Search Results

You are looking at 31 - 40 of 229 items for :

  • Refine by Access: All x
Clear All
Free access

Thomas W. Walters, LeRoy A. Ellerbrock, Jan J. van der Heide, James W. Lorbeer, and David P. LoParco

Greenhouse and field methods were developed to screen Allium spp. for resistance to botrytis leaf blight (causal agent Botrytis squamosa Walker). In greenhouse evaluations, plants were sprayed with laboratory-grown mycelial fragment inoculum and were incubated at 20C in a chamber with an atomizing fogger. For field inoculations, a portable fog system with windbreaks was erected around experimental plots, and the plants were sprayed with the inoculum on evenings when windless, temperate (18 to 22C) conditions were forecasted. The most effective mycelial fragment inoculum was <21 days old and had ≈45 to 50 colony-forming units/μl, resulting in an absorbance at 450 nm of 0.2 to 0.3. Rubbing the wax cuticle from leaves was essential to disease development in greenhouse but not in field experiments. Evaluations of eight Allium species, including 55 A. cepa L. accessions, were in agreement with previous studies.

Free access

David Hannaway

To demonstrate current electronic communication capabilities, an on-line demonstration of the Forage Information System ( is planned. This will include accessing various forage and grassland web sites and exploring available information resources, thereby demonstrating existing global connectivity and cooperatively developed projects. What does the future hold for electronic communications? We've seen some of the tremendous progress that has been made over the course of the last 100 years. Even the changes of the last decade have been astounding. Since 1969 (the year of the manned moon landing), the number of networked servers has grown from 4 to 13 million! How can we even pretend to forecast the future of development? It's probably sheer folly.

Free access

Steven E. Woerner and Douglas A. Hopper

A computer simulation model was developed to be used in evaluating irrigation scheduling techniques and assisting irrigation scheduling decisions under greenhouse conditions in Colorado. The model simulates variable greenhouse conditions and shows how each of four irrigation scheduling techniques responds to these conditions. Reports from the model detail numbers of irrigation events, sensitivities to parameters, and forecasts water usage. The model was also used to determine appropriate accumulation triggers for Colorado conditions.

Four techniques evaluated here include: time clock control; accumulated radiation; accumulated vapor pressure deficit; combination method (radiation and vapor pressure deficit). The model has shown the combination method to be the most sensitive to changes in environmental conditions, while the time clock method proved to be least sensitive (and most wasteful of water).

The model may evaluate additional irrigation scheduling techniques by including additional parameters in the model, and may readily be adapted to different climatic regions.

Free access

Ji Heun Hong, Douglas J. Mills, C. Benjamin Coffman, James D. Anderson, Mary J. Camp, and Kenneth C. Gross

Experiments were conducted to compare changes in quality of slices of red tomato (Lycopersicon esculentum Mill. `Sunbeam') fruit from plants grown using black polyethylene or hairy vetch mulches under various foliar disease management systems including: no fungicide applications (NF), a disease forecasting model (Tom-Cast), and weekly fungicide applications (WF), during storage at 5 °C under a modified atmosphere. Slices were analyzed for firmness, soluble solids content (SSC), titratable acidity (TA), pH, electrolyte leakage, fungi, yeasts, and chilling injury. With both NF and Tom-Cast fungicide treatments, slices from tomatoes grown with hairy vetch (Vicia villosa Roth) mulch were firmer than those from tomatoes grown with black polyethylene mulch after 12 days storage. Ethylene production of slices from fruit grown using hairy vetch mulch under Tom-Cast was ≈1.5- and 5-fold higher than that of slices from WF and NF fungicide treatments after 12 days, respectively. The percentage of water-soaked areas (chilling injury) for slices from tomatoes grown using black polyethylene mulch under NF was over 7-fold that of slices from tomatoes grown using hairy vetch under Tom-Cast. When stored at 20 °C, slices from light-red tomatoes grown with black polyethylene or hairy vetch mulches both showed a rapid increase in electrolyte leakage beginning 6 hours after slicing. However, slices from tomatoes grown using the hairy vetch mulch tended to have lower electrolyte leakage than those grown with black polyethylene mulch. These results suggest that tomatoes from plants grown using hairy vetch mulch may be more suitable for fresh-cut slices than those grown using black polyethylene mulch. Also, use of the disease forecasting model Tom-Cast, which can result in lower fungicide application than is currently used commercially, resulted in high quality fruit for fresh-cut processing.

