Bt field trials produce interesting results for its use in tank mix or rotation with other chemistries. The numbers don’t lie, and the results are dramatic. Marcus Adair is the Senior Field R&D Scientist at Valent BioSciences in Oxford, MS. When he coordinated a series of Bt field trials with cooperators in Florida, California, Texas, and the Carolinas, the objective was to gather hard data on the economic impact of using Bt in tank mix and rotation alongside a variety of other effective chemistries.

Marcus Adair is the Senior Field R&D Scientist at Valent BioSciences in Oxford, MS. When he coordinated a series of Bt field trials with cooperators in Florida, California, Texas, and the Carolinas, the objective was to gather hard data on the economic impact of using Bt in tank mix and rotation alongside a variety of other effective chemistries.

The trials revealed what many progressive growers already know: an integrated program incorporating Bts has definitive and measureable economic impact. Economic impact was expressed as marketable yield and/or seasonal cost of applications. Trials integrated Bt with products such as Coragen, SpinTor, Warrior, Proclaim, and others. Complete information on all trials can be found by clicking here.

Side By Side Comparisons
Here’s a snapshot view of the results from each trial. In each example:
UTC = Untreated Control, Product + Product = Tank Mix combination, Product/Product = Rotation
DiPel and SpinTor – Cabbage

Conclusion: Both the Bt rotation and the Bt tank mix programs performed better than SpinTor as a stand alone, and a lower cost.
XenTari and SpinTor – Cabbage

Conclusion: The Bt tank mix and rotational programs produced higher yields at equal or lower cost than the SpinTor-alone program.

XenTari and Proclaim – Cabbage

Conclusion: Only Bt + Proclaim and Proclaim alone were commercially acceptable. The Bt + Proclaim treatments performed slightly better at a lower cost than Proclaim alone.

XenTari and Coragen – Fresh Market Tomato

Conclusion: Bt in rotation with Coragen works as well as Coragen alone, and at lower cost.

XenTari and Warrior – Cabbage

Conclusion: Programs that incorporated Bt performed better than the pyrethroid-alone program.

Within the species Bacillus thuringiensis (Bt), there are several types, or subspecies, with specific activity against various insect pests. Going one step further, thousands of strains – genetic lines, or subtypes, exist within the various Bt subspecies.

Each Bt strain displays an individual insecticidal protein toxin mix targeting specific groups of pests. It’s important to understand that Bt quality is determined by, among other variables, the particular strain(s) selected by the original provider

There are four subspecies of Bt that are staples in agriculture and forestry insect management programs:

• Bt kurstaki (Btk): A broad-spectrum subspecies used for worm/caterpillar (Lepidoptera) control for use on vegetables, fruits, nuts, vines, corn, cotton, soybeans, turf, and other crops. Btk is the most widely used biorational product in the world, and controls over 55 caterpillar pests including: leaf-rollers, corn borers, loopers, cutworms, hornworms, and bollworms.

• Bt aizawai (Bta): Another subspecies of Bt used for caterpillar control with specific activity on armyworms (Spodoptera) and Diamondback Moth (Plutella xylostella). Bta is frequently cited as the most effective resistance management tool available as it includes the widest range of Bt toxins.

• Bt tenebrionis (Btt): A subspecies of Bt strain used to control beetle (Coleoptera) larvae, most commonly Colorado Potato Beetle (Lepetinotarsa decemlineata), and Elm Leaf Beetle (Pyrrhalta luteola), among others. Btt is registered for use on potatoes, tomatoes, eggplant, shade trees, and ornamentals.

• Bt israelensis (Bti): A subspecies of Bt strain used to control mosquito, black fly and fungus gnat. This type of Bt also plays an important role in the realm of public health.

Understanding that each manufacturer must obtain and/or maintain its own strains of bacterial sources, from which products are derived, is a key to quality assurance. Growers need to know that the bacterial strains their manufacturer uses will grow and reproduce robustly, will produce the proper proportions and concentrations of proteins, and that the final formulated product will be strong enough, and has the proper tox profile, for the job at hand.

Integrated pest management (IPM) programs are especially important to organic fruit and vegetable growers. A critical component of IPM is building and maintaining beneficial insect populations. This process starts with creating a beneficial habitat, and it is where the use of Bt can fill an important role.

