Chapter 7.18

7.18 -Radish as a Companion Crop to Repel Pests

Aaron Vethanayagam, University of Guelph, Canada

Suggested citation for this chapter.

Vethanayagam,A. (2022) Radish as a Companion Crop to Repel Pests, The Encyclopedia for Small Scale Farmers. Editor, M.N. Raizada, University of Guelph, Canada. http://www.farmpedia.org

Background on Pests Affecting Smallholder Farmers

Unfortunately, pests affect the yield of crops farmers can cultivate (National Research Council, 1985), and this is very devastating for smallholder farmers. Pests can cause severe damage to these crops that can impair productivity and destroy it (National Research Council, 1985). For example, in Africa, it is estimated that the value of crop loss due to pests annually is USD $65.58 billion (CABI, 2024). This has a massive impact on the lives of many individuals as this results in food shortages and lost income. Farming is the only income source for these farmers and their families (Ritchie et al., 2023), and is especially limited for smallholder farmers due to their small land area (Food and Agriculture Organization of the United Nations, 2013).

Over time, many techniques have been used to repel pests, such as using pesticides (National Research Council, 1985). However, farmers can cultivate vegetables such as companion crops, which are crops that are planted in the same soil close to other crops (Harris & Streets, 2022). This enhances the production of crops and income significantly as smallholder farmers can plant various crops in the same plot, and critically, certain crops can repel pests (Harris & Streets, 2022). A notable example of this are radishes. Once they are fully grown, their leaves can attract pests towards themselves and protect nearby crops (The Land Connection, 2022). This also allows smallholder farmers to save more money as they can stop purchasing pesticides and also reduce labour required to apply these chemicals.

Benefits of Using Radishes as Companion Crops

There are numerous benefits for smallholder farmers just from planting radishes alone. It does not require any usage of special equipment, with minimal cost and labour. Smallholder farmers can plant a thick line of radishes that goes across the width of their plots every few feet to protect as many crops as possible (Four String Farm, 2013). It is an intercrop, that has been shown to be a good companion crop for peppers, tomatoes, eggplant, corn, squash (University of Saskatchewan, n.d.) and members of its family, as well as beets, beans, carrots, chervil, cucumber, lettuce, nasturtium, and peas (Gardenia, n.d.b). It can repel pests because of the scent that it releases into the air, which can also confuse the pests (Four String Farm, 2013) such as cabbage maggot, cucumber beetle, carrot rust fly, spider mite, squash bug, and squash vine borer (Gardenia, n.d.b). It also provides shade once it is fully grown for crops that need shading such as peppers, tomatoes, eggplant, corn, squash, and many more (University of Saskatchewan, n.d.).

Figure 1. A Carrot Rust Fly (Psila rosae) standing on a piece of leaf.

Planting radishes as a companion crop may be beneficial to protect home gardens and high value vegetables known to suffer from these pests. Radishes would be less useful in mesh greenhouses which create a closed environment.

A controlled study (DeJong, 2017) was carried out to determine if there is a correlation between using radishes as a companion crop and if it increases or decreases the number of pests it can repel. The result of this study concluded that radishes did decrease the number of pests affecting nearby crops (DeJong, 2017).

Also, radishes can benefit livestock as well. Feeding livestock with low-quality bulky food (forage) can create significant problems to livestock; instead dry-season forage crops are considered a better alternative, including radishes (Mbambalala et al., 2023). Radishes can easily be produced in any climatic condition and soil type in a brief period of time, so it can provide livestock with nutritious forage for 90-180 days (Mbambalala et al., 2023). There have been studies determining if there is a positive or negative impact on livestock after having a radish diet (Mbambalala et al., 2023). Although the results were inconsistent in terms of the livestock’ feed intake, milk production, and quality of the milk, it is very evident that the radish diet did not negatively affect livestock. Therefore, smallholder farmers can take advantage of radish diets for their livestock, which in turn allows them to save more money from not having to buy forage and supplements (Mbambalala et al., 2023).

Critical Analysis

Unfortunately, radishes as a companion crop to repel pests are not suitable for potatoes, broccoli, cauliflower, and many more (Gardenia, n.d.a). This is due to a few reasons. Firstly, radishes can secrete allelopathic compounds (Rasul & Ali, 2020b) such as isothiocyanates and p-hydroxybenzoic acid (Rasul & Ali, 2020a), which are toxins that can be harmful to the growth of some nearby crops, especially to potatoes, broccoli, etc. (Bai et al., 2019). Secondly, radishes are a deep rooting species (Heuermann et al., 2019). This can lead to competition with other crops with shallow roots, because important nutrients such as nitrogen are more likely be found deeper into the soil, which would favour radish growth (Heuermann et al., 2019), inhibiting the growth and biomass of the shallow rooted crops (Anas et al., 2020).

