New Bt From Vestaron Will Help With Worm Pests

A New Bt Innovation For Worm Pests

Tree nut growers – large/small, conventional/organic – are familiar with Bt, or Bacillus thuringiensis. This spore-forming, gram positive bacterium has played a role in insect pest management since soon after isolation in 1901 by a Japanese biologist investigating a disease of silkworms.

Targeting lepidopteran larvae (caterpillars, loopers, “worms”), EPA has registered commercially available products such as DiPel, Javelin, XenTari and most recently Leprotec, a liquid formulation alternative. Among these are two lep-active subspecies, Bt ssp kurstaki and ssp aizawai.

Acceptance by modern-day growers partially stems from advantages common to most bioinsecticides: 4-hour REI, 0-day PHI and exemption from residue tolerances. Compared to conventional chemistries, Bt products have an excellent safety profile for workers, pollinators, natural enemies and the environment. Furthermore, most meet NOP guidelines for use in organic production.

Bt products also bring a distinct mode of action for managing the development of insecticide resistance. Classified as a Group 11 insecticide, Bt officially operates as a “Microbial Disruptor of Insect Midgut Membranes.” The bacteria produce proteinaceous crystals that are denatured in the digestive tract, liberating toxins that bind to receptors on the midgut surface, forming pores in the membrane, causing ionic imbalance, septicemia, feeding cessation, paralysis and death.

Modern Bt formulations are the outcome of decades of research and discovery. Among thousands of strains, the few commercially available have been carefully selected for efficacy against pest targets. Performance is driven by the Bt strain’s unique Cry toxin profile as well as the quality and quantity of fermentation products yielded by the manufacturing process.

An exciting new innovation in the use of Bt goes well beyond strain selection and fermentation advances. In 2019, EPA approved Spear®-Lep, a bioinsecticide from Vestaron that makes use of Bt’s midgut-disrupting activities to deliver a potent target-specific active ingredient to receptors in the insect nervous system. The active ingredient in this bioinsecticide (a 40-amino acid peptide called GS-omega/kappa-Hxtx), may be 30 times smaller than Bt, but is 10-20 times larger than conventional active ingredients. How to get it to target sites on receptors in the insect nervous system? Tank mix with a low rate of Btk, apply to foliage for ingestion by lepidopteran larvae, and open pathways through the midgut for the Spear peptide.

The partnership between Spear peptide and Btk translates to high performance with much less active ingredient. Add in proven field efficacy (such as against navel orangeworm), plus a novel mode of action (with no cross resistance to current insecticides), and Spear-Lep emerges as a versatile and innovative tool for tree nuts and other high-value field crops.

California Ag Today2021-05-12T11:00:35-07:00April 27th, 2020|

Lorsban Under Scrutiny

Chlorpyriphos (Lorsban) Must be Used More Carefully

By Patrick Cavanaugh, Deputy Editor

California Department of Pesticide Regulation (DPR) reports an important, broad-spectrum organophosphate insecticide known as Chlorpyriphos, or Lorsban, may be further restricted due to evidence of potential human health and environmental risks, presence (parts per billion) in some California waterways, and pressure from the EPA. Brian Leahy, director of the California Department of Pesticide Regulation, said, “Chlorpyriphos is an important tool and we know there are important times when you have to use it.”

Registered and widely used in agriculture across the nation for more than 40 years, DPR has made it a restricted-use material. Leahy said, “We are trying to work with the grower community to improve how they use it. We are also working with UC IPM to look at essential needs, but we know that as we look at Chlorpyriphos, we are going to have to put additional restrictions on it.”

“We simply need for it to stay on target, and not be getting into the human body. We are seeing that it is, and we are going to continue to make sure that people use it thoughtfully and wisely,” he said.

And Leahy is very confident that growers can use this material and keep it on target, “I have seen farms that use it only when they really need it, and that is what we want. We can’t lose this tool and we are going to keep it only by showing we can greatly reduce off-site movement to the human body and watersheds,” he noted.

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According to the University of California Agriculture and Natural Resources 2014 Chlorpyrifos Report entitled, “Identifying and Managing Critical Uses of Chlorpyrifos Against Key Pests of Alfalfa, Almonds, Citrus and Cotton“:

Chlorpyrifos plays a critical role in many IPM programs for controlling pests that threaten the productivity and economic well-being of California producers and in maintaining the high quality standards required by consumers and international export markets. This active ingredient also allows production of animal feed to support the important dairy industry in California. For some pests, chlorpyrifos is one of the last effective organophosphate insecticides available and may provide an important alternative mode of action for insecticide rotations to prevent the development of resistance to newer insecticide products. For others, this product is one of very few products with international registrations with established maximum residue limits (MRLs) that allow unhampered trade. Chlorpyrifos may also be a key tool for controlling invasive pests as well as endemic pests occasionally found in extremely high population densities.

The California Department of Pesticide Regulation reports that the combined use of chlorpyrifos in alfalfa, almonds, citrus, and cotton has decreased since 2006.

Although newer insecticides are also available to manage some pests in these four crops, there is a continued need to preserve the availability of chlorpyrifos for specific situations.

“Assessing the Health Risk of Pesticides,” California Department of Pesticide Regulation

California Ag Today2021-05-12T11:03:04-07:00February 16th, 2016|

Armyworms Invade Rice

Luis Espino: Armyworms Invade Rice

By Charmayne Hefley, Associate Editor

Larva of the armyworm, Mythimna unipuncta.
Photo by Jack Kelly Clark, UC IPM.

Farmers face many threats to their crops on a daily basis. Luis Espino, rice farm advisor UC ANR Cooperative Extension, Colusa County, said rice farmers are on the lookout for two caterpillar infestations during the year when armyworms invade rice fields. “The first one occurs sometime in June,” Espino said. “At that time all they do is just eat the foliage, and you can usually see it when you walk into a field. Nevertheless, the rice has a very good capacity to recover from that type of injury.” Espino’s UC Rice Blog explains it is difficult to accurately estimate yield losses due to early armyworm damage because it can reduce tillering, delay the crop, and cause uneven maturity.

“Heading” occurs when the rice plant prepares to enter its reproductive phase. The first sign, called the ‘booting’ stage, is when the leaf stem that conceals the developing panicle bulges. Then the tip of the developing panicle emerges from the stem and continues to grow. Rice is said to be at the ‘heading’ stage when the panicle is fully visible. Flowering begins a day after heading has completed. As the flowers open they shed their pollen on each other so that pollination can occur. Flowering can continue for about 7 days. (Source: Rice Development, Ricepedia.)

“The second infestation usually occurs in mid- to late-August when the rice is heading out,” Espino said. “At that time, armyworms can feed on the panicles, [causing the kernels to dry before filling], resulting in blanks [without kernels to harvest] on the panicles and broken panicle branches. That’s when armyworms are more important.”

Espino said that the first infestation this year was relatively large, making it harder for the treatments to control the armyworms as they devastated the rice fields. “There were some areas in fields where the rice was down to the waters,” Espino said. “so all the foliage was consumed, and sometimes only a little stem was left standing.”

During the second armyworm infestation, however, Espino said the rice fields were not as badly affected as they had been in the first attack. “We did see some fields with armyworm injury,” Espino said,“ and some farmers had to treat their fields. The numbers were just so big that the treatments were not controlling them.”

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