Grapefruit Trees Research Articles

Effect of pesticides on spiders occurring on apple and citrus in Israel

Field experiments in an apple orchard and in a citrus grove were carried out to evaluate the effect of four commercial pesticides in common use in Israel against apple and citrus pests, on the spider populations inhabiting the trees. The spider populations on apple were markedly suppressed by the pesticides, the order of toxicity being Talstar (biphenate) >Mavrik (fluvalinate) > Smash (fenpropathrin) > Dursban (chlorpyrifos). When grapefruit trees were treated with carbaryl + formothion, 232 spiders were sampled in the unsprayed plot, 55 days after treatment, as compared with only 11 spiders in the treated plot. Two and 7 days after treatment with chlorobenzilate, the sample from the treated plot numbered 68 and 55 spiders, respectively, as compared with 50 spiders collected 24 h before treatment. In addition, laboratory tests were carried out to determine the susceptibility of the spiderChiracanthium mildei L. Koch to 17 pesticides. When the spiders were exposed to grapefruit leaves which had been dipped 1 h previously for 5 sec in the aqueous emulsions of the pesticides, chlorpyrifos, fenpropathrin, fenvalerate, phosphamidon and biphenate caused 100%, and cypermethrin and fluvalinate 60% mortality, whereas all the other pesticides tested - acaricides, fungicides and herbicides - caused about 10-40% mortality.

14C-Gibberellic Acid Uptake, Translocation, Persistence, and Metabolism in Grapefruit

Abstract The uptake, translocation, and metabolism of 14C-gibberellic acid (14C-GA3) was studied in 3-year-old container-grown ‘Marsh’ grapefruit trees (Citrus paradisi Macf.). A total of 1.65 × 105 disintegrations per min (dpm) in 200 μl of solution was applied evenly over the entire fruit surface, or, on both surfaces of 3 to 5 subtending leaves of a fruit. Absorption of 14C-GA3 by leaves and peel began within 1 hr of application and continued for 8 hr. Translocation of labeled material from leaves to peel and the reverse began 4 to 8 hr after application and continued for 4 weeks. No labeled material was recovered from juice or seeds. Labeled material persisted in albedo, flavedo, and leaves for 8 weeks with the highest accumulations in the peel. Separation of 14C-GA3 metabolites from the 95% EtOH extract by reversed-phase HPLC produced 2 14C-labeled peaks. Analysis of these 2 peaks by β-D-glucosidase hydrolysis, n-butanol partitioning, and cochromatography with 14C-GA3 standards suggested that the major component was 14C-GA3 and the other a polar metabolite.

Studies on the population and distribution pattern of Parlatoria zizyphus (Lucas) in citrus orchards in Egypt

The population and distribution pattern of the black parlatoria scale, Parlatoria zizyphus (Lucas) have been investigated. This scale had two annual peaks of abundance in September and May. It passed through three annual generations, the first in September-October, the second in March-April and the third in June-July on grape fruit trees. The build up of insect population on different zones of grape fruit trees in different seasons of the year was studied. The insect distribution of different insect items were significantly affected at different heights and directions of the trees. The highest population tended to be accumulated on the lower and middle shady zones of the trees in different seasons. With regard to directions the central core of the tree harboured the highest population followed by the west direction and the lowest population was accumulated on the north or south direction in the fall and spring. In summer, the highest population settled on the south direction in contrast to the east or north directions, which harboured the lowest population. The mode of insect distribution is discussed in correlation with the environmental conditions.

Male-Male Interactions in Caribbean Fruit Flies, Anastrepha suspensa (Loew) (Diptera: Tephritidae): Territorial Fights and Signalling Stimulation

Laboratory experiments were made on 2 aspects of male-male interactions in Caribbean fruit flies, Anastrepha suspensav (Loew). Observations of males involved in territorial contests on a lab-caged grapefruit tree revealed that large size and residence gave males advantages in fights; large intruders usually were able to oust small residents. In a second experiment, groups of individually-caged males began to emit sex pheromone and produce acoustic signals earlier in the daily sexual display period when in contact with other males than when isolated from them.

