Delayed Crop Maturity Research Articles

Studies on Earliness of Bt Cotton Influenced by Moisture Conservation and Fertilizer Levels under Rainfed Condition

A field experiment was conducted at Cotton Research Station, Nanded (M.S.) India during kharif season of 2019 and 2020 to study effect of moisture conservation practices and fertilizer levels on earliness of Bt cotton under rainfed condition. The trial was conducted with Bt cotton hybrid NHH 44 (BG II) in split plot design and was replicated thrice. Four moisture conservation treatments (M1- flat bed, M2- opening of furrow at 60 DAS, M3- application of superabsorbent @ 12.5 kg ha-1 and M4- broad bed and furrow) were evaluated in main plot along with four NPK levels (F1- 80:40:40 kg ha-1, F2 - 100:50:50 kg ha-1, F3 -120:60:60 kg ha-1 and F4 - 140:70:70 kg ha-1) in sub plot. The broad bed and furrow (BBF) practice of moisture conservation was found to have significantly higher seed cotton yield (1369 kg ha-1) and per cent share to the total seed cotton yield was 58.58 per cent in first picking over control. However, opening of furrow recorded more seed cotton yield (1125 kg ha-1) and its share to total yield was 47.97 per cent at second picking. Seed cotton yield in second picking was significantly increased in moisture conservation practices. The BBF was found to have earliness with respect to various indices (Bartlett’s index, combined picking and day index, fraction of first picking index, mean maturity date index and production rate index) followed by other moisture conservation practices over flat bed.
 Fertilizer levels didn’t affect seed cotton yield in first picking. Higher fertilizer levels of F3 and F4 being significant over lower levels for seed cotton yield in second picking; showed delayed crop maturity based on various earliness indices.

Fertilization and Soil Nutrients Impact Differentially Cranberry Yield and Quality in Eastern Canada

High berry yield and quality of conventionally and organically grown cranberry stands require proper nutrient sources and dosage. Our objective was to model the response of cultivar “Stevens” to N, P, K, Mg, Cu, and B fertilization under conventional and organic farming systems. A 3-year trial was conducted on permanent plots at four production sites in Quebec, Canada. We analyzed yield predictors, marketable yield, and fruit quality in response to fertilization and soil properties. Cranberry responded primarily to nitrogen fertilization and, to a lesser extent, to potassium. Berry yield was closely related to the number of fruiting uprights (r = 0.92), berry counts per fruiting upright (r = 0.91), number of reproductive uprights (r = 0.83), and fruit set (r = 0.77). Nitrogen increased berry yield nonlinearly but decreased berry firmness, total anthocyanin content (TAcy), and total soluble solids content (°Brix) linearly, indicating a trade-off between berry yield and quality. Fertilizer dosage at a high-yield level ranged between 30 and 45 kg N ha−1 in both conventional and organic farming systems. Slow-release fertilizers delayed crop maturity and should thus be managed differently than ammonium sulfate. Berry weight increased with added K. Redundancy analysis showed a close correlation between marketable yield, berry quality indices, and soil tests, especially K and Ca, indicating the need for soil test calibration.

Effects of three frequencies of irrigation and nitrogen rates on lint yield, nitrogen use efficiency and fibre quality of cotton under furrow irrigation

