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Greg D. Hoyt and David W. Monks

Experiments were conducted to evaluate the effect of tillage systems and weed management on weed suppression and potato yield. Strip-tillage (ST) and conventional-tillage (CT) systems produced equal yields of Irish potato (Solanum tuberosum L.) or sweetpotato [Ipomoea batatas (L.) Lam.] when herbicide treatments were applied. Weeds in the nontreated control reduced yield of Irish potato and prevented storage root growth in sweetpotato. Excellent control of broadleaf signalgrass [Brachiaria platyphylla (Griseb.) Nash], henbit (Lamium amplexicaule L.), prickly sida (Sida spinosa L.), and common ragweed (Ambrosia artemisiifolia L.) was obtained with metribuzin + metolachlor applied preemergence at Irish potato planting, followed by sethoxydim + crop oil applied postemergence in ST and CT systems. Redroot pigweed (Amaranthus retroflexus L.) control was >98% at 4 weeks after treatment but was 73% to 84% at harvest across all herbicide treatments in both tillage systems. In sweetpotato, control of black mustard [Brassica nigra (L.) W.J.D. Koch], goosegrass [Eleusine indica (L.) Gaertn.], and fall panicum [Panicum dichotomiflorum Michx.] was >95% throughout the growing season for all herbicide treatments in both ST and CT.

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Jonathan R. Schultheis and David W. Monks

Bedded sweetpotatoes are often covered with a rowcover to enhance sprouting. Our study was conducted to evaluate several rowcovers for earliness, plant yield, and plant quality (weight). In 1993 and 1994, variety (`Beauregard' and `Jewel') and rowcovers (clear plastic; black plastic; photodegradable plastic; infrared transmissible plastic; Reemay polyester cover; and black plastic, which was then covered with a black plastic tunnel) were evaluated for their effects on plant production. Holes ≈1 cm in diameter were punched in the plastic ≈2 weeks after planting to prevent exposing the seed roots to excessively high temperatures. Rowcovers were removed when plants began emerging from the soil, except for Reemay and the black plastic tunnels, which remained in place over the bedded plants until first plant harvest. Black plastic tunnels were placed back over the treatment bed each time plants were harvested. When 50% of the plants were 25 cm tall, all plants from the plot were cut 1 to 2 cm above the soil line. Plots were arranged in a randomized complete-block design and replicated five times. `Jewel' produced plants earlier than `Beauregard'. Covering beds with black plastic mulch and tunnels resulted in the first plant cutting being up to 42 days earlier than the other treatments, with no rowcover treatments producing plants the latest. The second earliest cutting was obtained when beds were covered with Reemay rowcover. Plant fresh weight was greater with the no cover treatments; black plastic tunnel treatments produced the lowest weight plants. Using black plastic tunnels consistently produced more plants than the other treatments. In the future, using rowcovers to enhance slower sprouting varieties should be examined.

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Katharine B. Perry, A. Richard Bonanno and David W. Monks

A commercially available cryoprotectant (50% propylene block copolymer of polyoxyethylene, 50% propylene glycol; trade name FrostFree) and an antitranspirant (96% di-1-p-menthene, i.e., pinolene, a terpenic polymer, 4% inert; trade name Vapor Gard) were evaluated for their ability to protect `Pik Red' tomato (Lycopersicon esculentum Mill.) and `Keystone Resistant Giant #3' pepper (Capsicum annuum L.) plants during frost and freeze occurrences in the field. Tests were conducted during four spring and two fall seasons. Protection from these products was not observed under field conditions when minimum air temperature reached -3.5C and -l.0C on separate occasions. Yields for treated and untreated plants were similar. Neither cryoprotectant injured the foliage in the absence of cold events.

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Peter J. Dittmar, Jonathan R. Schultheis and David W. Monks

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 (pollenizers) specifically designed as a pollen source for triploid watermelon production. The objectives of this research were to characterize the vegetative, floral, and fruit growth and development of these pollenizers. Five cultivars were evaluated: `Companion', `Mickylee', `Mini Pool', `SP-1', and `Jenny'. When measuring the longest vine, `Companion' produced the smallest plants reaching a maximum vine length of 183 cm, 31 days after transplant (DAT). `Mickylee', `Mini Pool', `SP-1', and `Jenny' had similar vine lengths reaching maximum lengths ranging 294–335 cm, 31 DAT. The compact growth of `Companion' is consistent with the shorter node length of 3.8 cm, while the other pollenizers had a node length of 9.9–10.9 cm. `SP-1' produced more male flowers than the other pollenizers beginning 24 DAT and produced 30–40 male flowers per plant per day, 31–55 days after transplant. `Mickylee', `Mini Pool', and `Jenny' produced 9–15 male flowers per plant per day, 24–55 days after transplant. Early production of male flowers by `Companion' was similar to `Mickylee', `Mini Pool' and `Jenny'; however, flower production became the lowest compared with all pollenizer cultivars 24 DAT. `SP-1' produced more female flowers resulting in the most fruit production (4 fruit per plant). In contrast, `Companion' produced the fewest female flowers and produced 2 fruit per vine. `Mickylee' had the largest fruit weighing 5.9 kg, and `SP-1' and `Jenny' produced the smallest fruit weighing 3.1 kg. The use of specific pollenizers may provide the opportunity to customize production for specific cultivars for either early and or late harvests.

