Proper pond management

Water supply can be a limiting factor when scaling up a greenhouse operation or when growing in an area that can routinely experience droughts. Irrigation ponds are excellent safeguards to increase water supply. Unfortunately, irrigation ponds are often covered in algae, and the use of algae-rich water for irrigation can lead to plant disease. Although it may seem like a daunting task to keep irrigation ponds free from algae, the solutions are often simple and affordable. Benjamin Franklin famously stated, “An ounce of prevention is worth a pound of cure,” and irrigation pond management is no exception to this rule.

The main reason that algae-rich irrigation water is problematic for growers and overall plant health is that common pond algae are excellent hosts for biofilms — a slimy mixture of algae, bacteria, fungus, viruses and other potential plant pathogens. Algae-rich irrigation water can also lead to the growth of biofilms on filters and irrigation heads in the greenhouse — leading to clogging and creating another home for pathogens. The most problematic water-borne pathogens are:

Water molds (oomycetes): Pythium, Phytophthora, and downy mildew

• Colonize growing media and cause root rot
• Thrive in water with low/no oxygen such as the bottom water and pond sediment
• Produce spores that can remain dormant for years

Water-borne fungus: Botrytis, Rhizoctonia, Fusarium, and many rusts

• Can cause blights that effect stems, leaves, flowers and fruits as well as roots
• Thrive in algae mats and scums or on the surface of aquatic plants
• Overwintering structures (sclerotium) can remain dormant in ponds for years

Water-borne bacteria: Erwinia, Xanthomonas, Ralstonia, and Pseudomonas

• Cause leaf spots and blights
• More prolific in algae and/or nutrient rich pond water

Fortunately, recognizing a potential source of pathogens in pond water is fairly straightforward — if it doesn’t look like water you would want to swim in, then it likely has enough algae to harbor biofilms full of pathogens. Water samples can also be sent to analytical laboratories to test for the presence of common water molds and/or E. Coli, which is usually a cheap indicator of other detrimental bacteria. It is also helpful to periodically check your phosphorus levels, as phosphorus is the most common nutrient that stimulates algal growth. Phosphorus can be measured on the spot using affordable test kits or it may be more accurately determined by sending samples to a laboratory.

Solutions

An advanced disinfection water treatment system is the most reliable way to eliminate the risk of water-borne pathogens when using pond water for irrigation. However, these systems can be expensive, and upkeep can be difficult. Although a water treatment system may not be in most greenhouse growers’ budgets, there are still a variety of options to significantly reduce the risk of water-borne pathogens.

The quick fix. Treating the pond with an algaecide is the quickest solution to reduce the risk of water-borne pathogens. Suspended algae and the biofilms they support, die within a few days of the algaecide application, sinking to the bottom of the pond and removing most water-borne pathogens from the water column. Algaecides can also be toxic to water-borne pathogens and the dormant cells they may produce.

Algaecides are generally either copper or peroxide based. Copper-based algaecides are much more potent and cost-effective than peroxide-based algaecides. Although many people worry about copper phytotoxicity, the copper concentration needed to kill algae (parts per billion) is not a risk for plants and can serve as a micronutrient supplement. Captain XTR is the most powerful copper-based algaecide that works in all water types – soft, moderate or hard. While algaecides are quick to address the issue and tend to be more cost-effective in the short term, they only provide temporary relief because they do not address the root of the problem.

Addressing the root of the problem. Proactive solutions offer the advantage of providing longer-term control and addressing the root of the problem; however, they can entail higher upfront costs and an extended time window to see results. The most proactive approach is removing phosphorus, the primary driver of algae growth. Just 1 lb of phosphorus can lead to the growth of 500 lbs of algae, which will turn 4 acre-ft or 1.3 million gallons of water green.

Phosphorus management is simple and affordable using the EutroSORB platform of water quality enhancers — removing a pound of phosphorus can cost as little as $200. EutroSORB WC is an easy-to-apply liquid that can remove phosphorus from the water column. EutroSORB F is a filter bag that can capture phosphorus from flowing waters, such as drainage systems and culvert pipes.

Hybrid solutions. Hybrid solutions work quickly and often address the underlying issues. In addition to the aesthetic value, aquatic dyes can substantially limit the growth of unwanted plants and algae, consequently reducing the pathogens they might harbor. Aquashade is the only registered pesticide which has been proven to reduce the growth of algae and aquatic plants by reducing the specific spectrum of light that is used for photosynthesis. Aquashade is safe for irrigation and comes in a concentrated liquid, providing season-long control.

Another hybrid solution is SeClear Algaecide and Water Quality Enhancer. This product is the only algaecide that also removes phosphorus, the limiting nutrient for most algae. Many users have found that switching from a standard algaecide to SeClear has allowed them to gradually reduce the phosphorus concentration in their pond, reducing the future need to use algaecides. SeClear also tank mixes well with Aquashade to create a 3-way combination — killing algae while blocking light and removing nutrients, both of which substantially reduce rebound algae growth.

Through a combination of reactive, proactive, and hybrid solutions, greenhouse growers can optimize water quality and minimize the risks associated with algae-rich water. Investing in proper pond management not only safeguards the health of the plants but also contributes to the overall success of greenhouse operation.

Byran Fuhrmann, Ph.D. is a SePRO Aquatic Technology Development Scientist.