Practical solutions to optimise nitrogen use efficiency within modern surface irrigated cotton systems in Australia may be possible by regulating the frequency of water and reducing the N applied, compared with typical current practises. A two-year study examined the effect of irrigating at three different water deficits that applied a similar total irrigation volume: >−60 kPa (HF), between −80 and −100 kPa (IF) and between −100 and −120 kPa (LF) for a period from initial flowering throughout boll development, in combination with different nitrogen fertiliser rates on the growth, yield, nitrogen use efficiency and lint quality of cotton. It was hypothesised that shorter deficits would increase N uptake, and nitrogen use efficiency compared with longer deficits caused by consistently higher soil water potentials in the root zone. The major effects of irrigation treatment on growth was to increase plant height and number of bolls, delay crop maturity and decrease micronaire. The irrigation strategy according to yield was most consistently optimised over both seasons when soil matric potential was maintained between −80 and −100 kPa (IF treatment). Lint yield was reduced by 9–13% when the irrigation deficit was <−100 kPa. The most efficient fertiliser use varied between the two years but was always lowest in the treatment with the highest deficit. Irrigation deficit did not change nitrogen uptake or internal nitrogen use efficiency. Nitrogen, even at rates substantially lower than typically used commercially, did not affect fibre quality. There was no interaction between irrigation strategy and N fertiliser rate on yield, fibre quality and fertiliser use efficiency.

Evaluation of Tillage, At-Planting Treatment, and Nematicide on Tobacco Thrips (Thysanoptera: Thripidae) and Reniform Nematode (Tylenchida: Hoplolamidae) Management in Cotton

There are numerous early-season pests of cotton, Gossypium hirsutum L., that are economically important, including tobacco thrips, Frankliniella fusca (Hinds), and reniform nematode, Rotylenchulus reniformis (Linford &amp; Oliveira). Both of these species have the potential to reduce plant growth and delay crop maturity, ultimately resulting in reduced yields. A field study was conducted during 2015 and 2016 to evaluate the influence of tillage, at-planting insecticide treatment, and nematicide treatment on pest management, cotton development, and yield. Treatment factors consisted of two levels of tillage (no-tillage and conventional tillage); seven levels of at-planting insecticide treatments (imidacloprid, imidacloprid plus thiodicarb, thiamethoxam, thiamethoxam plus abamectin, acephate plus terbufos, aldicarb, and an untreated control); and two levels of nematicide (no nematicide and 1,3-dichloropropene). There were no significant interactions between tillage, at-planting insecticide treatment, or nematicide for any parameters nor was there a difference in the main effect of nematicide on thrips control or damage. The main effects of tillage and at-planting insecticide treatment impacted thrips densities and damage. The no-tillage treatments and aldicarb in-furrow or acephate seed treatment plus terbufos in-furrow significantly reduced thrips populations. Early-season plant response was impacted by tillage and at-planting insecticide treatment; however, that did not result in significant yield differences. In regard to nematicide treatment, the use of 1,3-dichloropropene resulted in lower yields than the untreated.

Effect of Growth Stage on Cotton Response to a Sublethal Concentration of Dicamba

AbstractThe introduction of auxin herbicide weed control systems has led to increased occurrence of crop injury in susceptible soybeans and cotton. Off-target exposure to sublethal concentrations of dicamba can occur at varying growth stages, which may affect crop response. Field experiments were conducted in Mississippi in 2014, 2015, and 2016 to characterize cotton response to a sublethal concentration of dicamba equivalent to 1/16X the labeled rate. Weekly applications of dicamba at 35 g ae ha−1were made to separate sets of replicated plots immediately following planting until 14 wk after emergence (WAE). Exposure to dicamba from 1 to 9 WAE resulted in up to 32% visible injury, and exposure from 7 to 10 WAE delayed crop maturity. Exposure from 8 to 10 and 13 WAE led to increased cotton height, while an 18% reduction in machine-harvested yield resulted from exposure at 6 WAE. Cotton exposure at 3 to 9 WAE reduced the seed cotton weight partitioned to position 1 fruiting sites, while exposure at 3 to 6 WAE also reduced yield in position 2 fruiting sites. Exposure at 2, 3, and 5 to 7 WAE increased the percent of yield partitioned to vegetative branches. An increase in percent of yield partitioned to plants with aborted terminals occurred following exposure from 3 to 7 WAE and corresponded with reciprocal decreases in yield partitioned to positional fruiting sites. Minimal effects were observed on fiber quality, except for decreases in fiber length uniformity resulting from exposure at 9 and 10 WAE.

