Timing Of Defoliation Research Articles

The Effect of Partial Defoliation on Vine Carbohydrate Concentration and Flavonoid Production in Cranberries

The effect of partial defoliation (rate and timing) on vine carbohydrate concentration and the development of phenolic compounds in field-grown `Stevens' cranberry fruit was investigated in two experiments. In Expt. 1, partial defoliation rates of 0%, 18%, 39%, and 53% of total leaf area were applied before new growth, at fruit set, at midfruit development, and preharvest. In Expt. 2, treatments of 0% and 34% removal of new leaves were applied at postfruit set, and at midfruit development. In both experiments, upright samples were harvested for carbohydrate analysis 10d after defoliation, and fruit were removed for analysis before commercial harvest of the site. While total berry phenolic concentration was unaffected by partial defoliation in both studies, the separate pools of flavonoid compounds were affected differently by treatment. In Expt. 1, total flavonol concentration at harvest was improved by the highest rate of partial defoliation (53% of total leaf area) at both fruit set and midfruit development. Total anthocyanin concentration was improved by partial defoliation rates of 39% and 53% of total leaf area compared to the 18% defoliation treatment, but was not affected by timing of defoliation. Pearson correlation coefficients indicated that total flavonol concentration was positively correlated with vine total nonstructural carbohydrate concentration at preharvest, while total anthocyanin concentration was negatively correlated with vine soluble carbohydrates, starch, and total nonstructural carbohydrate concentration at midfruit development. In Expt. 2, total phenolics, flavonols, and anthocyanins were unaffected by partial defoliation; however there was a negative correlation between total anthocyanin concentration in the fruit and soluble carbohydrate concentration in the vine at midfruit development. In these experiments, partial defoliation early in the growing season improved total flavonols and total anthocyanins. Production of flavonols and anthocyanins appeared to be regulated independently of each other.

Regrowth Interval Influences Productivity, Botanical Composition, and Nutritive Value of Old World Bluestem and Perennial Ryegrass Swards

Botanical composition of pasture in much of the Appalachian Region varies as weather patterns interacting with abiotic and biotic factors create conditions allowing a range of plant species to occupy temporal and spatial gaps in the stand. Field‐grown old world bluestem [Bothriochloa caucasia (Trin.) C.E. Hubb.] or perennial ryegrass (Lolium perenne L.) were defoliated at fixed time intervals (1‐, 2‐, or 4‐wk for old world bluestem and 2‐, 4‐, or 6‐wk intervals for perennial ryegrass). Herbage mass, sward botanical composition, and estimates of nutritive value were determined. White clover (Trifolium repens L.), black medic (Medicago lupulina L), and various common forbs and grasses volunteered in all stands. Old world bluestem yields ranged from 3.38 Mg ha−1 (1‐wk regrowth interval in 2002) to 9.42 Mg ha−1 (4‐wk regrowth interval in 2000). Perennial ryegrass yield increased with increasing regrowth interval in 2002, ranging from 3.16 to 7.29 Mg ha−1. The longest regrowth interval did not necessarily lead to the greatest productivity. Old world bluestem swards clipped at 4‐wk intervals decreased 60% by the third growing season, whereas perennial ryegrass swards clipped at 6‐wk intervals increased by 37%. The proportion of encroaching species increased substantially in perennial ryegrass but not old world bluestem swards by 2002, suggesting that combined effects of repeated defoliation and weather influenced sward composition and productivity. Choice of plant resource, timing and intensity of defoliation, and very likely nutrient inputs coinciding with requirements of sown species could influence sward composition and help manage diversity to sustain productivity.