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Bethany A. Galloway, Jonathan R. Schultheis and David W. Monks

A study was conducted in Fall 1995 at the Horticultural Greenhouse, North Carolina State University, to examine growth of banana (`Banana Supreme'), bell (`Camelot'), and jalapeno (`Mitla') pepper under overhead (OI), ebb and flood (EF), and float (F) irrigation systems. Plant emergence was fastest in the float system, but slowest in the OI system. Irrigation treatment was highly significant for all weekly sampling dates for root and shoot fresh weight, root and shoot dry weight, root length, stem diameter, height, and leaf area. Stem diameter of F plants was greater than both EF and OI. However, EF and OI plants had similar diameter regardless of sampling date. Root fresh weight did not differ among pepper cultivars. By 39 days after planting (DAP), F plants had 33% greater root fresh weight, by 46 DAP they were almost double, and at 53 DAP they were 44% larger compared to the EF treatment. Float plants had greatest root length, but EF and OI plants had denser root mass (visual observation) in the transplant container cell. At 46 and 53 DAP, EF plants were generally taller than OI plants, and by 60 DAP this difference was almost 30%. Float plants were about double the height of the EF and OI plants and this difference continued until the experiment terminated. Bell pepper had the greatest shoot fresh weight at all sampling dates after 25 DAP, while jalapeno was greater than banana only up to 39 DAP. Beyond 39 DAP, banana pepper fresh weight surpassed jalapeno pepper. By 53 DAP, shoot fresh weight of float transplants were almost 3 times greater than EF or OI plants. Float plants reached a satisfactory size (137 mm height) for transplanting by 8 weeks. Height of EF and OI plants at this time was 68 and 48 mm, respectively. This experiment is being repeated in Spring 1996.

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Peter J. Dittmar, David W. Monks and Jonathan R. Schultheis

An experiment was conducted during 2005 and 2006 in Kinston, NC, with the objective of maximizing triploid watermelon [Citrullus lanatus (Thunb.) Matsum. and Nak.] fruit yield and quality by optimizing the choice and use of pollenizers. Treatments were pollenizer cultivars planted singly [‘Companion’, ‘Super Pollenizer 1’ (‘SP1’), ‘Summer Flavor 800’ (‘SF800’), and ‘Mickylee’] or in pairs (‘Companion’ + ‘SP1’, ‘Companion’ + ‘SF800’, and ‘SP1’ + ‘SF800’). All pollenizers from these seven treatments were interplanted with the triploid cultivar Tri-X-313. Planting arrangement was compared by establishing ‘SF800’ in a hill versus an interplanted field arrangement. Effect of pollenizer establishment timing on triploid fruit yields and quality was evaluated by establishing ‘SP1’ 3 weeks after planting and comparing it with the establishment of ‘SP1’ at the time of triploid plant establishment. Finally, a triploid planting with no pollenizer (control) was included to determine pollen movement. Fruit yield from the control was 22% or less of yield of the other treatments containing a pollenizer and less than 10% in the initial or early harvests. Pollen movement was minimal among plots and differences in yield and fruit quality could be attributed to pollenizer treatment. In 2005, the use of ‘Companion’, ‘SP1’, or ‘Mickylee’ as pollenizers produced similar total yields, whereas ‘SF800’ produced the lowest yield. In 2005, ‘Companion’ produced more large fruit than the other individual pollenizer treatments. Combining the pollenizers generally did not enhance triploid yields or quality. Interplanting of pollenizers consistently resulted in greater yield compared with the hill system. Late planting of ‘SP1’ increased the incidence of hollow heart in the marketable fruit and decreased yield compared with simultaneously planting ‘SP1’ and triploid plants. Thus, selection of pollenizer, planting arrangement, and time of pollenizer establishment are all important considerations to optimizing triploid yield and quality.

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Stratford H. Kay, Ross B. Leidy and David W. Monks

Greenhouse studies examined the effects of an aquatic herbicide (fluridone) in irrigation water on four vegetable crops growing on two soils. Tests on Fuquay loamy sand (0.3% humic matter) and Portsmouth fine sandy loam (4.1% humic matter) examined fluridone concentrations ≤250 μg·L−1. Injury to sweet corn (Zea may L.), cucumber (Cucumis sativus L.), bell pepper (Capsicum annum L.), and tomato (Lycopersicon esculentum L.) on these soils varied with soil type and stage of plant growth. Seedlings or new transplants were more susceptible to fluridone damage than older plants. All plants showed more injury on Fuquay loamy sand, which had the lowest humic matter content. Injury to cucumber occurred only to seedlings exposed to 250 μg·L−1 on the Fuquay loamy sand. Bell pepper was the most sensitive crop to fluridone. The “no observed effects level” below which no significant injury of a crop occurred over both soil types and both stages of crop maturity was 5 μg·L−1 for sweet corn, bell pepper, and tomato and 100 μg·L−1 for cucumber.

