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S. Alan Walters

Plastic mulches and rowcovers were evaluated in southern Illinois to determine their influence on watermelon mosaic virus (WMV) disease incidence and symptom severity in susceptible and tolerant summer squash (Cucurbita pepo). The use of either black or white mulch produced greater early and total marketable yields than no mulch (bare soil) on `Dividend' and `Multipik'. More fruit had WMV symptoms with no mulch than with mulch, regardless of cultivar. However, more severe WMV symptoms developed on the fruit of susceptible `Multipik' compared to tolerant `Dividend'. The use of plastic mulches provided greater and longer protection to `Dividend' compared to `Multipik'. However, `Dividend' fruit did eventually develop virus symptoms as disease incidence in production fields increased. Rowcovers reduced the number of alate aphids landing on plants which resulted in fewer plants with WMV symptoms and suppression of symptoms on squash plants regardless of mulch type. Rowcovers had a greater influence on reducing the incidence of WMV and the severity of symptoms on `Dividend' compared to `Elite'. Rowcovers did not reduce WMV on `Elite' by the end of the season and were more effective when used with white mulch compared to black mulch. Rowcovers suppressed the incidence and severity of WMV symptoms that developed on a virus tolerant squash cultivar for a greater length of time compared to a susceptible cultivar, which related to increased yields and fewer culls with virus symptoms on the tolerant cultivar.

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S. Alan Walters

Watermelon mosaic virus (WMV) is often the most limiting factor to cucumber (Cucumis sativus) production in the midwestern U.S. The influence of WMV on farm-gate revenues for nine slicing cucumber (or fresh market cucumber) cultivars was determined under high WMV disease incidence during 2000 and 2001. Over the two growing seasons, most cucumber cultivars produced excessive amounts of unmarketable WMV symptomatic fruit; however, no WMV symptoms were observed on any fruit produced by `Daytona' or `Indy'. `Thunder' produced some WMV symptomatic fruit but was significantly (P ≤ 0.05) less than that produced by all other cucumber cultivars, except for `Daytona' and `Indy.' Consistent high total farm gate-revenues over both years were produced by `Daytona' and `Indy' compared to other cucumber cultivars evaluated with the exception of `Thunder'. `Daytona,' `Indy,' and `Thunder' tended to produce greater early-season farm-gate revenues. However, late-season revenues of `Thunder' were reduced compared to `Daytona' and `Indy'. `Dasher II,' `General Lee,' `Greensleeves,' `Marketmore 76,' `Speedway,' and `Turbo' produced excessive amounts of unmarketable WMV symptomatic fruit which led to reduced farm-gate revenues. Cucumber cultivars without some level of resistance to WMV produced substantially less cumulative farm-gate revenues than those that had some level of resistance. `Daytona,' `Indy,' and `Thunder' were not the highest yielding cucumber cultivars evaluated in this study, but produced the highest farm-gate revenues due to higher levels of genetic resistance to WMV.

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S. Alan Walters

Garlic (Allium sativum) is a popular specialty vegetable sold at many local market venues. Recently, the demand for high-quality garlic has prompted grower interest in producing this crop for direct markets. A 2-year study was conducted at the Southern Illinois University Horticulture Research Center in Carbondale to evaluate eight currently recommended garlic cultivars on a silty loam soil, as well as compare garlic produced on bare soil during the winter and wheat (Triticum aestivum) straw mulch in the spring to black plastic. ‘Idaho Silverskin’ (softneck, silverskin type) and ‘Persian Star’ (hardneck, purple-stripe type) were the best cultivars of those evaluated for the lower midwestern United States based upon various yield and quality characteristics. ‘Idaho Silverskin’ and ‘Persian Star’ had 100% winter survival (regardless of production method), high bulb quality, low amounts of foliar disease, high marketable yields with low cull production (>96% of bulblets developed marketable bulbs), and low amounts of bulb rot (<7%). Black plastic provided greater winter protection for garlic (95% survival rate) compared with bare soil (85% survival rate). Greater marketable weights and bulb diameters (50% and 23% increase, respectively) resulted when garlic was grown in black plastic compared with the bare soil/wheat straw mulch treatment.

