September Planting Research Articles

Yield and Water-Use Efficiency of Eight Wheat Cultivars Planted on Seven Dates in Northeastern Oregon

Wheat (Triticum aestivum L.) yields in the inland Pacific Northwest are limited by inadequate water supply late in the growing season. Choosing a suitable planting date and genotype with the appropriate phenology that matches crop growth to the water supply will produce optimum grain yields. The objectives of this study were to investigate the effects of (i) planting and (ii) wheat genotype differences on grain yield, evapotranspiration (ET), and water-use efficiency (WUE). A 3-yr experiment was conducted on a Walla Walla silt loam (coarse-silty, mixed, mesic Typic Haploxeroll) near Pendleton, OR. Six winter and two spring wheat cultivars were planted in seven planting treatments (planting practices that include planting date, seeding rate, drill type, row space, and seeding depth). Soil water content was measured to determine ET. Planting treatments greatly influenced winter wheat yield. Different winter wheat cultivars responded differently to planting treatments. The optimum yield was produced at October plantings for all cultivars. Yield from September plantings was 745 to 1550 kg ha−1 less than that from the October plantings, and yield also decreased when planting was delayed beyond October. For spring wheat, effect of planting treatments on yield was not statistically significant and there was no significant cultivar effect. Planting treatments significantly affected ET after adjusting for vapor pressure deficit (ET/VPD). Winter and spring wheat planted in the spring had approximately 380 to 650 mm kPa−1 less ET/VPD (approximately 110–160 mm ET) than that planted in the fall. However, WUE was not significantly affected by planting treatments and cultivars.

Severe Root Pruning of Strawberry Bare Root Transplants Is Yield Neutral

In Florida annual hill strawberry (Fragaria ×ananassa Duch.) production, bare-rooted transplants are hand-planted for establishment. Northern latitude or high-elevation nurseries produce these transplants during the summer months and begin digging plants in September for winter production areas. The green-topped bare-root transplants arrive in Florida with varying amounts of root development and number of mature leaves. These plants are planted on raised, black polyethylene mulch beds. Commonly, the root mass exceeds the size of the planting hole, requiring a folding of the roots (J rooting). The objective of this study was to determine if mechanical root pruning has an effect on early or total season fruit yield of strawberry bare-root transplants in a winter production system.

Effect of Planting Date on Vegetable Amaranth Leaf Yield, Plant Height, and Gas Exchange

Field studies were conducted during 1992 and 1993 to determine the effect of six monthly planting dates from April to September on gas exchange, plant height, and leafy fresh and dry yields of vegetable amaranth (Amaranthus tricolor L.). Vegetative growth was satisfactory for May to August planting. Seeds planted in April failed to germinate due to low soil temperatures. Plant growth was significantly reduced in the September planting possibly due to low fall temperatures and shortened day length. Soil and air temperatures 25 °C or higher promoted optimal stand establishment and growth. The vegetative growth of June seeded amaranth took place during the warmest part of the summer and as a result had maximum CO2 exchange rate (CER), plant height, and leafy fresh and dry yields. The relationship between planting date and CER, transpiration rate (E), stomatal conductance (gs), plant height, and leafy fresh and dry yields was quadratic, while a cubic equation provided best fit between the planting date and internal leaf CO2 concentration (Ci). The results suggest that it is possible to stagger the planting of Amaranthus tricolor in the southeastern United States to assure availability of fresh leafy greens throughout the summer. However, the crop produces maximum leaf biomass when grown during the warmest part of the summer.

Effects of solar UV radiation on photosynthesis of the marine angiosperm Posidonia oceanica from southern Spain

