Light Crop Load Research Articles

Internal Flesh Browning in Apple and Its Predisposing Factors—A Review

This review article is focused on internal flesh browning (IFB)-related physiological disorders affecting apple (Malus domestica Borkh.) fruit. The expression of different physiological and metabolic IFB-related disorders during post-harvest storage are investigated along with the pre-harvest factors contributing to development. The effectiveness of commercially available pre-harvest technologies for preventing IFB-related disorders are also examined. Internal flesh browning-related disorders are erratic and devastating disorders that result in post-harvest deterioration of fruit quality in apples. Internal flesh browning-related disorders can result in severe economic losses to the apple industry through reduced consumer trust and market acceptability of susceptible cultivars. There are several IFB-related disorders and incidence can range from 0 to 100% of a crop, with severity ranging from no brown flesh to browning of the entire fruit flesh. While IFB-related disorders are found in several apple cultivars, some cultivars are more prone than others. The development of IFB-related disorders involve complex mechanisms depending upon the different types and causes, or factors involved in loss of structural integrity and functional stability of the cell membranes and cell components. Membrane disruption followed by enzymatic oxidation of fruit phenolic compounds by polyphenol oxidases and the production of brown polymers is considered to be the general underlying mechanism causing the browning of flesh tissue. It can be observed in different patterns based on the injured portion of the fruit flesh and the cause of membrane disruption. Three broad categories of IFB-related disorders, including chilling injury, internal CO2 injury, and senescent-related browning disorders, are discussed along with their sub-types. The development of IFB-related disorders can be influenced by both pre-harvest factors and post-harvest conditions and their interactions. Although commonly associated with storage, IFB can also be found immediately after harvest and sometimes in unharvested fruit prior to full maturity. As pre-harvest conditions are a strong contributor to IFB-related disorders, the influence of several pre-harvest orchard conditions, including fruit size, crop load, maturity at harvest, cultivar, climatic conditions, seasonal temperatures, growing degree days, and major mineral nutrients, such as nitrogen (N), phosphorus (P), potassium (K), and calcium (Ca) are reported. Although there are contradictory findings in the studies reported, in general, factors such as larger fruit size, light crop load and delayed harvesting, along with cool temperatures after bloom and warmer temperatures before harvest, increase the risk of IFB-related disorders. In relation to fruit mineral concentrations, high N and low Ca have been associated with increasing IFB, while there is conflicting evidence in relation to the impact of both P and K. This review also examines the effectiveness of commercial pre-harvest technologies such as 1-methylcyclopropene, aminoethoxyvinylglycine and diphenylamine in the prevention of IFB-related disorders, but none of these technologies were found promising due to varied and contradictory results.

Behavior of leaf nutritional status in ‘on’ and ‘off’ year bearing trees of ‘Bengal’ litchi (Litchi chinensis)

The major problems reported in litchi in several countries include irregular flowering, poor fruit retention, small fruit size and alternate bearing. This study assessed the time course (all-year-round, on a monthly basis) of the leaf macro- and micronutrient concentrations, in ‘on’ and ‘off’ year bearing ‘Bengal’ litchi trees. In December 2012, fifty uniform trees, half of them with a heavy fruit load (‘on’ year) and the other half with a very light crop load (‘off’ year) were tagged to trace their nutritional status. The trees were twelve years old, with an approximately 5 m canopy diameter and 4 m in height, and have received the same cultural practices and fertilization since the orchard establishment. Leaves were sampled monthly from December 2012 to November 2013 and analyzed for nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), iron (Fe), manganese (Mn), copper (Cu), zinc (Zn) and boron (B). Data were submitted to analysis of variance and means compared by multiple range test at 5% probability. Leaf analysis showed differences between ‘on’ and ‘off’ year bearing trees for N, K, Mn and Cu. Leaf macronutrients were higher in the 4th month and lower around the 10th month, whereas leaf micronutrients were higher around the10th month and lower in the 4th month. These results open the possibility to use leaf analysis as a tool to predict potential yield and manage fertilization accordingly to minimize alternate bearing in litchi.

