Dr. Daniela Kruse, Director New Markets, Interface & Performance at Evonik
Agricultural solutions based on microbial actives could become attractive alternatives to chemical products with new modes of action, not least because of regulatory pressure on chemical pesticides.
Microbial agrosolutions are often not effective in the field and are therefore still not widely established. There are several root causes for this performance gap. First and very important is the limited shelf life.
For products based on sensitive microbes such as fungal spores, shelf-life is often only of a few weeks. Many of these actives are sensitive to moisture and pH changes, and need cold storage and are difficult to formulate. Therefore, most products are solid with low dispersing properties in water. All these reasons complicate the
transport, storage, application, and handling of these products.
A second reason for the performance gap is an insufficient field delivery. Some of the product is lost during spray application due to drift and/or low adhesion and retention on the leaves. If soil applied, the distribution in the soil is limited. These delivery issues lead to low and/or inconsistent field efficacy. The price/performance ratio is considered as too high, and this prevents the acceptance for such products.
Importance of water activityThere are important physical requirements for an increased shelf life of microbial agrosolutions. The viability of microorganisms depends on several criteria.
Besides suitable growth conditions during production and appropriate downstream processing, the right formulation and suitable additives help to reduce the loss of viability of microbial active ingredients. One essential requirement for a long viability of microorganism is the optimal water activity (aw) within the formulation.
At specific low water activities, fungal spores reduce their metabolism, remain viable in the dormant phase and survive during storage and transport. The water activity describes the availability of water in a solid or liquid formulation rather than the amount of water present. It defines to what extent water acts as a plasticizer for cell membranes. Values range from 0.0 – so to say “no free water” - to 1.0 as it is in distilled water. If the water activity is very high, the cell
membranes are very mobile leading to cell proliferation and ending the dormant state of microbial spores. If the water activity is too low, cell membranes are too brittle, and the cells die. Microbial spores usually need water activity values of about 0.2 to stay dormant.
Manufacturers try to reach this water activity by creating solid products. However, this method is not always sufficient so many commercial solid products require cooling during storage and yet have a limited shelf life of not more than 12 months. Examples include the commercially relevant species Trichoderma harzianum, Coniothyrium minitans, Clonostachys rosea and Metarhizium anisopliae.In addition to an improved shelf life, microbial based agrosolutions need to be improved with respect to an enhanced and consistent field performance and a more convenient handling to achieve more acceptance in the market.
Water-free carrier fluidEvonik has developed a biocompatible carrier fluid and biocompatible additives to overcome these issues with microbe-based agrosolutions.
BREAK-THRU® BP 787 is a water-free carrier fluid with the ability to coordinate water and to lower the water activity if mixed with microorganisms. It secures optimal conditions for living microbial actives like Trichoderma spp., Bacillus spp., Clonostachys rosea, and Beauveria bassiana and thereby enhances their shelf life, even without cooling. Due to the stability of the microbes in the carrier fluid hybrid solutions – the combination of microbial and chemical actives - in one formulation are possible.
BREAK-THRU® BP 787 also enables convenient handling as it is a cold stable liquid with good rheology behaviour. It is water soluble with no need for an emulsifier and thereby reduces complexity in the formulation and eases the handling in foliar, soil or seed applications.
With BREAK-THRU® BP 787 the formulations can be customized as it is mixable with Evonik BREAK-THRU® additives and Silica products to achieve properties needed in the different applications.
Table 1: Water free Guideline Formulation for microbial spores(water activity (aw) = 0.2): Dispersible Concentrate (DC)
The BREAK-THRU® BP 787 formulation is easily dispersible in water and when the readily biodegradable BREAK-THRU® S 301 is added it provides excellent soil distribution. The water activity value of this formulation is 0.2, which is optimal for Trichoderma harzianum spores and therefore the formulation is storage stable for several months at room temperature.
The viability of spores has been tested at different temperatures.
Figure 1a shows longer viability of the spores within the DC formulation at 25°C. The formulation is also physically stable as no syneresis could be detected after four weeks at 40°C.
Figure 1a:Viability of Trichoderma harzianum in formulationat 25°C (CFU = colony forming unit)
Figure 1b:Viability of Trichoderma harzianum in formulation at 25°C
Greenhouse trialThe DC formulation of T. harzianum based on BREAK-THRU® BP 787 has also been tested in a greenhouse trial for nutrient stress tolerance in maize in infertile soil.
Oxisol soil has extremely low availability of nutrients, particularly of phosphate. Soil was sampled from the Vogelsberg area, Lich in Hessen, Germany (0.32 mg CAL-P / kg soil; 6.67 mg CAL-K / kg soil; 3300 mg Total C / kg soil; pH 5.5 (0.01 mol / L CaCl2). The soil was mixed with expanded clay (v/v 1:1) and supplemented with NK fertilizer and 50 ml of a 0.5% tricalcium phosphate suspension (slowly soluble). Two maize seeds per plot were inoculated after germination and two weeks after sowing with the different T. harzianum formulations. The spore concentration was adjusted to 105 cfu/ml and 10 ml were applied per plant. Each treatment had five
replicated pots. Figure 2 showsthe significantly higher amount offresh corn weight under nutrient stress when maize seedlings were treated with the guideline formulation of T. harzianum based on BREAK-THRU® BP 787 in comparison with the commercial T. harzianumWP product.
Figure 2: Maize fresh weight 4 weeks after treatment
Biodegradable technologyBREAK-THRU® BP 787 is readily biodegradable (OECD 301F), has no tox labelling and is a patented Evonik technology. The multifunctional carrier fluid enables physically stable dispersible concentrates based on living microorganism with extended shelf life. Due to its compatibility with high performing, biocompatible BREAK-THRU® additives it enables customized solutions with excellent dispersing of microbial actives and a targeted field delivery. Depending on
the application drift control, adhesion and retention of spray droplets, spray coverage, uptake, penetration, and soil distribution can be adjusted and thereby the biological efficacy can be improved.
Seed treatmentsShelf-life enhancement of microbials in the formulations can also be achieved for the microbes once applied on the seeds. In addition, together with Silica, BREAK-THRU® BP 787 provides binder functionality with excellent dust reduction. As it is readily biodegradable, it is a microplastic free binder solution. As BREAK-THRU® BP 787 is mixable with Evonik BREAK-THRU® additives and AEROSIL® silicas, other seed treatment parameters like low rub-off, good flowability and coverage can be achieved. BREAK-THRU® BP 787 is compatible with water-based
products and thereby enables easy handling and low complexity.
When used as seed treatments a significant acceleration of seed germination has been achieved showing an improved biological efficacy also in this application. ●
