Pests and Diseases - Problems for the Plants

Unit 5: Monday, May 3, 1999

Friday, May 7, 1999

Monday, May 10, 1999

Friday, May 14, 1999


Be Ready, Problems Will (Probably) Happen


     We would all like our plants to grow perfectly, look beautiful and be healthy until the crop is ready to eat. But gardening usually doesn't happen that way because we are working with nature. Many other living things - mostly bugs and fungus - eat or live on plants. That's just part of nature. We need to figure out, as best we can, how to protect the plants and keep them as healthy as possible. We also need to understand that problems with pests and diseases will probably happen because it's a natural process.




Prevent Problems If You Can - Keep the Plants Healthy


     By using hydroponics you have already eliminated some garden problems that come mainly from the soil, but your plants depend on your care. You have learned about the water, nutrients and pH necessary for your plants. Be sure to keep these at the proper levels. Plants will survive some problems with pests and disease if they are healthy and strong.

     Check other growing conditions such as proper light and air ventilation. Wind and rain conditions should also be checked. It's hard to have a perfect place for your plants, but use the best place available.

     Follow the assignments closely. Try not to be careless or let your responsibility slip. A regular time is needed to check the garden and take care of the water, nutrients and pH when it's needed. This will keep your plants as healthy as possible. Then, when pests and diseases happen, healthy plants will have a chance to continue growing.


Observe Your Plants Carefully and Often. Find Pests and Diseases When They Begin.


     As part of your regular care, look carefully at your plants. Check all the parts: roots, stems, leaves (both sides), flowers and fruits. Look for problems that show up as spots, holes, or bumps. Is an insect or spider living on the plant and causing damage? You might see fuzzy-looking or discolored places, and droopy leaves. Is it fungus or mildew? If you SEE a problem when it first starts, you might be able to prevent more damage and keep the plant healthy.


Assignment #5     

"Pest and Disease Log"
  • Do a regular check for problems with pests and diseases. Schedule a few minutes at each class session to look closely at the plants.
  • Keep a record in your journal of what you see. If there are no problems, write "No pests or diseases." If you see something, describe what you see or draw a sketch.
  • Update your journal every class session.


The habit of observing and recording problems is used by farmers, experienced gardeners and plant scientists. It gives basic data needed to keep plants as healthy as possible.



Research Information to Identify Problems and Learn About Them


     If you see a problem, try to figure out what it is. Insect? Fungus? Nutrients? Growing conditions?  To identify problems you'll need a lot of information.

     Go back and review the information you already have about nutrients and the growing conditions needed for your plants. Know what the plants must have to grow properly.

     In addition, you need to do research and learn about common insect pests and diseases that might attack you plants. Start with what you already know from science classes and other experiences. Talk to friends and other people about pests and diseases in gardens. People can be good help, but check what they say to be sure it is correct. Finally, learn more by finding and studying information sources at websites and in books. Keep these information sources handy so you can refer to them for detailed information when you need it.


Assignment #6:

"Common Pest & Diseases"
  • Think and remember what you already know - or think you know - about insects, fungus, mildew and mold. Try to recall school assignments or TV shows or any experience when you learned about these things. Do you know about their life cycles, where/how they live or what they eat? As you think and remember, write down a brainstorm list of everything you know or think you know. Don't worry too much now about how to organize the list or how it looks. You can do that in another part of the assignment. 
  • Talk with the site facilitator, a friend or another person. (Try to find someone who is interested in gardening.) Show them your list and ask them to help you add to it. Talking and sharing with someone usually helps us remember what we know and that's the important reason for this assignment. Don't worry too much about new things to learn right now. Stay focused on common knowledge and background information. Add more to your brainstorm list if you can.
  • Rewrite your brainstorm list and post it as a report to your website. Title your report: Brainstorm - What I Already Know About Common Garden Problems
  • Organize your list with the headings: 

            1. Insect Pests 

            2. Diseases - Fungus, Mildew and Mold. 

  • You may choose to write phrases or short sentences, either is fine. Add a sentence with the name of the person you talked with. Post your list to your website.


Assignment #7:

"Name That Pest or Disease!"
  • This activity will help you get familiar with the names of some common garden pests and diseases. You'll visit the website for the College of Tropical Agriculture and Human Resources at the University of Hawaii in Manoa. The information is for college level study, but you can use the lists to develop the vocabulary you'll need to solve garden problems. The lists also might be useful later as checklists to track down information on problem insects or diseases.
  • Go to the URL

          On the Crop Knowledge Master screen, click on         Lettuce. (Later when you're growing other kinds of plants,         you can come back and check this site.)

                Read through the list of insects that attack lettuce. Notice         the names and groups, but don't worry too much about the         scientific name for this project.

  • Optional: As an example, click on the scientific name of vegetable mite. At the next screen, click on the heading for Damage. Try reading about how mites damage plants. You may understand some and you may need help to get the meaning. Click on the link to webbing. You'll see a picture.
  • Go back to the page titled Lettuce and click on the heading Plant Disease Pathogens. Notice the common names and groups for the diseases listed there. Some of the diseases on this list grow in soil, so they should not affect your plants. Many do affect leaves or stems, so you may need to know about them.
  • Optional: Explore other parts of the College of Tropical Agriculture website for more information.