Growth regulator and low-volume irrigation effects on grapefruit quality and fruit-drop

‘Marsh’ ( Citrus paradisi Macf.) grapefruit trees on rough lemon ( C. jambhiri Lush.) rootstock received irrigated and unirrigated treatments. Half of each irrigation treatment received a GA 3 + 2,4-D spray at color break. Pre-harvest sprays of GA 3 and 2,4-D extended the grapefruit harvest season by increasing fruit removal and rind puncture force, delaying development of mature color and decreasing late-season and post-freeze fruit-drop. Although soil moisture content in the top 0.9 m of unirrigated blocks was reduced by approximately 40%, xylem pressure potentials of these trees and performance of GA 3 + 2,4-D were unaffected. Soil moisture content was not an accurate indicator of tree water status for large grapefruit trees.

Translocation of Carbohydrates and Proline in Young Grapefruit Trees at Low Temperatures

Girdling and defoliation of fruit-bearing grapefruit (Citrus paradisi Macf.) branches inhibited the accumulation of soluble carbohydrates and proline in fruit tissues during low temperature treatment of trees. These treatments did not inhibit hydrolysis of sucrose to reducing sugars. Flavedo and albedo tissues responded similarly to low temperatures but little or no change occurred in the juice. Therefore, soluble carbohydrates and proline do not appear to interchange between different tissues of the fruit at low temperatures but instead are translocated into the fruit from other parts of the plant. Girdling fruit-bearing branches immediately after low temperature treatments inhibited the accumulation of sucrose in fruit tissues at dehardening temperatures. Also, proline levels decreased rapidly in fruit on girdled branches at dehardening temperatures. This rapid decrease suggests proline may serve as a source for respiratory energy in grapefruit during rapidly changing temperatures that favor active growth and during recovery of citrus from environmental stress.

Growth, Mineral Uptake, and Evapotranspiration of Air Layers from Blight-affected and Healthy Grapefruit Trees with Two Nutrient Regimes1,2

Abstract Air layers from 6 blight-affected and 6 healthy grapefruit, Citrus paradisi Macf., trees were grown in a greenhouse with low N, low S, and lime and high N, high S, and no lime regimes, one air layer from each tree in each treatment. Shoot fresh weight of air layers from healthy trees was 25%, and root fresh weight was 38% greater than that of air layers from blighted trees, after 8 months of treatment (shoot/root ratios of 1.59 and 1.90). Shoot weight was the same with both nutrient treatments; root weight was 40% smaller with high N, high S, and no lime than with low N, low S, and lime (shoot/root ratios of 2.12 and 1.37). Air layers from blighted trees had higher concentrations of N, P, and water-soluble phenolics, and lower Ca and Na in the wood; more S, Fe, Zn, Cu, and Mo in the bark; more N and K, and less Mg, Na, and Cl in the roots, and more P and less B and Cl in the leaves than air layers from healthy trees. Low N, low S, and lime induced higher K and Mo in the wood, higher K in the bark, and lower Na and Cl in the roots of air layers from blighted trees; high N, high S, and no lime increased Mg and Zn in the roots, Fe in the wood, and Zn in the leaves of air layers from blighted trees above the levels of healthy air layers. There were curvilinear relationships between evapotranspiration and root weight and the shoot/root ratio; air layers from blighted trees transpired more water than those from healthy trees on a per unit shoot and root weight basis.

Limited Systemic Spread of Impietratura and Psorosis-A in Graft-Inoculated Grapefruit Trees

Limited Systemic Spread of Impietratura and Psorosis-A in Graft-Inoculated Grapefruit Trees

Citrus Rust Mite Control with Vydate L, 1981

Abstract Vydate L alone and Vydate L with citrus oil spray (Sunspray 6N) and Vendex 50WP were compared for residual control of citrus rust mite (CRM). Tests were conducted on 30-yr-old Ruby Red grapefruit trees planted on 25 ft x 30 ft spacing. Treatments were arranged in a randomized block design with each treatment replicated on two 12-tree plots. Treatments were applied on May 15 and reapplied on Jul 14 and Oct 1 using a Lockwcod-Hardie air-blast sprayer with speed, nozzle adjustment and pressure regulated to apply 250 gal/acre. At each count date 50 fruit/replicate were randomly selected and CRM counted in a 1 cm2 lens field at 10X on the top, medium and bottom of each fruit. CRM counts were not continued after the Oct 1 spray. At harvest, 100 fruit/replicate were randomly selected and evaluated for CRM damage. Damage was expressed as percent russet, i.e. fruit with moderate to severe damage (US#2 fresh or process fruit).

