OCTOBER 2000 - VOLUME 10, NUMBER 10
Edited by
Frank J. Dainello, Ph.D.
Extension Horticulturist - Commercial Vegetable Crops
The Texas A&M University System
College Station, Texas 77843-2134
Edited by
Frank J. Dainello, Ph.D.
Extension Horticulturist - Commercial Vegetable Crops
The Texas A&M University System
College Station, Texas 77843-2134
Methods for Releasing Encarsia formosa to Control Greenhouse Whitefly
This article by Cathy Thomas, Integrated Pest Management Program, Pennsylvania Department of Agriculture, appeared in the "Vegetable and Small Fruit Gazette," September 2000, Vol. 4, No. 9.
our methods of releasing Encarsia formosa to control Greenhouse whitefly listed below have been developed in Europe, and are used by commercial vegetable producers. The effectiveness and success of these programs are based on the level of honeydew- and sooty-mold development on foliage and fruit. If sooty-mold levels are acceptable for a marketable product, control of greenhouse whitefly has been achieved.
1. Pest in First.
With this method, adult whiteflies are introduced into the crop at a fixed rate when transplants are installed in production houses. Encarsia formosa is then introduced at regular intervals when whitefly nymphs develop. This method has not been widely adopted because of the concern of releasing pests into the crop.
2. Banker Plants.
The bank plant system uses established colonies of parasitoids, reared on whitefly-infested plants, that are introduced into the crop. Mesh screens can be used to cage banker plants to contain whiteflies, and allow only the tiny parasitoids to disperse into the production area. Using this method may require other facilities (greenhouses or growth chambers) to establish the pest and biocontrol on the banker plant; however, there would be the advantage of having a sustainable, on-site supply of parasitoids.
3. Inundative.
With inundative introductions, high numbers of E. formosa are introduced on a regular basis. This method might be used when establishment and reproduction of the biocontrols are not expected. Inundative releases are used in ornamental crops or short-term crops. Inundative introduction of biocontrols may not be cost effective.
4. Dribble method.
With the dribble method, weekly parasitoid introductions begin at planting, in anticipation of naturally-developing whitefly populations, or introduction of E. formosa can be made when whiteflies are first observed. Parasitoids are introduced every two weeks until there is a high level of parasitized whitefly pupae in the crop. This is usually more cost effective than introducing E. formosa every week of the crop cycle. The dribble method is the most common introduction method used in Pennsylvania greenhouses.
These introduction methods should be discussed with your supplier, who can also advise you on the number of E. formosa needed for your crop. These numbers will be based on whitefly populations; hence, the need for careful crop observation and scouting. These introduction methods can also be used for other parasitoids and predators.
Announcements
Thanks for a Job Well Done!
Plant Protection
Conference
December 4, 5, &6, 2000
Pebble Creek Country Club
College Station, Texas
For information, contact Pat Miller at (512) 259-2118.
National Spinach Conference
San Antonio, Texas
December 14, 15, and 16, 2000
Attention spinach enthusiasts, growers, Extension personnel, plant breeders, researchers, seed company and technical development representatives, shippers, processors, and all others interested in spinach! The Cooperative Texas A&M University and The University of Arkansas Spinach Program will host the National Spinach Conference in San Antonio, Texas in December.
Registration fee: $50 - meals and tours - Late registration (after November 1, 2000) - $75 Send registration fee to Larry Stein or Frank Dainello.
Conference headquarters will be the Omni Hotel in San Antonio. We have secured a special room rate of $70 for a single, and $89 for a double for this event. Reservations are due by November 14, 2000, to insure you receive the conference rate. Call 1-800-THE OMNI (800-843-6664) to reserve your room today.
Check out our web site for registration forms and other information at:
http://aggie-horticulture.tamu.edu/PLANTanswers/publications/spinach/index.html
For additional information, contact Larry Stein or Frank Dainello:
Dr. Larry Stein
TAMU-Agricultural Research & Extension Center
P. O. Box 1894
Uvalde, TX 78802-1849
e-mail: larrystein@tamu.edu
fax: (830) 278-4008Dr. Frank Dainello
Department of Horticultural Sciences
Texas A&M University
College Station, TX 77843-2143
Phosphorus Availability and Response of Tomato to Phosphorous Fertilizer in Calcareous SoilsThis article by Yuncong Li appeared in the
"Vegetarian Newsletter," August 1999.
alcareous soils that contain a large amount of calcium carbonate (usually from 1 to 100 percent CaCO3 equivalent) are common in Florida (ed. note: and also in Texas). Calcium carbonate can occur in the surface soils naturally or as a result of land preparation (plowing, bedding, etc.). Soils also can be calcareous through over-liming or long-term irrigation with calcium-carbonate enriched ground water. Calcareous soils induce an array of nutritional problems for crops, and Phosphorus (P) is one of them.Application of P fertilizer is important for vegetable production on calcareous soils. However, most growers apply too much P fertilizer for their crops. Over-fertilization leads to unnecessarily high production costs, may decrease yield and quality, and poses a risk to the environment.
A two-year field experiment was conducted in a commercial vegetable field on a typical Krome very-gravelly loam soil in Miami-Dade County during 1997-1998.
Dry fertilizer was applied in 2 bands along the top of the bed at three rates of P (37,63,100 percent of the grower rate, equivalent to 96, 163, 260 lb P2O5/ac) in the 1997 growing season, and at 4 rates of P (0, 70, 140, and 280 lb P2O5/ac) in the 1998 growing season as triple superphosphate with 6 replications. All of the treatments received the same amounts of N and K as dry and liquid fertilizers. 'Sunbeam' tomato plants were transplanted in a single row in the center of each bed, with 20 inches between plants. Tomatoes were harvested three times at mature-green stage. Total number, total weight, and color of fruit from each plot were recorded. Soil and leaf samples were also analyzed for P.