‘Hass’ avocado tree growth on four rootstocks in California. II. Shoot and root growth

We investigated the relationship between alternate cropping and shoot and root growth in mature ‘Hass’ avocado (Persea americana Mill.) trees growing on ‘Thomas’, ‘Topa Topa’, ‘Duke 7’, or ‘D9’ rootstocks over five years in Southern California. Shoot growth occurred during two distinct flushes each year: one in spring and one in late summer. Root growth occurred throughout the year, with higher rates during spring and summer but slower growth rates during shoot growth flushes. There was no effect of rootstock on shoot growth rate. There was no direct relationship between alternate bearing and shoot and root growth. It is possible that cropping affected shoot growth, with extensive shoot development occurring in a year with virtually no crop. The summer growth flush accounted for a greater proportion of the total shoot growth in years with light crop loads than in years with heavy crop loads. There were differences in root growth rate among rootstocks, but these relative differences varied among years. Root growth did not exhibit dormant periods as shoot growth did, but in general, root growth rate was greatest when soil temperatures were high and when shoots were not growing. This information gives us insight into the relative timing and relationships among growth events of avocado in Southern California and will help growers determine the optimal timing of cultural practices. Our results suggest that the best timing for fertilizing, spraying, and pruning is similar in trees growing on different rootstocks.

Fruit thinning in ‘Conference’ pear grown under deficit irrigation: Implications for fruit quality at harvest and after cold storage

Fruit thinning in pear is feasible for mitigation of water stress effects. However, it is not well known how fruit quality at harvest and after cold storage is affected by pre-harvest water stress. Even less is known about the effects of fruit thinning on quality under these circumstances. To elucidate these, we applied deficit irrigation (DI) and fruit thinning treatments to ‘Conference’ pear over the growing seasons of 2008 and 2009. At the onset of Stage II (80 and 67 days before harvest in 2008 and 2009, respectively), two irrigation treatments were applied: full irrigation (FI) and DI. FI trees received 100% of crop evapotranspiration (ETc). DI trees received no irrigation during the first three weeks of Stage II to induce water stress, but then received 20% of ETc to ensure tree survival. From bud-break until the onset of Stage II and during post-harvest, FI and DI trees received 100% of ETc. Each irrigation treatment received two thinning levels: no thinning leaving commercial crop load (∼180 fruits tree −1), and hand-thinning at the onset of Stage II leaving a light crop load (∼85 fruits tree −1). Under commercial crop loads, DI trees were moderately water-stressed and this had some positive effects on fruit quality. DI increased fruit firmness (FF), soluble solids concentrations (SSC) and acidity at harvest while no changes were observed in fruit maturity (based on ethylene production). Differences in FF and acidity at harvest between FI and DI fruit were maintained during cold storage. DI also reduced fruit weight loss during storage. But fruit size was reduced under DI. Fruit thinning under DI resulted in better fruit composition with no detrimental effect on fresh-market yield compared to un-thinned fruit. Fruit size at harvest and SSC values after five months of cold storage were higher in fruit from thinned trees than fruit from un-thinned trees. Fruit thinning increased fruit ethylene production, indicating advanced maturity. This may lead to earlier harvest which is desirable in years with impending drought. Fruit thinning is therefore a useful technique to enhance pear marketability under water shortage.

Mitigation of severe water stress by fruit thinning in ‘O’Henry’ peach: Implications for fruit quality

Fruit thinning can be used to relieve water stress in peach but it is not known how fruit quality will respond under water limited conditions. To elucidate this, we applied, over the growing seasons of 2003 and 2004, irrigation and fruit thinning treatments to ‘O’Henry’ peach at the onset of Stage III of fruit development. The treatments were full irrigation (FI) and no irrigation (NI) with each receiving three crop load levels: light, commercial and heavy. Fruit size and fruit skin colouration were lower in NI than in FI but the following were higher in NI fruit: firmness, juice titratable acidity and electrical conductivity, and concentrations of dry matter and soluble solids. All the quality parameters were significantly correlated with tree water status, expressed as midday stem water potential. NI fruit matured 5–10 days later than FI fruit. The increased dry matter concentration, juice acidity, and electrical conductivity in NI fruit were indicative of lower quality at harvest. Choosing a light crop load was not effective in improving NI fruit quality except for the size. Since fruit size is the most important fruit quality attribute, its increase might compensate for yield losses resulting from heavy fruit thinning. Nevertheless, when heavy thinning is performed for mitigation of water stress in Stage III, the overall fruit quality will suffer if severe water stress is inevitable because of shortage or lack of irrigation water.