The effects of solar irradiance on the photosynthesis of the marine angiosperm Posido- nia oceanica L. Delile were investigated by means of pulse amplitude-modulated (PAM) fluorescence in the Natural Park of Cabo de Gata-Nijar, southern Spain. The study was conducted in 2 different seasons, summer (September 1996) and winter (February 1997). Daily variation in the effective quan- tum yield (∆F/Fm') was determined in plants growing at 2.5 m and in plants transferred from 15 m to 0.5 and 2.5 m depth. Three different experimental designs were conducted: (1) Incubation of shoots under 3 different solar radiation treatments using cut-off UV filters: full solar radiation (PAR + UV-A + UV-B), solar radiation without UV-B (PAR + UV-A) and solar radiation without UV (PAR); (2) short- term exposure (30 min) to high solar irradiance (photoinhibitory phase) under all treatments followed by transfer fo the plants to low irradiance for 4 h (recovery phase); (3) Preincubation of plants for 4 d under the 3 cited treatments followed by short-term exposure (30 min) to high solar irradiance under PAR + UV-A + UV-B, PAR + UV-A and PAR. A significant decrease in ∆ F/Fm' occurred from dawn to noon (18% in September and only 6% in February), followed by total recovery during the afternoon in both seasons. The highest decrease in ∆F/Fm' occurred in shoots illuminated with PAR + UV-A radi- ation. This decrease was more pronounced in winter than in summer, and was substantially higher in plants transferred from deep (15 m) to shallow water than in plants harvested at 2.5 m. Moreover, the recovery in the afternoon was higher in plants incubated at 2.5 m than in those transferred from 15 m to shallow waters. In the second set of experiments, short exposure (30 min) of plants collected from 2.5 m confirmed that inhibition under PAR + UV-A was higher than under PAR + UV-A + UV-B. In general, full recovery after exposure to high solar irradiance (PAR + UVA + UV-B) occurred only in PAR-treated plants in September. Finally, when shoots of P. oceanica were preincubated for 4 d under PAR, PAR + UV-A or PAR + UV-A + UV-B and then submitted to full solar irradiance at the water sur- face, the greatest reduction in ∆ F/Fm' was seen in plants grown under PAR, while the lowest occurred in PAR + UV-A + UV-B pretreated plants in both seasons. Recovery was higher in PAR + UV-A + UV- B pretreated plants. UV solar irradiance also affected both maximal electron transport rate (ETR) and the initial slope of the ETR-irradiance curves. P. oceanica seems to be well acclimated to high solar irradiance, showing a high capacity for recovery. Solar UV-B might be involved in the impairment and recovery of photosynthesis, since removal of UV-B promoted higher inhibition by solar irradi- ance. The absence of UV under high PAR for several days resulted in a partial loss of the capacity for photoprotection. We conclude that UV radiation could act in the natural habitat as a trigger for the induction of photoprotective mechanisms against high solar irradiance. The ecological implication of the beneficial role of UV-B in well-acclimated marine plants to high irradiance is discussed.

Comparative performance of indica and japonica rice (Oryza sativa) varieties under late planted rainfed lowland condition

An experiment was conducted during the rainy (kharif) season of 1996 and 1997 at Pusa, Bihar, in silty loam soil under rainfed lowland conditions to compare the performance of japonica type and 4 photosensitive varieties (PSV) of indica rice (Oryza sativa) planted under late planted conditions on 21, 31 August and 10 September with a seedling age of 65, 75 and 85 days. The HYV Kanak and Mahsuri were not found suitable for late planting due to their staggered flowering and maturity, high incidence of insect pests and diseases, poor yield and profit. In September planting both HYV did not perform well. Weakly PSV, medium bold seeded Rajshree was found suitable up to 31 August planting. Coarse grained PSV Vaidehi was found suitable only up to 21 August planting, with a profit of Rs 7,7081ha. Scented PSV were found suitable in all 3 dates due to less incidence of pests, optimum yield attributes and better market price of grains although their profit in 10 September planting was very marginal (Rs 2,467lha). Highest profit of Rs 9,3281ha was found in Kamini planted on 21 August. Highest uptake of nutrients (N, P,O, K,O) was in PSV Rajshree with 54.3, 32.05 and 61.03 kglha while lowest of 44.1 1, 27.45 and 58.02 in HYV Kanak under this condition.

Relationship Among Seed Size, Planting Date, and Common Root Rot in Hard Red Winter Wheat.

