Fresh Market Sweet Corn Research Articles

A Review of Fresh Market Sweet Corn Production and Price Trends from 2010 to 2022

This publication provides information on conventional fresh market sweet corn acreage, volume, and pricing for the top four producing states: California, Florida, Georgia, and New York. (Other states produce a substantial amount of processed market sweet corn but are not the focus here.) This is one in a series of Ask IFAS publications focused on trends in Florida’s five most economically important specialty crops (excluding citrus): fresh market sweet corn, bell peppers, tomatoes, watermelons, and strawberries. This information will be useful to producers, Extension agents, and others interested in trends concerning specialty crop commodities. This publication serves as a unique source summarizing important information about the specialty crop market and production trends.

Substrate and Moisture Affect the Pupation Depth of the Corn Silk Flies Chaetopsis massyla and Euxesta eluta (Diptera: Ulidiidae).

Corn silk flies, or picture-winged flies (Diptera: Ulidiidae), are important pests of fresh market sweet corn in commercial production areas in southern Florida. Issues with pest management related to insecticide resistance, problems in insecticide application, and alternate crop population sources constitute a significant challenge for the protection of developing corn ears. Developed larvae leave cobs and pupate in the soil; however, relatively little is known about these behaviors. In this study, two soil types collected from fields were compared with sand under six different moisture levels in the laboratory to determine the pupation depths of the larvae. Comparisons were carried out concerning the pupation depth of Chaetopsis massyla and Euxesta eluta, which are major pest species in Florida. Both soil type (muck, loamy sand, and sand) and moisture levels (0, 10, 25, 50, 75, 100% field holding capacity) significantly affected pupation depth, with shallow pupation observed under dry or saturated wet conditions. The addition of structures such as pipe cleaners simulating corn roots resulted in deeper pupation under most conditions.

Exploring lethal and sublethal effects of conventional insecticides and insect growth regulators on a picture-winged fly (Diptera: Ulidiidae) pest of sweet corn

Picture-winged flies (Diptera: Ulidiidae) known as corn silk flies are intensively managed with pyrethroids in fresh market sweet corn, Zea mays L., grown in Florida. The identification of alternatives to pyrethroids is needed to increase the efficacy of insecticidal management and to allow the rotation of modes of action for insecticide resistance management (IRM). This laboratory study determined the lethal and sublethal effects of six pyrethroids, five neonicotinoids, four insect growth regulators, two diamides, one spinosyn, one avermectin, and one oxadiazine on adults of the corn silk fly, Euxesta eluta Loew, following topical or ingestion exposure. For topical exposure, pyrethroids caused the highest mortality (≥89%), followed by spinetoram (50%), whereas the remaining insecticides caused <15% mortality. For ingestion exposure, spinetoram caused 95% mortality, followed by dinotefuran, clothianidin, and thiamethoxam, which caused ≥74% mortality. The further evaluation of insecticides causing <15% mortality showed that topical exposure to abamectin reduced by 61.5% the fertility of E. eluta females expressed as the number of larvae per cumulative female-day. None of the insecticides causing <15% mortality following ingestion exposure affected E. eluta fertility. This study confirms that pyrethroids represent the main commercial insecticide option for effective foliar applications targeting adult corn silk flies. Potential alternatives to pyrethroids were highly effective only through ingestion exposure, suggesting the need for the development of management tactics promoting ingestion of insecticides. This study complements pyrethroid susceptibility monitoring for the development of an IRM program in Florida sweet corn.

The impact of post-harvest storage on sweet corn aroma

Fresh market sweet corn ( Zea mays L .) is a high sugar, high moisture vegetable that, due to its fast metabolic rate, is susceptible to rapid post-harvest decay at ambient temperatures. Immediate cooling and storage at low but not freezing temperatures are well established industry practices for maintaining post-harvest sugar content. Less is known about how post-harvest storage temperature impacts other important sweet corn consumer traits, such as aroma. In this study we measure the production and stability of the cooked sweet corn aroma compounds dimethyl sulfide, dimethyl disulfide, dimethyl trisulfide, 3-methyl furan, 3-methyl butanal and 2-methyl butanal. We reveal that these aroma compounds are also susceptible to post-harvest decay if sweet corn is stored at ambient rather than cool temperatures. Furthermore, the quantities and post-harvest decay rates of aroma volatiles vary among different sweet corn lines, indicating that sweet corn genetics can impact maintenance of post-harvest flavor. Some aroma compunds found in cooked sweet corn. • Low temperature post-harvest storage maintains sugar content of sweet corn. • Post-harvest storage also impacts the stability of cooked sweet corn aroma. • Sweet corn varieties can have different aroma profiles and post-harvest stability. • Genetic factors exist to improve the flavor related shelf life of sweet corn.