Pengaruh Interval Pemotongan Rumput Brachiaria humidicola (Rendle) Schweick terhadap Konsentrasi Amonia dan Asam Lemak Terbang (In Vitro)

The existence of weeds significantly depressed productivity and quality of herbage. Physically weed controlled by defoliation could be expected to sustain quality and production of herbage, and able to control weeds expansion. The aims of study were to find the effect of interval defoliations of B. humidicola that invited by C. odorata and its effect on concentration of ammonia and volatile fatty acid of B. humidicola herbage (in vitro). The experiment was carried out at Laboratory of Agrostology, Faculty of Animal Science Bogor Agricultural University. In vitro digestibility of herbage was analyzed at Ruminant Nutrition and Feed Chemistry Laboratory, Faculty of Animal Husbandry, Padjadjaran University. Split plot design in time was used in the field experiment. The treatments were nine different planting methods and different defoliation intervals. Defoliation times are divided on the first defoliation and the last defoliation. The results showed that concentration of both ammonia and volatile fatty acid of herbage, which defoliated every 60 days were found significantly higher than those defoliated every 30 days and 90 days. Present and defoliation of C. odorata didn’t give significant effect on the concentration of ammonia and volatile fatty acid of B. humidicola herbage.

Influence of Defoliation on Overwintering Carbohydrate Reserves, Return Bloom, and Yield of Mature Chardonnay Grapevines

The carbohydrate (CHO) reserve physiology of Chardonnay grapevines growing in the cool climate of New Zealand was examined in relation to subsequent flowering and fruiting using defoliation treatments. Vines were defoliated by removing all but the four basal leaves from shoots at monthly intervals starting at four weeks postbloom. Throughout the following season, CHO reserves in the roots and trunks were measured and detailed assessments of vine flowering and yields were recorded. Previous season’s vine defoliation decreased concentrations of overwintering CHO reserves (mostly starch) in both roots and trunks, with earlier defoliation times resulting in the largest reductions. Roots were most sensitive, with early defoliation reducing starch concentrations at budburst to 1.5% DW compared with 17% DW in non-defoliated vines. Reductions in root and trunk CHO reserves were closely associated with significant decreases in inflorescence number per shoot and flower number per inflorescence (up to 50% less than in control vines). Differences in CHO concentrations in both the root and trunk were maintained to veraison, but at flowering had no effect on the percent fruit set in the first season after defoliation. Therefore, lower yields in the following season were caused by fewer inflorescences per shoot and flowers per inflorescence. Shoot growth and total vine pruning weight were also decreased in vines where CHO reserves were reduced. These findings suggest that restricted CHO reserve accumulation as a consequence of defoliation may have a negative impact on subsequent grapevine flowering and productivity, particularly so in a cool-climate environment where there is no postharvest CHO reserve accumulation period.

Consequences of the Elimination of Old Leaves upon Spring Phenological Events and the New Leaves Nutrient Concentration in a Wintergreen Woody Species in the Southern Hemisphere

Previous studies analyzed the importance of old leaves conservancy for wintergreen species plant growth only after early spring old leaves elimination. However, carbon and nutrient resources for growth could have already been translocated from old leaves to shoots during autumn. In this work, the effect of old leaves absence on the leaf mass per area (LMA, g m 2 ) and nutrient concentration of new spring leaves, shoot growth, and flowering was studied in Aristotelia chilensis, an Andean Patagonic woody wintergreen species of Argentina. Plants were studied after autumn defoliation (AD) or late winter defoliation (WD) and results were compared to those of undamaged control plants (CO). The new leaves LMA and mineral nutrient (N, P, K, and Mg) concentration values did not decrease in AD or WD compared to CO plants. Conversely, CO plants showed higher flowering intensity and shoot lengthening compared to AD or WD plants. There were not remarkable differences regarding the defoliation time, though non-flowering shoots grew in a lesser degree than the flowering shoots in WD plants. It was concluded that A. chilensis old leaves cohort is an important source to shoot growth and flowering but their absence does not affect the new leaves structure or nutritional status from early spring in either AD or in WD plants. New leaves formation probably is guaranteed by resources (carbon and nutrients) previously stored in stems or even in the buds containing the preformed leaves since March, by the end of summer. Provided the availability of complete resources for the new leaf flush independently of the old leaves A. chilensis would restore the carbon balance as soon as possible to resume the growth of heterotrophic tissues at normal rates. Endogenous response to counterbalance the old leaves absence on non-flowering shoots was more effective when there was greater lag time between defoliation and shoot growth resume. Flowering and non-flowering shoots compete for the available resources when A. chilensis have not yet expanded leaves and shoots supporting reproductive structures were stronger sinks compared to non-flowering shoots in WD plants.