Effects of simulated seedling defoliation on growth and yield of cotton in southern New South Wales

Early-season leaf loss due to damage by thrips (Thysanoptera: Thripidae) is considered an important issue by Australian cotton growers. To understand the potential impact of early-season leaf loss in the southern region of New South Wales, we investigated the effects of artificial defoliation on cotton growth, maturity timing and lint yield over four seasons (2013–14 to 2016–17) in commercial cotton crops in the Riverina district. Four defoliation scenarios were investigated: (i) complete defoliation, 100% removal of all true leaves from all plants; (ii) partial defoliation by plant, 100% removal of all true leaves from 75% of plants; (iii) partial defoliation by leaf, removal of 75% of leaf area from all individual true leaves on all plants; and (iv) no defoliation. Defoliation was done by hand at the onset of the 2-, 4-, and 6-node growth stages. Defoliated plants were initially shorter than undefoliated (control) plants, but by ~100-days post seedling emergence, height differences were no longer statistically significant in two of the four seasons. Defoliation did not affect the total number of bolls shortly before harvest. However, complete defoliation delayed crop maturity by up to 18 days and partial defoliation by plant delayed crop maturity by up to 8 days. Because of the delays, fully defoliated plants often had fewer open bolls shortly before harvest and yielded significantly less than undefoliated plants in three of the four seasons. A laboratory experiment with caged cotton seedlings showed that weekly introductions of up to10 thrips per seedling (predominantly onion thrips (Thrips tabaci), the most abundant species on cotton in the region) caused significant clubbing in true leaves, but the total leaf area was not significantly reduced at the 6-node stage. Implications of the results for southern cotton integrated pest management are discussed.

Sources of plant resistance to thrips: a potential core component in cotton IPM

AbstractThrips (Thysanoptera: Thripidae) are important pests of seedling cotton and their damage can delay crop maturity and/or reduce yield. Plant resistance to thrips in cotton would reduce the need to treat crops with insecticides for their control. This would support integrated pest management strategies by reducing the risk of selecting insecticide resistance in concomitant pests and of disrupting the natural enemy complex. Traits that reduce thrips abundance in cotton are poorly understood, but dense leaf hairs and high gossypol content are implicated to negatively affect thrips. Furthermore, some diploid cottons are resistant against thrips. Thrips abundance and damage on a range of Gossypium (Malvaceae) genotypes including hairy leaf, smooth leaf (glabrous), okra leaf shape, and diploid species was evaluated over four crop seasons. Thrips were significantly less abundant and they caused less damage on diploid cotton genotypes from Gossypium arboreum L. (BM13H, Roseum A256), Gossypium thurberi Tod. (GOS5310), and Gossypium trilobum (Moc. &amp; Sess. ex DC.) Skov. (GOS5332) than on the standard commercial Gossypium hirsutum L. cv. Sicot 71. There was no significant relationship between thrips abundance or damage and leaf hairiness, leaf hardness, or leaf shape, though conclusions about the value of these traits must be made cautiously as they are confounded across genotypes that differ in a range of traits simultaneously. The diploid cottons had a lower damage per thrips ratio, indicating that they are more tolerant of thrips feeding damage and thus could be valuable sources of host plant resistance to thrips.

Tolerance to Feeding Damage by Cotton Fleahopper (Hemiptera: Miridae) Among Genotypes Representing Adapted Germplasm Pools of United States Upland Cotton