Pyrethroid Susceptibility in Field Populations of Picture-Winged Flies (Diptera: Ulidiidae) Infesting Fresh Market Sweet Corn in Florida

Picture-winged flies (Diptera: Ulidiidae) are the most damaging insect pests of sweet corn (Zea mays L.) produced in Florida for the fresh market. Management of these pests, referred to as corn silk flies, relies on frequent pyrethroid applications targeting adults. In response to the need for an insecticide resistance management (IRM) program for corn silk flies in this highly intensive crop system, glass vial bioassays were conducted to determine the susceptibility of 12 corn silk fly populations to the pyrethroid beta-cyfluthrin. Two Euxesta eluta Loew and nine Euxesta stigmatias Loew populations were obtained by collecting infested ears in commercial and experimental fields in 2020 and 2021. One E. eluta laboratory colony was used as a susceptible reference population. The E. eluta reference colony was the most susceptible population, with an LC50 value of 0.01 µg/vial. The E. stigmatias field populations were generally less susceptible to beta-cyfluthrin than the E. eluta field populations, with the highest LC50 values attaining 3.51 µg/vial and 0.19 µg/vial, respectively. In addition, the five E. stigmatias populations from commercial sweet corn fields were as much as 17.6 times less susceptible than the four E. stigmatias populations from nontreated fields. Results suggest that E. stigmatias is less susceptible to pyrethroids than E. eluta. Results also suggest that corn silk flies in commercial sweet corn fields are selected for reduced pyrethroid susceptibility throughout the growing season. This study successfully used the glass vial bioassay method for corn silk flies, providing a new tool to initiate an IRM program.

Attraction, Oviposition Preferences, and Olfactory Responses of Corn-Infesting Ulidiidae (Diptera) to Various Host-Based Substrates.

Fresh market sweet corn (Zea mays L., convar. saccharata var. rugosa, Poales: Poaceae) ears produced in Florida are damaged by the larvae of Euxesta stigmatias Loew, Euxesta eluta Loew, and Chaetopsis massyla Walker (Diptera: Ulidiidae) that renders ears unmarketable. No standard lure exists for monitoring these pests. Oviposition substrate and attractant bioassays were designed to identify attractive substrates for further semiochemical investigation. Frass from the fall armyworm, Spodoptera frugiperda J.E. Smith (Lepidoptera: Noctuidae), was more attractive than other ovipositional substrates tested for E. eluta and C. massyla, and resulted in greater ovipositional output. Tassel-derived armyworm frass was more attractive than leaf-derived frass for oviposition. Frass also resulted in greater oviposition output by two species. In attraction bioassays, frass was generally preferred over the corresponding corn tissue, and only C. massyla demonstrated a preference for silk-frass over tassel-frass. The most promising substrates were then evaluated by electroantennography (EAG) to quantify olfactory responses. Frass volatiles also elicited greater antennal responses than corn volatiles. With tassel-frass, greater amplitude EAG responses were recorded from immature E. eluta female antennae, while mature female E. stigmatias exhibited greater responses. Equivalent antennal response to silk-frass was observed from E. eluta. Overall, silk-frass elicited the greatest EAG responses among all three fly species. Our results indicate that armyworm frass is an important resource in the chemical ecology of corn-infesting silk flies, and this substrate warrants further investigation for potential attractants that may facilitate development of novel management tools for these pests.

Evaluation of Two Insecticide Regimens for Control of Sweet Corn Ear Pests, 2015: Table 1

Fresh market sweet corn grown in Southern Florida requires frequent insecticide applications to prevent ear damage by picture-winged flies (Diptera: Ulidiidae, Euxesta spp., Chaetopsis spp.) and fall armyworm (FAW). Pyrethroid rotation efficacy was compared with a reduced-risk insecticide mixed with a protein feeding stimulant to evaluate insect damage to harvested ears. Three 20-row blocks of var. ‘Obsession’ sweet corn were planted on 76.2 cm (30 in.) beds at the Everglades Research and Education Center, Belle Glade, FL on 16 Sept using …

Effects of Brown Marmorated Stink Bug (Hemiptera: Pentatomidae) Feeding Injury on Sweet Corn Yield and Quality.