Crop Load Overwhelms Effects of Gibberellic Acid and Ethephon on Floral Initiation in Apple

Potential strategies against biennial bearing in apple [Malus × sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] include promotion of return bloom with an “on”-year application of ethephon or inhibition of return bloom with an “off”-year application of gibberellic acid (GA), but the influence of initial crop load on the efficacy of these bioregulators is poorly understood. In 2004 and 2005, six total trials were initiated in which whole trees were manually adjusted shortly before anthesis to one of three levels of crop load (100%, 50%, 0%) in ‘Cameo’, ‘Honeycrisp’, and ‘Fuji’; GA4 + 7 was overlaid on trees of each crop level in four trials and ethephon in two. In all trials, initial crop load was the primary determinant of return bloom; proportional influence on flower density, fruit density, and yield was generally most pronounced at the 50% crop level. GA4 + 7 consistently reduced floral initiation, whereas ethephon promoted it. Flowering responses from a historically alternating ‘Cameo’ trial site showed greater sensitivity to ethephon and less sensitivity to GA4 + 7 than did responses from parallel trials established in an annually bearing ‘Cameo’ block, suggesting a predilection of nascent buds to a specific fate before the influence of exogenous bioregulators or gibberellins from seeds produced in developing fruit. Light crop loads and GA4 + 7 applications generally promoted shoot extension, whereas heavy crops and ethephon had the opposite effect.

Role of Crop Load in Chloroplast Ultra-structure and Zonal Chlorosis, a Physiological Disorder in ‘Honeycrisp’ Apple Trees

‘Honeycrisp’ is a relatively new apple cultivar (Malus ×domestica Borkh.) with a unique crisp fruit texture that makes it highly desirable. However, the leaves often develop a zonal chlorosis that resembles potato leafhopper damage. Other researchers have determined that the symptoms correlate with decreasing crop load rather than leafhopper damage. This study investigates the possibility that the zonal chlorosis is related to the buildup of starch grains causing rupture of chloroplasts. Transmission electron microscopy was used to document ultrastructural changes in chloroplasts in trees with three different crop loads from the beginning of the season to the end of the season. In trees with extremely low crop loads, we observed abnormalities of chloroplast membrane structure and accumulation of larger and more numerous starch grains. These appear before the appearance of chlorotic symptoms. By early August, the chloroplasts from chlorotic regions of leaves on trees with light crop loads are completely disrupted and abnormally large starch grains are found in place of chloroplasts. As the season progresses, trees with moderate and heavy crop loads showed less severe chloroplast disruption and smaller starch grain accumulation than trees with light crop load.

(331) In Brazil, Preharvest Calcium Sprays Were Not Always Needed to Improve Fruit Quality of `Gala' Apples

Calcium sprays have improved quality and storage life of apples throughout the world as a result of Ca prevention of many fruit physiological disorders. The efficacy of Ca sprays, however, varies according to soil, cultivar/rootstock, orchard cultural practices, and weather conditions. This study was carried out from 1998 to 2004 in southern Brazil in order to assess the effect of Ca sprays on quality of `Gala' fruits in an orchard planted in 1988 on a density of 1234 trees/ha. Treatments consisted of 0, 4, 8, and 12 sprays of 0.5% CaCl2. Fruits of same size and maturity level were annually analyzed at harvest and after 5 months of cold storage. In five out of six seasons, fruits from all treatments were free of any physiological disorder, and Ca sprays had no effect on leaf composition and on fruit quality attributes (soluble solids, acidity, starch pattern index, flesh firmness, and concentrations of N, K, Ca, and Mg). In the 2000–01 season, however, when yield was 18 t·ha-1 and fruits had an average weight of 175 g, the incidence of bitter pit plus lenticel blotch pit on stored fruits decreased from 24% in the treatment with no calcium to 2% in that with 12 calcium sprays. Two seasons later, yield was also light (25 t·ha-1) and fruits were big in size (168 g), but they did not show any disorders regardless of Ca sprays. It seems that the incidence of Ca related disorders in `Gala' apples grown on limed soils in Brazil only occurs in seasons with a light crop load as a result of large fruits and a high leaf/fruit ratio, associated with some unknown climatic factor.