Cotton fleahopper [Pseudatomoscelis seriatus (Reuter)] (Hemiptera: Miridae) is one of the most damaging insect pests of cotton (Gossypium hirsutum L.) in Texas and Oklahoma because of their feeding on small floral buds which are termed squares. Damage to early season squares can reduce yield, delay crop maturity and increase the risk of crop loss because of late season insect pests and adverse weather. Insecticide applications are the only control tactic. The objectives of this study were to determine the tolerance to cotton fleahopper injury to squares among upland cotton genotypes representing the adapted germplasm pools and breeding lines available to cotton breeders in the United States and to evaluate leaf hairiness as a resistant trait. Results of the choice and no-choice trials indicated that four entries, 'Stoneville 474', 'Suregrow 747', 'Deltapine 50', and 'TAM 96WD-22 h', were more tolerant to cotton fleahopper injury relative to the other 11 entries. In choice trials, cotton fleahopper density was significantly correlated with the density of trichomes on leaves, bracts and stems. However, there was no correlation between cotton fleahopper density and percent square damage in the choice trials, suggesting that in some genotypes the response to feeding injury is mediated by host plant resistance factors expressed as tolerance. Results of the no-choice studies also indicate that some genotypes express tolerance to cotton fleahopper feeding.

Weed Ecology and Nonchemical Management under Strip-Tillage: Implications for Northern U.S. Vegetable Cropping Systems

In northern U.S. vegetable cropping systems, attempts at no-till (NT) production have generally failed because of poor crop establishment and delayed crop maturity. Strip tillage (ST) minimizes these problems by targeting tillage to the zone where crops are planted while maintaining untilled zones between crop rows, which foster improvements in soil quality. ST has been shown to maintain crop yields while reducing energy use and protecting soils in vegetable crops, including sweet corn, winter squash, snap bean, carrot, and cole crops. Despite potential benefits of ST, weed management remains an important obstacle to widespread adoption. Increased adoption of ST in cropping systems for which effective, low-cost herbicides are either limited (e.g., most vegetable crops) or prohibited (e.g., organic systems) will require integration of multiple cultural, biological, and mechanical approaches targeting weak points in weed life cycles. Weed population dynamics under ST are more complex than under either full-width, conventional tillage (CT) or NT because weed propagules—as well as factors influencing them—can move readily between zones. For example, the untilled zone in ST may provide a refuge for seed predators or a source of slowly mineralized nitrogen, which affects weed seed mortality and germination in the tilled zone. Greater understanding of such interzonal interactions may suggest manipulations to selectively suppress weeds while promoting crop growth in ST systems. Previous studies and recent experiences in ST vegetable cropping systems suggest a need to develop weed management strategies that target distinct zones while balancing crop and soil management tradeoffs. For example, in untilled zones, optimal management may consist of weed-suppressive cover crop mulching, combined with nitrogen exclusion and high-residue cultivation as needed. In contrast, weed management in the tilled zone may benefit from innovations in precision cultivation and flame-weeding technologies. These short-term strategies will benefit from longer-term approaches, including tillage-rotation, crop rotation, and cover cropping strategies, aimed at preventing seed production, promoting seed predation and decay, and preventing buildup of problematic perennial weeds. However, a concerted research effort focused on understanding weed populations as well as testing and refining integrated weed management strategies will be necessary before ST is likely to be widely adopted in vegetable cropping systems without increased reliance on herbicides.

Effect of water management on dry seeded and puddled transplanted rice. Part 1: Crop performance