The brown marmorated stink bug, Halyomorpha halys (Stål), is an Asian species that now dominates the stink bug complex in many cultivated crops throughout the mid-Atlantic United States. Sweet corn (Zea mays L.) is a preferred host of H. halys, and the bug can cause kernel injury on developing ears. Currently, there is limited information available on which plant growth stages are most sensitive to H. halys feeding or density of bugs required to cause yield and quality reductions on processing and fresh market sweet corn ears. In 2011 and 2012, sweet corn ears were infested at three different corn growth stages: silking (R1), blister (R2), and milk (R3) at densities of zero, one, three, and five H. halys adults per ear for 7 d. At harvest, four yield measurements were assessed and ears were inspected for quality reductions. The greatest yield loss from H. halys occurred when infestations were initiated during early stages of ear development, and the greatest quality reductions (damaged kernels) occurred during later stages of ear development. A density of one H. halys per ear resulted in levels of kernel damage great enough to cause significant quality reductions. This study highlights the ability of H. halys to cause substantial economic losses in both fresh market and processing sweet corn in a relatively short period of time at low population densities. Therefore, infestations by this insect in sweet corn must be considered when making pest management decisions in regions where it has become established.

First Report of Phoma terrestris Causing Red Root Rot on Sweet Corn (Zea mays) in North Carolina.

Red root rot, caused by Phoma terrestris E. M. Hansen, caused premature senescence and yield reductions to fresh-market sweet corn in Hyde County, North Carolina in July 2006. Foliar symptoms developed over a period of 5 to 8 days approximately 1 to 2 weeks after anthesis and included desiccation of leaves and poor development of ears. By 3 weeks after pollination, when the sweet corn was harvested, crowns and the first aboveground internode of affected plants were rotted and reddish colored, but roots appeared normal. The root mass of affected plants tended to be greater than that of unaffected plants. Incidence of symptomatic plants was greater than 30% in some fields and was lower on crops planted and harvested early. Symptomatic and asymptomatic plants were adjacent in affected fields. Diseased plants were more common in fields of sweet corn that followed soybean (Glycine max) or a double-crop of onions (Allium cepa) than in fields that followed corn. Incidence of symptomatic plants also differed among adjacent plantings of different sweet corn hybrids. Hybrids '173A', '182A', '378a', and 'XTH1178' had a high incidence of symptomatic plants and '372A', '278A', '8101', and '8102' were less affected. Samples of symptomatic plants of the hybrid '182A' were examined at the North Carolina Plant Disease and Insect Clinic during August. Olivaceous black pycnidia with long setae around the ostioles were imbedded in the stalk near the first node aboveground. Numerous conidia (1.8 to 2.3 × 4.5 to 5.5 μm) were released in cirri from pycnidia. When cultured on potato dextrose agar (PDA), the fungus produced a red pigment and intercalary and terminal chlamydospores. Pathogenicity was demonstrated in the greenhouse by transplanting corn seedlings or direct-seeding corn into pots of soil infested with plates of PDA containing chlamydospores and hyphae. A suspension of chlamydospores and hyphae also was injected into the stems of plants 28 days after transplanting. Five replicates of the pathogenicity experiments were repeated twice with noninoculated controls. After 8 weeks, P. terrestris was recovered from the roots of all inoculated plants. Soil inoculation resulted in necrotic root tissue in approximately 25% of inoculated plants. Approximately 90% of inoculated plants had discolored crowns that resembled symptoms from field infected plants. Stem inoculations resulted in necrosis extending 2 to 5 cm from the point of injection and resulted in shoot death of 40% of inoculated plants that resulted in the development of an adventitious shoot. Red root rot was prevalent on field corn in the Delmarva Peninsula throughout the late 1980s and 1990s (1). To our knowledge, this is the first report of this disease causing damage to sweet corn in North Carolina. Foliar symptoms and discoloration of crowns of diseased sweet corn plants were similar to previously described symptoms of red root rot on field corn (2), however, roots of affected sweet corn plants were not substantially rotted and did not have a symptomatic reddish pink or dark carmine color, presumably because sweet corn is harvested prior to the development of root symptoms.

