Jonathan R. Schultheis

North Carolina State University | NCSU · Department of Horticultural Science

Grafting watermelon scions to interspecific squash hybrids has been found to increase fruit firmness. Triploid (seedless) watermelon are prone to hollow heart (HH), an internal fruit disorder characterized by a crack in the placental tissue expanding to a cavity. Although watermelon with lower tissue firmness tend to have a higher HH incidence, ass...

In triploid (seedless) watermelon [Citrullus lanatus var. lanatus (Thunb. Matsum. and Nakai)], hollow heart (HH) is a disorder that is expressed as a crack in the center of the fruit that expands to an open cavity. Although HH incidence and severity is part of a screening process for marketable watermelon fruit during cultigen evaluations, HH incid...

Internal necrosis (IN) is a physiological disorder that affects Covington, the most commonly grown sweetpotato ( Ipomoea batatas ) cultivar in North Carolina. Because IN affects the quality of sweetpotato storage roots, studies have been conducted since the first report of IN in 2006. Field studies (three in 2016 and two in 2017) were conducted to...

The grower advisory committee for the US Sweetpotato Council reported that a critical need exists for management options to limit sweetpotato yield loss due to weeds. Therefore, studies were conducted in 2018 at the Syngenta Greenhouse complex in Greensboro, NC, and in the field from 2016 to 2018 at the Horticultural Crops Research Station, Clinton...

Palmer amaranth is the most common and troublesome weeds in North Carolina sweetpotato. Therefore, field studies were conducted in Clinton, NC in 2016 and 2017 to determine the critical timing of Palmer amaranth removal in ‘Covington’ sweetpotato. Palmer amaranth was grown with sweetpotato from transplanting to 2, 3, 4, 5, 6, 7, 8, and 9 wk after t...

Herbaceous grafting can be used to manage numerous soilborne pathogens in cucurbits. Rootstocks have been reported to increase the growth of the scion possibly due to more efficient use of nitrogen compared with non-grafted plants. The first objective of this study was to determine if the commercial rootstocks ‘Strongtosa’, ‘Carnivor’, or ‘Macis’ i...

Field and greenhouse studies were conducted in 2016 and 2017 to determine sweetpotato tolerance to herbicides applied to plant propagation beds. Herbicide treatments included PRE application of flumioxazin (107 g ai ha ⁻¹ ), S -metolachlor (800 g ai ha ⁻¹ ), fomesafen (280 g ai ha ⁻¹ ), flumioxazin plus S -metolachlor (107 g ai ha ⁻¹ + 800 g ai ha...

Hollow heart is an internal fruit disorder found predominantly in triploid (seedless) watermelon and is known to cause load rejection if at moderate to severe stages. Cultivar selection, tissue density, pollination and environmental factors affect hollow heart incidence. We used NC Variety trial evaluations to correlate hollow heart to tissue firm...

Watermelon [ Citrullus lanatus (Thunb.) Matsum & Nakai] grafting is commonly used for management of diseases caused by soilborne pathogens; however, little research exists describing the effect of grafting on the weed-competitive ability of watermelon. Field experiments determined the response in yield, fruit number, and fruit quality of grafted an...

Studies were conducted to determine the tolerance of sweetpotato and Palmer amaranth control to a premix of flumioxazin and pyroxasulfone pretransplant (PREtr) followed by (fb) irrigation. Greenhouse studies were conducted in a factorial arrangement of four herbicide rates (flumioxazin/pyroxasulfone PREtr at 105/133 and 57/72 g ai ha –1 , S -metola...

Field experiments determined the critical period for weed control (CPWC) in grafted and nongrafted watermelon [ Citrullus lanatus (Thumb.) Matsum. & Nakai] grown in plasticulture. Transplant types included ‘Exclamation’ seedless watermelon as the nongrafted control as well as Exclamation grafted onto two interspecific hybrid squash (ISH) rootstocks...