A dryland field study was conducted to determine the effect of seed size and planting date of hard red winter wheat on the severity of common root rot caused by Bipolaris sorokiniana (Sacc.) Shoemaker. Seed of cvs. Hawk, TAM 200, TAM 107, Scout 66, and Siouxland 89 were separated into three size categories of small, mixed, and large and were planted in the first weeks of September and October 1994 and 1995. Disease ratings for incidence and severity of subcrown internode infections were made in March and at harvest. At harvest, grain yields were collected. In both years of the study, there was no interaction between seed size and cultivars for any of the measured variables. Overall, seed size had no effect on disease severity or grain yield for either year. However, when sorted by planting date, plants from small seed yielded less than plants from other seed. October plantings showed lower disease indices than September plantings at the March evaluation. At the harvest disease evaluation, there were no differences in disease severity between planting dates for the first year but, in the second year of the study, plants from the October planting had lower disease than those from the September planting. There was no significant correlation among seed size, final yield, and disease index. The results of this study suggest that the expense of planting higher-quality certified seed cannot be justified for producing hard red winter wheat in dryland conditions in the Texas Panhandle, considering the current price of wheat and the average dryland yield.

Efeito de época de semeadura e adubação na mancha-foliar de Phaeosphaeria em milho

O aumento da área de cultivo de milho, aliado a algumas práticas culturais, tem favorecido o surgimento da mancha-foliar causada pelo fungo Phaeosphaeria maydis. Como conseqüência, o rendimento de grãos tem decrescido, especialmente em áreas com plantio direto e maior amplitude da época de semeadura. O trabalho teve como objetivo avaliar a severidade de P. maydis em seis híbridos de milho, em cinco épocas de semeadura e em dois níveis de adubação. O experimento foi conduzido em Xanxerê, SC, na safra 1997/98, em blocos casualizados, com parcelas subdivididas, em duas repetições. As plantas foram avaliadas 30 dias após o florescimento, e a porcentagem da área foliar afetada foi registrada. Na medida em que a semeadura do milho foi retardada, houve um aumento na severidade da moléstia e uma redução no rendimento de grãos. As doses de adubação não apresentaram diferença quanto à severidade da moléstia. O mês de setembro apresentou menor severidade da mancha-foliar e maior rendimento de grãos. Houve uma correlação significativa entre o rendimento de grãos e a severidade da moléstia.

Effects of Fallow Bermudagrass (Cynodon dactylon) Control Programs on Newly Planted Sugarcane (Saccharumspp. hybrids)

Field experiments were conducted in Louisiana to evaluate the effectiveness of tillage, tillage plus herbicide, and herbicide-only fallow programs in controlling bermudagrass. Tillage of fallow fields three times at 3- to 4-wk intervals between row formation in late May and planting in late September or early October reduced bermudagrass infestations in the newly planted crop in December 44 to 51%. When the final tillage operation was replaced by glyphosate postemergence at either 2.24 or 3.36 kg ai/ha in late August, bermudagrass infestation level in December on the surface of the newly planted rows was reduced to below 20%. Two applications of glyphosate at 3.36 kg/ha were more effective than tillage only and as effective as tillage twice followed by glyphosate in reducing bermudagrass infestation levels in the newly planted crop. Application of atrazine at 3.36 kg ai/ha, imazapyr at 0.68 kg ai/ha, metribuzin at 1.68 kg ai/ha, or sulfometuron at 0.14 and 0.28 kg ai/ha to newly formed rows in late May of the fallow period did not reduce the need for tillage or an application of glyphosate during the fallow period to control bermudagrass, but imazapyr at 1.12 kg/ha did. Sugarcane shoot populations in December of the fallow year were similar for the treatment programs despite differences in bermudagrass infestation levels, which ranged from 11 to 94%. However, sugarcane stalk number and height and cane and sugar yield in the plant-cane crop the following year were highest when glyphosate was applied to bermudagrass as two applications either alone or following the application of atrazine or metribuzin, when tillage was followed with one application of glyphosate, and in 1 yr when imazapyr alone was applied to newly formed rows.