Effect of timing of defoliation on wheat ( Triticum aestivum) in central Queensland : 2. N uptake and relative N use efficiency

Aspects of nitrogen uptake and use efficiencies were studied in trials quantifying the impact of artificial defoliation on wheat yield and protein content. Late defoliation (after ca. 50 days after sowing, especially in later sowings) led to an increase of hay production, a reduction of N as grain, and nearly always an increase in total N removal. The optimum range of N removal in hay by defoliation was 8–12 kg ha −1 leading to a maximum grain N of 75–79 kg ha −1 and a significantly greater total N recovery and use efficiency. This may be due to greater uptake per se, to reduced plant volatilization of N, or to a combination of the two. The ecological consequence of capturing more N in hay before it is possibly volatilized from plants later in the season is an added benefit to defoliation.

Timing of partial defoliation affects carbohydrate concentration of vegetative tissues and concentration of phenolics in berries of potted De Chaunac (Vitis sp.) grapevines

Partial defoliation of grapevines often increases fruit phenolic content; however, improved light interception by fruit and possible improved photosynthetic efficiency of leaves are confounding factors. In this study, potted De Chaunac grapevines were partially defoliated at three phenological stages, but cluster light environment was unaffected. Partial defoliation at berry set significantly reduced glucose and fructose concentrations in the leaf/shoot tissue, and also reduced total flavonols and total phenolics in the fruit. Vines partially defoliated pre-harvest had increased sucrose concentration in the leaves and roots, increased glucose in the roots, and produced fruit with improved total anthocyanins compared to the control. Key words: Grapevines (French hybrid), carbohydrates, phenolics

Differences in Plastic Responses to Defoliation due to Variation in the Timing of Treatments for Two Species of Sesbania (Fabaceae)

Plastic responses to stress in components of reproduction can have important effects on plant fitness and can vary both within and between species. Responses may also depend on when in the life cycle stress occurs. Here, it is predicted that the timing of initiation of a stress, defoliation, would affect the pattern of plastic responses. These differences should occur because some components of reproduction, such as flower number, are determined earlier in a plant's life than others, such as individual seed mass. To test this prediction, 50 % artificial defoliation treatments were initiated at four different times for Sesbania macrocarpa and S. vesicaria. Responses were measured in plant size, number of flowers, number of flowers/plant size, fruit set, number of seeds per fruit, individual seed mass and total seed mass per plant. For S. vesicaria, changes in the timing of stress changed the severity, but not the pattern of response. For S. macrocarpa, plastic responses to defoliation varied strikingly between early and late treatments. Late treatments resulted in over-compensation in this species. Sesbania macrocarpa was generally more plastic than S. vesicaria and the species showed opposite responses for most components of reproduction. While there were effects of timing of defoliation and differences between species, the nature of these effects did not precisely fit our predictions. Our results suggest that differences in the length and flexibility of the life cycles of the two species allowed for unexpected variation in responses. For example, because flower production continued after the last treatment in S. vesicaria, responses were not constrained to reductions in individual seed mass.

Survival Analysis of Time to Abscission of Blueberry Leaves Affected by Septoria Leaf Spot