Field studies were conducted in 2015 and 2016 in North Carolina to determine the response of ‘Covington’ and ‘Murasaki-29’ sweetpotato cultivars to four rates of linuron (420, 560, 840, and 1,120 g ai ha –1 ) alone or with S -metolachlor (803 g ai ha –1 ) applied 7 or 14 d after transplanting (DAP). Injury (chlorosis/necrosis and stunting) to both...

Tomato (Solanum lycopersicum L.) is a warm-season, cold-sensitive crop that shows slower growth and development at temperatures below 18 8C. Improving suboptimal temperature tolerance would allow earlier planting of field-grown tomato and a reduction in energy inputs for heating greenhouses. Grafting tomato onto high-altitude Solanum habrochaites (...

Improvement of crop water use is imperative. Plants’ responses to limited water can dictate their ability to better use available resources and avoid prolonged and severe stress. The following study was conducted to determine how tomato (Solanum lycopersi-cum) rootstocks with different root system morphologies respond to drying soils. Plants were g...

Grafting of watermelon (Citrullus lanatus) is an established production practice that provides resistance to soilborne diseases or tolerance to abiotic stresses. Watermelon may be grafted on several cucurbit species (interspecific grafting); however, little research exists to describe root systems of these diverse rootstocks. A greenhouse study was...

Field studies were conducted in North Carolina to determine the critical period for Palmer amaranth control (CPPAC) in pickling cucumber. In removal treatments (REM), emerged Palmer amaranth were allowed to compete with cucumber for 14, 21, 28, or 35 d after sowing (DAS) in 2014 and 14, 21, 35, or 42 DAS in 2015, and cucumber was kept weed-free for...

Grafting watermelon (Citrullus lanatus) is a common practice in many parts of the world and has recently received increased interest in the United States. The present study was designed to evaluate early season growth, yield, and fruit quality of watermelon in response to grafting and in the absence of known disease pressure in a fumigated system....

Field studies were conducted to determine watermelon tolerance and yield response when treated with bicyclopyrone preplant (PREPLANT), POST, and POST-directed (POST-DIR). Treatments consisted of two rates of bicyclopyrone (37.5 and 50 g ai ha –1 ), fomesafen (175 g ai ha –1 ), S -metolachlor (802 g ai ha –1 ), and a nontreated check. Preplant treat...

The following study was conducted to address water use efficiency in grafted tomato ( Solanum lycopersicum ) in an on-farm environment. The commercial rootstock cultivars Beaufort (BE) and Shield (S) were chosen as these two have different root system morphologies that may benefit water use efficiency. The heirloom cultivar Cherokee Purple (CP) was...

The reason for internal necrosis occurrences in sweetpotato ( Ipomoea batatas ) storage roots is not well understood. This disorder begins internally in the storage roots as small light brown spots near the proximal end of the root that eventually can become more enlarged as brown/black regions in the cortex. The objective of this study was to dete...

Grafting tomato (Solanum lycopersicum L.) onto disease resistant rootstocks has grown in use in North America over the past two decades. Rootstocks have traditionally been bred and used for their resistance packages to numerous soil-borne diseases but some rootstocks appear to improve scion yield and vigour in comparison to non-grafted plants in co...

Field studies were conducted to determine the influence of herbicides on the development of internal necrosis (IN) in sweetpotato storage roots. In a slip propagation study, herbicide treatments included PRE application (immediately after covering seed roots with soil) of clomazone (0.42, 0.84 kg ai ha ⁻¹ ), flumioxazin (0.11, 0.21 kg ai ha ⁻¹ ), f...

Studies were conducted in 2012 and 2013 to compare Evangeline to various sweetpotato (Ipomoea batatas) varieties (Bayou Belle, Beauregard, Bonita, Covington, NC05-198, and Orleans) for commercial production in North Carolina. In another study, microwaved and oven-baked ‘Evangeline’ and ‘Covington’ sweetpotato roots were subjected to analysis of che...