Free access

Aleta L Meyr

Ideally, a vigor test should provide a reasonably accurate forecast of greenhouse or field quality under a wide range of conditions. A vigor test could provide useful data any time during the different stages of development: Before harvest, after harvest, through handling, natural maturation, and decline. Vigor information on a lot of seed is desirable before distribution and conditioning, after conditioning and before planting. Can one vigor test meet all these needs? The most practical seed vigor test should include several different tests which could be combined and indexed. At the Ransom Seed Laboratory we have developed a series of vigor tests which we combine for a vigor index. We perform four tests: 1. Seed weight or seedling length in pelleted seed. 2. Standard % germination as set forth by A.O.S.A. 3. Stand uniformity index at an early count which includes a photograph of one replicate of 25 seedlings. 4. Stress test: % germination at an alternative temperature. (varies from cold tests to heat tests). No single test is sufficient to communicate seed vigor. If several tests are used to form a vigor index, the actual data for each test should be communicated along with the vigor index, so the user can evaluate the data and utilize the vigor index to its fullest potential.

Free access

Ming Zhang and Eric E. Roos

All kinds of plant seeds evolve volatile compounds during storage. However, a reliable deterioration forecast method is still not established using volatile evolution, even though some preliminary work indicated a relationship between volatile evolution and seed deterioration (Fielding and Goldsworthy, 1982; Hailstones and Smith, 1989; Zhang et al., 1993). Here we review some of the previous work concerning seed volatiles and present some more recent research on the effects of seed moisture content on deterioration. We found that volatile evolution from seeds was controlled by seed moisture level. Generally, seeds tended to evolve more hexanal and pentanal under extremely dry conditions (below 25% equilibrium RH). The production of hexanal and pentanal decreased with increasing seed moisture level. On the other hand, methanol and ethanol increased with increasing seed moisture. All of the volatile compounds accumulated in the headspace of the seed storage container during storage. Therefore, it should be possible to use different volatiles to indicate the deterioration of seeds stored under different moisture levels. We suggest that hexanal may be used for seed assessing deterioration under dry storage conditions (below 25% equilibrium RH), while ethanol may be used for seeds stored under higher moisture conditions (above 25% equilibrium RH). [References: Fielding, J.L. and Goldsworthy, A. (1982) Seed Sci. Technol. 10: 277–282. Hailstones, M.D. and Smith, M.T. (1989) Seed Sci. Technol. 17: 649–658. Zhang et al. (1993) Seed Sci. Technol. 21:359–373.]

Free access

J.J. Ferguson and G.D. Israel

During Summer 1996, a disproportionate systematic sampling procedure was used to obtain an initial sample of 955 citrus growers from the mailing lists of extension agents in 27 counties. Of these, 451 usable responses were returned (67% response rate), providing an expected error of ± 4.3% with a 95% confidence interval. Surveyed growers obtained weather information during the 1995–96 winter from multiple sources, including the National Weather Service (NWS) (48%), commercial radio/TV (48%), Extension offices (18%), private meteorologists (9%), and other sources (10%). After the NWS discontinued agricultural freeze forecasts in Apr. 1996, growers indicated they would rely on commercial radio/TV (72%); private meteorologists (20%), and their County Extension Office (32%) for weather reports. When deciding which cold protection method to use, respondents adopted Extension (35%) and consultants' recommendations (30%), assessed the costs and benefits of cold protection (32%), and assessed risks based on grove history (38%). Cold protection methods used by percent respondents included: flooding groves (22%); grove heaters (2%); wind machines (2%); permanent overhead irrigation systems (2%); ground microsprinklers (76%); in-tree microsprinklers (18%); tree wraps (13%); and tree wraps or covers with microsprinklers (6%). Seventy-three percent of growers reported that their cold protection methods were very effective for a freeze with minimum temperatures of –2°C for at least 4 hr, with 12% and 3% reporting cold protection measures being very effective at –7 and –9°C, respectively.