ABSTRACT In the southeastern United States, Septoria leaf spot, caused by Septoria albopunctata, can result in premature defoliation of blueberry plants during summer and fall, thereby reducing yield potential for the following year. The effects of disease severity and leaf attributes (leaf age and leaf location in the canopy) on the dynamics (timing and extent) of defoliation were quantified in field plots of Premier rabbiteye blueberry (Vaccinium ashei) in 2002 and 2003. In each year, 50 shoots were selected for assessment in early spring, and all leaves on these shoots (n = 410 and 542 in 2002 and 2003, respectively) were monitored individually for disease progress and time of abscission at 3- to 10-day intervals throughout the season. In both years, disease progress was characterized by an exponential increase in disease severity up to late September, followed by a decline toward the end of the assessment period in late November. Defoliation was sporadic up to late August, followed by more rapid and sustained levels of leaf loss. Abscission of severely infected leaves could explain the decline in disease severity toward the end of the season. Final disease severity (i.e., disease severity on the last assessment date before leaf drop) was highest for leaves that abscised early and lowest for leaves that had not abscised by the end of the assessment period. Survival analysis revealed that older leaves (located on the lower halves of shoots) and leaves with high levels of disease (>/=5 spots/leaf at the time of fruit harvest in mid-June) abscised significantly (P < 0.0001) earlier than younger leaves and leaves with lower disease severity. Relative to their respective reference groups, mean times to abscission were approximately 2 weeks shorter for the older leaf group and approximately 3 weeks shorter in the leaf group afflicted by high disease severity. When an accelerated failure time model was fitted to the data, the resulting parameter estimates indicated that each additional leaf spot present at harvest accelerated time to leaf abscission (expressed using late August as a starting point) by 1.9 and 4.5% in 2002 and 2003, respectively. Leaf location in upper or lower portions of the canopy had no significant effect on time to abscission (P > 0.05).

Do rhizome severing and shoot defoliation affect clonal growth of Leymus chinensis at ramet population level?

Leymus chinensis (Trin.) Tzvel. is a perennial species of Gramineae, usually subject to defoliation from grazing and mowing. We examined whether shoot defoliation and rhizome severing affected rhizome and ramet growth, and vegetative bud outgrowth of L . chinensis ramet populations. We also tested the hypothesis that clonal growth of the ramets subject to defoliation would benefit from clonal integration between interconnected ramets besides from possible compensatory growth. To 48 experimental plots, we applied six treatments resulting from interactions between two rhizome connection states (unsevered/severed) and three defoliation regimes (non-defoliated, mildly-defoliated and heavily-defoliated). Defoliation affected rhizome growth and bud outgrowth, but had little effect on shoot growth. Mild and heavy defoliation exerted similar effects on rhizome growth. Only heavy defoliation significantly reduced bud outgrowth while mild defoliation did not. The fact that shoot growth did not change after defoliation and that the bud numbers remained unchanged after mild defoliation suggest that the compensatory response enable the species to tolerate grazing to some extent. Neither rhizome severing nor the interaction of rhizome severing and defoliation had effect on any tested variables. Lack of the effect of rhizome severing falsified the first half of our hypothesis, that is, clonal integration was unimportant in our experiment. The probable reasons were suspected to be the short duration of the experiment and/or the buffer effect of carbohydrate reserves in rhizomes for shoot growth and bud production in time of defoliation.

Regionalization of disturbance‐induced nitrogen leakage from mid‐Appalachian forests using a linear systems model

AbstractThe ‘leakage’ of nitrate‐nitrogen (nitrate‐N) to surface waters is a common (but not universal) response of forest ecosystems to both human‐induced and natural disturbances. There are several reported examples of the transient leakage of nitrate‐N to surface waters from eastern US forests that have sustained outbreaks of defoliating insects, such as the introduced gypsy moth (Lymantria dispar) larva. Previous research has suggested that annual nitrate‐N leakage from disturbed forests can be modelled using an empirically derived unit nitrogen export response function (UNERF) model. The model represents annual nitrate‐N export as a linear deterministic process in both space and time and is analogous to a unit hydrograph. The goal of the present study was to verify and apply a regionalized, lithology‐based UNERF model that references the geographic distribution of bedrock class and the timing and extent of gypsy moth defoliation of forests in the non‐glaciated highlands of the Chesapeake Bay watershed. Despite an inability to verify the model for most individual watersheds within the study area, the model was able to reproduce the statistical distribution of annual nitrate‐N export to streams that comprised our target population. During water year 1991 (the year following peak defoliation) the model results indicated that regional annual nitrate‐N export had transiently increased by nearly 1500% from a baseline rate of about 0·1 kg ha−1 to a peak value approaching 1·5 kg ha−1. We thus conclude that natural vegetation disturbance is an important mechanism by which dissolved nitrogen is leaked from forested lands to small streams, rivers, and Chesapeake Bay. The present study also illustrates how simple, empirically derived linear systems approaches like the UNERF model can be successfully applied to problems where regionalization is a primary goal. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Does plant growth phase determine the response of plants and soil organisms to defoliation?