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S. Alan Walters

Mini triploid (seedless) watermelons (Citrullus lanatus) are a growing segment of the U.S. watermelon market due to their small, one-serving size. Although mini triploid watermelons were first released and commercially grown about 6 years ago, little information is available for optimum planting densities that are needed to achieve the greatest percentage of marketable fruit in the 3- to 8-lb range. In 2006 and 2007, the fruit grade distribution response to six plant densities (2489, 3111, 4149, 6223, 8297, and 12,446 plants/acre) of four mini watermelon cultivars (Betsy, Petite Treat, Valdoria, and Vanessa) was measured at the Southern Illinois University Horticulture Research Center in Carbondale. ‘SP-1’ was used as the in-row pollenizer at 25% of the total planting. Although all cultivars responded similarly to the plant densities evaluated, ‘Vanessa’ provided the greatest fruit number and weight per acre, and percentage of fruit in the mini grade, compared with the other cultivars. Marketable mini triploid watermelon yield dramatically increased with closer in-row spacings. At lower plant densities (wider in-row spacings), a greater proportion of icebox-sized fruit (>8 lb) was produced, and the amount of marketable, mini-sized fruit (3–8 lb) declined. The grade distribution of mini triploid watermelon numbers and weights were the greatest at the highest plant density evaluated [0.5 ft in-row spacing (12,446 plants/acre)], with about 80% of the total yield in the mini grade. The greatest net revenues were also obtained at this high density. This study indicated that it is critical for producers of mini triploid watermelons to recognize the dramatic impact that plant density has on marketable fruit yield (3–8 lb). Growers of mini triploid watermelons will see a drastic improvement in revenues with closer in-row spacings compared with the approximate 2 ft in-row spacings currently used (about 4000 plants/acre). The increased cost of higher plant densities are more than offset by the greater return on investment.

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S. Alan Walters

Honey bees (Apis mellifera L.) are important pollinators of triploid watermelon [Citrullus lanatus (Thunb.) Matsum & Nakai]. Pistillate (or female) watermelon flowers require multiple honey bee or other wild bee visitations after visiting staminate (or male) flowers for fruit set, and pollination is even more of a concern in triploid watermelon production since staminate flowers contain mostly nonviable pollen. Six honey bee visitation treatments—1) no visitation control, 2) two visits, 3) four visits, 4) eight visits, 5) 16 visits, and 6) open-pollinated control—were evaluated to determine the effectiveness of honey bee pollination on `Millionaire' triploid watermelon fruit set, yield, and quality utilizing `Crimson Sweet' at a 33% pollenizer frequency. `Millionaire' quality characters (hollow heart disorder or percent soluble solids) did not differ (P > 0.05) between honey bee pollination treatments. The open-pollinated control provided the highest fruit set rate (80%) and the greatest triploid watermelon numbers and weights per plot compared to all other honey bee visitation treatments. Fruit set, and fruit numbers and weights per plot increased linearly as number of honey bee visits to pistillate flowers increased from 0 (no visit control) to the open-pollinated control (about 24 visits). This study indicated that between 16 and 24 honey bee visits are required to achieve maximum triploid watermelon fruit set and yields at a 33% pollenizer frequency, which is twice the number of honey bee visits required by seeded watermelons to achieve similar results. This is probably due to many honey bees visiting staminate triploid watermelon flowers (that are in close proximity) before visiting pistillate flowers thus providing mostly nonviable pollen that is useless for fruit set and development. Therefore, more honey bee visits to pistillate triploid watermelon flowers would be required to achieve maximum fruit set and subsequent development compared to seeded watermelons.

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S. Alan Walters

Cucurbit vegetable crops, such as watermelon (Citrullus lanatus), require insect pollination for fruit set, which is usually achieved by placing honey bee (Apismellifera) colonies in a field or relying upon natural bee populations. Pistillate (or female) watermelon flowers require multiple honey bee (or other bee) visitations after visiting staminate (or male) flowers for fruit set, and pollination is even more of a concern in triploid watermelon production since staminate flowers contain mostly nonviable pollen. Six honey bee visitation treatments, 1) no visitation control, 2) two visits, 3) four visits, 4) eight visits, 5) 16 visits, and 6) open-pollinated control, were evaluated to determine the effect of honey bee pollination on `Millionaire' triploid watermelon fruit set, yield, and quality utilizing `Crimson Sweet' at a 33% pollinizer frequency. No differences (P> 0.05) between honey bee pollination treatments were observed for `Millionaire' quality characters (hollow heart disorder or percent soluble solids). The lowest pistillate flower abortion rate (20%) and subsequently the greatest triploid watermelon yields (fruit numbers and weights per hectare) occurred with the openpollinated control compared to all other honey bee visitation treatments. Fruit abortion rates decreased linearly, while fruit numbers and weights per hectare increased linearly as number of honey bee visits to pistillate flowers increased from 0 (no visit control) to the open-pollinated control (≈24 visits). This study indicated that >16 honey bee visits are required to achieve maximum triploid watermelon fruit set and yields, which is twice the number of honey bee visits required by diploid watermelons to achieve similar results.