Citrus Red Mite Control, 1981

Abstract Four compounds were evaluated in dilute sprays vs. citrus red mite in a block of double-bedded ‘Star Ruby’ grapefruit trees planted in 1978 on a 17.5 x 26.25 ft spacing. A randomized complete block design with 4 replications was used. Each plot consisted of a single tree. Spray applications were made Feb 25 with a John Bean Royalier JK-20T hydraulic sprayer operated at 200 psi and equipped with a double Boyce hand-gun. Approximately 1 gal of spray was needed to spray each tree to run-off. Approximately 1 gal of spray was needed to spray each tree to run-off. At the indicated pre- and post-treatment intervals, 10 leaves, randomly selected while circling each tree, were picked into a pt Mason jar containing 50% alcohol and brought to the lab. Each jar was vigorously shaken and then leaves removed separately and surface rinsed into the funnel of a Millipore filter system with a stream of 50% alcohol from a wash bottle. The leaf-wash and the liquid from the Mason jar were drawn through the filter. Mites on the filter disc were counted with the aid of a binocular dissecting scope.

Spatial Distribution of Citrus Mealybug on Grapefruit Trees12

Grapefruit trees, chosen at random in five orchards in Texas, were sampled monthly (May through November) in 1977 and 1978 to determine the spatial distribution of Planococcus citri (Risso) within infested trees during the fruiting season and to find the optimum sample unit (fruit, leaf, or terminal) for estimating within-tree populations. Results showed that there was no difference in the preference of citrus mealybugs by tree strata (0 to 0.91, 0.92 to 1.83, and 1.84 to 2.74 m) or quadrant (N, E, S, and W), and that fruit was the optimum sample unit for indexing population densities of P. citri; underneath the calyx proved to be the best place to search when there were extremely low mealybug population densities.

Lack of genetic relatedness among animal and plant acholeplasmas by nucleic acid hybridization

The present study compared the genetic characteristics of three previously unclassified acholeplasmas of plant origin with those of the eight established species ofAcholeplasma. A radiolabeled DNA probe was derived from the lemon (L1) strain acholeplasma by using the nick translation method and hybridized to the excess unlabeled DNA isolated from the eight established species ofAcholeplasma and three new isolates from plants. Nucleic acid hydridization and serological tests confirmed that the L1 acholeplasma was distinct from all eight established species ofAcholeplasma but closely related to strains isolated from the flowers of grapefruit trees (GF1) and powder puff plants (PP2). The results suggest that these new acholeplasmas isolated exclusively from plants may represent a new species ofAcholeplasma.

Citrus Rust Mite Control in Texas, 1980

Abstract Experimental acaricides were compared to VendexR in a randomized block design on 20-year-old grapefruit trees planted on a 30 x 25 ft spacing. MitacR was tested in combination with 1% citrus spray oil (OrchexR 796). Each treatment was replicated 4 times in single tree plots with a handgun of a John Bean MTET Sprayer at 250 psi, ca. 15 gal /tree. Treatments were applied on Jun 24, with rust mite counts at ca. 2-week intervals until acaricides lost residual effectiveness. One hundred fruit (25/tree) were randomly selected in each treatment and rust mite counted in a l-cm2 lens field at lOx on the top, medium and bottom of each fruit.

Some Effects of Grapefruit Tree Canopy Position on Microclimate, Water Relations, Fruit Yield, and Juice Quality1

Abstract Positional differences among leaf and fruit surface temperatures and water relations of ‘Ruby’ grapefruit (Citrus paradisi Macf.) were related to fruit load and juice quality. Southern top canopy positions experienced the highest temperatures and lower water potentials and yielded more fruit with more soluble solids than other canopy positions. Canopy depth was also an important determinant of fruit yield and early season juice quality. Based on data from 3 trees during 2 seasons, there were greater fruit loads with higher °Brix and lower acidity in the outside canopy positions than in the inside positions. Upper canopy positions tended to have lower acidity and consequently higher °Brix/acid ratios than the lower positions. Abaxial fruit hemispheres were smaller and had a lower percent juice than their paired adaxial fruit hemispheres. Grapefruit from sunlit canopy positions mature earlier than fruit from shaded positions. Since there were more fruit with higher soluble solids in the most exposed canopy positions, daily heat stress and leaf and fruit water stress were not limiting factors in grapefruit yield and juice quality with respect to different tree canopy positions.

