By Gucci Fan
The Nature Academy is focused on training a new generation of environmental leaders in sustainability, conservation, and ecological restoration. As part of the Nature Academy program, each intern writes a blog post and develops a project. The project provides an opportunity to take on responsibility in an area of interest, contribute to the goals of their team, and develop a skill or area of knowledge that can be added to the intern’s portfolio. The post may reflect the project or be a nature-related topic of personal interest to the intern.
The tropical house in the conservatory at Matthaei Botanical Gardens contains three different biomes: tropical, temperate, and arid. Most plants found here wouldn’t grow naturally outside in Michigan or survive a northern winter.
If you’ve been to the conservatory at Matthaei Botanical Gardens, you know that it’s home to many rare and beautiful plants that would never be found naturally growing outside in Michigan. Growing them indoors under glass is made possible by carefully controlling the temperature, irrigation, and humidity of the conservatory. Under these conditions plants such as chocolate, guava, and date palm can grow into trees without having to endure our winter temperatures.
Unfortunately, these ideal growing conditions also appeal to unwanted organisms such as weeds and insect pests. They can easily enter the conservatory on new plants brought from the greenhouse, and thrive due to the nice environment and lack of predators. Because the conservatory is a public space, there are limits on the methods we can use to combat pests, so we are constantly experimenting with new approaches.
Integrated pest management (IPM) is a practice widely used today by gardeners and landscapers. Essentially, IPM is a system of different methods of pest control combined to minimize cost and damage to the environment while maximizing suppression of the target pests. The different methods used include a variety of chemical, mechanical, and biological controls. This multifaceted approach helps reduce reliance on a single method such as sprayed insecticides. IPM depends on vigilant monitoring of pest populations and continuous application of techniques, which has been a big part of my internship in the conservatory this summer.
Chemical controls are often what comes to mind when thinking of pest management, and some of our pests do require sprayed insecticide. One of my main internship goals is to become a certified pesticide applicator to help spray in the conservatory, as we occasionally spray different kinds of insecticidal soap and oil. More powerful insecticides would likely be more effective, but since the conservatory is open to the public it becomes a safety concern to our visitors and staff. Instead, the milder products used don’t require the conservatory to be closed, nor are they harmful to the environment or to visitors. Insects are also less likely to develop resistance insecticidal soaps and oils because the ingredients these products contain generally work by clogging the insect’s pores and blocking its means of breathing.
Since chemical controls alone do not maintain pest populations at an acceptable level, other methods in the IPM system are needed. The most important for our conservatory may be mechanical controls, which entail physical removal of pests without using chemicals. Techniques I have been using a lot this summer include hand-weeding unwanted plants, pruning of foliage infested with insect pests, and spraying infested plants with high pressure water, which washes larvae and eggs into the dirt where they can’t survive. Mechanical controls are effective in targeting specific populations without the risk of pests developing resistance to a pesticide, but they can be tedious as they require constant attention and labor.
A third method in integrated pest management is biological control. This technique utilizes natural enemies of the targeted pest to keep populations under control. Examples you may have heard of include releasing ladybugs to control aphids on crops, or Galarucella beetles to control the invasive plant purple loosestrife. (Read about the use of the Galarucella beetle here in a blog post by intern Katie Ferran.)
This method comes with the risk that the organism released as a biocontrol could either be ineffective in controlling the target pest or become a pest itself. In the conservatory, the biological controls currently used are the mealybug destroyer (Cryptolaemus montrouzieri), a beetle which feeds on mealybugs, and the thrips predatory mite (Amblyseius cucumeris). As you can probably deduce from their common names, the mealybug destroyer feeds on mealybugs and the thrip predatory mite attacks thrips. These are very successful in targeting specific pests, but may be sensitive to chemical pest controls.
An example of the thrips predatory mite and typical damage done by thrips. Both organisms are very small and hard to see, but over time the predatory mite has reduced the amount of thrips damage in the conservatory. Photos: laidbackgardener.blog/ and greenmethods.com/cucumeris/
Mealybugs are a common pest that we control in the conservatory with spraying high pressure water and releasing a biological control, the mealybug destroyer. Photo: salisburygreenhouse.com.
Larva (middle) and adult (bottom) of the mealybug destroyer. Unfortunately the larva kind of looks like the mealybug, but is slightly larger and more active. Thanks to the mealybug destroyer’s effectiveness in controlling mealybug populations, most of what looks like mealybugs in the conservatory is actually the mealybug destroyer larvae. The adult looks like a small black and orange ladybug.
As long as plants grow in the conservatory, pests will be a problem. It’s an ongoing fight to suppress and maintain pest populations at an acceptable level. We may never eradicate all unwanted organisms, but we can apply techniques of integrated pest management to continue enjoying our beautiful plants without putting the environment or our visitors in harm’s way.
Gucci Fan, originally from Okemos, Michigan, is an intern in the conservatory and greenhouses at Matthaei. She is a rising senior at the University of Michigan double majoring in Program in the Environment and ecology, evolution, and biodiversity. When she’s not watering plants at work, you can find her beekeeping, petting cats, or watering more plants at home.