Fresh market sweet corn production with clear and wavelength selective soil mulch films

Earliness of fresh market sweet corn (Zea mays L.) is important to increasing profitability and maintaining market occupancy. Maturity of fresh market sweet corn may be advanced by the use of plastic soil mulch films. In 2000 and 2001, the effects of clear (CMF) and wavelength selective (WLSMF) mulch films on soil temperature and moisture and the performance of fresh market sweet corn with and without N fertilization were evaluated in a Granby loamy sand soil in southwest Ontario. Both mulch films increased soil temperature and moisture compared with bare soil. Soil temperatures were 1.8°C higher at 5 cm and 1.6°C higher at 15 cm soil depth under CMF than WLSMF averaged over the growing season in two years. Both mulches increased soil moisture levels relative to bare soil, but less increase occurred under CMF than WLSMF. Both CMF and WLSMF advanced sweet corn maturity by 6-7 d relative to the bare soil. Compared with bare soil, marketable yields increased by 25 to 63% without added N and by 72 to 114% with added N under CMF. Under WLSMF, the corresponding increases in marketable yields were 97 to 98% without added N and 120 to 200% with added N. While WLSMF was superior to CMF for increasing fresh market sweet corn yields in southwestern Ontario, the relative economic advantage of each mulch type needs to be studied. Key words: Marketable yield, nitrogen, soil cover, soil moisture, soil temperature

Large‐scale releases of Trichogramma ostriniae to suppress Ostrinia nubilalis in commercially grown processing and fresh market sweet corn

Abstract: We evaluated the egg parasitoid Trichogramma ostriniae (Pang et Chen) (Hym.: Trichogrammatidae) for control of European corn borer [Lep.:Crambidae: Ostrinia nubilalis (Hübner)] in fields of commercial processing sweet corn in New York in 2002 and 2003. We made inoculative releases of 75 000 T. ostriniae/ha when corn was at mid‐whorl and regional O. nubilalis activity had begun. Each release field was paired with a similar non‐release control. The incidence of egg mass parasitism, number of stalk tunnels, incidence of ear damage and effect on insecticide spray decisions were evaluated. Parasitism of cumulative number of O. nubilalis egg masses was 51.3 ± 7.2% and 43.5 ± 5.7% (mean ± SEM) in release fields in 2002 and 2003 respectively. The incidence of ear damage by O. nubilalis was not affected by T. ostriniae in either year of the study. There was no difference in stalk damage between release fields and control fields in either 2002 or 2003. However, individual comparisons between paired release and control fields showed reduced stalk tunnelling in 10 of 19 fields, but ear damage was reduced in only two of 19 fields. Neither the number of actual insecticide sprays nor the number of decisions to spray based on sequential sampling were affected significantly by releasing T. ostriniae. In a separate but related study, where releases were conducted in commercial fresh market sweet corn and used higher rates of release, T. ostriniae had no effect on the number of insecticidal sprays. In an additional experiment using small plots of sweet corn, ear damage was similar whether plots were treated with T. Ostriniae or with insecticide. Additional research should focus on improving the timing, frequency and rate of releases.

Pre‐Sidedress Nitrate Test and Other Crop‐Based Indicators for Fresh Market and Processing Sweet Corn

Commercial sweet corn (Zea mays L.) production requires significant quantities of fertilizer N, leading to inefficient N use and negative environmental impact. A field experiment was conducted for 4 yr (2001–2004) in Ottawa, Canada, to assess and compare presidedress soil nitrate test (PSNT) with some crop‐based measurements (canopy reflectance, leaf chlorophyll and plant total N) for improved N management. A fresh market sweet corn (FMSC, hybrid ‘Temptation’) grown from 2001 to 2003, and a processing sweet corn (PSC, hybrid ‘Hollywood’) from 2002 to 2004, both received five fertilizer N rates (0, 50, 100, 150, and 200 kg N ha−1). Soil samples taken from the V4 to V8 growth stages were analyzed for NO3−–N. Leaf chlorophyll content (SPAD) and canopy reflectance were also measured for FMSC at the same time. All N treatments affected the number of marketable ears, kernel dry weight and total biomass production. However, in most cases, there was no difference between N treatments from 100 to 200 kg ha−1. The PSNT NO3−–N increased linearly with the fertilizer N rates, and there were significant positive correlations between PSNT at V4 to V6 and the number of marketable ears. It was evident that PSNT, plant N concentration at V6, SPAD and canopy reflectance all differentiated sweet corn N response similarly, and they were highly correlated with one another. We concluded that PSNT at V4 to V6 was effective in predicting sweet corn N requirement in this cool and short‐growing region.

