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L.P. Brandenberger and R.P. Wiedenfeld

Bare soil, 13 different polyethylene mulching films, and K-Mulch kenaf paper film were compared to one another for use in early spring production of cantaloupe melons. The mulching treatments were applied to the top of raised beds spaced 200 cm apart in late January and seed of the cantaloupe variety Cruiser were planted in early February. Treatments were replicated five times in a complete randomized block design. Plots were irrigated throughout the season utilizing a drip irrigation system. Crop responses to mulches throughout the growing season were determined by measuring vine growth, fruit yield, Fruit quality and earliness. Mulch tensile strength was determined throughout the season, and ease of cleanup and disposal were evaluated after the growing season. Differences were recorded for treatments particularly regarding ease of cleanup.

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L.P. Brandenberger and R.P. Wiedenfeld

Melon growers in the Lower Rio Grande Valley of Texas have observed in the past that particular sizes of melons and the earliness of melons had a direct effect upon economic returns. A replicated study was carried out during two seasons to determine what specific effects plant density, row arrangement, and cultivar would have on fruit size and yield. The study combined six spacing treatments with three cultivars in a randomized design utilizing five replications on top of raised beds on 80-inch centers. Work was initiated by direct seeding and then thinning to the desired spacing interval in plots located in a commercial field. Plots were harvested by commercial harvesting crews. Results indicate that different plant spacings and honeydew cultivars can result in differences in fruit size, earliness, and returns/acre over different seasons and environments although spacing and cultivar acted independent of one another. Lower plant populations resulted in the production of larger fruit and higher plant populations resulted in the production of smaller fruit. Cultivar did affect the size of fruit produced, with some cultivars resulting in larger melons and others producing more small melons. In both seasons, the double-row 24-inch spacing resulted in an earlier harvest and exhibited a higher percent harvest for the first harvest in both years. Cultivar Sure 7050 was significantly later than either `Honeybrew' or `Morning Ice'. Returns/acre were significantly different between spacing treatments for a majority of harvests. The double-row 24-inch spacing resulted in the highest returns/acre. Both `Morning Ice' and `Sure7050' had significantly higher returns when compared to `Honeybrew'.

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L.P. Brandenberger and R.P. Wiedenfeld

The squash leaf curl virus (SLCV), transmitted by the sweet potato whitefly (Bemesia tabaci biotype B), is widespread on fall-planted watermelon in the Rio Grande Valley and Coastal Bend areas of south Texas. The objective of the study was to evaluate colored mulches for their effects on whitefly populations, virus incidence, and watermelon yield. Eleven polyethylene films were included as treatments in both a spring and fall study and were replicated five times in a randomized block design. Plastic mulches caused substantial improvement in melon yields (40%) in the spring crop, similar to responses obtained in other studies on cantaloupes. Fall yield increases due to the use of mulches did not occur. Whitefly populations were much lower in 1996 than they have been in previous years, therefore this was not an adequate test of its effects on whitefly behavior. Even so, there were indications in the fall crop that the use of plastic mulch tended to result in lower whitefly numbers. No evidence was found of any difference between the various mulch materials regarding whitefly counts.

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L.P. Brandenberger, R.P. Weidenfeld, J. Lopez and R. Mercado

Evaluation of new southernpea cultivars and advanced breeding lines for spring and fall cropping is important for both producers and processors of this crop in South Texas. The spring trial included three commercially available cultivars and 17 advanced breeding lines from the Univ. of Arkansas breeding program. Foliage color ratings taken in the spring correlate with similar ratings taken in 1995 and indicate that Arkansas 435-87-68 may be tolerant to high pH soils that caused yellowing in several other cultivars. The highest producing varieties, Arkansas 87-435-68 and Arkansas 92-552, produced net yields > 1000 lb/acre. The fall trial included the same material as the spring trial plus four more commercially available cultivars. Maturity ratings taken in early October varied widely between cultivars and breeding lines. Recorded ratings represented growth stages ranging from cultivars with no flowering to those that had set pods that were filling. The most mature types included Arkansas breeding lines 96-593, 95-368, 96-556, and 95-301, which had maturity ratings of 3.8, 3.5, 3.5, and 3.3, respectively. Net yields varied widely among cultivars in the fall trial. Yields ranged from 23.8 to 522.8 lb/acre. Those with the highest net yields included 'Early Scarlet', Arkansas 91-285, Arkansas Blackeye #1, and Arkansas 95-368, with yields of 522.8,402.2, 401.2 and 400.5 pounds per acre, respectively. Although yields in the trial were considerably lower than expected, several cultivars produced 400 or more pounds of peas per acre compared to many commercial fields that were not harvested.