Antioxidant activity in meiwa kumquat as affected by environmental and growing factors

The effects of photosynthetic photon flux density (PPFD), crop load, and ethephon application on antioxidant activity and antioxidant substances during fruit development were investigated in the meiwa kumquat ( Fortunella crassifolia Swingle). The IC 50 values of superoxide (O 2 −)- and 1-diphenyl-2-picrylhydrazyl (DPPH)-radical scavenging activity in the skin decreased in the days after full bloom (DAFB) from 60 DAFB to harvest. In contrast, the IC 50 values of those in the flesh increased with DAFB. The IC 50 values of DPPH in the skin under high PPFD and O 2 − in the flesh at a light crop load were higher than those of the control. The IC 50 of O 2 −- and DPPH-radical scavenging activity in fruit that had been administered ethephon treatment were lower than those in the untreated control. Ethephon-treated fruit also inhibited lipid peroxidation in the red blood cell system. Ascorbic acid or β-cryptoxanthin concentrations in the skin or flesh were higher under high PPFD, at a light crop load, and with ethephon application. These results suggest that environmental and growing factors may regulate the antioxidant compounds in the fruit, influencing antioxidant activity.

PREHARVEST CALCIUM SPRAYS IMPROVE FRUIT QUALITY OF "GALA" APPLES IN SOUTHERN BRAZIL

Calcium sprays have improved quality and storage life of apple fruits throughout the world. The efficacy of Ca sprays, however, varies according to soil, cultivar, and climatic conditions. This study has being carried out since 1998, in Southern Brazil, to evaluate the effect of calcium sprays on fruit quality of ‘Gala’ apples. Treatments consisted of 0, 4, 8, and 12 applications of 0.5% CaCl2 sprays. Fruits of same size and maturity level were analyzed for soluble solid content, titratable acidity, starch pattern index, flesh firmness, skin background color, russeting, physiological disorders, and for N, K, Ca and Mg, at harvest and after five months of cold storage at –1 °C and 90-95% RH. In the first two years, yield was greater than 45 t ha-1, fruits from all treatments were free of any disorder, and Ca sprays had no effect on any leaf or fruit attribute. In the third season, however, when yield was 18 t ha-1, fruits did not develop any disorder at harvest, but, after storage, the incidence of bitter pit and lenticel blotch pit was inversely related to the number of Ca sprays, ranging from 25% with no calcium to 2% in the treatment with twelve calcium sprays. Averaged across years and treatments, the concentration of Ca in the fruits was 41 mg kg-1. It seems that the incidence of calcium related disorders in ‘Gala’ apples on high pH soils in Southern Brazil only occurs in seasons with light crop load as a result of large fruits and a high leaf/fruit ratio.

CARBON BALANCE MODELING APPROACHES TO INTEGRATING THE EFFECTS OF FOLIAR PESTS, ENVIRONMENT, AND CULTURAL PRACTICES IN APPLES

A basic tenet of integrated pest management (IPM) is that many crop plants can tolerate some threshold level of leaf injury from foliar pests before the crop is affected. In practice, foliar pests are monitored, and pesticides are used only when pests reach a density that is thought to cause too much damage. Sound monitoring methods for many pests have been developed, but our understanding of plant responses to pests is weak. A problem is that pest thresholds are usually used independently for each pest, and do not take into account other factors that affect the crop. We propose that in apple trees; (1) foliar pest injury primarily reduces leaf carbohydrate production and effects of multiple pests are additive, and (2) the effects of foliar pests and other factors on the crop can be integrated by the balance of the tree's carbohydrate supply from the leaves to the demands for crop and tree growth. A dry matter production model developed by Lakso and Johnson in 1990 and subsequently expanded was tested as an integrator of the effects of pests, environmental variations, and cultural practices (initially crop load adjustments) on fruit development. The model simulated the measured effects of European red mites (Panonychus ulmi Koch) on apple fruit growth at different crop levels. Simulations suggest that a threshold response of fruit growth to foliar pests occurs with light crop load, but may not at high crop loads. This is in agreement with empirical studies of pest stress interactions with tree crop load. The model provides a plant-based integration of multiple foliar pests, environment and cultural practices of apples.