Assignment #8:

"Sample Facts About Insect Pests, Diseases"


This activity will help you learn about reference books and on-line sites to get detailed information on pests and diseases. You will also be adding to your own knowledge which will help you identify problems you see on your plants.

For each of the resources listed below, do the following things:

  • Get to know the resource: Browse through the headings or follow some of the links in each information source...
  • Look at the illustrations. Figure out how the information is organized. By topic? Alphabetically?
  • Skim through parts of the text to see the kinds of information given.
  • Learn about one problem that might affect lettuce plants: In each source, choose one insect or disease that might damage lettuce.
  • Read the section about that problem.
  • Write a report showing facts you have learned:

    Title your report "Sample Facts About Insect Pests, Diseases"

  • For each book or website, record the title and the insect or disease you read about.
  • Write a brief paragraph telling two or three facts you learned from that source.
  • Post the report to your website.


Information Sources:






PP. 102 - 154. Bugs, Slugs & Other Thugs, Controlling Garden Pests Organically, by Rhonda Massingham Hart. Storey Publishing, 1991. ISBN 088266-664-9.


PP. 95 - 101 Beginning Hydroponics; Soilless Gardening, by Richard E. Nicholls. Running Press, 1997. ISBN 0-89471-741-3.


PP. 71 - 107. Garden Pests & Diseases. Sunset Publishing, 1993. ISBN 0-376-03302-9


Please note that these sources are written for adults. Students should get help with difficult vocabulary and meaning.


Also, please note that poisons such as Malathyon are mentioned. Chemical poisons should NOT be used for this project. Safe treatments and controls for problems are a topic later in this section.


     The books listed can be found at your school library or the Public Library and at book stores. The site facilitator can help you find them. Other books or websites can be substituted, but be sure to give the title, author, date and pages of whatever source you're using.

     Now that you have done these activities, you should be able to identify problems that might damage your plants. Keep these information sources throughout this project so you can use to them if you need to.


Assignment #9:

"Journal Writing"
  • In your journal, tell about any insect pests and diseases you identify on your plants. 
  • Add the information to the observations in the assignment above. 
  • Update your journal at every class session.




Decide on a Control or Treatment to Prevent Further Damage


     The information sources you explored included some suggested treatments and controls for pests and diseases. Please, remember that when working with nature, you cannot expect to prevent or stop all damage. But many times you can find effective ways to help your plants stay healthy.

     In this project we will use organic methods to control problems. Chemical pesticides should NOT be used because they can be difficult and dangerous to handle. Also, short-term controls with chemicals are often outweighed by longer-term bad effects in the environment. Strong natural insecticides such as rotenone, pyrethrum, nicotine, sabadilla and neem should also NOT be used for this project.

     They can be toxic to sensitive human beings so crops cannot be eaten for several days. Fish and all insects - including beneficial ones like ladybugs - are destroyed by many of these strong natural pesticides.

     When a problem is identified, consider the controls and treatments listed in the information sources you have read. Removing pests by hand, gently washing the leaves or cutting away diseased parts of the plant may be the best treatment. Be sure to wash hands and tools often so problems are not spread by the fingers or blades.  Insecticidal soaps, commercial or home made, can be used safely, but cautiously. Some plants, like cucumbers, can be damaged by soap spray. Find reliable information or test the spray on one plant before using soap.

     For general information on organic pest control, read pp. 92 - 101 in Bugs, Slugs and Other Thugs by Rhonda Massingham Hart.


     Some excellent organic methods of controlling pests and diseases are complicated and best suited for long-term hydroponic gardening. For example, covering plants with screen held on a sturdy frame protects plants from flying insects. However, building the cover is probably beyond the amount of work that can be done of this project.

     With some luck added to careful observation, well researched information and thoughtful treatments, it is hoped that you'll be able to minimize damage from pests and diseases. Look forward to a good harvest from your plants.


Assignment #10:

"Treatment and Controls"
  • In your journal, describe any treatments or controls you try for insect pests and diseases. Tell what you did and follow up with any effects - positive or negative - that you observe later. 
  • Update your journal at every class session.


Mosquitoes, An Annoying Pest


     Mosquitoes may become a problem pest for you, not your plants. They lay their eggs in non-moving water such as used for non-circulating hydroponic growing systems. The mosquito population may be high and become annoying. One possible control is to place mosquito fish in the nutrient solution to eat the larvae.



Learner Outcomes
Student Template

Unit 1

What is Hydroponics?

Unit 2

History of Hydroponics

Unit 3

Starting a Simple Hydroponic Garden

Unit 4

Care and Maintenance

Unit 5

Pest and Diseases

Unit 6

Explorations into Plant Research

Unit 7

Independent Study:

Explorations in Hydroponic Gardening

Assessment Rubric


T3 Participants

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