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Stratford H. Kay, David W. Monks and Ross B. Leidy

In 1992, we initiated a study to determine the effects of fluridone in irrigation water applied to container-grown azaleas. Azaleas (Rhododendron indicum L. `George Tabor') were grown in containers with a 3 pine bark: 1 sand mixture and were irrigated daily for 5 weeks (except weekends) with solutions containing fluridone concentrations ≤2000 g·L−1. The threshold for appearance of visible injury symptoms (bleaching of new growth) was 250 g·L−1 at 5 and 12 weeks after treatment initiation. Visible symptoms did not appear until at least 35 days after treatments began. No statistically significant injury occurred to azaleas treated with solutions containing fluridone concentrations <250 g·L−1. This treatment rate was well above the maximum fluridone concentration (<90 g·L-1) normally occurring in ponds immediately following fluridone application. It appears unlikely that even long-term irrigation of `George Tabor' azaleas from fluridone-treated ponds would cause any significant injury.

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Peter J. Dittmar, David W. Monks and Jonathan R. Schultheis

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 over time, and measure exterior and interior fruit characteristics of pollenizer cultigens. Sixteen commercially available and numbered line (hereafter collectively referred to as cultigens) pollenizer and two triploid cultigens were evaluated in 2005 and 2006 at Clayton, NC. Vegetative growth was measured using vine and internode length, and staminate and pistillate flower development was counted weekly. Fruit quality and quantity were determined by measuring individual fruit weights, soluble solids, and rind thickness. Based on vegetative growth, pollenizer cultigens were placed into two distinct groups. Pollenizers, which produced a compact or dwarf plant were ‘Companion’, ‘Sidekick’, ‘TP91’, ‘TPS92’, and ‘WC5108-1216’. Pollenizers having a standard vine length were ‘Jenny’, ‘High Set 11’, ‘Mickylee’, ‘Minipol’, ‘Pinnacle’, ‘Summer Flavor 800’ (‘SF800’), ‘Super Pollenizer 1’ (‘SP1’), and ‘WH6818’. Cultigens with compact growth habit had shorter internodes and vine lengths compared with the cultigens with standard growth habit. Cultigens with the greatest quantity of staminate flower production through the entire season were ‘Sidekick’ and ‘SP1’. The lowest number of staminate flowers was produced by ‘TP91’ and ‘TPS92’. Based on fruit quality characteristics and production, pollenizers currently or possibly marketed for consumption include ‘Mickylee’, ‘SF800’, ‘Minipol’, ‘Jenny’, and ‘Pinnacle’. The remaining cultigens evaluated in this study should be used strictly as pollenizers based on fruit quality. Arrangement of diploid pollenizers in a commercial planting of triploid watermelons is an important consideration depending on plant vegetative development. Based on staminate flower production, cultigens with higher staminate flower production are potentially superior pollenizers and may lead to improved triploid quality and production. Furthermore, pollenizer selection by fruit characteristics should include a rind pattern easily distinguished from triploid fruit in the field.

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Jonathan R. Schultheis, Sylvia M. Blankenship, David W. Monks and Michael D. Boyette

The `Beauregard' sweetpotato variety is very prone to damage to its skin. We evaluated several preharvest treatments to reduce skinning so that less damage was done at harvest, during transport, and packing. Three field tests were conducted in 1998 (two tests) and 1999 (one test) in North Carolina. Treatments were implemented 1 and 2 weeks prior to harvest and were either chemical or mechanical. The three mechanical treatments were flail mowing, flail mowing and barring off, and vine snatching. The following chemical treatments were made: PREP, Diquat, Dessicate II, and 2,4-D at various rates. Sweetpotatoes were harvested and roots were graded. Subsequently, U.S. No. 1 root subsamples were obtained from each plot in order to evaluate the effects of treatment on skin tightening of roots. Roots were evaluated from each plot for skin toughness using a “skin-o-meter” where a pressurized stream of water was directed at a sweetpotato. The roots were then evaluated for skinning by checking if the skin was broken using the skin-o-meter. A second method was used to evaluate the effect of treatment for its effect on skin tightening (reduced skinning). One bushel of roots from each treatment plot was transported to Clinton, N.C., and run through a small packing line at the Horticultural Crops Research Station the next day after harvest. The sweetpotatoes were then evaluated in Raleigh for the number of incidences where skin had been removed during the harvesting, transport, or packing process. The severity of skinning was characterized by counting the number of small (<5 mm), medium (width 5-10 mm) and large (width 10+ mm) skinned areas on a root. An overall appearance rating for roots was also recorded for each subsampled plot with 10 being the best rating and 1 being the worst. Results indicate that treatment 14 days prior to harvest rather than 7 days prior to harvest seems to be advantageous in most cases for reducing skinning and maintaining yield of sweetpotato when compared with not treating the vines. Regardless of whether the treatment was chemical or mechanical, treatments were apparently beneficial in these tests. Application of PREP 7 days prior to harvest resulted in sweetpotatoes with the most resistance to skinning in 1999, the fewest large-size skinning abrasions on roots, and best appearance. PREP shows promise as a means to reduce skinning in sweetpotatoes, but presently is not labeled for use on sweetpotatoes.