Free access

M.H. Maletta, W.P. Cowgill Jr., and S.A. Johnston

A research trial evaluation of fungicides and fungicide combinations in conjunction with weekly or TOM-CAST (an early blight forecast system) spray schedules was conducted in 1998. Fungicide regimens were: Quadris (alternating with Bravo Weatherstik); Bravo Weatherstik; Manzate followed by Bravo Weatherstik; Champ; Champ and Bravo; Nu-Cop; NuCop and Bravo The weekly schedule resulted in 15 fungicide applications; the TOM-CAST schedule required five applications. Foliar disease was rated weekly. Mature fruit were harvested weekly to obtain total and marketable yields. All fungicide treatments reduced foliar disease compared to the untreated control. Quadris alternating with Bravo Weatherstik on a weekly or TOM-CAST schedule provided better disease control than any other material on either schedule. There were no significant differences in disease control among the other materials applied weekly. Disease control achieved with the TOM-CAST schedule was somewhat less than with the weekly schedule for all materials. Quadris/Bravo or Bravo provided the best control and Champ or Nu-Cop alone provided the least control on the TOM-CAST schedule. Total yield was not affected by fungicide or schedule. Marketable yield was reduced by weekly applications of copper fungicides compared to most other treatments. Chemical names used: tetrachloroisophtalonitrile (chlorothalonil); [methyl (E)-2-{2-[6-(2-cyanophenoxy) pyrimidin-4-yloxy]phenyl}-3-methoxyacrylate (asoxystrobin); copper hydroxide; manganese ethylene bisdithiocarbamate and zinc.

Free access

D.J. Mills, C.B. Coffman, J.R. Teasdale, J.D. Anderson, and K.L. Everts

In the production of fresh-market vegetables, off-farm inputs, such as, plastic, nitrogen fertilizer, fungicides, insecticides, and herbicides are routinely used. One aim of the sustainable agriculture program at the Beltsville Agricultural Research Center is to develop systems that reduce these inputs. We have completed the second year of a study designed to examine foliar disease progress, foliar disease management, and marketable fruit yield in staked fresh-market tomatoes grown in low- and high-input production systems. Specifically, four culture practices (black plastic mulch, hairy vetch mulch, dairy manure compost, and bare ground) were compared in conjunction with three foliar disease management treatments (no fungicide, weekly fungicide, and a foliar disease forecasting model, TOMCAST). Within all culture practices, use of the TOMCAST model reduced fungicide input nearly 50%, compared with the weekly fungicide treatment, without compromising productivity or disease management. With regard to disease level, a significant reduction of early blight disease severity within the hairy vetch mulch was observed in 1997 in relation to the other culture practices. Early blight disease severity within the black plastic and hairy vetch mulches was significantly less than that observed in the bare ground and compost treatments in 1998. In addition, despite a 50 % reduction in synthetic nitrogen input, the hairy vetch mulch generated yields of marketable fruit comparable to or greater than the other culture practices. It appears that low-input, sustainable, production systems can be developed that reduce the dependence on off-farm inputs of plastic, nitrogen fertilizer, and pesticides, yet generate competitive yields.

Free access

Makki A. Al-Kahafaji

This study was conducted during two season (1993-1994) to formulate a suitable mathematical model to determine optimal chilling conditions for deciduous fruit trees from different areas of Iraq (Baghdad, Diyala, Karbala, and Naynawa). A hygrothermograph was utilized to record the average chilling temperature: Baghdad (571), Diyala (874), Karbala (548), and Naynawa (1206). Temperature information gathered 1982-1994 from weather forecasting records also proved beneficial to our study. The model designed for this project was then used to measure optimal chilling conditions of deciduous fruit trees in 11 areas of Iraq: 1000-1200 h in northern areas (Douhook, Sulaymaniyah, Arbeel Naynawa); 700-800 h in the north central areas (Al-Taameen, Salah al din, Diyala), 500-600 h in the middle and south centeral areas (Baghdad, Karbala, Babil, Al-Najaf, Wasit), and 200 h in the southern areas (Al Qadissiyah, Thi-qar, Misan, Basrah). The chilling temeperature differences recorded in the central areas were due primairly to variations in water surface and plant coverage. Temperature proved to be the determining factor for chilling hours accumulations recorded during the growing seasons.