There is a research gap with respect to documenting the effects of sweetpotato (Ipomoea batatas) seed root density and size on transplant yield and quality. Field studies were conducted in 2012 and 2014 to determine the effect of sweetpotato seed root (canner size) density [12, 24, 37, 49, 61, 73, and 85 bushels [bu (50 lb)] per 1000 ft²] on ‘Covin...

Sweetpotato certified seed producers rely on fast propagation of virus-indexed slip plants in the greenhouse to obtain transplants for the production of first generation of storage roots. Effective fertilization is important for greenhouse vegetative propagation, but relevant guidelines are rare. Greenhouse experiments were conducted in 2011 and 20...

Studies were conducted in 2007 and 2008 at Clinton, NC to determine the effect of glyphosate applied POST via a Dixie wick applicator on Palmer amaranth control and sweetpotato yield and quality. In 2007, treatments consisted of glyphosate wicked sequentially 6 and 8 wk after transplanting (WAP) and glyphosate wicked sequentially 6 and 8 WAP follow...

Studies were conducted in a stale field production system in 2012 and 2013 to determine the effect of herbicide timing on Palmer amaranth control and 'Covington' sweetpotato yield and quality. Treatments consisted of flumioxazin at 72, 90, or 109 g ai ha⁻¹ applied 45 d before transplanting (DBT) or 1 DBT, or sequentially the same rate at 45 DBT fol...

Studies were conducted in 2012 and 2013 to determine the effect of fomesafen based Palmer amaranth control program in 'Covington' and 'Evangeline' sweetpotato cultivars. Treatments consisted of fomesafen pretransplant alone at 0.20, 0.28, 0.36, 0.42, 0.56, and 0.84 kg ai ha-1 or followed by (fb) S-metolachlor at 1.12 kg ai ha-1 0 to 7 d after trans...

Grossing over $33.7 million in annual sales, North Carolina ranks 7th in the US for the production of tomatoes (Solanum lycopersicum). A replicated on-farm trial was conducted in Rowan County, NC. On May 30th, 2013, 8.1 ha of two bacterial wilt (BW; R. solanacearum (race 1)) resistant rootstocks were planted. The objective of this trial was to eval...

In 2013, the US melon industry grossed over $394 million from approximately 34 thousand hectares of cantaloupe and honeydew crops. North Carolina (NC) and South Carolina (SC) produced about 5% of the USA acreage and value, yet the melon crop in these two states are still valued at several million dollars. Most melon production involves various type...

A series of studies were conducted to better understand the occurrence and causes of internal necrosis (IN) in ‘Covington’ sweetpotato (Ipomoea batatas). Assessment of the problem among the industry was done for 2 years and revealed that IN was widespread in commercial storage facilities throughout the state of North Carolina; both incidence and se...

The objective of this study was to determine the effect of fomesafen-preplant on Palmer amaranth control and sweetpotato tolerance, yield and quality. Studies were conducted at the Horticultural Crops Research Station, Clinton, NC on a sandy loam soil. The experimental design was a randomized complete block with three (2012) or four (2013) replicat...

Optimizing yields for any crop is critical in order to maximize profitability. An important yield component in the production system is plant arrangement and density. The main objectives of this experiment were to determine the ideal plant density for yield, quality and economics for sweet corn. Two sweet corn field trials were conducted in Swan Qu...

Two distinct syndromes have emerged in some production areas that have caused losses of sweetpotato (Ipomoea batatas) storage roots during postharvest storage: a complex of fungal rots (end rots) progressing from either end of storage roots and a necrotic reaction (internal necrosis) progressing internally from the proximal end of storage roots. Th...

Field studies were conducted to determine the effect of halosulfuron at 0, 13, 26, 39 or 52 g ha(-1) applied 10, 22, and 31 d after planting (DAP) on 'Beauregard' and 'Covington' sweetpotato. Storage roots were harvested, graded, cured, and stored in controlled environment for 2 mo. Where injury on storage roots was observed, external injury occurr...

