Alternative soil fumigants are needed to replace methyl bromide (MBr). One possible MBr alternative is dimethyl disulfide (DMDS). Highly impermeable plastic films such as virtually impermeable film (VIF) and totally impermeable film (TIF) can be used to increase fumigant retention. Possible advantages of increased fumigant retention are decreased fumigant use rates, decreased buffer zone requirements, reduced fumigant emissions, and improved pest control. Reduced fumigant emission may be especially important with DMDS because it has a sulfur odor, which is easily perceivable by the human nose. One potential drawback of decreasing film permeability may be longer plant back intervals, especially during periods with cool wet soils. The objective of these experiments was to evaluate the effect of TIF on DMDS retention at various rates compared with VIF. Experiments were conducted at the Virginia Tech Eastern Shore Agricultural Research and Extension Center (ESAREC) in Painter, VA, using high (561 L·ha−1), standard (468 L·ha−1), and reduced application rates (374, 281, and 187 L·ha−1) of DMDS in combination with TIF and VIF during spring and fall seasons. Soil temperature and fumigant concentration within the soil were recorded. A stepwise decrease in fumigant retention was seen as fumigant rates were reduced under TIF. Retention periods were impacted by soil temperature. High temperatures decreased the retention period and low temperatures increased the retention period. Standard fumigant rates (468 L·ha−1) under VIF resulted in similar fumigant concentrations in the soil as 281 L·ha−1 under TIF. Similar fumigant concentrations and possibly similar planting interval can be achieved by reducing fumigant use rates ≈40% to 50% under TIF compared with VIF.
Theodore P. McAvoy and Joshua H. Freeman
Stephen M. Olson and Joshua H. Freeman
Nine collard (Brassica oleracea acephala group) cultivars were evaluated on six experiments over 4 years to determine how well they performed with respect to yield, plant weight, and bolting tolerance. Experiments covered spring, fall, and winter seasons to determine if one cultivar would be useful for all conditions. ‘Top Pick’, ‘Flash’, and ‘Blue Max’ were found to be the best performing cultivars with respect to yield and plant weight. In general, the hybrid cultivars outperformed the open-pollinated cultivars. Only during one experiment were the cultivars subjected to environmental conditions favorable for bolting, but there were no significant differences in incidence of bolting among the cultivars. Although top-performing cultivars were hybrids, the cost associated with hybrid seed must be considered.
Joshua I. Adkins, Joshua H. Freeman, and Stephen M. Olson
Diploid watermelon (Citrullus lanatus) pollenizers are planted within triploid watermelon fields to provide viable pollen for triploid fruit set. In recent years, pollenizer cultivars with desirable characteristics for planting in-row with triploid watermelons have been commercially available. The degree of plant competition from in-row pollenizers grown in the commercially common arrangement where pollenizers are placed equidistant from neighboring triploid plants has not been reported. Field experiments were conducted in 2005, 2006, and 2007 in Quincy, FL, to examine the competitive impact of in-row pollenizers grown equidistant from neighboring triploid plants. Four ratios of pollenizers-to-triploids: 1:1, 1:2, 1:3, and 1:4 were used to provide various levels of pollenizer competition. No significant difference in yield based on the weight or number of fruit per triploid plant resulted from the varied pollenizer ratios. Therefore, pollenizers grown in-row at an equidistant spacing from the neighboring triploid plants had no competitive impact on the yield of the triploid watermelon crop.
John W. Scott, Samuel F. Hutton, and Joshua H. Freeman
Samuel F. Hutton, John W. Scott, and Joshua H. Freeman
Joshua H. Freeman, Stephen M. Olson, and William M. Stall
Successful fruit set in triploid watermelons [Citrullus lanatus (Thunb.) Matsum. & Nakai] requires a diploid watermelon cultivar, or pollenizer, to be planted nearby as a pollen source. Pollenizer cultivars have been developed to be planted in-row with triploid plants without spacing change, which decreases area per plant. These cultivars have different growth habits, from highly reduced foliage to standard foliage, and it is uncertain how pollenizer growth habit may affect triploid plant growth and yield. Two diploid watermelon pollenizers, ‘Mickylee’ and ‘SP-1’, with markedly different growth habits were planted at five in-row spacings from triploid plants to determine the effect of plant competition on triploid watermelon yield. All treatments used a 1:1 pollenizer to triploid ratio to measure the direct effect of pollenizer growth on associated triploid yields. Experiments were conducted at two locations during Spring 2006 (Quincy and Citra, FL) and one during Fall 2006 (Quincy). Triploid plants paired with ‘Mickylee’ yielded 11.4% (Citra) and 22.4% (Quincy) less weight in the spring and 8.5% less in the fall than plants paired with ‘SP-1’ and also produced fewer fruits per plant. However, the results from the fall trial were not significant. Pollenizer to triploid spacing had a linear effect on yield per plant and fruits per plant, and there was no interaction between pollenizer cultivar and spacing. The use of ‘Mickylee’ as a pollenizer may be an attractive option because of lower seed costs compared with other pollenizers, but these results indicated lower triploid watermelon yields from plants paired with ‘Mickylee’, which is most likely a result of increased plant competition.