To test a hypothesis that the effects of defoliation on plant ecophysiology and soil organisms depend on the timing of defoliation within a growing season, we established a greenhouse experiment using replicated grassland microcosms. Each microcosms was composed of three plant species, Trifolium repens, Plantago lanceolata and Phleum pratense, growing in grassland soil with a diverse soil community. The experiment consisted of two treatment factors—defoliation and plant growth phase (PGP)—in a fully factorial design. Defoliation had two categories, i.e. no trimming or trimming a total of four times at 2 week intervals. The PGP treatment had four categories, i.e. 1, 3, 7 or 13 weeks growth following planting before the first defoliation (subsequently referred to as PGP1, PGP2, PGP3 and PGP4, respectively). In each PGP treatment category, microcosms were harvested 1 week after the final defoliation. Harvested shoot and root mass and total shoot production (including trimmed and harvested shoot mass) increased with time and were lower in defoliated than in non-defoliated systems. The fraction of root biomass of harvested plant biomass decreased with time but was increased by defoliation at PGP3 and PGP4. The proportion of T. repens in total shoot production increased and those of P. lanceolata and P. pratense decreased with time. Defoliation increased the proportions of P. lanceolata and P. pratense in total shoot production at PGP3 and PGP4. Root N and C concentrations increased and root C-to-N ratio decreased with time in non-defoliated systems. Defoliation increased root N concentration by 38 and 33% at PGP1 and PGP2, respectively, but decreased the concentration by 22% at PGP4. In contrast, defoliation reduced root C concentration on average by 1.5% at each PGP. As with the effects on root N concentration, defoliation decreased the root C-to-N ratio at PGP1 and PGP2 but increased the ratio at PGP4. Among soil animal trophic groups, the abundance of herbivorous nematodes was higher at PGP4 than at PGP1–3 and that of predacious nematodes higher at PGP2-4 than at PGP1, while the abundance of bacterivorous, fungivorous and omnivorous nematodes and that of detritivorous enchytraeids did not differ between the PGP categories. Among bacterivorous nematodes, however, Acrobeloides, Chiloplacus and Protorhabditis species decreased and that of Plectus spp. increased with time. Defoliation did not affect the abundance of soil animal trophic groups, but reduced the abundance of herbivorous Coslenchus spp. at each PGP and raised the abundance of herbivorous Rotylenchus spp. and bacterivorous Eucephalobus spp. at PGP4. Confirming our hypothesis, the results suggest that the effects of defoliation on the attributes of grassland plants, such as biomass allocation between roots and shoots and root quality, may depend on the timing of defoliation within a growing season. However, contradicting our hypothesis, the results suggest that significant changes in plant attributes after defoliation may not always lead to substantial changes in the abundance of belowground organisms.