DEVELOPMENT OF A PHENOLOGICAL MODEL OF AVOCADO TREE GROWTH IN CALIFORNIA

Mature 'Hass' avocado (Persea americana Mill.) trees four rootstocks (Thomas, Topa Topa, Duke 7, or D9) were monitored from 1992 to 1996 to determine the relative timing of shoot and root growth, bloom, and carbohydrate levels, as well as the relationships between these variables and yield in southern California. Trees exhibited typical alternate bearing patterns with heavy and light crop loads (on and off years, respectively) alternating from year to year. Shoot growth occurred during two distinct flushes each year, one in spring and one in late summer. Although yield varied among rootstocks, neither the rate of shoot growth during flushes nor the total cumulative shoot growth over a season differed among rootstocks. However, cumulative shoot growth was 35 times higher in 1993, when yield was almost nil, as compared to other years. The spring growth flush accounted for the majority of total shoot growth in most years; however, the summer growth flush accounted for more of the total shoot growth during 1993. Root growth did not exhibit dormant periods as shoot growth did, but in general, root growth was greatest when shoots were not actively growing. Crop load did not appear to affect root growth patterns or intensity. Bloom occurred each year from mid-March to mid-May. Bloom did not differ among rootstocks; however, bloom in on years occurred earlier and for a longer period than the bloom in off years. Shoot starch concentrations exhibited greater fluctuations during the year than trunk starch concentrations and were highest immediately before the onset of the spring shoot flush. This information gives us insight into the relative timing of and relationships between growth events of avocado in southern California and will help growers determine the optimal timing of cultural practices.

Production of aroma volatiles in response to deficit irrigation and to crop load in relation to fruit maturity for ‘Braeburn’ apple

Abstract Aroma volatiles are important quality attributes for apples and there is not enough information on how their production is affected by deficit irrigation (DI) or by crop load. We investigated effects of irrigation, crop load, and their interaction on maturity-related quality attributes (aroma volatiles, total soluble solids (TSS), titratable acidity (TA), and firmness) and maturity attributes (internal ethylene concentration, ‘percent ripening fruit’, and starch pattern index) for ‘Braeburn’ apple. Multivariate relationships between these two sets of attributes were also explored. Irrigation treatments were commercially irrigated control (CI) and DI applied throughout the season. Crop load treatments were commercial crop load (CCL) having six fruits per cm 2 of trunk cross-sectional area and light crop load (LCL) having four. There was no interaction between irrigation and crop load on any individual quality attributes. Control and DI fruit had similar maturity at harvest but DI fruit became more advanced in maturity during storage at 20 °C and after cold storage. DI enhanced volatile production during ripening and after cold storage. Firmness and TSS also increased in DI fruit but the increased firmness was lost during subsequent storage. Firmness and TSS increased in LCL in some occasions but crop load had no effect on maturity or aroma volatiles. Fruit TA was not affected by irrigation or crop load. Aroma volatiles poorly correlated with each individual maturity attribute. Canonical correlation analysis showed high multivariate correlation between maturity attributes and maturity-related quality attributes with two underlying dimensions that characterised their relationships. Quality enhancement in DI fruit was related, in part, to the advancement in ripening.

Water use, yield and fruit quality of lysimeter-grown apple trees: responses to deficit irrigation and to crop load

Effective irrigation scheduling for maximum crop yield and quality in a sustainable environment requires a good understanding of crop water use in relation to crop load and soil water availability. This study determined tree water use (TWU), fruit growth, yield, and quality of 'Braeburn' apple grown in lysimeters in response to two irrigation regimes and two crop loads in the growing season of 1997/1998. The irrigation regimes tested were control level of irrigation (CI) and deficit irrigation (DI) and the crop loads were commercial crop load (CCL) and light crop load (LCL) which was equivalent to 60% of the CCL. Tree water use was measured using two methods: soil-water balance through lysimetry and by a heat-pulse technique. There was no significant interaction between irrigation and crop load treatments and therefore only results for the main effects, irrigation and crop load, are presented. DI and LCL reduced TWU. Higher stomatal conductance (gs) was responsible for the higher TWU in CI but not in CCL. Increased mean fruit weight but decreased gross yield was observed in LCL. DI reduced mean fruit weight but had no significant effect on gross yield. Fruit quality, in terms of flesh firmness, total soluble solids, and dry matter concentration, was improved in DI both at harvest and after 12 weeks of cold storage but was, generally, not affected by crop load.