An alarming rate of ground water depletion and increasing labour scarcity are major threats to future rice production in north west India. Management strategies that reduce the irrigation amount and labour requirement while maintaining or increasing yield are urgently needed. Dry seeded rice (DSR) has been proposed as one means of achieving these objectives, but little is known about optimal water management for DSR. Therefore a field study was conducted on a clay loam soil in Punjab, India, during 2008 and 2009, to investigate the effects of irrigation management on the performance of puddled transplanted rice (PTR) and dry seeded rice. Irrigation scheduling treatments were based on soil water tension (SWT) ranging from ponding/saturation (daily irrigation) to alternate wetting and drying (AWD) with irrigation thresholds of 20, 40 and 70 kPa at 18–20 cm soil depth. Rainfall was above average and well distributed in 2008 (822 mm), and average and less well distributed in 2009 (663 mm). With daily irrigation, crop duration of PTR and DSR was the same. Shifting from daily irrigation to AWD delayed crop maturity by 8–17 d, and DSR was more affected than PTR, and more so in the drier year. Crop performance in terms of tiller density, leaf area index and growth rate was better in DSR than PTR with daily and 20 kPa irrigation scheduling. However, crop performance was poorer in DSR than PTR at higher (40 and 70 kPa) irrigation thresholds, more so in the drier year when DSR showed signs of severe iron deficiency which was not overcome with iron sprays. Yield components were similar in both establishment methods when irrigation was scheduled daily or at 20 kPa, but panicle density and the number of filled grains per panicle were significantly lower at 40 and 70 kPa in DSR than PTR. Each year, yield of DSR and PTR were similar when irrigation was scheduled daily or at 20 kPa. Yields of both PTR and DSR declined under higher water deficit stress (40 and 70 kPa irrigation thresholds), but more so in DSR, and more so in the drier year. There was a very large and significant decline in irrigation water input with irrigation at 20 kPa compared to daily irrigation in both establishment methods, but only a very small decline in irrigation amount when the threshold was increased from 20 to 40 and 70 kPa. Irrigation water use in DSR-AWD treatments was significantly lower than in respective PTR treatments (e.g. by 33–53% when irrigation was scheduled at 20 kPa). The results suggest the feasibility of reducing irrigation amount while maintaining yield by replacing PTR with DSR with AWD, provided that soil tension is kept lower than 20 kPa at 20 cm depth, but that this threshold needs to be tested over a wider range of seasonal and site conditions and varieties.

An Evaluation of Blueberry Cultivars Grown in Plastic Tunnels in Douglas County, Oregon

Growing fruits and vegetables in plastic tunnels is known to accelerate maturity and protect quality. There are several studies on highbush blueberry (Vaccinium corymbosum) that demonstrate the ability of row covers to advance or delay crop maturity depending on how they are manipulated. Accelerating or delaying harvest time can prove to be very lucrative for producers. However, before producers start putting plastic tunnels over their crops it is important to know how blueberry cultivars will behave when grown under plastic. Six cultivars of southern highbush blueberry and eight cultivars of northern highbush blueberry were grown in a high hoop plastic tunnel for two seasons. Blueberry plants were grown under plastic from February 1 until their harvest was completed each year. After harvest, the plastic covering over the hoops was removed to help the blueberry plants develop fruit buds and meet winter chill requirements. On February 1 the plastic covering was returned to the high hoop tunnel after chilling requirements were met. As expected, fruit maturity dates were 1-3 weeks earlier for all the highbush blueberries grown inside the tunnel versus the same cultivars grown outside. The difference in maturity dates between cultivars grown under plastic and outside did change from one year to the next because of variation in the weather. Despite potential for poor pollination of blueberries in plastic tunnels, yields were significantly enhanced for four cultivars when grown under plastic tunnels. ‘Toro’, ‘Nui’, ‘Legacy’, and ‘Misty’ showed yield gains ranging from 1 to 4 times when grown under a plastic tunnel. Seed numbers per fruit were not significantly impacted by growing plants inside our tunnel.

A Survey of Thrips (Thysanoptera) Species Infesting Cotton Seedlings in Alabama, Arkansas, Georgia, Louisiana, Mississippi, and Tennessee

