Ben Mullinix

Differences in chilling sensitivity of cucumber varieties depends on storage temperature and the physiological dysfunction evaluated

Abstract Fruit from eight Plant Introduction (PI) lines, 12 F 1 hybrids of crosses between chilling-sensitive and chilling-resistant lines and two commercial cultivars of cucumber ( Cucumis sativus L.) were stored for 7 days at 1 or 4°C followed by 2 days at 24°C and evaluated for chilling injury. The chilling-induced symptoms and physiological dysfunctions compared included visible pitting, decay, weight loss during storage at low temperature, electrolyte leakage, chlorophyll fluorescence ratios, respiration rates and pyruvate accumulation in the mesocarp tissue. Severity of chilling-induced injury among the lines, hybrids and cultivars depended on the particular symptom or physiological dysfunction examined. Fruit from all lines, crosses and cultivars exhibited greater injuries after storage at 1°C than after storage at 4°C. Other than visible pitting and decay, only small, sometimes indistinguishable, differences were observed among the various lines as to their sensitivity to low temperatures. In this study, chlorophyll fluorescence ratios proved to be of little value in distinguishing between chilling-sensitive and chilling-resistant lines of cucumber. Decay and weight loss were the only measurements that were significantly correlated with chilling-induced visible pitting. Respiration rates were correlated with weight loss, but not with visible pitting and decay, during storage at 1 and 4°C. It is concluded that low temperatures do not affect all biochemical and physiological processes of cucumber to the same extent. Furthermore, there is a continuum of sensitivity of each process to low temperature, and whether a cultivar is deemed to be chilling-sensitive or chilling-resistant depends on which particular biochemical or physiological process is evaluated.

Effect of Prey Species on Plant Feeding Behavior by the Big-Eyed Bug, Geocoris punctipes (Say) (Heteroptera: Geocoridae), on Cotton

Abstract The effect of prey species on plant feeding behavior by Geocoris punctipes (Say) females was determined by observing prey and plant feeding behavior on cotton plants for three prey treatments: 1) corn earworm, Helicoverpa zea (Boddie), eggs, 2) H. zea first instars, and 3) cotton aphid, Aphis gossypii Glover, adults. Feeding behavior of individual G. punctipes females was observed in the laboratory using caged cotton terminals with prey on the leaves. A. gossypii adults were less acceptable to G. punctipes females as prey than H. zea eggs and first instars. Female G. punctipes fed much less on cotton plants than prey when more acceptable prey, H. zea eggs and first instars, were available but exhibited no feeding preference for the cotton plant versus prey when less acceptable prey, A. gossypii adults, were available. Nevertheless, because G. punctipes females fed on cotton plants regardless of acceptability of prey even in the presence of abundant prey, we conclude that plant feeding is an integral part of the feeding behavior of G. punctipes in cotton. Conservation of G. punctipes by reducing applications of insecticides that are toxic to these predators when they feed on insecticide-treated foliage or by providing nutritionally good plant resources could increase their effectiveness as natural enemies of H. zea and other pests in cotton.

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.

Grain Sorghum as a Trap Crop for Corn Earworm (Lepidoptera: Noctuidae) in Cotton

Abstract This 2-yr on-farm study was designed to evaluate the ability of grain sorghum, Sorghum bicolor (L.) Moench, to serve as a trap crop for the corn earworm, Helicoverpa zea (Boddie), by attracting corn earworm females into the sorghum as they emerged from cornfields. Three plots of sorghum trap crops and three equally sized plots of cotton, Gossypium hirsutum L., trap crops were planted in a strip between a commercial cornfield and a commercial cotton field. The cotton field adjacent to the trap crop plots was divided into field cotton plots associated with the sorghum trap crop plots and field cotton plots associated with the cotton trap crop plots. Three commercial cotton fields adjacent to corn, but without trap crops, also were sampled. The number of corn earworm eggs per plant and the percentage of plants with corn earworm eggs was higher in the sorghum trap crop plots than in the cotton trap crop plots for both years, demonstrating that corn earworm females preferred to oviposit in the grain sorghum over cotton. A higher percentage of plants with corn earworm eggs was found in cotton in control fields compared with fields with trap crops, indicating that the grain sorghum trap crop was not the source of corn earworm. An economic threshold of 5% corn earworm young (first and second instars) was exceeded more times for cotton in control fields compared with cotton in fields with trap crops. Thus, for two seasons the grain sorghum trap crops helped reduce the need for insecticide applications for this pest. Percentage of parasitization by the egg parasitoid Trichogramma pretiosum Riley and the number per plant of the predator Orius insidiosus (Say) were higher in the sorghum trap crop plots than the cotton plots. However, the grain sorghum trap crop plots were not sinks for these natural enemies. We conclude that grain sorghum could serve as an effective trap crop for corn earworm in cotton.

Calcium level in the peanut fruiting zone as influenced by gypsum particle size and application rate and time

Abstract The peanut requires a readily available source of Ca in the fruiting zone during fruit development. Field studies were conducted for three years on two soils to compare rates of fine and coarse gypsum material applied to peanuts shortly after planting and at early flowering in supplying Ca to the peanut fruit and its effect on yields. The fine and coarse gypsum was applied at three rates and at two different times in randomized complete block experiments. At approximately every four weeks, composite soil samples were collected at 0–5 and 5–10 cm depths and extracted with (0.05N HC1 + 0.025N H2 SO4) extractant. On the Lakeland soil fine gypsum applied at early flowering gave higher Ca levels at the 0–10 cm depth than coarse material applied shortly after planting or at early flowering. Yield data showed that at low rates coarse gypsum applied at planting was superior to early flowering application. In most instances on the Greenville soil, coarse gypsum applied at planting produced higher levels o...