Samuel F. Hutton, John W. Scott, and Joshua H. Freeman
Adam F. Wimer, Steven L. Rideout, and Joshua H. Freeman
Bacterial wilt of tomato caused by Ralstonia solanacearum is one of the most devastating diseases of tomato (Solanum lycopersicum) on the Eastern Shore of Virginia (ESV). Four research trials were conducted on the ESV over three growing seasons to determine the temporal and spatial distribution of bacterial wilt throughout commercial tomato fields. Individual plants were assessed at ≈1-week intervals throughout the growing seasons with the incidence of bacterial wilt for each individual plant being recorded. Bacterial wilt increased gradually during each growing season. An increase in the clustered distribution of symptomatic plants was determined to exist within rows but not across rows. There were positive correlations between disease incidence and the percentage of rows exhibiting a significantly clustered distribution in every trial. These findings suggest that as bacterial wilt incidence increases in tomato fields by either the intimate contact between roots of adjacent tomato plants or the movement of the pathogen in surface irrigation water, symptomatic plants become more clustered within rows.
Mary C. Stevens, Rui Yang, and Joshua H. Freeman
A novel methyl bromide alternative, ethanedinitrile (EDN), has been reported to be efficacious against soil-borne pathogens, weeds, and plant-parasitic nematodes. Degradation products of EDN include NH4 +and NH3, but it is currently unknown at what quantities these degradation products are being released into the soil at a given use rate of EDN. To address this issue, field studies were performed using the raised-bed plasticulture system. Deposition of NH4 + and NO3 − in top 0–15-, 15–30-, and 30–45-cm soils were evaluated 3 weeks after fumigation with EDN applied at 336, 448, and 560 kg·ha−1. Change of pH and transformation of NH4 + to NO3 − in top 0–15- and 15–30-cm soils were tracked weekly after fumigation with EDN at 448 kg·ha−1 for 10 weeks. This study found that fumigation with EDN significantly increased soil pH of the top 0–15-cm soil and soil NH4 + in top 0–15- and 15–30-cm soils, but soil NO3 − was unaffected. Nitrification process in top 0–15-cm soil was inhibited by fumigation with EDN for at least 7 weeks. These results indicate that N deposited by fumigation with EDN could be an important preplant N source for crop production, and the inhibition of nitrification could help mitigate nitrate leaching. This study provides helpful information for quantification of N deposited from fumigation with EDN.
Theodore McAvoy, Joshua H. Freeman, Steven L. Rideout, Stephen M. Olson, and Mathews L. Paret
Seven hybrid tomato rootstocks with possible resistance to bacterial wilt caused by Ralstonia solanacearum and a known resistant cultivar were tested as grafting rootstocks to impart resistance to a bacterial wilt-susceptible cultivar, BHN 602. Greenhouse studies showed resistance of all the rootstocks to bacterial wilt. The disease incidence and yield of ‘BHN 602’ grafted to these rootstocks were evaluated in open-field tomato production in Florida and Virginia over four seasons. Significant differences in bacterial wilt incidence were observed between grafted entries in three of the four trials. In these three trials, grafted entries consistently exhibited the least bacterial wilt incidence compared with the controls; the self-graft, and non-grafted entries. Over all the trials, tomato plants grafted onto ‘Cheong Gang’, ‘BHN 1054’, and ‘BHN 998’ displayed the least bacterial wilt incidence. Rootstocks had a significant effect on total marketable yield in all the trials with certain grafted entries yielding significantly greater than non-grafted ‘BHN 602’. Field studies show that grafting holds promise for decreasing the impact of bacterial wilt on tomato cultivars as well as increasing the overall productivity of tomato cultivars.