Regrowth and production of herbaceous riparian vegetation following defoliation

Stubble height regulations are frequently used to manage livestock grazing of herbaceous riparian vegetation. The objective of this study was to determine the impact of stubble height, time of clipping and soil water status on production and regrowth of herbaceous riparian vegetation. We used a randomized block design with 4 study sites on each of 3 small (< 2m width) streams in northern Harney County, Ore. In June and July of 2000–2003, 40 × 50 cm experimental plots were clipped to stubble heights of 5.1 (2 inch), 10.2 (4 inch), or 15.2 cm (6 inch), and paired control plots were left unclipped. Complete treatment sets were located adjacent to the stream and 4 m from the stream at each site. All plots were clipped to 1 cm in October and regrowth was calculated by comparing clipped and control plots. Water table depth was measured weekly using PVC wells. Results indicate that height regrowth was associated positively with stubble height (P < 0.01) and was less with July compared to June clipping (P = 0.02). Weight regrowth was also positively related to stubble height (P < 0.01) and decreased with July compared to June clipping (P = 0.04) whereas annual aboveground production increased with July clipping (P = 0.02). Annual production values for clipped plots were higher than for unclipped plots, indicating compensatory production in response to defoliation. Plots distant from the stream had less water availability, but regrowth and production were not strongly influenced by distance from active stream channel. Timing and intensity of defoliation were reliable predictors of regrowth and production performance. Most clipping height × time combinations produced end of season heights sufficient to meet current federal stubble height requirements (i.e., 10–15 cm). Our results provide insight on the timing and intensity of defoliation that will allow for adequate regrowth to meet different management objectives. However, other factors such as stream channel morphology, animal selectivity, and annual weather variation will need to be considered.

Impact of Defoliation on Corn Forage Yield

Farmers, agronomists, and crop insurance adjusters question whether leaf defoliation damage caused by hail or other factors affects corn (Zea mays L.) forage yield the same as grain yield. Our objective was to evaluate the effects of defoliation on corn grown for forage production. In studies conducted during 3 yr at two sites in Wisconsin and one site in Pennsylvania, forage yield decreased as leaf removal increased in severity, and as time of defoliation neared silking. Forage yield response to increasing levels of defoliation was quadratic. Averaged across all environments, forage yield decreased 16% when 100% defoliation occurred at V7. Likewise 100% defoliation decreased forage yield 43, 70, and 40% at V10, R1, and R4 growth stages, respectively. Greater forage yield decreases are measured with early defoliation (V7–V10) than predicted grain yield decreases currently used by hail adjusters. This likely occurred because both increased leaf removal and decreased grain yield combine to reduce forage yield. The response to defoliation from simulated hail damage is different between corn forage and corn grain. Alternative predictive models for estimating forage yield losses should be used by insurance adjusters.

Applications of Survival Analysis in Botanical Epidemiology

ABSTRACT Data on the occurrence and timing of discrete events such as spore germination, disease onset, or propagule death are recorded commonly in epidemiological studies. When analyzing such "time-to-event" data, survival analysis is superior to conventional statistical techniques because it can accommodate censored observations, i.e., cases in which the event has not occurred by the end of the study. Central to survival analysis are two mathematical functions, the survivor function, which describes the probability that an individual will "survive" (i.e., that the event will not occur) until a given point in time, and the hazard function, which gives the instantaneous risk that the event will occur at that time, given that it has not occurred previously. These functions can be compared among two or more groups using chi-square-based test statistics. The effects of discrete or continuous covariates on survival times can be quantified with two types of models, the accelerated failure time model and the proportional hazards model. When applied to longitudinal data on the timing of defoliation of individual blueberry leaves in the field, analysis with the accelerated failure time model revealed a significantly (P < 0.0001) increased defoliation risk due to Septoria leaf spot, caused by Septoria albopunctata. Defoliation occurred earlier for lower leaves than for upper leaves, but this effect was confounded in part with increased disease severity on lower leaves.

Effect of timing of defoliation on wheat ( Triticum aestivum) in central Queensland : 1. Crop response and yield