Evaluation of color mulches and oil sprays for yield and for the control of silverleaf whitefly, Bemisia argentifolii (Bellows and Perring) on tomatoes

Orange, yellow, and aluminum color mulches were compared to white (fall) or black (spring) for their effect on the silverleaf whitefly, Bemisia argentifolii (Bellows and Perring), and on the yields of staked, fresh market tomato, Lycopersicon esculentum, Mill, cv. Sunny. In addition, plants were sprayed weekly with a mineral oil emulsion or as needed with a soybean oil emulsion in treatments with orange and yellow mulches, respectively. Under high stress by the whitefly transmitted tomato mottle virus (TMOV), plants in September and October 1990 were taller with the aluminum, yellow and yellow + oil, than with the other mulch treatments ( P < 0.05). Later, in November and December, plants were tallest on the aluminum mulch. Virus symptoms developed slower on plants with the orange + oil, yellow + oil, and aluminum, than with other mulches. Yield of extra-large (70 mm diameter) fruit was higher with the yellow + oil, than with orange, orange + oil, and white mulch ( P < 0.05). Marketable yield was also higher with the yellow + oil, than with any other treatment except with the aluminum mulch. Yields of extra-large and marketable fruits also depended on the first apparent signs of virus infection. Averaged over all mulch treatments, extra-large and marketable yields, respectively, were 0.26 and 3.90 kg/plant when symptoms appeared during the first 30 days after planting (DAP), and 1.01 and 5.39 kg/plant when virus symptoms developed 61 to 77 DAP. In spring 1991, with large whitefly populations towards the end of the season and few plants with virus symptoms at harvest, yields were similar with all mulch treatments. Most immature and adult whiteflies were on the white in the fall and on the black mulch in the spring. With other mulch treatments, a definite trend could not be established between mulch color and number of whiteflies observed on the plants. Yellow mulched tomato plants, when sprayed as needed with the soybean oil emulsion or the aluminum mulch, would be better than using black and white mulches in the full-bed polyethylene mulch system where high whitefly populations are present during the growing season.

Controlled-atmosphere Storage Suppresses Leaf Growth and Flowering in Onion Bulbs

This study was conducted to examine onion bulb sprout and flower induction during controlled-atmosphere and ambient storage, and the suitability of such a system for keeping selected bulbs. This study demonstrated that onion bulbs can be stored for 4 months at 4 °C air or with 1 % O 2 without excessive sprouting and flowering for planting in September to early October. Onion bulbs can be kept up to 7 months in preparation for crossing or general seed production when stored at 4 or 11 °C with 1 % O 2 air

Planting date and nitrogen fertilization effects on lesquerella production

Lesquerella ( Lesquerella fendleri (Gray) Wats.) produces seed containing hydroxy fatty acids similar to castor oil and has good commercial potential. An important step in the commercialization of this plant for the southwestern desert regions of the United States is the development of an efficient agronomic production system. Field experiments were conducted during the 1991–1992, 1992–1993, and 1993–1994 growing seasons at the University of Arizona, Maricopa Agricultural Center, Maricopa, Arizona to determine the effect of planting date and nitrogen fertility on lesquerella seed yield. Results indicate that fall plantings are necessary to obtain high seed production. September plantings generally produced higher yields than the October or November plantings. February plantings produced low yields and appear to be too late for a growing season that ends in June in central Arizona. In all years, lesquerella responded to nitrogen (N) fertilizer. The addition of 60 to 120 kg N/ha increased biomass and seed yields. Nitrogen fertilizer did not affect 1000-seed weight, but decreased seed oil content in the 1993–1994 planting. There is evidence that increasing the N application rate decreases seed oil content in lesquerella.

No-Till Seeding of Grazing-Tolerant Alfalfa as Influenced by Grass Suppression, Fungicide, and Insecticide