The common species of thrips that are considered pests of cotton, Gossypium hirsutum (L.), include flower thrips, Frankliniella tritici (Fitch); tobacco thrips, Frankliniella fusca (Hinds); western flower thrips, Frankliniella occidentalis (Pergande); onion thrips, Thrips tabaci (Lindeman); and soybean thrips, Neohydatothrips variabilis (Beach). Thrips feeding on cotton seedlings can inhibit plant growth, reduce plant stand, delay crop maturity, and reduce seed-cotton yield. Surveys were conducted in Alabama, Arkansas, Georgia, Louisiana, Mississippi, and Tennessee to determine the thrips species infesting cotton seedlings during 1996 to 1999. Cotton seedlings were sampled weekly between 7 and 48 days after plant emergence at one to four field sites in each state. Over 12,000 thrips adults were collected using plant washing procedures with 9,005 individuals mounted on slides, and identified to species. The tobacco thrips was the most common species collected in all states, except Georgia, and comprised at least 63% of the thrips adults in all instances, except four. The occurrence of flower thrips and soybean thrips was variable; however, neither species accounted for more than 21% of thrips identified in each state. Western flower thrips accounted for less than 15% of adults collected in all instances except two (28% and 30%) in Louisiana. Also, individual specimens of Thrips nigropilosus Uzel and Anophothrips obscurus Müller were collected in Alabama, and several specimens of Microcephalothrips abdominalis (Crawford) were collected in Arkansas and Louisiana.

Nitrogen Fertilizer Effect on Grain Amaranth

AbstractGrain amaranth (Amaranthus spp.) is an ancient crop that is now receiving fresh attention. This has led to a demand for crop management information, including that on N fertilization. This study evaluated the effect of N fertilizer on amaranth grain yield, yield components, and growth and development. The study was carried out in three Missouri environments with five levels of N fertilizer (NH4NO3 broadcast preplant at 0, 45, 90, 135, and 180 kg N ha−1) and three cultivars (Plainsman, D136, and K266). Averaged across cultivars and environments, N fertilizer at the top rate of 180 kg N ha−1 produced a yield increase of 42% relative to plots receiving no N fertilizer. Yields were consistently improved by additions of 45 and 90 kg N ha−1, but additional N fertilizer above the 90 kg N ha−1 rate increased yield in only one out of three environments. At the one site where yield components were evaluated, yield differences were due to increases in seed number per plant, since seed weight and plant population at maturity were unaffected by N fertilizer rate. Plots with high rates of N fertilizer had later maturity, as indicated by time of flowering and seed moisture. Average moisture of seeds harvested from plots receiving 180 kg N ha−1 was 320 g kg−1, while seeds from plots with no N fertilizer had 240 g kg−1 moisture. Comparing the same high‐N treatment to the control with no N showed height increases of 14, 24, and 44% in the three environments. Although amaranth yield is responsive to N fertilization, high rates of N fertilization can negatively affect grain harvest in terms of excessive plant height, increased lodging, and delayed crop maturity.

Potato Leafhopper Management: Effects on Production and Quality of Alfalfa‐Timothy Mixtures

AbstractAlfalfa (Medicago sativa L.) mixtures with grasses, especially timothy (Phleum pratense L.), are widely planted in the Great Lakes Region, but most information on potato leafhopper [Empoasca fabae (Harris)] (PLH) management for new stands is based on alfalfa monocultures. Field research was conducted in 1991 and 1992 to evaluate the ability of alfalfa to recover from PLH injury following insecticide application and to compare the effect of injury on yield and quality of first‐year monocultures or mixtures. Four replicates of alfalfa monoculture and alfalfa‐timothy mixtures were established each year. One week after the first harvest in early July, eight split‐plot treatments were established in each main plot: an uncaged check, a caged check, and six combinations of two PLH infestation densities (25 or 50 PLH adults m−2) and three insecticide application dates (1 wk after infesting plots, 3 wk after infesting plots, and unsprayed). Crop mixture had no effect on PLH nymphal populations on a per stem basis. Although differences between years were noted, delaying insecticide application generally reduced forage yield and quality, delayed crop maturity, and increased weed content, particularly in forage mixtures. There was little evidence that seedling timothy could compensate for PLH injury to alfalfa. Data on stem elongation and dry matter accumulation indicated that alfalfa can recover from leafhopper injury; however, dry matter production did not increase for at least 2 to 3 wk following a spray application. Reductions in forage crude protein due to PLH injury were a result of both reduced crude protein content in the alfalfa and an increase in the proportion of weed biomass in the forage. Early detection and rapid response to economically significant populations are necessary to realize the greatest benefit from treatment. The presence of timothy in the mixture does not alter PLH management recommendations for new stands.