Yield Loss in Sweet Corn Caused by Puccinia sorghi: A Meta-Analysis.

Data sets meeting established criteria were included in a meta-analysis of the relationship between percent common rust severity and percent relative yield loss in sweet corn (processing: 20 data sets; fresh market: 14 data sets). The slope of the linear, zero intercept relationship was estimated from each data set. Overall slopes and their respective 95% confidence intervals for the processing and fresh market situations were estimated by a random effects meta-analysis. Results indicated that for processing sweet corn, every 10% increase in rust severity reduced yield by 2.4 to 7.0%; the corresponding reduction for fresh market sweet corn was between 3.0 and 6.2%. A meta-regression analysis did not identify any factors that could account for the observed variability between data sets. An expression was then obtained for Δs, the reduction in rust severity a single strobilurin fungicide spray ought to cause for the cost of the treatment to be offset by the value of the resulting yield improvement. The empirical distribution of Δs,was derived by stochastic simulation, which showed that fungicide usage could be cost effective 90% of the time when rust severity is reduced by 12% in processing sweet corn and by 5% in fresh market sweet corn.

Rates of Seed Treatment Insecticides and Control of Stewart's Wilt in Sweet Corn.

Neonicotinoid insecticides applied as seed treatments reduce the incidence of Stewart's wilt. The objectives of this study were to examine the efficacy of different rates of seed treatment insecticides to control Stewart's wilt on susceptible sweet corn hybrids and to compare the economic value of Stewart's wilt control in sweet corn grown for processing and fresh market. Clothianidin (Poncho), imidacloprid (Gaucho), and thiamethoxam (Cruiser) applied to seed at rates ranging from 0.125 to 1.25 mg a.i. per kernel were evaluated in 11 field trials in Illinois and Delaware from 2000 to 2003. Incidence of Stewart's wilt was significantly lower when seed was treated with insecticides than when plants were grown from nontreated seed in all but one trial. The level of control usually was between 50 and 90%. Small but statistically significant differences in incidence of systemically infected plants occurred among rates of insecticides in all trials except those in 2001. Usually, incidence of systemic Stewart's wilt was lower when higher rates of insecticides were applied; however, increasing the rate of insecticides from 0.125 mg a.i. to 1.25 mg a.i. per kernel had a relatively small effect on the level of Stewart's wilt control compared with the difference between treated and nontreated sweet corn seed. Based on a regression analysis, the lowest rates of the insecticides provided 64 to 72% control. The level of control increased about 1.85% with each additional 0.1 mg a.i. of insecticide per kernel from 0.125 mg a.i. to 1.25 mg a.i. Clothianidin provided an 8 or 9% higher level of control than thiamethoxam or imidacloprid at the same rate. Recommendations for application of seed treatment insecticides to processing and fresh market sweet corn differed somewhat due to substantial differences in the value of the crops. Based on estimated costs of $6 to $12 per 0.4 ha for the seed treatments, the economic break even point (i.e., cost of control = value from control) occurred in the range of 3 to 6% Stewart's wilt incidence for processing sweet corn valued at $325 per 0.4 ha and at about 1% Stewart's wilt incidence for fresh market sweet corn valued at $1,625 per 0.4 ha. Relatively small differences in levels of control conferred by commercially available rates of clothianidin (0.25 mg a.i. per kernel) and thiamethoxam (0.125 mg a.i. per kernel) were of little consequence in processing sweet corn but had considerable economic value in fresh market sweet corn.

