea mays L.) silage (control), 33.5% NDF; 2) 15% bermudagrass hay and 30% corn silage, 39.5% NDF; 3) 30% bermudagrass hay and 15% corn silage, 46.6% NDF; 4) 15% alfalfa hay and 30% corn silage, 35.5% NDF; or 5) 30% alfalfa hay and 15% corn silage, 33.5% NDF. The DMI was greater with alfalfa diets than with bermudagrass diets, with low hay diets than with high hay diets, and with the control diet than with the hay diets. Digestibility of NDF in bermudagrass diets was greater than that in alfalfa diets, in high hay diets than in low hay diets, and in hay diets than in the control diet. In vitro NDF digestion was most rapid for bermudagrass hay, intermediate for corn silage, and slowest for alfalfa hay. Results suggest that NDF from bermudagrass was digested more completely and rapidly than was NDF from corn silage or alfalfa, which improved the rate of passage despite the high NDF content of diets containing bermudagrass. Milk yield followed trends for DMI. The control diet and diets containing alfalfa elicited the greatest DMI and milk yield, but DMI per 100 kg of body weight for Holsteins was equal for diets containing either bermudagrass or alfalfa. High quality bermudagrass can be used in rations for lactating dairy cows.

Diversity and Longevity of the Soybean Debris Mycobiota in a No-Tillage System.

The survival of the mycobiota on pod and stem debris of soybean produced in a no-tillage system with cover crops of alfalfa, canola, rye, or wheat or with no cover was studied during 1994 and 1995. Fiberglass mesh bags containing pods and stems were assayed every 28 to 31 days to determine the isolation frequency of fungi. Over 90% of the 11,906 isolates obtained were members of the Deuteromycotina. The most common genera isolated were Alternaria, Cercos-pora, Colletotrichum, Epicoccum, Fusarium, and Phoma. Alternaria spp. had the greatest isolation frequencies and constituted 40% of the total cultures. Numbers of total fungi (all fungi isolated) on sampling dates in 1994 were similar to the totals in 1995. In May 1994, the mean isolation rates for many of the fungal species were significantly lower (P = 0.05) in several of the cover crops, but no consistent pattern could be determined. Common soybean pathogens isolated included Colletotrichum spp., Diaporthe spp., and Cercospora kikuchii. Fusarium graminearum, which is responsible for several diseases of maize and wheat, was commonly isolated during this study. Of the Diaporthe spp. (anamorph Phomopsis spp.), 87% were identified as D. phaseolorum var. sojae. Colletotrichum spp. were identified as C. truncatum in 85% of the isolates, C. destructivum (teleomorph Glomerella glycines) in 12%, and both species in 3%. Cercospora kikuchii was more commonly isolated from pods than from stem tissue, and Colletotrichum spp. occurred more frequently on stems. Isolation frequencies of Diaporthe spp. were greater in May of both years than in the preceding months. These results show that no-tillage soybean debris harbors numerous fungi pathogenic to soybean, and producers who grow soybeans continuously may find more disease in this crop and lower yields. Fungi that attack crops such as maize and wheat were commonly isolated from soybean debris in both years, and a no-tillage rotation which includes maize or wheat could result in increased disease in these crops. Isolation frequencies of the fungi from cover crops varied with the sampling date, but no consistent patterns could be determined for a particular cover crop or fungal species. This is the first detailed study of survival rates of soybean, maize, and wheat pathogens that overwinter on soybean debris in a no-tillage system.

Frequency and geographical distribution of plant-parasitic nematodes on cotton in georgia.

A survey was conducted to examine the geographical distribution of plant-parasitic nematodes in Georgia cotton fields. A total of 778 fields in 11 Georgia counties were sampled from 1 September through 15 December 1995. Four nematode genera parasitic on cotton were found in this survey: Meloidogyne spp., Rotylenchulus sp., Hoplolaimus sp., and Belonolaimus sp. Meloidogyne spp. was present in 9% to 56% of the fields in individual counties. Rotylenchulus sp. was found in 10 counties, Hoplolaimus sp. was found in 6 counties, and Belonolaimus sp. was found in 2 counties. From all of the samples collected for this survey, Meloidogyne spp. were found in 31% of the samples, Rotylenchulus sp. was found in 14%, Hoplolaimus sp. was found in 7%, and Belonolaimus sp. was found in 0.3%. Burke County had the greatest number of fields infested by at least one of these genera (67%) and the greatest number of fields above Georgia's action thresholds (38%). Laurens County had the fewest fields where these genera were present (13%), and only 3% of fields had nematode populations above threshold levels. Data from samples collected from cotton fields and submitted by county agents from 1993 through 1994 were compiled to provide historical information about nematode distribution and population density. The results from this survey show that the major nematodes damaging to cotton are not present in all counties in Georgia. Counties in which cotton has historically been a major crop are likely to have higher levels of Meloidogyne spp., Hoplolaimus sp., and Rotylenchulus sp. in current cotton crops. Counties in which soybean has historically been a major crop are likely to have higher levels of Hoplolaimus sp. and Rotylenchulus sp. in current cotton crops.