Bell pepper transplant height control is essential to produce a strong plant capable of surviving the transplant process. Transplant producers are interested in environmental, physical, and chemical methods to control plant height in the greenhouse. One emerging technology for transplant height control on bell pepper is the use abscisic acid (ABA);...

Vegetables transplants can become tall and leggy prior to field establishment, producing challenges for the growers using mechanical transplanter to establish their crops. Thus, controlling the height of vegetable transplants prior to planting could be an advantage for commercial vegetable growers. A greenhouse experiment was conducted in 2008 and...

Zucchini squash (Cucurbita pepo) is a rich source of lutein, containing 2.1 mg/100 g. Lutein is a carotenoid pigment found to be helpful in preventing macular degeneration in the eye, and may also offer antioxidant protection of eyes in those who smoke or are overweight. Analysis of lutein is tedious and expensive, and requires use of HPLC for iden...

Vegetable transplants can have excessive internode elongation before field establishment, producing challenges for the growers using mechanical transplanters to establish their crops. Thus, controlling the height of vegetable transplants before planting could be an advantage for commercial vegetable growers. A greenhouse experiment was conducted in...

Cucumbers require adequate nitrogen (N) for growth and development. This study was undertaken to determine the most effective tillage system and N rate for hand-picked, processing, cucumber (Cucumis sativus L.) production. Three tillage systems and five N fertilizer rates were compared for effects on yield, fertilizer N use efficiency (NUE), and ef...

Three studies were conducted to determine the effect of preceding crop on wireworm (Coleoptera: Elateridae) abundance in the coastal plain of North Carolina. In all three studies, samples of wireworm populations were taken from the soil by using oat, Avena sativa L., baits. Treatments were defined by the previous year's crop and were chosen to refl...

Studies were conducted in 2007 and 2008 to determine the effect of flumioxazin and S-metolachlor on Palmer amaranth control and ‘Beauregard’ and ‘Covington’ sweetpotato. Flumioxazin at 0, 91, or 109 g ai ha−1 was applied pretransplant 2 d before transplanting alone or followed by (fb) S-metolachlor at 0, 0.8, 1.1, or 1.3 kg ai ha−1 PRE applied imme...

Herbicide trials were conducted in 2009 to examine the effects of four herbicides on grafted watermelon. Field trials were located in Quincy, FL, Charleston, SC, and Kinston, NC. Watermelon plants utilized in the study include non-grafted Tri-X-313 watermelon and Tri-X-313 watermelon grafted onto gourd, inter-specific hybrid squash, wild watermelon...

Field studies were conducted in 2007 and 2008 at Clinton and Faison, NC, to evaluate the influence of Palmer amaranth density on 'Beauregard' and 'Covington' sweetpotato yield and quality and to quantify the influence of Palmer amaranth on light interception. Palmer amaranth was established at 0, 0.5, 1.1, 1.6, 3.3, and 6.5 plants m⁻¹ within the sw...

Studies were conducted in 2003 and 2004 to determine the effect of application timing and halosulfuron rate on sweetpotato yield and quality. Halosulfuron was applied 1, 2, and 4 wks after transplanting (WAP) sweetpotato in 2003, and 2, 3, and 4 WAP in 2004. Treatments within each timing included halosulfuron at 13, 26, 39, 52, and 65 g ai/ha plus...

Studies were conducted in 1996 and 1997 to determine the effect of irrigation systems used to produce transplants on subsequent tolerance of banana and bell pepper (Capsicum annuum) transplants to field-applied herbicides. The irrigation systems were overhead (OH), ebb and flood (EF), and float (F). At 2 and 4 wk, banana and bell pepper injury was...

