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- Author or Editor: Milton E. McGiffen Jr. x
Many careers involve working at multiple locations with unpredictable daily schedules. Professionals may have several locations from which they conduct business. Electronic mail (e-mail) and other features of the Internet have facillitated the evolution of the virtual office, which gives the appearance of a single point of contact with mobile, busy people. E-mail is the most obvious use of the Internet. E-mail groups allow for effective discussions with people of similar interests and the exchange of hard-to-acess expert information. Websites and e-mail groups allow rapid dissemination and discussion of multimedia information. The Vegetable Research and Information Center is an example of how to extend the virtual office concept to the departmental level, allowing spatially scattered researchers, extension workers, and their clientele to work together and exchange information.
Organic agriculture is growing in importance worldwide. In the United States, the rate of increase of organic growers was estimated at 12% in 2000. However, many producers are reluctant to undertake the organic transition because of uncertainty of how organic production will affect weed population dynamics and management. The organic transition has a profound impact on the agroecosystem. Changes in soil physical and chemical properties during the transition often impact indirectly insect, disease, and weed dynamics. Greater weed species richness is usually found in organic farms but total weed density and biomass are often smaller under the organic system compared with the conventional system. The improved weed suppression of organic agriculture is probably the result of combined effects of several factors including weed seed predation by soil microorganisms, seedling predation by phytophagus insects, and the physical and allelopathic effects of cover crops.
Path analysis is a statistical method for determining the magnitude and direction of multiple effects on a complex process. We used path analysis to determine the direct effects of nightshade density on yield components (number of green fruit per plant, rotted fruit per plant, total fruit per plant, and weight per fruit) of the processing tomato cv. Heinz 6004. In addition, the analysis indicated the direct and indirect effects of yield components on total yield per ha and marketable yield per ha. The greatest direct effects of eastern black nightshade and black nightshade were on green fruit per plant and total fruit per plant. Effects other than density (density-independent factors) were more important in determining the number of rotted fruit per plant and weight per fruit. Path analysis showed that the total number of fruit per plant was the most important yield component determining total yield and marketable yield per ha.
A 2-year field project was conducted in Thermal, Calif., to investigate cowpea [Vigna unguiculata (L.) Walp.] mulch as an alternative weed control option in pepper (Capsicum annuum L.) production. Treatments included: bare ground (BG) with hand weeding, BG with no weeding, cowpea mulch (CM) with hand weeding, and CM with no weeding. Cowpea was seeded in July on 76-cm beds and irrigated with buried drip line. Two weeks prior to transplanting peppers, irrigation water was turned off to desiccate the cowpea plants. In September, cowpea was cut at the soil line, mulch was returned to the top of the bed, and pepper plants were transplanted into the mulch and fertilized through the drip line. Every 2 weeks, the number of weeds emerged and pepper plant height were recorded. Fruit production, pepper plant dry weight, and weed dry weight were recorded at harvest in December. Fewer weeds emerged in CM than in BG. The final weed population in nonweeded CM was reduced 80% and 90% in comparison with nonweeded BG in 1997 and 1998, respectively. Weed dry weights in nonweeded CM were 67% and 90% less than those in nonweeded BG over the same period. In 1997 and 1998, respectively, pepper plants produced 202% and 156% more dry weight, as well as greater fruit weight, in CM than in BG. There were no differences in mean fruit weight. Cowpea mulch provided season-long weed control without herbicides while promoting plant growth and fruit production.
Poor root color is a recurring problem in carrot (Daucus carota L.) production. Consumers prefer dark orange carrots that are high in carotene. However, unfavorable environmental conditions and certain production practices can lead to light orange roots with low carotene content. Growers sometimes refer to this as “white root.” No one has clearly established the causes or cures for this disorder. Several environmental factors are known to affect the color of carrots, but to date there is no practical treatment. High-density planting often reduces carotene content. Field studies were conducted in the 1995-96 and 1996-97 winter growing seasons to determine if foliar applications of ethephon would improve carrot color, carotene content, and yield. Carotene content and root color increased as the number of applications or the amount of ethephon applied with each application increased. Root weight was not significantly affected.
Economic analyses compared the returns of weed control methods for drip and sprinkler irrigated celery (Apium graveolens L. `Sonora'). The nine treatments included an untreated control, cultivation as needed for weed control, a pre-emergent herbicide (trifluralin), and six post-emergent herbicides. The effect of each treatment on weed control, yield, crop value, cost of control, costs for additional hand-weeding, net return, and dollar investment (marginal rate of return) was determined. The treatments that reduced weed populations under drip and sprinkler irrigation also increased yield, net returns, and rate of returns. Effective weed control reduced the additional costs of hand-hoeing the weeds not killed by herbicides, resulting in greater net return. The net returns of weed control were even greater when celery was drip irrigated than when sprinklers were used. In 1998, the sprinkler irrigated field returned $1148 to $3921/ha, compared with -$5984 for the untreated control. Net returns for drip irrigation were much higher, ranging from $3904 to $9187/ha compared with -$8320 for the untreated control. Net returns were also higher in 1999, ranging from $2466 to $5389 when weeds were controlled compared with a net loss of $5710 for the untreated control in the sprinkler irrigated field. The returns on the drip-irrigated field were much higher, from $6481 to $8920 when weeds were controlled, compared with -$8046 for the untreated control. The associated returns for every dollar invested (marginal rate of return) in the non-dominated treatment (more return and lower cost) ranged from 52% to 156% for sprinkler irrigation, and 59% to 144% for drip irrigation in 1998. In 1999, the rate of return for each dollar invested ranged from 104% to 324% for sprinkler and 2.4% to 321% for drip irrigated fields.
While there are published reports of varietal differences in competitiveness with weeds, no crop varieties have been specifically developed for tolerance to weed interference. We explored several methods that mechanistically compare potential sources of tomato varietal tolerance to purslane, velvetleaf, and black night-shade: 1) The influence of canopy structure and development was studied with a wide range of crop and weed germplasm with different growth habits. Leaf expansion rate and other morphological characters were used to select crop genotypes for more-detailed study. 2) Replacement series experiments with selected cultivars found that purslane and other species can adapt to avoid competition. The greatest varietal differences in competitiveness were with nightshade species that had a canopy structure similar to tomatoes. 3) Field measurements of canopy development and light interception found that competitive advantage shifted over time as height and leaf area of weeds and crops changed. 4) A systems analysis method, sensitivity analysis, found that changes in plant architecture over time were more important than initial or final crop characteristics in determining competitive outcomes.
Eastern black nightshade (Solanum ptycanthum) and black (Solanum nigrum) nightshade are difficult to control in tomato, interfering with harvest and decreasing fruit quality and yield. In irrigated tomatoes, soil water depletion was greater as nightshade density increased. However, tomato yield loss due to black nightshade was greatest at the lower weed densities. As density increases, photosynthetic activity (photosynthetic rates, stomatal conductance, intercellular CO2 concentration, and stomatal resistance) of black nightshade is more affected than eastern black nightshade. Photosynthetic activity of tomato is the least affected. In greenhouse experiments where water was denied for approximately a week prior to measurement, tomatoes were more sensitive to water stress than were nightshades. Nightshades were more adapted to drought stress than were tomatoes.