Through reduction of water demand by defoliation during the vegetative growth period of wheat, it may be possible to optimize use of soil water and in-crop rainfall for enhanced grain yield and water use efficiency. Trials conducted in the field in the sub-tropical and semi-arid region of central Queensland (CQ), Australia, over 3 years (1997–1999) were set up under various water and fertility regimes to test this hypothesis. With an early maturity wheat (cv. Sunstate), under rainfed conditions with no fertilizer application, defoliation treatments at early (DE), or middle (DMT) tillering had not effect on grain yield while those imposed at late (DLT) tillering and booting (DB) reduced grain yield. In 1998, with 76 kg basal N ha −1 and 100 mm irrigation during cropping, an early-sown late maturity wheat (cv. Batativa at the end of April) responded to DLT with an increased grain yield (by 7.3%) through an increase of harvest index (HI by 10.7%) and grain water use efficiency (WUE by 22%) compared to the control, but DB had negative effects on almost all components. Both defoliation treatments of a crop sown 2 months later resulted in yield reduction. In 1999, a similar late maturity wheat cultivar (Batavia 2) was sown on 27 April with 55 kg basal N ha −1 under entirely rainfed conditions. DMT had similar positive effects on grain yield (7.4%), HI (5.9%) and WUE (12.7) to DLT in 1998, but reduced protein content compared to the control. Reduction of plant density by 30% at middle tillering was without effect on grain yield; while DLT raised grain WUE it had no effect on grain yield due to a reduction of above-ground dry matter (AGDM). It also reduced grain protein content. Defoliation treatments of a crop sown one month later had no effect on grain yield. Analysis of physiological data collected in 1999 suggests that defoliation suppressed vegetative growth, optimized the ratio of AGDM at anthesis to that at final harvest (0.5–0.8, peak 0.66) and led to more AGDM post-anthesis for maximal grain production. Defoliation that led to a yield increase also increased the leaf area ratio and enhanced stomatal conductance and photosynthetic capacity at anthesis. It is concluded that defoliation of early (April)-sown wheat defoliated at the middle to late tillering stage could let to greater yield and WUE, and would not result in yield reduction. The value of foliage removed and overall economic and risk analyses are discussed in a further paper.

Management optimization of dual-purpose barley (Hordeum spontaneum C. Koch) for forage and seed yield

Dual-purpose barley (Hordeum spontaneum C. Koch.) is a winter annual native to Southern Mediterranean regions. It is used to establish permanent pasture because it has a brittle rachis. Crude protein, crude fiber contents, and responses of dual-purpose barley to time of defoliation were investigated in the northern mountains of Jordan. Field trials were conducted in the 1999–2000 and 2000–2001 growing seasons in Samta (32° 23′N, 35°50′E) at an elevation of 1043 m. The highest protein contents (P ≤ 0.05) of 25% were recorded in February 2001. Protein content declined gradually and reached the lowest values (2.5%) at maturity. Clipping produced shorter plants, but did not impact tillering.Clipping individual plants on 28 February (14.3 and 10.2 g plant−1, respectively in 2000 and 2001) and 15 March (10.3 and 9.2 g plant−1, respectively in 2000 and 2001) did not reduce the plant shoot weight. Forage production from plants clipped on 28 February (2902 and 1274 kg ha−1, respective years), 15 March (1793 and 1394 kg ha−1, respectively in 2000 and 2001) and 15 April (1554 and 994 kg h−1, respectively in 2000 and 2001) were similar to forage production from unclipped plants. Clipping on 15 April inhibited seed production. Defoliation during early growth stages optimized seed yield and forage quantity and quality.

Effects of Timing of Copper Sprays, Defoliation, Rainfall, and Inoculum Concentration on Incidence of Olive Knot Disease.

The olive knot pathogen, Pseudomonas savastanoi, causes galls on shoots, branches, fruit, and leaves. Shoots girdled by galls die. Any fresh wound is susceptible to infection, but the most common entry sites are leaf scars. Leaf scars are most susceptible to infection during the first 2 days after leaf fall and remain susceptible for 7 more days. Simulated leaf scars on 'Manzanillo' olive trees were created by removing leaves from healthy shoots at approximately monthly intervals from December through June 1997-98, 1998-99, and 1999-2000. Trees were treated with a water suspension of cupric hydroxide (Kocide DF40) at 3 g/liter one, two, or three times in 1998-99 and 1999-2000 with a hand-gun sprayer. Generally, disease control improved with more applications (P = 0.008 and 0.032 in 1999 and 2000, respectively). Disease incidence was greatest on shoots that were defoliated in March 1998, April and June 1999, and March and May 2000. Cumulative rainfall 2 and 9 days after each defoliation was recorded. Disease incidence was positively correlated (P = 0.031 and 0.023 for 2 and 9 days, respectively) with spring (March through June) but not winter (December through February) rainfall. Comparable simulated leaf scars were inoculated in December and April 1997-98 and 1998-99 with 104, 106, and 108 CFU/ml of the pathogen and treated with a water suspension of cupric hydroxide at 3 g/liter using a handheld pump sprayer. Inoculated and noninoculated, nontreated shoots were included. More disease developed in April than in December inoculations (P = <0.0001) in both years. Disease incidence increased with increasing inoculum concentration (P = <0.0001) in both years and was lower in shoots treated with Kocide DF40 (P = <0.0001). Our work demonstrated that the common grower practice of one post-harvest application of copper bactericide provides only minimal protection against olive knot, and that additional sprays in spring are needed to substantially improve disease control.

