Broadening Crop Protection Options with Biostimulants

 

Author: Dr David Pennell

 

Biostimulants and related products are likely to form a crucial part of future crop protection programmes to complement other means of controlling the sources of biotic and abiotic stress which limit production.

Orion Future Technologies, based in the UK, have been developing the use of biostimulants, natural elicitors, nutrient, silicon and salicylic acid technologies since 2005. Their products are now used in Europe, Africa and Central America on a wide range of crops to improve crop performance. Initially based on developing a consistent formulation of bioavailable silicon OrionFT have used this technology as a base to build formulations of silicon with other nutrients and biostimulants.

Over the years the team has worked with a number of academic and research partners including the University of Hertfordshire, and the University of Reading.  OrionFT products are also included in research projects funded in UK by growers via AHDB Horticulture.
Work on strawberry mildew with Dr Avice Hall’s team at the University of Hertfordshire, has been especially successful and is useful in both demonstrating the effectiveness of the OrionFT silicon product, Sirius in contributing to controlling the disease but they have also begun to demonstrate how silicon behaves within plants.

Early work on silicon products (Sirius) from 2008 to 2011 showed that spraying of the silicon nutrient onto leaf surfaces results in accumulation of silicon in all strawberry varieties tested and resulted in increased length of leaf hairs and also in increased density of leaf hairs on all varieties tested. In one variety which naturally had no leaf hairs on upper surfaces, leaf hairs grew.  Silicon nutrient applied to the roots as a soil application resulted in more silicon being accumulated in the plants than when comparable amounts/concentrations were sprayed onto the leaves. When silicon nutrient was used as a spray in the field a reduced germination of ascospores, led to a reduction in the initial inoculum for the development of epidemics of powdery mildew of strawberry.

Field trials between 2011and 2013 with open field soil grown crops compared treatment of potassium bicarbonate alone, Silicon nutrient alone, Silicon nutrient combined with K50. Results showed that when silicon was sprayed onto the leaves silicon accumulated in the plants in proportion to the concentration of silicon applied, the trials also showed that the build-up of the epidemic was slower when the plants were sprayed with silicon alone as compared with K50 alone. The spraying of silicon resulted in smaller and fewer powdery mildew colonies on the leaf surface, this had a subsequent effect of reducing the overwintering stage of the pathogen (chasmothecia) and thus reducing disease carry over from one season to the next. The spraying of silicon also postponed the start of the disease epidemic build up on treated plants. The trial also showed that silicon treated leaves were thicker than untreated leaves. The trial also suggested that if the silicon was to reduce epidemic build-up of mildew the silicon needed to be applied to the plant before the pathogen spores started to germinate.

In 2013 and 2014 trials confirmed that uptake was much more efficient when the silicon was applied via the roots and that plants needed to start accumulating silicon before the epidemic started (i.e. before the conidiospores started to develop and germinate in large numbers). Applying silicon nutrient (Sirius) in the fertigation system twice a week from planting through to end of harvest was trialled for the first time.

Epidemic start was delayed by 8 to 9 days in treatments receiving silicon through the fertigation tubes. Leaves on plants receiving silicon nutrients were thicker than those not receiving silicon with leaf hair length and density increased on their upper and lower leaf surfaces. Silicon accumulation in plant is in proportion to amount of silicon applied. The leaf cuticle increases in thickness with differences observed in structure of wax on leaf surface. There is also an accumulation of silicon in vascular areas of strawberry plant. Silicon is taken up more readily through the roots of strawberries and it needs to be applied throughout the season to maintain its effectiveness.

Early work demonstrated that the onset of powdery mildew epidemic in crops was delayed in Sirius treated crops and that in crop protection programmes including conventional fungicides significant benefits both in disease control and use of fungicides could be achieved. Treatment with Sirius increased the concentration of the silicon in strawberry leaves and petioles and increased the location in epidermis of strawberry root, petioles. This accumulation in the epidermis correlates with the reduced susceptibility to strawberry powdery mildew.
 

 

Fi.1. University of Hertfordshire strawberry research using hydroponic systems with Sirius applied in the nutrient solution.
 

The research at University of Hertfordshire also demonstrated that silicon, as formulated in Sirius, could be applied to strawberry as a foliar spray or through fertigation system, entering plants via roots. However maximum effect can be achieved by root application which complements current substrate and hydroponic crop production systems.

The increased length of leaf hairs found in these studies may mean that the germ tube of germinating disease spores can’t reach the leaf surface and so cannot penetrate. The thicker cuticle and changed structure of wax would also deter penetration. Overall the cumulative effects of these changes to structure result in the delay of the start of powdery mildew epidemics and in their intensity. There may also be effects on invertebrate pests, deterring or otherwise altering feeding behaviour.

In the most recent studies, the bio-availablity of Sirius has been used in hydroponic experiments using Melling Centenary strawberry plants. These have given remarkably consistent responses to Sirius with significant increases fruit number, brix levels, fresh biomass and leaf chlorophyll. Flowering was also brought forward by 7days. A marked reduction of spotted spider mite numbers was also observed in Sirius treated plants. The way silicon was accumulated in strawberry leaves and observation of feeding behaviour suggest that mites may be deterred by a reduction of the palatability of leaves.

 

Fig.2. Silicon from Sirius application in strawberry Malling Centenary
 

Similar effects to those found in the work at University of Hertfordshire have been seen in a wide range of crops where OrionFT products have been widely used over the last two decades. These include plantation crops, cereals, ornamentals, vegetables and a wide range of fruits. Utilising the silicon

Rigel is a formulation combining silicon with salicylaldehyde to utilise the ability to trigger a number of plant defence responses to stress from pests and pathogens. In work undertaken by Dr Glynn Percival, Bartlett Tree Laboratory at The University of Reading demonstrated a beneficial effect of Rigel-G in controlling apple scab, but its main activity was tested in combating the effects of some pest species. Effectiveness in reducing crop damage from vine weevil larvae, slugs, flea beetle and cabbage root fly larvae and pupae have been seen.

Trident contains a new and unique formulation of zinc, copper and silicon micro-nutrients, complexed with naturally acidic, chelate polymers, which improves photosynthetic function, chlorophyll production and sugar formation. In a number of crops, it reduces susceptibility to fungal and bacteria diseases. Trials have shown Trident can reduce susceptibility powdery mildew, downy mildew, Phytophthora and bacterial diseases without the harmful residues that can exist when using traditional chemicals controls. Studies by Dr Glynn Percival have scanned a wide view of crops with the range of crops where benefits have been seen including crop powdery mildew and botrytis on roses, powdery mildew on grapes, spear rot in broccoli, botrytis in lettuce, powdery mildew in courgette, melon and cucumber. A common factor in most crops is an enhanced photosynthetic performance following application of Trident.

This article was initially published in AgroPages '2019 Biologicals Special ' magazine. Download the PDF version of the magazine to read more articles.