No-till planting of grazing-tolerant alfalfa (Medicago sativa L.) offers an opportunity to improve the nutritive quality and seasonal production of endophyte-infected tall fescue (Festuca arundinacea Schreb.) but grass competition and pest problems reduce dependable alfalfa establishment in the southeastern USA. The objectives of this research were to study the following effects on no-till establishment and yield of 'Alfagraze' alfalfa: (i) grass suppression and insecticide and fungicide application with September-planted alfalfa, and (ii) fungicide application date for September and March plantings. Sixteen field experiments were conducted in the limestone valley area near Calhoun, GA, and in the mountains at Blairsville, GA, over 3 yr. Alfagraze alfalfa was no-till planted in September and paraquat (used as a herbicide) grass suppressant, vinclozolin [3-(3,5-dichlorophenyl)-5-ethenyl-5-methyl-2,4-oxazolidinedione] fungicide, and chlorpyrifos [O,O-diethyl O-(3,5,6 - trichloro-2-pyridinyl) phosphorothioate] insecticide were applied alone and in all combinations to compare alfalfa stand and yield with that of a nontreated check. The effect of fungicide application dates on alfalfa forage yield and stand when planted in September or in March were determined in additional experiments. Sod suppression in September was necessary to obtain good alfalfa stands. Insecticide application had little effect on yield. In 2 out of 3 yr at both locations, there was a significant (P < 0.05) response to suppressant and fungicide. For September-planted alfalfa, monthly fungicide application improved forage yield, indicating substantial control of fungal diseases, primarily crown and stem rot caused by Sclerotinia trifoliorum Eriks. In 2 out of 3 yr at two locations, alfalfa yields increased from 48 to 89% with monthly fungicide application on September plantings. March no-till planting resulted in poorer stands and lower alfalfa yields than September plant-ing. Grass suppression was beneficial in no-till planting of alfalfa in northern Georgia. Autumn was superior to winter plant-ing despite potential disease losses in no-till planted alfalfa.

Enhanced denitrification in plots of N2-fixing faba beans compared to plots of a non-fixing legume and non-legumes

Denitrification rates were studied using the C2H2 inhibition technique in a 2-year field experiment within plots of nodulated and non-nodulated faba beans, ryegrass, and cabbage. Denitrification rates ranged from 14.40 to 0.02 ng N2O−N g−1 soil dry weight h−1. Mean denitrification increased fourfold in plots of N2−fixing Vicia faba compared to non-nodulated V. faba mutant F48, Lolium perenne, and Brassica oleracea. The results with and without C2H2 treatment indicate that in the field the major part of this enhanced denitrification led to the endproduct N2 rather than to the ozone-degrading N2O. Higher denitrification rates of plots with N2−fixing plants in September seemed to be caused by an increase in soil NO inf3 sup- of about 20 kg ha−1 found between July and August. Soil NO inf3 sup- and soil moisture explained 67% of the variation in denitrification rates of the different soil samples over the growing seasons in the 2 years. Soil moisture explained 44% of the variation for soil planted with N2−fixing plants and 62% for soil planted with non-fixing plants. Positive exponential relationships were obtained between denitrification rates and soil nitrate (r=0.71) and soil moisture (r=0.82).

Timing of Transplanting Affects Survival of Prairie Perennial Forb Seedlings

Seedlings of six species of native prairie perennial forbs were installed monthly from Oct. 1993 to Nov. 1994 on two highway sites near West Lafayette, Ind. Survival varied significantly among species. Overall, 85% of Aster novae-angliae seedlings survived compared to 15% survival of Liatris pycnostachya seedlings. Survival also varied significantly with time of installation. Three species (Aster novae-angliae, Ratibida pinnata, and Veronicastrum virginicum) exhibited 95% survival when planted in mid-October, compared to 50% survival when planted in March. Fifty-seven percent survival of Echinacea pallida seedlings was observed with April plantings, compared to 9% survival of September plantings. Results of this study indicate that transplant survival rates of particular prairie species may be enhanced by precise timing of planting in late fall or early spring.

Seasonal and Cropping Effects on Total and Fertilizer Nitrogen Use in June-bearing and Day-neutral Strawberries