The results showed that phosphorus fertilization increased AB-DTPA extractable P in the soil, but did not affect the concentration of leaf P, yield, and quality of tomato, with the exception that the quantity of red fruit at the time of the first harvest (1997) was increased slightly. It was also found that there was no response to bean, Malanga, potato, and sweet corn to P fertilizer during three-year experiments on calcareous soils in Miami-Dade County.
Phosphorus removal via the harvested fruit usually accounts for less then 38 lb P2O5 for 1,000 cartons of tomato. A large portion of the applied P remains in the soil. It is important to know the availability of remaining P in calcareous soils. In 1998, surface soil samples (0- to 6 -inch depths) were collected from 6 typical vegetable fields in south Miami-Dade County. Soil samples were extracted sequentially with water, AB-DTPA, and the mixture of nitric acid and hydrochloric acid, to determine water-soluble, plant-available, and residual P in soils. Average concentrations of water-soluble P in soil samples collected from various vegetable fields were 1.2 ppm, and ranged from 0.87 to 1.69 ppm. Water-soluble P is available to the crop; however, this type of P is also subject to leaching out of the root zone through excessive irrigation or heavy rainfall. Concentrations of AB-DTPA extractable P in these soils range from 46.4 to 94.8 ppm, with a mean concentration of 70.9 ppm. AB-DTPA extractable P is plant-available, and highly correlated to the uptake rate by the crop-grown calcareous soils. Acid-extractable P in soils represent the P residue in soils that is not directly available to plants. About 95 percent of total P in 6 soil samples were in residual form. Concentrations of residual P ranged from 1,123.8 to 1,877 ppm, with a mean concentration 1,404.4 ppm.
Phosphorus fertilizers applied in calcareous soils are fixed through adsorption and precipitation. In 1999, a P sorption and desorption experiment was conducted with 24 soil samples collected from natural lands, vegetable fields, and tropical fruit groves. Adsorption was the dominant reaction at low P concentrations, and P precipitated with calcium carbonate at high P concentrations.
Results from this study indicate that soils from vegetable fields which were saturated with P, and excessive P applied as fertilizer, often precipitate and become less available to crops. The desorption rate from vegetable soils is higher than the desorption rate from natural soils, because of high initial soil P in those soils.
In summary, large amounts of P are accumulated in most cultivated calcareous soils from fertilizer application. No P fertilizer application is necessary for calcareous soils with high available P levels. Growers should conduct a pre-fertilizer soil analysis to determine supplemental P fertilizer rates.
Cover Crops Can Accomplish Many Important Tasks for Growers
This article by Lee Dean, Managing Editor, appeared in "The Vegetable Growers News," May 1999.
ichigan State University Extension specialists are working to 'cover' the state's vegetable growers with information about an important practice -- the use of cover crops.Researchers say cover crops are planted to improve soil quality, enhance nitrogen management, provide erosion control, and suppress weeds, insects, and nematodes.
Cover crops can enhance nitrogen production and can also reduce nutrient losses. Grass can be used to take up excess nitrogen and help alleviate groundwater leaching. Cover crops can be used to reduce wind and water erosion. Maintaining ground covers through fall, winter, and early spring drastically reduces soil loss.
Soil texture affects both nutrient availability and water management. It also affects how much herbicide the soil will hold. All soils contain amounts of sand, silt, and clay particles. Soil texture is determined by the relative amounts of these three types of particles.
Cover crops provide organic matter to the soil system. They stimulate biosystems, microbial, and macro-organism activity.
Cover crops reduce soil compaction while increasing water percolation and retention. They help soils maintain a high organic-matter level, and help improve soil aggregation, porosity, infiltration, and bulk density.
MSU researchers are also looking at the use of cover crops for weed control without reducing crop yields. Cover crops can shade and interfere with weed germination and establishment, while cereal ryes actually produce chemicals that suppress weeds.
Researchers are trying to build on the small existing bank of knowledge about how cover crops fit into weed-control programs. For instance, some crops are good hosts for Trichograma wasps, which control European corn borer in seed corn. The researchers say that having cover crops in, especially in the early spring, helps provide habitat for beneficial insects.
A wide range of cover crops is available. Grasses include annuals, such as ryegrass, winter rye, oats, and sorghum sudangrass. Perennial legumes commonly used include alfalfa, while annual legume possibilities include hairy vetch, field peas, crimson clover, lupines, and clovers. Among the brassicas are rape, forage turnips, and oilseed radish. Other possibilities are buckwheat, medics, canola, and triticale.
When and how cover crops should be established depends on what a grower wishes to accomplish by their use. Four common methods are used for establishment. Overseeding is when cover-crop seed is placed between rows of a growing crop. In frost seeding, the cover crop is seeded into an established crop in late winter to early spring. Cover crops can be drilled or spread into crop residue following harvest. Aerial application is another option.
Cover crops should be managed in a way that prevents them from becoming weeds. They must be controlled in spring, to prevent them from competing with the crop.
A grower can choose cultural, mechanical, or chemical methods to manage a cover crop. Several cover crop species, such as oilseed radish, cannot survive Michigan winters, and can be allowed to die naturally. Mold-board plowing is a traditional mechanical control method. Legumes may be killed at flowering by flailing or mowing. The job is more difficult with reduced-tillage systems, where chemical solutions (2,4-D or Roundup) may be viable options. Researchers stress the importance of timing herbicide applications to the correct growth stage of the cover crop.
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