Citrus Rust Mite Control, 1979

Abstract Experimental acaricides LY 131117, LY 127063, and LY 131215 were compared to Dimilin in a randomized experiment on 5-year-old grapefruit trees (24 × 24 ft spacing). Each treatment was replicated 4 times on single-tree plots by hand gun of a John Bean Model 1010- MTBT sprayer at 225 psi, ca. 10 gal/tree. Treatments were made on May 15 and reapplied on Jul 12, with citrus rust mite (CRM) counts at 3-4 week intervals postspray. Twenty-five fruit were randomly selected in each tree (100/treatment) and CRM were counted on top, median, and bottom of each fruit using a 10X handlens with a 1-cm2 grid.

Accumulation of Free Proline in Citrus Leaves during Cold Hardening of Young Trees in Controlled Temperature Regimes

Free proline increased in leaves of orange (Citrus sinensis [L.] Osb. cv. Valencia) and grapefruit (Citrus paradisi Macfad. cv. Star Ruby) trees on a wide range of citrus rootstocks during cold hardening. Increases in sugars accompanied proline accumulation. During cold hardening, the rate of proline accumulation was greater in old than in young leaves. In leaves of grapefruit trees kept in the dark during cold hardening, neither proline nor sugars increased and the degree of cold hardiness was less than in trees exposed to light. Like sugar accumulations, proline accumulation does not reflect specific degrees of cold hardiness in citrus cultivars.

Citrus Rust Mite Control, 1978

Abstract Experimental acaricides were compared to Vendex in a completely randomized experiment on 20-yr-old grapefruit trees (30 ft x 25 ft spacing). Each treatment was replicated on three single-tree plots by hand gun of a John Bean Model 1010-MTBT sprayer at 225 psi, ca. 15 gal/tree. Treatments were applied on Jul 10, with citrus rust mite counts made at 30-day intervals posttreatment. Eighteen fruit were selected at random in each tree, and citrus rust mites were counted on the top, median, and bottom of each fruit using a 10X handlens with a 1-cm2 grid.

Mite Control on Texas Citrus, 1978

Abstract Six acaricide treatments and a control were arranged in a completely randomized design with each treatment replicated on 6 single trees. The 4-yr-old grapefruit trees, on a 24 ft x 24 ft spacing on sandy loam soil, were sprayed by hand gun with a John Bean Model 1010-MTBT sprayer at 225 psi, using ca. 10 gal/tree. Treatments were applied on May 28 and mite counts made at 30-day intervals posttreafment. Twelve fruit/tree were selected at random and rust mite were counted on the top, median, and bottom of each fruit using a 10X handlens with a l-cm2 grid. Texas citrus mite were counted by collecting 15 to 20 leaves/tree at random, brushing the mites from leaves onto counting plates with a Henderson-McBurnie mite brushing machine, and counting at 40X under a binocular microscope. Acaraben and efhion + 1% citrus spray oil were the standard acari cides.

Citrus Mealybug Control, 1978

Abstract Experimental insecticides were compared to Supracide for citrus mealybug (CMB) control. Treatments were replicated three times on single-tree plots in a completely randomized design. Grapefruit trees were 9 years old (15 x 25 ft spacing) growing on sandy clay loam soil. Spray applications were made on Aug 15 using a 2-gal Hudson Sprayer with CO2 at 80 psi as a propellant. An area on each tree of ca. 20 sq ft was sprayed to runoff. At 7 da posttreatment, 10 CMB-infested fruit were collected from the sprayed area in each tree and examined under a binocular scope. Percent mortality was determined for the crawler, 2nd and 3rd nymphal, and adult stages.

Relation of citrus leaf nutrients to internal fruit quality in Sierra Leone

Abstract In a mineral nutrient survey, fruits from grapefruit, sweet orange and tangerine trees whose leaves were sampled were analysed for internal quality and then correlated with the respective leaf analysis values. Correlations amongst leaf nutrients were also studied. Statistically significant simple correlations were found between some internal quality parameters and certain leaf nutrients. Due to sampling limitations, a multi‐element consideration in the nature of multiple regression studies was not considered thus limiting the utility of the results in evaluating interionic effects on internal quality of citrus in Sierra Leone.