Since the program's release, according to project leader Gail Wilkerson, it has been used by Extension agents in North Carolina, Georgia, and Mississippi and by pest management cooperatives, consultants, and producers throughout the Southeast to minimize application of unnecessary or inappropriate herbicides and, at the same time, maintain or even increase yields.
    HERB translates a large amount of complicated information into an easily used form and makes it possible to transfer the latest research results directly to end users. With annual spring updates to the program, the length of time between completion of field experiments and distribution of advisories has been as short as six months.
    Through information about types and numbers of weeds present in a field, HERB helps users determine:

• the potential crop damage from multispecies weed complexes
• the economic justification of a herbicide treatment in a particular field
• the most appropriate herbicide and application rate if treatment is necessary.

The original DOS-based program ran on desktop computers, but now palmtop computers are available with sufficient power so that HERB can be loaded onto the computer and carried into the field. There, scouts can enter data as they survey the field and obtain an instantaneous recommendation.
    The newest version of HERB makes it possible to easily update the databases. Weed scientists can also customize the program for a particular state, which is especially helpful because weed problems and management techniques differ from location to location.
    With the first HERB, growers could get recommendations for weed control in soybean and corn crops after both crop and weeds had emerged. Now, several customized versions of HERB have been created to include peanuts and cotton. HERB-peanut has been evaluated extensively during the past two summers in North Carolina and Georgia. Evaluation of HERB-cotton is currently under way in North Carolina, Alabama, Mississippi, Tennessee, and Texas.
    Extension personnel in North Carolina found, in on-farm trials, that using HERB to manage weeds in peanuts resulted in no decrease in yield compared to plots managed in more traditional ways, yet reduced herbicide costs by more than 40 percent. In extensive on-farm trials in Georgia, when weed control was accomplished using HERB recommendations, peanut yield was equal to yield produced under weedfree conditions and to yield produced with weed management prescribed by professional weed scientists. The HERB-peanut program was extended to all peanut-producing counties in Georgia during 1998.
 

Greater Reduction of Herbicide Use Now Possible

Recent advances in Global Positioning System (GPS) technology and herbicide application equipment make it possible to use HERB to further reduce herbicide applications. These advances are especially useful because weeds tend to occur in patches, and there may be large areas that are below a treatment threshold, even if they are not entirely weed-free. (The economic threshold is that point at which the expected yield loss if no herbicide were applied would be greater than the cost of treatment.)
    The weed population maps on this page show the results of analyzing the potential for site-specific weed management in a particular soybean field and illustrates how HERB can be used to increase return and reduce herbicide use.
    The program was first used in this study to develop a map that shows the types and estimated numbers of weeds in each area of the field. In this example, two weed species, sicklepod (Map A) and morningglory (Map B), predominated and were clumped as shown. The second step was to run HERB for each portion of the field to determine the best treatment for each section and for the field as a whole.
 

Analysis Pinpointed Treatment Threshold

Once the treatment that would offer the highest profit potential had been selected, each area of the field was analyzed to determine if the weed population in that area was above an economic treatment threshold.
    In this example (Map Q, the analysis showed that return could be increased by 95 percent and the amount of herbicide could be reduced by 60 percent if herbicide was applied only to those portions of the field above an economic treatment threshold.
    If variable-rate spray equipment is available, a map can be generated that tells the spray equipment when to turn herbicide application on and off as the sprayer moves across the field.
Producers without GPS and variable- rate application equipment can still benefit from a site-specific approach to weed management.
    The program requires no commercial mapping software or GPS equipment; growers can map a field by pacing off a set distance along the row.
    If variable-rate spray equipment is not available, fields can be divided into tank- size areas, and a different spray option is possible when the tank becomes empty. In the example below, the field might be broken into two sections, with the upper section receiving a herbicide treatment and the lower section receiving none.
    Mapping weed distributions and subsequent yearly changes should help producers to determine the long-term effectiveness of their approach to weed management and help them identify potential problems early.
    This work has been partially supported by the Southern Region IPM Grants Program, the North Carolina Center for IPM, the U nited Soybean Board, the North Carolina Corn Producers Association, and the North Carolina State University Agricultural Experiment Station.