Field showing beneficial shelter foliage

One of the advantages of Bt is its specific mode of action.

“Unlike most insecticides, Bt insecticides do not have a broad spectrum of activity, so they do not kill beneficial insects,” notes W.S. Cranshaw, Extension entomologist at Colorado State University. “This includes the natural enemies of insects (predators and parasites), as well as beneficial pollinators, such as honeybees.”
Planting some refuge vegetation for beneficials within field crops as shown in this California field, can help maintain populations of beneficials.

Cranshaw says that’s why , Bt integrates well with other natural controls in an organic program. For example, in Colorado, Bt use to control corn borers in field corn has been stimulated by its ability to often avoid killing beneficials and creating later spider mite problems. Mite outbreaks commonly result following destruction of their natural enemies by less selective treatments.

Dr. Gary Leibee, a researcher at the University of Florida, has found Bt to be especially useful in controlling diamondback moth and cabbage loopers. For Leibee, Bt’s ability to maintain beneficials is another benefit that enters strongly into the equation. “It really is the perfect IPM tool,” he says,”because it only kills the caterpillars and has no effect on predators and parasites (beneficials), which are extremely important in keeping the populations at a low level.”

For organic growers, the maintenance of both beneficial insects and habitats is a one-two punch. The results of a national survey of more than 1,000 organic farmers conducted by the Organic Farming Research Foundation (OFRF) indicates that organic farmers see organic farming as a management system of applying inputs to supplement cultural practices. Organic growers rely heavily on cultural strategies including beneficial habitats, crop rotation, and resistant varieties. Bt is reported as the most commonly used insect control tool, followed by insecticidal soap according to Brian Baker at the Organic Materials Review Institute (as part of the Organic Farming Compliance Handbook). In fact, these materials were the only ones used by more than half of all growers responding to the survey.

With nearly 40 years of proven performance in the field, Bt’s ability as effective pest control is well known. Pest management professionals will also tell you biorationals demand morework best with careful management.

Extra management time can equates to better timed and fewer applications, and lower populations for the balance of the season. It means improved economics in tank mix or rotation since Bts are very affordable. It also means unparalleled resistance management capabilities that extends the life of other important chemistries. It means no residues, and the lowest allowable re-entry interval. It means confidence and peace of mind.While Bts have long been a mainstay in production agriculture, adoption continues to rise due to the unique combination of benefits Bts bring. It’s an equation especially relevant for today’s growers: efficacy, economics, and residue management benefits that deliver value to suppliers and buyers alike.

When evaluating return on investment (ROI) for a program using Bts, the sum of these many benefits is what makes the proposition unique. In today’s crop systems, though, it’s their effectiveness in other key areas, such as avoiding residue, managing resistance, and field work flexibility that are bringing bottom line benefits to more and more growers every season.

Avoiding Residue
“It’s a cost-effective bioinsecticide,” says Max Jehle, pest control adviser for Sunview Vineyards in California. “Bts have improved our bottom line because we can achieve the same thing, with the same amount of control, with a very safe material, without all the issues.”

Jehle says that for Sunview, a key benefit is the global acceptance of Bt-treated produce. As postharvest residue tolerances become more and more stringent, the value of Bt goes up. “You don’t always know where your produce is going,” he says. “When using this material, you don’t worry about residues. Worldwide, it’s a safe material.”

Field Work Flexibility
Worker safety and re-entry interval (REI) is another key benefit. Labor can be one of the toughest things a grower has to manage, and pest pressure doesn’t always emerge at the most convenient time. A program including Bt can provide flexibility when many other materials can’t. Workers can get right back in the field just four hours after a Bt application – the lowest REI allowable by law. The same dynamic applies to late season applications required just prior to hand harvesting.

Resistance Management
It’s true that programs including Bt often cost growers less than programs that rely heavily exclusively on other materials, but the resistance management benefits of Bt aren’t always directly linked to dollars and cents.

“That’s one of the things we’re always telling our growers,” says University of Florida Vegetable Extension Specialist Dr. Stephen Olson. “You’ve got some new product out there but if you abuse it, you’re going to lose it. Very quickly. If we want to keep these products as effective tools, we’ve got to use rotation.”