Bentazon Tank-Mixtures for Improved Redroot Pigweed (Amaranthus retroflexus) and Common Lambsquarters (Chenopodium album) Control in Navy Bean (Phaseolus vulgaris)

Field studies were conducted from 1991 to 1994 to investigate the effectiveness of reduced rates of bentazon in tank-mixtures with imazethapyr, thifensulfuron, or HOE 075032 for improved control of redroot pigweed and common lambsquarters in navy bean. Tank-mixtures of bentazon at 600 g ai/ha plus imazethapyr at 25 g/ha or HOE 075032 at 5 to 15 g/ha controlled both redroot pigweed and common lambsquarters. These rates represent an approximate 45% reduction in total amount of active ingredient needed to control these weeds compared with full label rates. Bentazon tank-mixtures with 2 or 4 g/ha of thifensulfuron controlled these weeds but caused severe injury and delayed crop maturity. In greenhouse studies, the GR25for HOE 075032 in navy bean was &gt; 90 g/ha, while in soybean it was 16 to 24 g/ha.

Yield and Growth Response of Onion to Simulated Storm Damage

Severe storms with high winds, hail, rain, and blowing soil particles can injure onion (Allium cepa L.) leaf and neck tissues. Our study was conducted to determine the growth response of onions to simulated storm damage during bulb development. The effect of removing 33% and 67% of the onion foliage at 14, 28, 42, and 56 days before maturity was examined. In 2 years, 67% defoliation reduced yields more than 33% defoliation. At both levels, defoliation had a greater impact on total marketable yield and yield of individual market classes when it occurred near the onset of bulbing. Of the different market classes of onions, the jumbo (&gt;8.25 cm in diameter) was most consistently affected by defoliation. A moderate (33%) and a severe (66%) foliage loss delayed crop maturity, decreased total marketable yield and potential market value, and changed the market class distribution of a sweet Spanish-type onion.

An analysis of the impact of lygus on cotton

Validation of the cotton simulation model GOSSYM against a commercial crop grown in 1976 at Scott, Mississippi, revealed that a 32% yield loss had occurred due to lygus ( Lygus lineolaris) (Palisot de Beauvois) damage to squares and to fruiting branch development at the eighth and ninth nodes on the plant. Model crops grown under soil and weather conditions at Mississippi State University with various rates of lygus infestation at 0, 11 115, and 22 230 insects per hectare indicate that yield loss due to damage beginning the first week of squaring may be quite variable (7% to 60%) depending on the insect population. The higher insect population delayed crop maturity by two weeks. Simulated yield loss due to damage beginning after the first week of squaring was much less variable averaging about 25%.

Response of Barley to Ethephon: Effects of Rate, Nitrogen, and Irrigation

Lodging incidence in cereal crops depends upon both crop management and environmental conditions. Ethephon [(2‐chloro‐ethyl)phosphomic acid] controls lodging, thus preserving yield. The objective of this study was no investigate the effects of ethephon on spring barley (Hordeum vulgare L.) with different N rates, irrigation treatments, or application rates of ethephon. Ethephon was applied at Zadoks Growth Stage 43 at 0.28 kg ha‐1 in the N and irrigation studies, and at rates between 0.1 and 0.5 kg ha‐1 in the ethephon rate study. Plant height and lodging were reduced by ethephon in each study; however, ethephon did not consistently reduce lodging at Belgian indices of 7.0 and above. Differences in cultivar response were observed. In the ethiphon rate trial, 0.1 kg ha‐1 ethephon reduced lodging of ‘Harrington’, while 0.25 kg ha‐1 was required to similarly reduce lodging of ‘Leduc’. Ethephon reduced the number of kernels per spike, had variable effects on grain mass, and delayed crop maturity by up to 4 d. Whole plant protein was unaffected by ethephon. Ethephon reduced grain protein by 25% and decreased straw protein by 9% in 1986, and had no effect on grain protein in 1987. Ethephon was an effective antilodging agent only under moderate lodging pressures; it is not likely to preserve an increased yield under conditions of intense irrigation and high fertility.