In-row Spacing and Cultivar Affects Ear Yield and Quality of Early-planted Sweet Corn

Early-planted fresh market sweet corn (Zea mays) is prone to nonuniform ear length and quality due to uneven germination in cool soils. Growers compensate by reducing in-row spacing at seeding, to increase final plant stand. This risk management strategy was suspected to be reducing quality of early-planted sweet corn, based upon buyer feedback. Four experiments were conducted in upstate New York, to examine the effects of in-row spacing and cultivar on early-planted sweet corn ear yield, length and uniformity. Cultivars examined included `Temptation' (4 years), `Sweet Symphony' (3 years) and `Seneca Spring' (2 years). In-row spacings tested ranged from 6 to 9 inches (15.2 to 22.9 cm), using a 30-inch (76.2-cm) between-row spacing. In-row spacing and cultivar influenced marketable yield, husked ear weight and length of early-planted corn, but the extent varied by year. Despite improvements in individual ear weight and length at wider in-row spacing, marketable yield was usually higher at more narrow spacings. Increases in ear weight at wider spacings were usually associated with increases in weight of the outer, green husk. Average ear length of a cultivar varied between 0.2 and 0.6 inches (0.5 to 1.5 cm) in response to spacing. If ears longer than 7 inches (17.8 cm) were desired, 40% to 60% of ears satisfied this criteria if harvested from plants grown at 8-inch (20.3-cm) in-row spacing or a plant population of 26,000 plants/acre (64,200 plants/ha). Ear weight and length of `Seneca Spring' was not as affected by the in-row spacing treatments compared to the other two cultivars, perhaps due to the small size of this cultivar. Selection of smaller sized sweet corn cultivars for planting at high plant populations (6-inch in-row spacing) may reduce the variation in ear weight under challenging early season conditions. For cultivars with similar growth characteristics and maturities of `Temptation' and `Sweet Symphony,' a minimum in-row spacing of 8 to 9 inches or a plant population of 23,200 to 26,000 plants/acre (57,300 to 64,200 plants/ha) was recommended to minimize variation in ear yield and quality from first bareground plantings in the northeastern United States.

281 Impact of Plant Population, Nitrogen, and Variety on Early Fresh-market Sweet Corn Quality

Early fresh-market sweet corn expressed concern is prone to variability in ear length and quality due to uneven germination rates in cooler soils, smaller plant size of early corn, and single ear per stalk trait of early varieties. In an informal survey of current practices, growers reported using in-row spacings between 0.5 and 0.25 m (0.76 m between rows) for their first bare-ground corn, representing a range of plant populations from 86,000 to 43,000 plants/ha. However, no information had been gathered on the impacts of these various in-row spacings on early corn ear length and overall quality and how different sweet corn types (se, sh2, sweet breeds) might respond to these spacings under cool conditions of early spring. Four trials were conducted over the last 2 years, in upstate New York, examining three sweet corn types, five plant populations, and two nitrogen sidedress rates for effect ear length, quality, and uniformity. In general, results thus far indicate that all three parameters can influence ear quality and variability. Among treatments, ear length varied by up to 1 cm. The variety `Sweet Symphony' was less affected by high populations than `Temptation'. In 1998, no difference in ear length due to spacing was found. It is suspected that the warm spring in 1998, coupled with adequate moisture, reduced plant stress during early growth. Higher nitrogen sidedress rates reduced variability of early season corn, at all populations. In 1999, plant population was found to be the most important factor affecting ear physical characteristics.

Optimum Plant Population for Fresh-market Sweet Corn in the Northeastern United States

There is little published data to support current recommended plant populations of 11,500 to 17,500 plants/acre (28,600 to 34,600 plants/ha) for fresh market sweet corn (Zea mays L.) in the northeastern United States. The plant population likely affects marketable yield and recovery of nitrate. Residual soil nitrate is of concern because of the potential for nitrate contamination of water supplies. Our objectives were to determine the effect of plant population on the yield of sweet corn grown for fresh market without irrigation and on the amount of nitrate in the surface 1 ft (30 cm) of soil at harvest. Seven main-season sweet corn varieties were planted in a total of eight experiments in 1995, 1996, and 1997. Seven experiments were in Connecticut and one was in New Hampshire. All but one of the varieties were standard (su) or sugary enhanced (se) varieties. The experimental design was a randomized complete block with four replications, and the treatments consisted of 12,000, 16,000, 20,000, 24,000, and 28,000 plants/acre (29,600, 39,500, 49,400, 59,300, and 69,200 plants/ha). The yield of marketable ears was classified based on the length of the ears. The results suggest that the current recommendations for plant population in the Northeast US may be too low. Populations of 20,000 and 24,000 plants/acre produced consistently greater yields of ears greater than 7.0 inches (178 mm) long. Soil nitrate-N concentrations at harvest were about 8 mg·kg-1 lower with 16,000 plants/acre or greater, compared with 12,000 plants/acre, which suggests that populations of 16,000/acre or greater should decrease the potential for nitrate contamination of water supplies in the fall, winter, and early spring.