Total N and fertilizer N (FN) recovery and use by June-bearing `Redchief' strawberry (Fragaria ×ananassa Duch.) and day-neutral `Tribute' grown in matted-row beds were studied over l-year periods. Fertilizer N was field-applied as NH NO at planting in June or September, and all plants were harvested from bed sections in late autumn (November) and at the completion of the spring harvest (June). Distribution patterns of vegetative biomass were similar in both cultivars, with leaf tissue comprising the bulk of the vegetative dry weight per plant at both sampling dates. The fall and spring fruit crops each contributed &gt;40% of the total biomass per plant. Total N accumulation from soil N and FN increased as total biomass increased. Due in part to the additional biomass of the fall fruit crop, `Tribute' recovered 38% more total N per unit bed area than `Redchief'. Over 30% of the fall N total in `Tribute' and the spring N total in both cultivars was partitioned to the fruit. In both cultivars, greater recovery of FN applied in September that at planting time was observed by the postharvest sampling date. However, `Tribute' recovered only 14.2% of the FN applied in September, much less than the amount recovered by `Redchief' during the same interval, implying a diminished ability to absorb FN during fruiting. In all vegetative tissues, soluble reduced N (SRN) was consistently less than insoluble reduced N (IRN) in November and June. Consistent seasonal trends in SRN and IRN values were not evident in any tissue except roots, where SRN content declined from November to June. Allocation of FN to the SRN and IRN pools was related to FN application date, cropping pattern, and total biomass of the component tissue. In both cultivars, the FN content was greater in the IRN than the SRN pool and leaf IRN was the single largest vegetative sink for FN. Fruit N concentration was constant for most of the fall `Tribute' harvest period and declined in both cultivars during spring harvest. The spring `Tribute' fruit crop received more FN from the September than the planting application, while the fall crop exhibited the opposite pattern, suggesting the fruit crop receives more storage than newly absorbed FN. The accumulation of FN in the root SRN pool in November and its depletion through the spring harvest reveals that root SRN plays a significant role in the temporary seasonal storage and internal cycling of N remobilized during spring growth.

Copper deficiency a probable cause of stem deformity in fertilised Eucalyptusnitens

Serious malformation of tree stems and branches was first observed 17 months after planting Eucalyptusnitens (Deane &amp; Maiden) Maiden trees on an improved pasture site in southern Tasmania. The trees were planted in a 52 factorial fertiliser trial with application of nitrogen at 0, 60, 120, 240, and 480 kg/ha and phosphorus at 0, 30, 60, 120, and 240 kg/ha. The phosphorus was semibroadcast as a single dose just after planting in September 1990 and the nitrogen was applied over a 2-year period from planting. At 21 months of age, the degree of malformation increased significantly with increasing levels of nitrogen or phosphorus fertilisers and was most severe at the highest levels of application. There was a significant linear trend of decreasing diameter growth with increasing levels of phosphorus fertiliser. The concentration of Cu in the foliage was significantly lower in malformed than unaffected trees whilst other macro- and micro-nutrient foliar levels were within the normal range for healthy individuals. Whilst the symptoms appear similar to those of "Toorour syndrome" previously reported for Pinusradiata D. Don on improved pasture sites in Australia, we believe the present symptoms may result from Cu deficiency induced at high fertiliser levels. The deformations substantially reduce the merchantability of trees from the plantation.

DETERMINATION OF OPTIMAL SPAN FOR PLANTING AMARANTH IN MIDDLE GEORGIA

Amaranth, Amaranthus spp., is a promising summer leafy vegetable for the Southern United States. Planting of greens is usually spread over a period of time to enable growers to supply the market on a continuous basis. This study was carried out to establish the time span for planting amaranth in Middle Georgia. A. tricolor, genotype “RRC 241” was planted in a randomized complete block experiment on six planting dates one month apart between 14 April and 14 September. Data on plant height, photosynthetic rate and green fresh weight were collected 40 days after planting. June, July and August plantings had similar plant height, which was significantly greater than other planting dates. The plants from June seeding had the highest photosynthetic rate of 25.2 μmol m-2 s-1. Green yields from April, May, June, July, August and September plantings were 0, 0.1, 9.1, 7.4, 5.7 and 2.5 Mg ha-1, respectively. It was inferred that June and July were the best months for planting amaranth in Middle Georgia.