The Influence of Defoliation Timing on Yields and Quality of Two Cotton Cultivars

The timing of certain cotton (Gossypium hirsutum L.) management practices varies according to the yield potential and quality characteristics associated with a variety. A defoliation timing study was performed to (i) determine if certain cultivars respond differently to defoliation timings and (ii) compare the use of the open boll percentage at defoliation (OBPD), nodes above cracked boll (NACB), and micronaire readings at defoliation for their effectiveness in timing defoliation. The study was conducted in 1999, 2000, and 2001. Treatments consisted of two proprietary cultivars (ST 474 and DP 5409), each defoliated on the basis of OBPD measurements. At the time of defoliation, NACB was recorded and lint samples were retained for later high volume instrumentation (HVI) analysis. Neither variety produced consistently higher yields than the other in this study. In 2000, delaying defoliation from 40 to 60 OBPD would have resulted in a significant addition of approximately 75 kg lint ha−1 for either variety. Stoneville 474 micronaire was highest in all years suggesting that timely defoliation is more critical to ST 474 cotton compared with DP 5409 in years when overall conditions are favorable for high micronaire. DP 5409 fiber length (UHM) values were consistently higher than ST 474 and UHM was unaffected by changes in OBPD values regardless of variety. Stoneville 474 had higher uniformity index (UI) values in all three years and delaying defoliation produced mixed results. The data demonstrate that proper defoliation timing strategies aimed at optimizing quality can vary across varieties. Proper defoliation timing in the two varieties examined in this study varied little with respect to yields. Both NACB and micronaire readings taken at defoliation were more effective for timing defoliation to optimize micronaire readings than OBPD.

The Influence of Defoliation Timing on Yields and Quality of Two Cotton Cultivars

The timing of certain cotton (Gossypium hirsutum L.) management practices varies according to the yield potential and quality characteristics associated with a variety. A defoliation timing study was performed to (i) determine if certain cultivars respond differently to defoliation timings and (ii) compare the use of the open boll percentage at defoliation (OBPD), nodes above cracked boll (NACB), and micronaire readings at defoliation for their effectiveness in timing defoliation. The study was conducted in 1999, 2000, and 2001. Treatments consisted of two proprietary cultivars (ST 474 and DP 5409), each defoliated on the basis of OBPD measurements. At the time of defoliation, NACB was recorded and lint samples were retained for later high volume instrumentation (HVI) analysis. Neither variety produced consistently higher yields than the other in this study. In 2000, delaying defoliation from 40 to 60 OBPD would have resulted in a significant addition of approximately 75 kg lint ha−1 for either variety. Stoneville 474 micronaire was highest in all years suggesting that timely defoliation is more critical to ST 474 cotton compared with DP 5409 in years when overall conditions are favorable for high micronaire. DP 5409 fiber length (UHM) values were consistently higher than ST 474 and UHM was unaffected by changes in OBPD values regardless of variety. Stoneville 474 had higher uniformity index (UI) values in all three years and delaying defoliation produced mixed results. The data demonstrate that proper defoliation timing strategies aimed at optimizing quality can vary across varieties. Proper defoliation timing in the two varieties examined in this study varied little with respect to yields. Both NACB and micronaire readings taken at defoliation were more effective for timing defoliation to optimize micronaire readings than OBPD.