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Wilton P. Cook and Douglas C. Sanders

The effects of fertilizer placement and soil moisture level on soil N movement, uptake, and use by tomato plants (Lycopersicon esculentum Mill) grown with drip irrigation and plastic mulch were evaluated at two locations on two types of sandy soils. Broadcast or band fertilizer placement had no effect on fruit size, fruit number, or total yield. Fruit size was increased at one location, and the incidence of blossom-end rot was decreased by increased frequency of irrigation. Nitrate-N distribution within the bed was not affected by initial N placement. In the soil with a rapid infiltration rate, NO3-N levels in the center of the bed were always low, with highest concentration observed in the areas of the bed most distant from the drip tube. In the soil with the slower infiltration rate, NO3-N concentrations were more uniform throughout the bed, with highest concentrations in the bed center: Increasing soil moisture levels (–20 kPa vs. –30 kPa) resulted in increased leaching and reduced NO3-N concentration throughout the bed. Foliage N concentration was not affected by N placement, but decreased seasonally. Total N uptake by the above-ground portion of the plants was not affected by fertilizer placement or soil moisture level.

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Wilton P. Cook and Douglas C. Sanders

Studies were conducted to determine the effect of N application frequency through drip irrigation on soil NO3-N movement in the bed profile and on yield and N uptake by tomato plants (Lycopersicon esculentum Mill. `Sunny') at two locations. Increasing N application frequency resulted in increased yields at Clayton, N. C., but not at Charleston, S.C. The number of fruit produced was not affected by N treatment at either location, but fruit size increased with increasing N application frequency at Clayton. Foliage N concentration decreased seasonally, but neither foliage N concentration nor total N content of the above-ground portion of the plants was affected by N application frequency. Regardless of N application frequency, NO3-N concentrations within the raised bed decreased with time due to plant uptake and leaching. Nitrogen levels declined most rapidly in the area closest to the drip tube.

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James W. Rushing, Wilton P. Cook and Anthony P. Keinath

Transmission of watermelon fruit blotch was not observed during the first week of postharvest storage at either 11 °C or 20 °C when the diseased surface of an affected watermelon was placed in direct contact with the surface of a healthy fruit. Abrasion of either the diseased fruit, the healthy fruit, or both fruit did not facilitate transmission of the disease compared to unabraded controls. After 3 weeks' storage, disease transmission was significantly greater at 20 °C than at 11 °C, illustrating the importance of appropriate temperature management during postharvest handling. Harvesting appears to arrest the development of watermelon fruit blotch if the disease symptoms cover less than approximately 5% of the fruit surface at harvest.

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James W. Rushing, Anthony P. Keinath and Wilton P. Cook

Watermelon fruit blotch (WFB) symptoms did not appear on healthy watermelon [Citrullus lanatus (Thunb.) Matsum. and Nakai] fruit placed in contact with the diseased surface of other fruit and stored at either 52 or 68 °F (11 or 20 °C) for 1 week. After 3 weeks in storage, some WFB transmission was observed and the frequency of transmission was greater at 68 than 52 °F. Surface abrasion of either the healthy fruit, diseased fruit, or both fruit did not promote transmission of WFB compared with unabraded controls. Some healthy fruit harvested from a field with diseased fruit developed very minor symptoms of WFB in postharvest storage, but the symptoms were not severe enough to cause market problems. Harvesting appeared to halt the spread of WFB symptoms on individual fruit with less than ≈10% of the fruit surface affected at harvest. If care is taken during harvest and grading to exclude diseased fruit, and if proper precooling and subsequent temperature management is implemented for marketable fruit, WFB does not appear to be of concern for the marketing of watermelons.

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James W. Rushing, Wilton P. Cook and Larry Spell

Water analyses from six commercial tomato packinghouse dump tanks in South Carolina revealed that metal and pesticide residues accumulate in the dump-tank water during daily operation. The amount that accumulated varied widely as follows: Asana (esfenvalerate), 0.3 to 13.8 ppb; Bravo (chlorothalonil), 0.1 to 2.7 ppm; copper, 2.0 to 7.3 ppm; and manganese, 0.1 to 2.5 ppm. Contamination appeared to be lowest when growers implemented integrated pest management (IPM) during production. In a subsequent controlled study, tomatoes were produced under the following pest-management practices: IPM protocol with pesticide applications based on scouting reports, modified IPM with one arbitrary pesticide application at bloom, and weekly pesticide application regardless of pest pressure. In a small-scale dump tank simulating commercial packinghouse operation, the water used for tomatoes that were produced with a weekly spray schedule had about 2 to 10 times the amount of pesticide and metal residues found in the water used for tomatoes grown under IPM protocol. Modified IPM protocol resulted in intermediate levels of residues. These results confirm that IPM field practices can reduce residues in tomato packinghouse wastewater.

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James W. Rushing, Wilton P. Cook and Stanley Schumann

Water analyses from all commercial tomato packinghouse dump tanks in South Carolina in 1989 revealed that heavy metals and pesticides accumulate in the dump tank water throughout the course of daily operation. The amount that accumulated varied widely as follows: esfenvalerate, 0.6 to 13.8 ppb; chlorothalonil, 0.1 to 2.85 ppm; copper, 2.0 to 7.3 ppm; manganese, 0.3 to 2.4 ppm. Contamination was lowest when growers were implementing integrated pest management (IPM) practices during production.

In 1990, tomatoes were grown under the following pest management practices: IPM protocol; modified IPM with more frequent spray; or weekly pesticide application regardless of pest pressure. In a small scale dump tank study the water used for tomatoes on the weekly spray schedule had from 2 to 10 times the amount of pesticide and metal residues found in water used for tomatoes grown under IPM. These results confirm that IPM programs can be effective in reducing residues in tomato packinghouse wastewater.