Chemical Efficacy of Early Square Removal and Subsequent Productivity of Superokra‐Leaf Cotton

Delaying fruit set of superokra‐leaf cotton (Gossypium hirsutum L.) can potentially improve yields and provide an excellent trap‐crop system for boll weevil (Anthonomus grandis Boh.) management if a practical means of early‐season square removal could be obtained. We determined the efficacy of ethephon (2‐chloroethylphosphonic acid) applications on removing early squares, effectiveness of Ag+ at reducing damaging effects of ethephon on plant terminals, and subsequent effects of these treatments on the reproductive development of field‐grown superokra‐leaf cottons. All square‐removal treatments caused a significantly greater number of early squares to abscise than occurred normally in untreated plots, but ethephon treatment results were variable. Side‐directed applications of 8 or 12 mM ethephon at 0.28 kg ha−1 and 20 mM ethephon at 0.68 kg ha−1 removed an average of 124% more squares than manual square removal in 1986. In 1987 and 1988, however, 0.28 kg ha−1 ethephon removed 16 and 24% fewer squares than manual methods, respectively. A 200‐mg L−1 AgNO3 pretreatment on plant terminals significantly reduced the number of squares abscised in the ethephon treatments by 20 and 36% in 1986 and 1988, respectively, and did not consistently improve yield or earliness. Removal of early squares delayed the initiation of fruiting, which continued into a delayed crop maturity. Fruiting occurred more rapidly in square‐removal treatments than controls, but the fruiting period still extended later into the growing season, regardless of the accelerated rate. The effect of square removal on seedcotton yield was variable. Square‐removal treatments averaged 2261, 1914, and 2652 kg ha−1 of seedcotton in 1986, 1987, and 1988, respectively. Controls averaged 2585, 1546, and 2839 kg ha−1 in the same respective years. A difference in environmental conditions during fruiting was considered an important factor in yield differences. Although side‐directed applications of ethephon were effective in removing early squares, the variability in yield and the delay in crop maturity offset any potential advantages it may have in a boll weevil trap‐crop system.

Orobanche ramosa L. (broomrape) control in tomato (Lycopersicon esculentum Mill.) with chlorsulfuron, glyphosate and imazaquin

Summary:Chlorsulfuron, giyphosate and imazaquin were evaluated in pot and field studies for their efficacy in controlling broomrape (Orobanche ramosa L.) in tomato (Lycopersicon esculentum Mill.) in Northern Greece. All herbicides were applied four to five weeks after tomato transplanting, when the crop was at early flowering stage and broomrape had started to develop underground attachments. The number of emerged broomrape shoots and underground attachments were less affected by herbicide treatments than the dry weight, suggesting that the herbicides suppress the growth of broomrape rather than kill its underground organs. In the pot experiments, chlorsulfuron applied at 5 g AI ha−1 was the most effective treatment for broomrape control and the least toxic to the crop. Imazaquin and glyphosate applied at 37 and 180 g AI ha−1, respectively, controlled broomrape but imazaquin reduced crop yield. In the field, similar rates of glyphosate and higher rates of imazaquin were not toxic to the crop but were less effective on broomrape. Chlorsulfuron applied at 10 g AI ha−1 controlled broomrape emergence by 88%. When the herbicide was applied twice (5+10 g AI ha−1), it gave complete control of broomrape but delayed crop maturity. The yield of tomato was not increased as a result of these treatments because of low broomrape infestation and a short competition period.