Time to give your irrigation systems some attention?

During the main growing season, irrigation systems can take a beating. During this quieter time of year, it is a good idea to check pumping and control systems, sprinklers, drippers, filtration, tanks and covers – to facilitate any cleaning, repairs or replacements. Getting irrigation systems set up correctly now can help optimise water use next season. While uneven watering is not conducive to even plant growth, overwatering or drips can provide an opportunity for disease to take hold.

Root rot reduction via filtration & disinfection of irrigation water

As part of his BASIS project, Technical Area Sales Manager Peter Robinson worked with a busy HNS nursery keen to overhaul and improve its irrigation system.  With an initial audit completed, he submitted a report and action plan. Having assessed options including potential improvements to the sprinkler/drip irrigation system and to increasing water storage, Peter prioritised the filtration and disinfection systems as delivering the most cost to benefit advantage.

Root rot losses

In 2018, a Dove Associates’ pesticide gap analysis exercise estimated the retail value of UK ornamentals as £1 billion/year, with retail sales losses from key root diseases – which can be introduced and transported around nurseries in water supplies and irrigation systems – estimated at £66million.

Filtration  

“Filtration is key to the performance of any irrigation system,” says Peter. “Pathogens are contained in water sources such as rivers and bodies of still water, particularly reservoirs, which are breeding grounds for diseases including brown rot, 17 Phytophthora spp, 26 Pythium spp, Fusarium and Verticillium.

“The total suspended solids depend on the water source, with rivers generally containing the highest levels of organic materials. Reservoir water is reliant on the supply. Multiple source supplies are more difficult to predict, but filtration should always be based on the worst-case scenario.

“The key requirement of irrigation water disinfection systems is to provide the cleanest water in terms of total suspended solids. This is achieved using a filtration system with the level dictated by the disinfection method, eg 25 microns for UV, 100 microns for chemical injection systems.”

Filtration systems

The most common filtration systems are screen, disc and media – each with its own merits and uses. Two stages are routinely used; pre or primary filtration to clean the water before any treatments or fertigation and secondary filtration, the final defence prior to the water being used to irrigate. These filters can be in the pump house or located around nurseries at strategic points.

“This nursery’s existing filtration system was installed after the pumping system,” explains Peter. “With high contamination loading and planned increases to pumping capacity – to accommodate a new production area – filtration had, at times, proved inadequate and was set to worsen. Maintenance often involved manual cleaning, creating conflicts with staff watering and reduced flows and/or pressure.”

Media filtration system

Having explored various methods to pre-filter the water entering the water storage tank, Peter recommended a media sand filtration system.  “This immediately reduced the dirt loading into the tank and therefore the amount of target organisms transferred from the reservoir,” he says. “It greatly impacted the effectiveness of the disinfection system, enabled reduced chemical rates – from those advised for river and reservoir water – and eliminated disinfection during colder months when disease levels are lower.”

Peter recommended a media sand filtration system. This immediately reduced the dirt loading into the tank and therefore the amount of target organisms transferred from the reservoir. Greatly impacting the effectiveness of the disinfection system, it enabled reduced chemical rates (from those advised for river and reservoir water) and eliminated disinfection during colder months when disease levels are lower.

Disinfection

“On this nursery, contamination in the water was hampering the existing disinfection system,” he explains.  “Physically, with the chemical unable to contact the target organisms, and during dosing – when the flow rate changed due to filter and system clogging.”

Irrigation water can be disinfected by various methods including UV, Chlorination, Ozonation and Hydrogen Peroxide.

“We had two cost-effective practical options to disinfect the irrigation water – chlorine and hydrogen peroxide, both of which eliminate the shadow effect associated with UV,” says Peter. “We chose the latter, due to its safety and environmental profiles.

“Using the media filtration significantly reduced the dirt and disease loading in the water supply, which has a major impact on the advised dose rate of the chemical.  It resulted in a 40% reduction in the dosing rate while maintaining the same impact at the furthest point in the irrigation systems.

“Furthermore, the use of hydrogen peroxide meets the Sustainable Use Regulations as it is sustainable and proven to be effective, chlorine-free, has no harmful by-products and leaves no traceable residue in the crop. It’s also safe to handle in relation to chlorine.  The reliance on plant protection products has also been positively impacted by cleaning the water.”

Two cost-effective disinfectants – chlorine and hydrogen peroxide – were identified. Both mitigate the shadow effect associated with UV. The latter was employed due to its safety and environmental profiles. The new media filtration significantly reduced the dirt and disease loading in the water supply therefore the dosing rate could be reduced by some 40% while maintaining the same impact at the furthest point in the irrigation systems. The reliance on plant protection products has also been positively impacted by cleaning the water

Results

Several weeks after the new filtration and disinfection system had been commissioned, water samples taken from the river, reservoir, post sand filter (storage tank) and post disinfection were sent away for analysis.

*   Saprolegnia sp. and other species not yet identified.  No Phytophthora

**   All sorts!  Very diverse (incl. very small (<3%) amount of Phytophthora CFU)

Commenting on the results, Peter said; “pathogen levels in the river and reservoir were to be expected.  The results from the storage tank and post disinfection were extremely clean.  The unexpected slight increase, at the end of line (end of the hosepipe in the propagation area) could have been caused by a dirty hose/nozzle.

“Overall, the results show a marked decrease in pathogens with the addition of the sand filter array. This positively impacted the effectiveness of the hydrogen peroxide, and the rate required to achieve the same results as before.  The year prior to installing the dosing system, the nursery applied 75% more root rot drenches.  While some of this improvement can be attributed to the new growing areas, better drainage and irrigation and replacing susceptible varieties, it has resulted in a significant reduction in crop protection chemicals usage.”

Results

Technical Area Sales Manager Peter Robinson joined the BASIS professional register in 2022.  A rigorous and highly effective industry self-regulation scheme, BASIS demonstrates professional competency and up-to-date expertise in the rapidly changing and technically demanding area of pesticides.

Only advisers with the BASIS qualification can legally advise growers on the full range of crop protection products.