Water relations, photosynthesis, growth, yield and fruit size of ‘Braeburn’ apple: Responses to deficit irrigation and to crop load

SummaryInteractions were investigated between irrigation and crop load on photosynthesis, fruit growth and size, and fruit water relations of ‘Braeburn’ apple. The irrigation treatments were a commercially irrigated control (CI) and deficit irrigation (DI) applied throughout the season. The crop load treatments were commercial crop load (CCL) having six fruit per cm2 of trunk cross-sectional area and light crop load (LCL) having four. There were interactions between irrigation and crop load on fruit water potential (Ψfw), fruit turgor potential (Ψfp), and photosynthetic rate (Pn) during mid and late season, and on mean fruit weight at harvest. These parameters were the same for CCL and LCL under CI except for Ψfp which was lower in CCL. Under DI they were lower in CCL than in LCL. For both crop loads DI reduced Ψfw and Ψfp early in the season but from mid-season Ψfp was maintained through osmotic adjustment. Photosynthetic rates were lower in DI than in CI for both crop loads but differences late in the season were significant only for CCL. Mean fruit weight at harvest was similar for CI and DI for LCL, but was lower in DI for CCL. Interactions between irrigation and crop load on fruit size could be due to effects on fruit water relations and photosynthesis.

166 Influence of Crop Level on Growth and Quality of `Braeburn' Apple Fruit

Crop load and the genetic biological carrying capacity (source–sink relationships) determine the potential for fruit size development on apple; however, the environment within which the fruit grows attenuates this potential. The effects of different crop loads on the growth pattern and the progress of maturity in apples were evaluated at the Comahue National Univ., Argentina (lat. 38 56'S long 67 59'W), during the 1998–99 growing season. Our experiment was conducted on 6-year-old `Braeburn'/Malling Merton 111 apple (Malus domestica Borkh.) trees spaced 4.0 × 2.3 m and trained to palmette leader. Treatments were 1) light crop load (LC), 2.5 fruit/cm2 trunk cross-sectional area (TCSA), 2) moderate crop load (MC), 6.5 fruit/cm2 TCSA (standard commercial crop load) and 3) high crop load (HC), minimum 8 fruit/cm2 TCSA, no fruit removed from tree. Whole trees were hand-thinned 19 days after full bloom (DAFB). Fruit diameter (FD) was taken at two weekly intervals (n = 24 per date and treatment) and maturity indexes were determined at harvest. Analysis of variance was used and mean separations were computed with Student's t test. From 38 DAFB until harvest, fruit size was significantly reduced (P < 0.01) in the HC trees, indicating that they were source-limited during growth. At 166 DAFB, FD was 7.48, 7.14, and 6.89 cm for the LC, MC and HC treatments, respectively. Adequate carbon was apparently available to support a commercial crop load since no differences were found between LC and MC trees. Crop level influenced flesh firmness; at 173 DAFB, it was significantly lower in HC trees than MC and LC trees (84.33, 92.51, and 91.57 N, respectively). These results suggest some goals of thinning for ensuring sizable `Braeburn' fruit.

Effects of crop load on fruit water relations and fruit growth in peach

SummaryMany studies have reported the effect of crop load on leaf water relations of fruit trees but none have dealt with the effect of crop load on water relations of the fruit and how such an effect might influence fruit growth. This is of interest because it could improve our understanding of the relationship between crop load and fruit size. In this study, we measured fruit water potential, fruit osmotic potential, fruit turgor potential and fruit growth, and leaf water potential and leaf conductance on nine-year-old ‘Yanco Queen’ peach ‘Prunus persica (L) Batsch’ trees carrying different levels of crop load. The trees were trained on Tatura trellis and had been either left unthinned (heavy crop load: 450 fruit per tree in 1986 and 560 fruit per tree in 1987) or were thinned (light crop load: 310 fruit per tree). Trees carrying the heavy crop load had lower fruit water potential and higher fruit osmotic potential, and consequently lower fruit turgor potential compared with trees carrying a light crop ...