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S. Alan Walters

The use of no tillage (NT) integrated with cover cropping is a management practice that is becoming more popular with commercial ‘jack-o-lantern’ pumpkin (Cucurbita pepo) growers in the eastern and midwestern United States, although little is known about nitrogen (N) fertilizer requirements for this production system. A field study was established at the Southern Illinois University Horticulture Research Center in Carbondale to evaluate the yield response of pumpkin and associated revenues to N fertilization in a NT production system after wheat (Triticum aestivum) harvest. Nitrogen application rate affected pumpkin leaf chlorophyll content, and resulting yields and revenues. At all sampling dates, pumpkin fertilized with 224 kg·ha−1 N had the greatest leaf chlorophyll content. Quadratic relationships best described pumpkin fruit size and diameter increase with N rates from 0 to 224 kg·ha−1. Furthermore, pumpkin fruit number and weight per hectare also increased in a quadratic manner, as N application rates increased from 0 to 224 kg·ha−1. The application of 168 kg·ha−1 N also provided high yields and large fruit sizes, although quadratic models indicated that maximum net revenues for NT pumpkins were achieved with 224 kg·ha−1 N. Growers applying 224 kg·ha−1 N would increase net revenues by ≈54%, 52%, and 51% at pumpkin fruit price points of $0.33, $0.44, $0.55 per kg, respectively, compared with 0 kg·ha−1 N fertilization. An additional 123 kg·ha−1 N from fertilizer was required for NT pumpkin production after wheat harvest in fields with high amounts of cereal straw residues on the soil surface compared with the 101 kg·ha−1 N recommended for conventional tillage systems with no cover crop residues. This study suggests that N fertilizer investments will provide significant monetary returns in NT pumpkin systems. However, the 168 kg·ha−1 N rate provided the highest return on fertilizer investment at all pumpkin pricing points compared with all other N rates evaluated. Additionally, pumpkins grown in NT systems using a winter grain crop that is ended at flowering should require similar N amounts, because little N is used during heading and grain ripening. Although growers often look for ways to reduce input costs in vegetable production systems, N fertilization is clearly an important investment that provides increased yields and revenues in NT pumpkins. The results of this study should provide additional information to establish N fertilizer recommendations for NT pumpkin production.

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S. Alan Walters* and Bradley H. Taylor

Most small pumpkin growers in Illinois have traditionally relied upon natural insect pollinators to achieve fruit set and development. Many growers fail to understand the importance of pollination and are not aware of the potential benefits of using honey bee colonies to improve pollination and subsequent fruit set of pumpkin. Therefore, a study was conducted over the 2000 and 2001 growing seasons to measure the effectiveness of honey bee colonies on jack-o-lantern pumpkin production. Yields (kg·ha-1) of several cultivars (e.g., `Appalachian' and `Howden') almost doubled when honey bee colonies were present during flowering. Pumpkin weights with the inclusion of honey bees averaged 31,547 kg·ha-1 compared to 22,353 kg·ha-1 for those without honey bees. However, the number of pumpkins per ha was not as drastically influenced by the addition of honey bees; total pumpkin fruits per ha averaged 1,896 with honey bees as compared to 1,704 without honey bees. These results indicate that there were sufficient natural pollinators to induce pumpkin fruit set under field conditions during the study, but fruit size can be significantly increased with the addition of a strong honey bee colony during flowering. Since pumpkins are generally sold on a weight basis, growers should realize greater revenues with the inclusion of honey bee colonies in pumpkin fields.

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S. Alan Walters and Bradley H. Taylor

The objective of this study was to measure honey bee (Apis mellifera L.) impact on seed set, fruit set, and yield of jack-o-lantern (Cucurbita pepo L.), large-sized (C. maxima Duch.), and processing pumpkins (C. moschata Duch. ex Poir.) under field conditions. There were sufficient natural pollinators [including bumblebees (Bombus spp.), carpenter bees (Xylocopa spp.), honey bees, and squash bees (Peponapis pruinosa Say)] provided under field conditions to induce fruit set of jack-o-lantern pumpkins as fruit number obtained per hectare was not affected by the addition of a honey bee colony. However, the addition of honey bees did increase fruit number per hectare of the C. moschata and C. maxima cultivars evaluated. Honey bee pollination resulted in larger-sized fruit, increasing individual fruit size of all but small-sized pumpkins (<0.5 kg). Individual pumpkin fruit weights of the Cucurbita pepo, C. moschata, and C. maxima cultivars evaluated increased by about, 26%, 70%, and 78%, respectively, when honey bee colonies were included. Natural pollination was insufficient to stimulate maximum fruit size development and seed number and seed weight per fruit. Although pumpkin fruit set will occur with natural pollinators, the addition of honey bee colonies will ensure the presence of pollinators to maximize fruit size. Since pumpkins are generally sold on a weight basis, growers may generate greater revenues with the addition of honey bee colonies in pumpkin fields.