ÉPOCA DE PLANTIO E SEUS EFEITOS NA PRODUTIVIDADE E TEOR DE SÓLIDOS SOLÚVEIS NO CALDO DA CANA-DE-AÇUCAR

Foi conduzido um experimento de campo na Universidade Federal de Santa Maria com o objetivo de determinar a época de plantio da cana-de-açúcar (Saccharum sp.) que maximiza a produção de colmos industrializáveis e o teor de sólidos solúveis no caldo (grau Brix). Foram testadas duas cultivares de cana-de-açúcar (NA 56-79 e IAC 50-134) em oito épocas de plantio, de 15 de agosto de 1985 a 15 de março de 1986. Não houve diferença entre a cana plantada em agosto e setembro e nem entre as cultivares. Na colheita da cana-planta a produtividade média foi de 82,5t/ha para estas duas épocas de plantio. A cana plantada em agosto-setembro alcançou altos rendimentos quando a colheita foi realizada aos 12 meses de idade. A cana-de-açúcar plantada em janeiro/1986 e colhida 19 meses após apresentou maior produção de colmos industrializáveis (167,2t/ha) e foi diferente dos plantios realizados em outubro/1985, janeiro, fevereiro e março/1986. NOS plantios efetuados em janeiro, fevereiro e março a produtividade foi máxima quando a cana-planta foi colhida a partir dos 18 meses de idade. O grau Brix médio, considerando as épocas de agosto e setembro em quatro colheitas foi de 19,8%, independente da cultivar. Em relação às outras épocas de planta, a cana plantada em fevereiro apresentou maior grau Brix (20,1%) e foi diferente das demais épocas, na média de três colheitas.

Germination Response of Subterranean, Berseem, and Rose Clovers to Alternating Temperatures

AbstractAnnual clover (Trifolium spp.) stands are sometimes poor because of low and slow germination due to unfavorable temperatures. The study was conducted to identify optimum temperature for germination of relatively new clover species to the U.S. Southeast to improve stand establishment. High temperature germination was also examined to estimate summer germination which usually results in seedling mortality and a decrease of the soil seed‐bank. Seed of 10 cultivars of T. alexandrinum L., T. brachycalycinum Katzn. and Morley, T. hirtum All., T. subterraneum L., and T. yanninicum Katzn. and Morley were subjected to alternating 12 h day/12 h night temperatures of 15/5, 20/10, 25/15, 30/20 and 35/25 °C. Germination counts were made at 3, 6, 9, and 12 d to determine percent germination and germination rate index (GRI). Germination was &gt;80% for all entries at the three lowest temperature treatments except ‘Larisa’ subclover at 25/15 °. At 30/20 °C, germination of ‘Bigbee‘ berseem and T. brachycalycinum subclovers decreased to 54 to 66%, while the other species decreased to &lt;35%. The 35/25 °C treatment suppressed germination to &lt;25%. The optimum temperature for GRI was 25/15 followed by 20/10, 15/5, 30/20, and 35/25 °C. The optimum germination temperature of 25/15 °C occurs in October along the Texas‐Louisiana Gulf Coast. September plantings (30/20 °C) in this area should be limited to T. alexandrinum and T. brachycalycinum species. Cultivars that germinate at summer temperatures of 35/25 °C or higher should be avoided unless they have a high hard‐seed content.

Seasonal Abundance and Within-Field Dispersion Patterns of Poplar Petiolegall Aphid (Homoptera: Aphididae) in Cabbage and Broccoli

Seasonal abundance and temporal variation in dispersion patterns of the poplar petiolegall aphid, Pemphigus populitransversus Riley, were examined in serial planting studies of cabbage and broccoli from 1986 to 1988 using variance/mean ratio S2 / |$\bar x$| , Green's C x , Standardized Morisita's Ip , and Taylor's regression of log variance on log mean. All indices predicted an aggregated dispersion of aphid numbers, with no apparent trends in seasonal variation in dispersion. Values of β from Taylor's regression were homogeneous among cultivars and plantings in 1986–1987, but the slope calculated for aphid dispersion in the September planting differed from the β values estimated in October and December plantings in 1987–1988. The estimated β calculated from the commercial cabbage field was not different from most of the serial plantings. Alate fundatrigenia began emerging from laboratory-held galls in early July, and peak emergence occurred from October through November. There was a corresponding empirical trend of higher aphid densities in September plantings and progressively less dense populations in the October–December plantings. It is hypothesized that there was differential exposure to aphid colonization among plantings. A pooled estimate of α and β were used to determine the number of samples required to obtain an estimate of the mean density of P. populitransversus in crucifers within 10 and 25% of the true mean. An alternate method of population estimation, using a presence–absence sample, was also presented.