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L.P. Brandenberger, R.P. Wiedenfeld and D. Makus

Fertilization programs used commercially for bell peppers (Capsicum annuum) in the subtropical Lower Rio Grande Valley of Texas may vary substantially from recommendations based on research. Therefore, a commercial fertilization program used on a significant fraction of the pepper production in this area was evaluated at two locations. Preplant soil tests showed NO3-N levels were low at one location and very high at the other. Nitrogen application where preplant soil NO3-N was low resulted in a six-fold yield increase (from 197 to 1203 kg·ha–1), and improvements in fruit weight, fruit volume, fruit density, wall thickness, wall strength, and carotenoid and chlorophyll a and b contents. No other nutrient application at either location or N application at the site where preplant soil NO3-N levels were high significantly affected yield by size class, fruit quality characteristics, storage properties, or mineral and organic components. Nitrogen application had the greatest effect on dry-weight accumulation and N uptake during fruit set and maturation when N demand was high. Where N responses were observed, N application increased total dry weight in plant and fruit by 150% and total N uptake by 186%, yet this increase amounted to a N fertilizer uptake efficiency of only 12%. Thus, N should be used judiciously to prevent pollution of drainage and ground waters.

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T.E. Morelock, J.C. Correll and L.P. Brandenberger

Downy mildew (Blue mold) is probably the most common spinach disease in most parts of the world, and it can be a problem in the mid-South. Frequently, other diseases such as white rust and fusarium cause major crop loss. The Arkansas breeding program was initiated 25 years ago to address white rust and fusarium, as well as other diseases that destroy spinach crops. Since single gene resistance is not available for most spinach diseases, it was necessary to utilize polygenic resistance to develop varieties that are resistant to most of the common spinach diseases that occur in the Arkansas River Valley of Arkansas and Oklahoma. Highly resistant genotypes have been developed by using disease nurseries and field screening, so frequent selections are made based on the reaction to 3-4 diseases.

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L.P. Brandenberger, T.E. Morelock and J.C. Correll

Spinach germplasm (707 accessions) from collections from six countries were screened for resistance to race 4 of the downy mildew pathogen Peronospora farinosa f. sp. spinaciae; these collections contained germplasm that originated from 41 countries. The predominant species examined was Spinacia oleracea L., however, eight accessions of S. turkestanica Iljin and two accessions of S. tetrandra Stev. were also tested. About 40 seedlings of each accession were inoculated. The cultivar St. Helens was included as a susceptible control in each test. The majority of accessions tested (>98%) were susceptible to race 4. Nine accessions exhibited some resistance to race 4 (9% to 38% of the seedlings within an accession were resistant), and two accessions, CGNO 9546 and SPI 82/87, exhibited a high level of resistance (60% and 80% resistant, respectively). Resistance identified in several of the accessions in this study may be useful for breeding for race 4 resistance.

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L.P. Brandenberger, T.E. Morelock and J.C. Correll

Field observations indicate that polygenic resistance to downy mildew (Peronospora farinosa f. sp. spinaciae) was observed during the course of a breeding program to develop polygenic resistance to white rust (Albugo occidentalis). Field studies were initiated using five cultivars and one breeding line to quantify the level of resistance to downy mildew and white rust. Separate plots were inoculated with each pathogen at a specific spore concentration and then subjected to a minimum dew period of 12h. Infection was quantified by measuring latent period, lesion number, lesion size, sporulation and percent leaf area infected.

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L.P. Brandenberger, T.E. Morelock and J.C. Correll

Field observations indicate that polygenic resistance to downy mildew (Peronospora farinosa f. sp. spinaciae) was observed during the course of a breeding program to develop polygenic resistance to white rust (Albugo occidentalis). Field studies were initiated using five cultivars and one breeding line to quantify the level of resistance to downy mildew and white rust. Separate plots were inoculated with each pathogen at a specific spore concentration and then subjected to a minimum dew period of 12h. Infection was quantified by measuring latent period, lesion number, lesion size, sporulation and percent leaf area infected.

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L.P. Brandenberger, J.C. Correll, T.E. Morelock and R.W. McNew

Resistance to race 3 and 4 of downy mildew (Peronospora farinosa f.sp. spinaciae) was examined in separate field inoculation tests. Three Arkansas cultivars and three other commercial spinach cultivars were compared by periodically scoring individual leaves for disease severity 7 to 28 days after inoculation. Leaves were scored on a 0 to 6 scale with 0 = 0% of the leaf surface being covered with sporulation and 6 = 90-100%. Resistance was evaluated by comparing disease ratings on a given day as well as the area under the disease progress curve. Arkansas spinach cultivars exhibited significantly lower disease severity ratings in field inoculation tests for all sample dates for both races 3 and 4 when compared to known susceptible cultivars.