Studies were conducted in 2006 at Clinton and Kinston, NC, to determine the influence of halosulfuron POST (over the crop plant) or POST-directed (to the crop) on growth and yield of transplanted `Precious Petite' and `Tri-X-313' triploid watermelon. Treatments included a nontreated control, 39 g/ha halosulfuron applied POST-directed to 25% of the...

A 3-yr field experiment was initiated in 2001 to evaluate weed suppression and sweetpotato productivity in three organic sweetpotato production systems. Organic systems were (1) compost and no cover crop with tillage (Org-NC), (2) compost and a cover crop mixture of hairy vetch and rye incorporated before transplanting (Org-CI), and (3) compost and...

No-tillage (NT) organic vegetable production presents several economic opportunities for growers in the southeastern United States while promoting natural resource conservation. This study was conducted to determine if removal of sorghum sudangrass (SS) cover crop biomass as hay, frequency at which the cover crop is mowed, and tillage affect weed s...

The goals of these studies were to determine how miniwatermelon (Citrullus lanatus) cultivars differed and responded to plant in-row spacing in terms of percentage of marketable fruit and yields, and if plant spacing impacted internal fruit quality. Three genetically diverse triploid miniwatermelon cultivars (Mohican, Petite Perfection, and Xite) w...

Insect pollinators such as honeybees (Apis mellifera L.) and humble bees (Bombus spp.) are strongly directional in their movements among flowers and typically move to the nearest neighboring inflorescence, which is often in the same row. Pollinator movements in watermelon [Citrullus lanatus (Thunb.) Matsum & Nakai] were determined by tracking polle...

Triploid (seedless) watermelon [Citrullus lanatus (Thunb.) Matsum. and Nak.] pollen is nonviable; thus, diploid (pollenizer) watermelon cultigens are required to supply viable pollen for triploid watermelon fruit set. The objective of this research was to characterize maximum potential vegetative growth, staminate and pistillate flower production o...

The sweetpotato, Ipomea batatas (L.) Lam., is tropical in origin and was considered an important food plant for ancient civilizations in tropical America; however, the plant was not grown extensively by North American Indians. The sweetpotato became widely established in North America by the end of the 18th century (Edmond, 1971a). It was dissemina...

'Covington' is an orange-fleshed, smooth-skinned, rose-colored, table-stock sweetpotato [Ipomoea batatas (L.) Lam.] developed by North Carolina State University (NCSU). 'Covington', named after the late Henry M. Covington, an esteemed sweetpotato scientist at North Carolina State, was evaluated as NC98-608 in multiple state and regional yield trial...

A 3-year field experiment was initiated in 2001 to evaluate different organic sweetpotato production systems that varied in cover crop management and tillage. Three organic systems: 1) compost and no cover crop with tillage (Org-NCC); 2) compost and a cover crop mixture of hairy vetch and rye incorporated before transplanting (Org-CCI); and 3) comp...

Introduction Feeding Value Identified Health Concerns Other Digestive Problems Recommendations for Feeding Sweetpotato By-products Summary Acknowledgments

The goal of this study was to evaluate miniwatermelon (Citrullus lanatus) cultivars/experimental hybrids (cultigens) for yield, quality, and adaptability in various growing environments. Eighteen cultigens were evaluated in field locations at southern Florida (Bradenton), northern Florida (Quincy), central South Carolina (Blackville), coastal South...

Most seedless watermelons are grown on black polyethylene mulch to aid crop establishment, growth, yield, and quality and weed control. However, nutsedge is a persistent problem in this production system, as it can easily penetrate the mulch. Halosulfuron-methyl is registered in some crops and provides excellent yellow nutsedge control. The objecti...

In 1999 and 2000, a total of 27 diploid watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] cultivars and advanced breeding lines (hereafter referred to as cultigens) were evaluated for staminate flower and pollen grain production to assess their potential to serve as pollenizers (pollen source plants) in triploid watermelon production systems....

