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Juan C. Diaz-Perez*, Darbie Granberry, Kenneth Seebold, David Giddings, and Denne Bertrand

Bell pepper (Capsicum annum L.) plants have a high demand for water and nutrients and are sensitive to water stress during the establishment period and fruit setting. High levels of irrigation are often applied in order to maximize yields. However, field observations suggest that excessive irrigations may negatively affect bell pepper plants. The objective was to evaluate the effects of irrigation rate on plant growth and fruit yield. The trial was conducted in Spring 2003 at the Coastal Plain Experiment Station, Tifton, Ga. Drip-irrigated bell pepper (`Stiletto') plants were grown on black plastic mulch in 1-m wide beds (1.8-m centers). Plants were irrigated with an amount of water that ranged from 33% to 167% the rate of evapotranspiration (ET), adjusted by crop stage of development. Soil moisture content (% by volume) over the season was continuously monitored with time domain reflectometry sensors connected to a datalogger. The results showed that the average soil moisture content for the season increased with increasing rates of irrigation. Vegetative top fresh wt. and marketable fruit yield were reduced at both, low (33% ET) and high (166% ET) rates of water application. However, irrigation rate had a stronger effect on fruit yield than on top fresh wt. Plants supplied with high irrigation rates appeared to be more chlorotic compared to plants irrigated at medium rates (100% ET). There was a tendency for higher incidences of soil borne diseases (Pythium sp., Phytophtora capsici) in plants receiving higher rates of irrigation. The conclusion is high irrigation rates (>166% ET) are not recommended since they waste water and may result in both, higher incidences of soil-borne diseases and reduced bell pepper yields.

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Juan C. Díaz-Pérez, Sharad C. Phatak, David Giddings, Denne Bertrand, and Harry A. Mills

Tomatillo (Physalis ixocarpa Brot. ex Hornem) is a popular crop in Mexico and other Latin American countries. There is an increasing demand for this vegetable in the United States, particularly from the growing Latino population. However, there is limited information about tomatillo production. The objectives of this study were to determine the effects of plastic mulches on plant growth, yield, and root zone temperature in two cultivars of tomatillo. The study was conducted in Spring and Summer 2000. The design was a randomized complete block with a split plot arrangement, where plastic film mulch (black, gray, and silver mulches, and bare soil) was the main plot and cultivar (`Toma Verde' and `Verde Puebla]) the subplot. In the spring, mulch treatments had little effect on plant growth during the first 30 days after transplanting and there were no significant differences in fruit yields. In the summer planting, both early growth and fruit yields were greatest with the silver and gray mulch treatments and lowest on bare soil. Plant growth during the establishment was related with subsequent plant growth and yield. In mature plants, vegetative top fresh weight and total fruit yield were higher (P < 0.01) in the spring than in the summer. Total fruit yield (both seasons), marketable yield (spring) and cull yield (spring) were lower in `Toma Verde' than in `Verde Puebla'. Root zone temperatures (RZTs) in the spring (mean = 26.4 °C) were lower than in the summer (mean = 29.3 °C). In both seasons, mean RZT was highest under black mulch and lowest in bare soil. In the summer, plant growth and fruit yields tended to decrease with increasing RZTs. Tomatillo plants grown on mulches with a mean seasonal RZT of 30 °C had fruit yields that were 65% (`Toma Verde') or 50% (`Verde Puebla') lower respectively than those of plants on mulches with a RZT of 27 °C. There were no significant differences in foliar concentrations of N, Ca, Mg, S, B, Zn, Cu and Na among mulches. Foliar concentrations of the majority of mineral nutrients were not related with the mean RZT for the season.

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Juan C. Díaz-Pérez, K. Dean Batal, Darbie Granberry, Denne Bertrand, David Giddings, and Hanu Pappu

Tomato spotted wilt virus (TSWV) is a serious constraint to tomato production worldwide. Losses are significant because the disease is difficult to control and most of the commercially available tomato cultivars are susceptible to TSWV. This study was intended to provide information that could be used to design more appropriate disease management strategies. The objective was to determine the relationship of tomato plant growth and fruit yield with the time of TSWV symptom appearance. Experiments were carried out during Spring 1999 and 2000, using drip irrigation and plastic film mulched beds with black plastic mulch alone (1999) or different colored mulches (2000). The mulches used were black, black-on-silver, gray-on-black, red, silver-on-black, silver (painted) and white-on-black, and bare soil. The 1999 experiment included a single TSWV-susceptible cultivar (Florida-47), while the 2000-experiment included two TSWV-susceptible (Florida-91 and Sun Chaser) and one TSWV-resistant cultivars (BHN-444). Colored mulches and tomato cultivars affected the time between transplanting and appearance of first symptoms of TSWV. For all tomato cultivars, vegetative top fresh weight (FW), fruit number and total fruit yield increased linearly with the time the plants remained free from TSWV symptoms. Marketable fruit yield also increased as the time from transplanting to the first appearance of symptoms increased. When data for cultivars were pooled, vegetative top FW and total fruit yield were reduced by 2.1% and 2.3%, respectively, for each day prior to harvesting that plants showed TSWV symptoms.

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Juan C. Díaz-Pérez, William M. Randle, George Boyhan, Ronald W. Walcott, David Giddings, Denne Bertrand, Hunt F. Sanders, and Ronald D. Gitaitis

Sweet onions (Allium cepa L.) are typically grown on bare soil and irrigated with high-pressure systems such as sprinklers or center-pivots. The objective of this study was to determine the effects of irrigation system and mulch on bolting, bulb yield and bulb quality over 3 years. The experimental design was a split plot, where the main plot was irrigation system (drip or sprinkler) and the subplot was the type of mulch (bare soil, black plastic film or wheat straw). The results showed that individual bulb weight and bulb yields under drip irrigation were similar to those under sprinkler irrigation. Plants grown on bare soil had the highest total yield during the three seasons and among the highest marketable yield. There were no consistent differences in the bulb number or yield of plants on plastic film mulch compared to those of plants on wheat straw mulch. Plants on wheat straw mulch had reduced foliar nitrogen content. Variability in yields among mulches and seasons was partly explained by changes in seasonal root zone temperature and soil water potential. Total and marketable yields and weight of individual bulbs increased with increasing root zone temperatures up to an optimum at 15.8 °C, followed by reductions in yields and individual bulb weight at >15.8 °C. Onion bolting increased with decreasing foliage nitrogen content, with plants on wheat straw having the highest bolting incidence. Bolting also increased with decreasing root zone temperatures for the season. Total and marketable yields increased with decreasing mean seasonal soil water potential down to -30 kPa. Irrigation system and mulches had no consistent effect on the soluble solids content or pungency of onion bulbs.