Companion Planting for Tomato Aphid Control
ISEF Category: Animal Sciences
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Subcategory: Ecology and Agriculture · Difficulty: Intermediate · Setup: Home Setup · Time: 1 to 2 Months
The Hook
Small changes in plant neighbors can change how many pests show up on tomatoes. That makes companion planting a real test of plant interaction, not just garden folklore. If you randomize your plants and count aphids the same way each time, you can turn a backyard idea into a clean experiment.
What Is It?
Companion planting means growing one plant near another because the neighbor might help, hurt, or change pest pressure. Marigold and basil are popular choices because they can change smell, canopy shape, and insect behavior. Aphids are tiny sap-sucking insects, so even a small shift in where they land can change the count on a plant.
Think of tomatoes as the main stage and the companion plant as the backstage crew. The companion may make the plant harder to find, easier to inspect, or more attractive to helpful insects that eat aphids. Your job is to test whether the effect is real, how big it is, and whether one companion works better than the other.
Why This Is a Good Topic
This is a good science fair topic because you can test a clear cause and effect question with simple materials and repeated measurements. It connects to pest management, crop protection, and food production, all real problems in agriculture. You can learn randomization, image-based counting, and basic statistics without needing a professional lab.
Research Questions
- How does planting marigold next to tomatoes change aphid counts compared with tomatoes grown alone?
- How does planting basil next to tomatoes change aphid counts compared with tomatoes grown alone?
- What is the effect of companion plant distance on aphid load on tomato leaves?
- To what extent does companion planting change the number of new aphid colonies over time?
- Which companion plant, marigold or basil, reduces aphid load more on tomatoes?
- Does companion planting change aphid counts on the top leaves differently from the lower leaves?
Basic Materials
- Tomato seedlings.
- Marigold seedlings.
- Basil seedlings.
- Matching pots or garden bed space.
- Potting mix or garden soil.
- Plant labels and waterproof marker.
- Watering can or hose with gentle nozzle.
- Smartphone with camera.
- Tripod or phone stand.
- Printed ruler or color card for scale.
- Spreadsheet or lab notebook for counts.
Advanced Materials
- Stereomicroscope or high-magnification loupe.
- Fixed-light photo box or greenhouse bench with constant lighting.
- Image annotation software for training aphid labels.
- Computer with Python access.
- GPU-capable computer or cloud notebook for model training.
- Statistical software for repeated-measures analysis.
- Environmental sensor for temperature and humidity.
- Plot-mapping tool for randomized layouts.
Software & Tools
- Google Sheets: Tracks randomization, counts, and summary tables.
- Python: Cleans images, runs counting scripts, and compares treatments.
- Label Studio: Marks aphids in training images for the detector.
- ImageJ: Checks scale, brightness, and photo consistency.
- R: Fits models that compare treatments across repeated counts.
Experiment Steps
- Define the treatments and the randomization unit, such as a pot, a bed, or a plant cluster.
- Standardize the photo setup so every plant is counted from the same angle, distance, and lighting.
- Build a labeled image set that teaches your detector to separate aphids from leaf texture, glare, and debris.
- Plan replication, control plants, and repeat observation dates so you can compare treatment trends, not one-off counts.
- Choose the summary metric and statistical test before you start, such as aphids per leaf, colony count, or change in count over time.
Common Pitfalls
- Mixing treatment and control plants in the same small space, which lets aphids move between groups.
- Counting plants in changing light, which makes phone images too uneven for a fair comparison.
- Training the CNN on close-up aphid photos only, which makes it miss real-world images with leaves, stems, and shadows.
- Using too few replicates, which makes normal pest swings look like a companion-planting effect.
- Summing all leaves on one plant as one number without checking canopy position, which hides where aphids actually cluster.
What Makes This Competitive
If you want this to feel more like ISEF than a class demo, focus on measurement quality and experimental design. Compare marigold, basil, and no-companion controls, then validate the CNN against hand counts on a separate test set. A repeated-measures model can show whether the effect grows, fades, or depends on plant stage. That makes your project about ecology and data quality, not just plant folklore.
Project Variations
- Test whether marigold or basil changes aphid load on peppers instead of tomatoes.
- Compare aphid counts on potted tomatoes and raised-bed tomatoes under the same companion planting setup.
- Measure whether companion planting changes the mix of aphid life stages, not just the total count.
Learn More
- PubMed: Search review articles on aphid ecology, intercropping, and botanical pest management.
- USDA National Agricultural Library: Find crop pest fact sheets and research summaries on aphids and tomato production.
- Cornell Cooperative Extension: Look up tomato pest guides, aphid scouting tips, and identification photos.
- USDA ARS: Read crop protection studies and integrated pest management reports on companion planting and pest suppression.
- ImageJ: Use this free tool to check image scale, brightness, and consistency before you count aphids.