June 2, 2014

Aphids, Ants and Mites: Confronting Insects at the Aquaponics Project

Laura Genello

Laura Genello

Guest Blogger

Johns Hopkins Center for a Livable Future

mosquito fish photo

Mosquito fish dart beneath the plants at the Aquaponics Project / L. GENELLO

The greenhouse enclosing the CLF Aquaponics Project affords us many advantages over farming in a field, including season-defying winter growing potential. However, even inside a greenhouse, a farmer’s control over nature is only an illusion. This is most evident when it comes to pest control.  Despite our plastic roof, or perhaps because of it, we attract swarms of insect visitors year-round.

While there are many different greenhouse designs, including some that feature bug screening and double-entry doors for biosecurity, our greenhouse is far simpler. It has roll up sides and an exhaust fan that pulls in fresh air in the hot summer months. This design maintains steady air flow, keeps temperatures down, and allows pollinators and other beneficial insects open access to our crops, but it also means we create a haven for many pest species. The most problematic pests in a greenhouse are different than the most notorious villains of the field. While we’re able to keep out larger pests, including deer and groundhogs, the small insects, such as spider mites, aphids, white flies or thrips, find life inside the greenhouse without wind, rain, and predators quite appealing.

We do not use pesticidal spray that could harm our fish, including insecticidal soaps and oil-based sprays, so we must take a creative and integrated approach to pest control. Our pest control strategies fall into two categories: cultural (i.e., preventative controls) and biological (i.e. treatment controls).

Cultural Practices: Good farming practices are essential for reducing the likelihood of a pest outbreak. We rotate our plantings and remove old plants before an infestation takes hold, even if this means sacrificing a harvest. We always grow a diversity of plants representing several plant families to lower the risk of a greenhouse-wide infestation, and we scout frequently to identify pest outbreaks in their infancy.

Biological Control: When we do have a pest population that requires treatment, we use biodiversity to our advantage by employing biological control. Biological control is the practice of using one species to control another. My favorite example of biological control is the population of tiny fish that have made the water in our plant beds their home. These minnows never grow to more than a couple of inches in size, yet they form a mosquito-eating army, providing a valuable service for any human visitors. For our crops, we release ladybugs to eat aphids, predatory mites to combat spider mites, and welcome the many species of spiders that spin their webs over our plant beds.

Biological control is a complex field that requires an understanding of the lifecycles of the pests and the beneficial species, and it cannot replace preventative practices. Last summer, pest outbreaks decimated our crops. We’ve learned the hard way that our sheltered greenhouse provides a haven for insects, and the importance of paying close attention to the early warning signs of pest outbreaks.

3 Comments

  1. Thanks for your article. Yes, Greenhouse growers have to be very vigiliant! I have found heat in the greenhouse my biggest issue. The heat leads to high humidity creating an environment that pests enjoy! I have a 96 foot L, 24 ft w and 10 ft tall house. The temperature has been close to 110 F many times the past few weeks. I have spray painted the plastic and closed the side walls to allow the fan to pull air all the way through the house. There are two shutters at the East end and a large fan on the west side. Seems that I will need to install another fan and maybe add a shade cloth. That’s money that is not available. Meanwhile, the plants are taking a beating!

  2. Laura Genello

    Posted by Laura Genello

    Hi Gregg, Yes heat is a challenge! Our greenhouse temps have gotten up to 105 in the afternoon of a hot summer day. We use an aluminet reflective shade cloth that works really well at keeping the temperature manageable. We also keep our side walls rolled up all summer for ventilation, and we have three box fans in the greenhouse for circulation. In addition, we use a few reflective tarps (brown on one side, silver on the other) to shade the fish tanks and parts of the greenhouse that don’t need a lot of light. Ventilation is key. Stay cool!

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