Effects of split-pit on elemental concentrations of peach fruit during pit hardening

Abstract Split-pit and normal peach fruit ( Prunus persica (L.) Batsch) ‘Junegold’ were sampled during endocarp (pit) hardening in 1981, 1982 and 1985. Split-pit fruit were heavier than normal fruit, primarily because of the heavier than normal exocarp and mesocarp (flesh). Flesh weight showed the same linear increase with time during pit hardening in both split-pit and normal fruit, and water content in the flesh remained constant. Water content in the pit was higher in normal fruit at the start of pit hardening, but at the end of pit hardening the reverse was true. Water content in the pit decreased linearly with time during pit hardening in split-pit fruit and in normal fruit. The Ca concentration in the pit and the flesh was lower in split-pit fruit than in normal fruit. The detailed study of 1985 showed that concentrations of K, Zn, Mn and Fe in the pit were lower in split-pit fruit than in normal fruit near the start of pit hardening, and were equivalent by the end of pit hardening. The 1985 study also showed that the flesh of split-pit fruit had lower than normal concentrations of P, K, Mg, Zn, Mn and Cu during pit hardening. The Fe concentration in the flesh was lower in split-pit fruit than in normal fruit only near the start of pit hardening. Sprays of calcium nitrate (1% w:v) applied before and near the start of pit hardening in 1982 increased Ca concentrations in the pit and the flesh reduced fruit weight, but did not reduce the incidence of split-pit.

Post-Harvest Hedging and Pruning of Three Year Pruning Trial on ‘Climax’ and ‘Tifblue’ Rabbiteye Blueberry

SUMMARY Control of bush height is a major problem in rabbiteye blueberries. Eight-year-old, moderately vigorous Vaccinium ashei cv. Climax, were roof-top hedged in early August to a height of about 2.2 m (7 ft). Fourteen-year-old, low vigor ‘Tifblue’ were roof-top hedged to a height of about 2.8 m (9 ft) 0, 2, 4, and 6 weeks after harvest. Average bush yield on ‘Climax’ was 5.3 kg (11.6 lbs) for the unpruned control, 4.6 kg (10.1 lbs) for the moderate roof-top hedged, and 4.8 kg (10.5 lbs) for the winter cane renewal pruning treatment. There were no significant differences among yields but there was a trend toward lower yields on the first harvest of ‘Climax’ with roof-top hedging compared to unpruned or cane renewal pruned. Average bush yield on ‘Tifblue’ was 2.9 kg (6.4 lbs) for the unpruned control, 2.5 kg (5.5 lbs) for pruning 0 weeks after harvest, 3.3 kg (7.3 lbs) for pruning two weeks after harvest, 2.8 kg (6.1 lbs) for pruning four weeks after harvest, and 2.8 kg (6.3 lbs) for pruning six weeks after harvest. ‘Tifblue’ that were roof-top hedged two weeks after harvest tended to produce the highest yields. Bushes that were roof-top hedged were much easier to hand harvest.

Changes in the interpretation of irrigation fertilizer experiments caused by blank alleys

Abstract Field plot technique is of continued interest to and concern of scientists. End trimming to remove border effects is expensive and time consuming. To determine if there was a more appropriate method to analyze field plot results, a split‐plot experiment with four replications of irrigated main plots and fertilizer subplots was utilized. Irrigation treatments consisted of irrigated and nonirrigated. Fertilizer treatments were ammonium nitrate and sulfur coated urea at 0, 112, 224, and 336 kg N/ha. Corn (Zea mays L.) was used as the test crop. Plots consisted of 6 rows 81 cm apart. The center two‐thirds of the two center rows of the 9.14 m long plots was harvested for plot yields. One remaining end of the center two rows (border) adjacent to a 3.05 m blank alley was selected at random within each replication and irrigation level to harvest for border yields. Results indicated the relation of the plot yield to the border yield varied with irrigation level and growing season. Inclusion of borders ind...

Selective limb pruning, tree removal, and paclobutrazol growth retardant for crowding pecan trees

Abstract Selective limb pruning, tree thinning, and the combination of selective limb pruning and paclobutrazol application as a basal drench were used to reduce overcrowding of pecan [ Carya illinoensis (Wangenh.) C. Koch] trees. Thinning increased yield per tree for the cultivar ‘Desirable’ and did not significantly reduce yield per hectare during the 7 year period of the study. None of the treatments significantly affected yield per tree or nut quality for the cvs. ‘Western Schley’ and ‘Wichita’. Selective limb pruning with or without the growth retardant did not affect either yield or nut quality. The paclobutrazol basal drench reduced terminal shoot growth.

Nutrient element concentration in leaves for 40 pecan cultivars

Abstract Mean leaf concentrations are presented for 40 named cultivars and USDA selections for leaf nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), zinc (Zn), manganese (Mn), iron (Fe), and copper (Cu) for a 3‐year period with mean separation by Tukeys Studentized Range Test. A General Linear Models Analysis of Variance revealed significant (p=0.0001) differences between cultivars and years for all nutrients and year x cultivar differences (p≤0.0002) for N, P, K, and Ca. Two studies indicate the pecan cultivar ‘Grabohl’ is a high user of K. Comparisons between cultivars for years and locations appeared inconsistent for many elements. The conservative Tukeys test did not reveal significant differences among cultivars as to their leaf Zn and Cu contents.