Reason for 1991 Delayed Pecan Shuck Opening Remains Elusive

Leaf N Yield In 1991, many reports of a delayed shuckopening malady on ‘Stuart’ pecans [Carya illinoinensis (Wangenh.) K. Koch] in the Albany, Ga., area were received regarding apparently well-managed orchards. This is not the late-season shuck necrosis malady attributed to stress (Sparks et al., 1995) and fungi (Reilly, 1994). Drought stress causes shucks to become flaccid and to eventually dry tightly stuck to the shell (Worley, 1982). For the malady described, the shuck remained green and turgid and kernels remained extremely moist with a dark brown seedcoat. Normal shucks would have been dehisced, and nuts would be dry and ready for harvest. A light crop load and low insect and disease pressure in 1990 induced an extremely large crop set in 1991. Abundant rain through the sizing stage made the nuts large, but a drought beginning in mid-August forced many growers to irrigate. Rainfall was 168, 193, 91, 13, 20, and 5 mm for June through November, respectively. The historical norms for these months are 115, 144, 128, 92, 55, and 58 mm, respectively. Mean air temperatures from June through November were 25, 27, 26, 24, 19, and 12C, respectively, with no hard freezes before harvest; historical means for these months are 26, 27, 27, 25, 20, and 15C, respectively. The degree of the malady varied among trees in a research orchard at Tifton. We attempted to determine if the extent of the malady could be associated with pruning, fertilizer treatments, or any of the usual measured characteristics. The orchard was drip-irrigated, insects were controlled, and foliage condition was excellent at harvest (6 Nov. 1991). Nuts were harvested from individual trees. Nuts free of shucks were considered “marketable.” The moist nuts with unopened shucks

Control of Pecan Nut Casebearer on Pecans, 1994

Abstract Six insecticides were evaluated for control of PNC on pecans. Trials were conducted at a commercial pecan orchard located near Longview, TX (Gregg Co.). A section of the pecan orchard was divided into 7 blocks of trees, with each block corresponding to one of the treatments. Each block was ca. one acre in size. Several cultivars were used due to the light crop load encountered. Determination of pretreatment PNC infestation levels was done on 12 May. Twenty-five nut clusters, on each of four trees per block (100 nut clusters per treatment), were inspected for the presence of PNC eggs. If an egg was found on any nut within a cluster, the cluster was considered to be infested. Treatments were applied on 13 May using a Nut Hustler, PTO-driven, air-blast sprayer. The sprayer was calibrated to deliver 90 gpa. Only one application was made. Posttreatment counts were made on 8 Jun. Twenty-five nut clusters, on eacji of 4 trees (100 nut clusters per treatment), were inspected for the presence or absence of PNC damaged nut clusters. A cluster was considered infested if one or more nuts within the cluster showed signs of larval entry.

Studies on Manganese Deficiency in Citrus

1. This investigation was made for clarifying some differences which controlled the manganase content in new mature leaves (3-month-old) of Satsuma orange trees grown on soils having fairly low available manganese.2. One-year-old shoots with new and old leaves were collected at flowering period and green mature stage from 10 trees growing in 5 groves at Yugawara region of Kanagawa Prefecture. Hitherto they had not been suffered from the manganase deficiency. In Ito region of Shizuoka Prefecture, old leaves were collected before bud break and at flowering period from 16 alternative fruit bearing trees, which showed the manganese deficiency symptoms on the new leaves of“off”year trees at their green mature stage. New flushes were collected at flowering period and their green mature stage from above trees, and fine roots were dug out from 3 places at the drip region of each tree.3. From flowering period to green mature stage of new leaves, both manganese contents of new and old leaves on healthy trees increased significantly, and a significant positive correlation existed between the manganese contents of new leaves at 3-month-old stage and those of old leaves at 15-month-old stage.4. Before bud break of first flush of growth cycle, the difference of manganese contents of old leaves on“off”year tree and“on”year tree was not found, but the significant difference was found in manganese contents of new 3-month-old leaves from above trees.5. At flowering period, differences in distributed percentages of absolute manganese contents in each part on 1-year-old shoots of“on”and“off”year trees were found only in the composition of new organs, but was not found in the rate of “old”and“new”part.6. Growth in fine roots in unit soil volume at the drip region of trees which had heavy crop load in previous year was less than that of the trees which had light crop load.7. These results confirmed that manganese contents of new mature leaves are controlled by soil available manganese contents, rates of growth of new flush to old flush, and volumes of fine roots which were affected by different crop loads in the previous year.