In the past six months, we went through basic principles of hydroponic growing. Here are some readers’ questions we’ve received along the way.

Question: What chemigation products are available that are labeled for pesticide use? What application system would you suggest for hydroponic or greenhouse use?

Answer: Chemigation is the application of a systemic pesticide introduced into the existing irrigation or hydroponic systems. It can be used as a stand-alone method or jointly with a foliar application, which sprays or mists a pesticide directly onto the plant.

Any potential systemic product must have a high degree of solubility in order to freely flow throughout the system. With that in mind, virtually any hydroponic system would accommodate chemigation, just as they allow fertigation, which is the introduction of fertilizer into the hydroponic system.

An informative article on the subject was written by Dr. Gerald Ghidiu and published in the September 2013 issue of Growing.

Most traditional chemigation products require a worker to receive specialized training, wear protective clothing and use a ventilator when mixing. The operator must also pay close attention to the tolerance (degradation) levels that indicate how quickly the substance breaks down, the pre-harvest interval (how closely the product can be applied to the harvest date) and re-application intervals (how long you must wait between applications).

In a perfect world, we wouldn’t need to use systemic measures, but the use of systemic pesticides is often necessary. Although greenhouses can create a barrier for entry for pets, any pests that do enter the environment can set up a colony that has an unlimited amount of food and can reproduce unchecked without the presence of predators. The use of chemigation in a greenhouse environment has both advantages and constraints. Primarily, traditional systemic pesticides control a broad spectrum of pests. Secondly, if the mixture is being administered through the use of a nutrient tank, much of the safety equipment that prohibits backflow into a water source may not be required, as the tank is “contained.” However, care must be taken not to introduce into a “run to waste” system, as that results in contamination of the runoff from the plants. There are traditional systemic pesticide products formulated specifically for greenhouse use, but I’m unable to endorse any. Check with your state’s agricultural department to inquire about specific regulations of a particular product intended for greenhouse use.

The hydroponic industry is moving toward the use of environmentally friendly crop-specific formulations and those that target a range of pests more prevalent in controlled environment agriculture.

The industry’s preferred choice is use of biopesticides. Biological pesticides have several ways of combatting pests, either by using predatory, parasitic or chemical means. The U.S. Environmental Protection Agency describes it as including “naturally occurring substances that control pests (biochemical pesticides) and substances produced by plants that contain added genetic material (plant-incorporated protectants [PIPs]).” These are often parts of an Integrated Pest Management program and are a viable alternative to using synthetic chemicals.

Any crop that PIPs have been used on is considered a genetically modified crop, so we will focus on bioderived chemicals. They have no effect on plant physiology but instead focus on the manipulation of a living organism, which is a form of biological control. They are usually concentrated forms of naturally occurring compounds that other plants produce to protect them from pests. These natural materials are biodegradable and are considered renewable resources, which organic farmers and consumers love.

Examples of bio-pesticides include azadirachtin/Neem oil (derived from the seed kernels of the Neem tree), pyrethrum (extracted from the dried flowers of a chrysanthemum) as well as other essential oils.

Advantages include a much shorter pre-harvest interval (most products can be used until the day of harvest), a lower required reapplication period if pests persist, as well as the lack of any synthetic chemical presence in the produce, irrigation or hydroponic system.

A disadvantage is that different pests (and the unique problems they create) may require distinct solutions, so the grower must identify a specific threat in order to defeat it. Additionally, sometimes a natural substance is slower to control the threat versus the use of a traditional pesticide. If a crop is in immediate peril, a combination of systemic and foliar applications may be required.

There will be a broader discussion on the subject of defending your crops from unwanted invaders in a supplement to be released in September.

Read more: Analyzing the Future of Hydroponics

Question: I noticed you mentioned double-ended bulbs in a Future Trends section of an article. Could you describe and compare them to other trending lighting options?

Answer: Two newer concepts in horticultural lighting include the development of digital ballasts and double-ended (DE) bulbs.

Digital ballasts contain modern circuitry and microprocessors, which monitor and maximize efficiency and allow for adjustable output settings. They can be 30 percent more efficient than their magnetic predecessors and generate much less heat. They have higher initial costs but lower operating costs. Many allow for the use of multiple voltage inputs and can be used with either high pressure sodium (HPS) or metal halide (MH) bulbs, including enhanced spectrum bulbs. Some high-frequency digital ballasts also allow for the use of double-ended bulbs.

The development of DE bulbs represents a major advancement in lighting technology. DE bulbs connect on both ends, similar to the connection of a fluorescent lamp. They are available for MH, HPS and ceramic metal halide (CMH) lighting systems. It should be noted that an upgrade to DE lighting would require changing the cord set and the reflector if running a MH or HPS system. CMH ballasts are not interchangeable with MH or HPS, but would similarly require the purchase of a new cord set and reflector. Advantages of DE bulbs include a slightly broader spectrum, increased yields and a longer period of operation before the light spectrum generated starts to deteriorate. A disadvantage is they generate extreme heat, which ironically is a contributing factor to their increased efficiency.

Read more: Hydroponics 101: What is Hydroponics?