212 Effects of Plant Density on Growth, Yield, and Quality of Fresh-market Sweet Corn

In summer 1998, two sh2, fresh-market, sweet corn cultivars (`Candy Corner'—large plant size, and `Swifty'—small plant size) were grown at 5, 6.5, 8, and 9.5 plants/m2 to investigate the effects of plant density on growth, photosynthesis, biomass, yield, and quality. Biomass and leaf area per plant were not affected by plant density. Therefore, biomass and leaf area per unit area were increased with increasing plant density. Plant height, leaf chlorophyll, leaf photosynthesis, and transpiration (measured with the LI-COR 6400 portable photosynthesis system) were not affected by plant density. Total cob weight (husk off) and number of ears harvested from plants were increased with increasing plant density. However, marketable yield (number of marketable ears) was not affected by plant density and marketable cob weight (husk off) decreased with increasing plant density due to the reduction in ear size with high plant density. There was a significant increase in percentage of unmarketable ears at plant density higher than 6.5 plant/m2 with `Candy Corner'. Kernel sugar content (°Brix) in both cultivars increased with plant density. According to the results of this experiment, the optimum plant density for fresh-market sweet corn was 5 to 6 plants/m 2.

Maturity of Fresh-market Sweet Corn with Direct-seeded Plants, Transplants, Clear Plastic Mulch, and Rowcover Combinations

Sweet corn (Zea mays L.) growers in the upper midwestern U.S. have used clear plastic mulch to improve early yield and advance crop maturity. Results of this practice have been inconsistent because of early season temperature variability and inadequate information on cultivar adaptation. Our objective was to improve the performance consistency by investigating earliness techniques with the early, sugary-enhancer (se) cultivar Temptation planted at two sites. Treatments were bare soil or clear plastic mulch, rowcovers or none, and direct-seeded or transplanted plants. Transplants were produced in the greenhouse in either 50-cell plastic trays or peat pot strips, 2.3 inches × 4.0 inches deep (6 × 10 cm) and were evaluated according to transplant age and cell size. In the cold springs of 1996 and 1997, the use of clear plastic mulch shortened maturity of sweet corn by 1 and 10 days, respectively, for the silt loam site; but no maturity advantage was observed for the loamy sand site. Clear plastic raised the minimum soil temperature by 3.8 to 4.0 °F (2.1 to 2.2 °C) at both sites. The 2-week-old 50-cell tray transplants matured 6 days earlier than the peat pot strip transplants or direct seeded at both locations in 1997. Marketable yield from the transplants was inconsistent by location and year. Four-week-old transplants did not withstand field stress and performed poorly regardless of type of container. Ear quality as indicated by row number, ear diameter, ear length, and tipfill was lowest with transplants.

Treatment Thresholds for European Corn Borer (Lepidoptera: Pyralidae) Infestations in Early-Season Fresh Market Sweet Corn

We examined the effect of varying thresholds for treatment of first generation European corn borer, Ostrinia nubilalis (Hübner), infestations in early-season fresh market sweet corn in eastern New York over a 3-year period. Seven treatment thresholds were compared: (1) 15% infested plants at whorl stage, 5% infested plants at tassel and silk stage, (2) 15% at whorl stage, 15% at tassel and silk stage, (3) 30% at whorl stage, 5% at tassel and silk stage, (4) 30% at whorl stage, 15% at tassel and silk, (5) 5% at tassel and silk stage, (6) 15% at tassel and silk stage, and (7) control (untreated). When thresholds were reached, permethrin was applied using an air-blast sprayer. Results indicated little difference in percentage marketable ears whether plants were treated or not at whorl stage, and the tassel stage threshold could be raised to 15% infested plants with no significant effect on percentage marketable ears. We found no difference in marketable yield among plots treated from one side or both sides with an air-blast sprayer.