Pollen from triploid (seedless) watermelon ( Citrullus lanatas ) is nonviable. Diploid (seeded) watermelons are required in seedless watermelon production for pollination and fruit set. In 2004, markets continued to increase for triploid watermelon but decrease for diploid watermelons. Seed companies are commercializing diploid cultivars (pollenize...

The goal of this research was to determine the effects of in-row spacing and planting time on yield and root grade of NC 98-608 over time. Two plantings were made in two grower locations (four total). An early planting was made 19 and 25 May and a late planting 19 and 24 June. NC 98-608 was evaluated at the following in-row spacings; 23, 31, 38, an...

Market demand for diploid fruit has been declining over the past ten years, especially the past three years. Thus, the watermelon industry is looking for ways to produce triploid fruit more efficiently. Several companies have developed pollinizers for planting in-row so as not to take up space like a commercial diploid cultivar. The objective of ou...

Salted and sweet watermelon rind pickles are commonly produced in North America, Europe, and Asia using traditional recipes. Homeowners and small industries use the leftover watermelon crop, especially from cultivars having thick and crisp rind, to produce pickles. Recently, we classified rind thickness for a set of obsolete and heirloom cultivars...

Demand for triploid watermelons has outpaced the demand for diploid watermelons in the United States in recent years. The size of most triploid watermelons sold in U.S. markets is from 6 to 9 kg. Recently, a new produce item, seedless watermelons weighing about 1.8 to 3.6 kg, have been introduced and created excitement in the produce industry. Seve...

Decline in sweetpotato yield and storage root quality has been attributed to the accumulation of viruses, pathogens and mutations. To document the effects of decline on yield and storage root quality, two micropropagated, virus-indexed, greenhouse produced G1 'Beauregard' meristem-tip cultured clones, B94-14 and B94-34, were compared with 1) microp...

To determine the effects of Sweet potato feathery mottle virus (SPFMV), and possibly other newly described potyviruses, on sweetpotato yield and storage root appearance, virus-indexed 'Beauregard' and 'Hernandez' mericlones testing free of known viruses were compared with virus-infected mericlones in two separate experiments over two years. The exp...

In 1998 and 1999, a total of 27 large-fruited and 15 miniature-fruited pumpkin (Cucurbita pepo) cultivars were evaluated for adaptation to eastern North Carolina growing conditions. Test categories were yield (fruit number and weight); fruit characteristics (shape, rind and stem attributes); and susceptibility to edema (wart-like growths on fruit e...

Researchers interested in evaluating watermelon (Citrullus lanatus(Thunb.) Matsum. & Nakai) cultivars for yield often use multiple-row plots to simulate the monoculture system growers use or ingle-row plots to save on land, labor, and seeds. An important question is whether there is significant interaction of border rows with center rows when diver...

Foliar ozone (O3) injury is common on watermelon grown in eastern North Carolina. During the 2000 and 2001 growing seasons, 93 cultivars and breeding lines (i.e., cultigens) were evaluated for foliar injury caused by ambient levels of O3. One tetraploid, 42 diploid, and 50 triploid cultigens were evaluated. Injury developed on all cultigens in both...

Very little is known about the rate at which pollen grains are mobilized within insect-pollinated crop systems, and this is especially true the for commercial production of field-grown cucumber (Cucumis sativus L.), monoecious muskmelon (Cucumis melo L.), and triploid watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai]. The rates of pollen depl...

Honey bees (Apis mellifera) and bumble bees (Bombus impatiens) were compared for three aspects of pollinating behaviour on field-grown cucumber (Cucumis sativus) and watermelon (Citrullus lanatus). We measured: (1), diurnal foraging activity periods (as related to anthesis); (2), floral visitation rates (number of flowers visited per min by individ...

Five studies were conducted from 1997 to 1999 to determine the effects of subsoiling on root quality (i.e., root length and shape) and on yield of `Beauregard' sweetpotato. The statistical design for all five studies was a completely randomized block design with six replications (four in Goldsboro in 1997). All studies were conducted on Norfolk fin...