Cost Analysis

A cost analysis (Afeworki et al., 2019) was done to find out if there are any cost benefits from planting radishes in general, not just as companion crops alone (Figures 2 and 3). It was conducted using radish as a sole crop in British Columbia, Canada, using the local currency (CAD). A farmer using their own equipment and tools, irrigation, land rent charges, soil test, etc. was considered as the fixed cost. It was concluded that the total annual cost including labour was $2,695.69 (CAD $1,107 without labour cost) and the fixed cost was $369, totaling CAD $3065 per 0.05-acre (CAD $1,476 without labour cost). The farmer was able to earn a revenue of CAD $4,800 per 0.05-acre,and therefore, the net income return (profit) was CAD $1,735 per 0.05-acre (CAD $3,323 without labour cost). This data can inform smallholder farmers that not only are radishes great as companion crops, but it can also provide income on their own (Afeworki et al., 2019).

Figure 2. Annual variable cost (CAD) including labour cost to plant and take care of radishes as a sole crop in British Columbia, Canada (Afeworki et al., 2019).

Figure 3. Annual fixed cost (CAD) of expenses including labour cost used to plant and take care of radishes as a sole crop in British Columbia, Canada (Afeworki et al., 2019).

Conclusion

In conclusion, it is very evident that radishes are a beneficial crop for farmers, especially for smallholder farmers. It can prevent pests from destroying a diversity of other crops, provides shade for some crops, is very adaptable to diverse climate conditions and soil, can be used as livestock fodder, and allows smallholder farmers to be able to gain lots of income. However, it can outcompete shallow rooted crops, so companion crops must be selected carefully or in initial small plot trials.

Helpful Links To Get Started

Smallholder farmers might not be sure where to get started, so here are some resources they can use to learn and gain more information about radishes:

The following link is a manual/guide that provides a step-by-step process on how to properly plant radishes into the soil: https://extension.usu.edu/yardandgarden/research/radishes-in-the-garden

Also, smallholder farmers might not be sure of what crops are suitable to be close to radishes, so here is a following link farmers can use to learn more information: https://extension.wvu.edu/lawn-gardening-pests/gardening/garden-management/compani on-planting

Furthermore, smallholder farmers can click on the following link that will redirect them to a YouTube video. It goes into detail and gives some good advice and suggestions to consider when planting radishes: https://www.youtube.com/watch?v=pC_gIqySZHU

References

1.Afeworki, E. A., Polasub, W. P., Chiu, C. C., & Mullinix, K. M. (2019). Southwest British Columbia Small-Scale Farm Enterprise Budget: Radish. Institute for Sustainable Food Systems Kwantlen Polytechnic University. https://www.kpu.ca/sites/default/files/ISFS/Radish_0.pdf

2.Anas, M., Liao, F., Verma, K. K., Sarwar, M., Mahmood, A., Chen, Z., Li, Q., Zeng, X., Liu, Y., & Li, Y. (2020). Fate of nitrogen in agriculture and environment: agronomic, eco-physiological and molecular approaches to improve nitrogen use efficiency. Biological Research, 53(1), 47. https://doi.org/10.1186/s40659-020-00312-4

3.Bai, Y., Wang, G., Cheng, Y., Shi, P., Yang, C., Yang, H., & Xu, Z. (2019). Soil acidification in continuously cropped tobacco alters bacterial community structure and diversity via the accumulation of phenolic acids. Scientific Reports 9(1), 12499. https://doi.org/10.1038/s41598-019-48611-5

4.CABI. (2024, January 25). African smallholder farmers benefit from reduced crop losses and higher incomes from a novel pest alert service. https://www.cabi.org/news-article/african-smallholder-farmers-benefit-from-reduced-crop-losses-and-higher-incomes-from-a-novel-pest-alert-service

5.DeJong, D. (2017). Companion Planting: Effects of Radishes on Squash Bugs. University of Nebraska. https://digitalcommons.unl.edu/envstudtheses/216

6.Drost, D. (2020, April). How to grow radishes in your garden. Utah State University. https://extension.usu.edu/yardandgarden/research/radishes-in-the-garden

7.FAO. (2013). Smallholders and family farmers. Food and Agriculture Organization of the United Nations. https://www.fao.org/family-farming/detail/en/c/273864/

8.Four String Farm. (2013, December 13). The scent of a radish. https://fourstringfarm.com/2013/12/10/the-scent-of-a-radish/

9.Gardenia. (n.d.a.). Do NOT grow these plants together.https://www.gardenia.net/guide/do-not-grow-these-plants-together

10.Gardenia. (n.d.b). Wonderful Plants That Repel Insects. https://www.gardenia.net/plant/raphanus-sativus

11.Harris, N., Streets, J. (2022, March). Companion planting. West Virginia University. https://extension.wvu.edu/lawn-gardening-pests/gardening/garden-management/companion-planting

12.Heuermann, D., Gentsch, N., Boy, J., Schweneker, D., Feuerstein, U., Groß, J., Bauer, B., Guggenberger, G., & Von Wirén, N. (2019). Interspecific competition among catch crops modifies vertical root biomass distribution and nitrate scavenging in soils. Scientific Reports, 9(1), 11531. https://doi.org/10.1038/s41598-019-48060-0

13.Mbambalala, L., Rani, Z. T., Mpanza, T. D. E., Mthana, M. S., Ncisana, L., & Mkhize, N. R. (2023). Fodder Radish as a potential alternative feed source for livestock in South Africa. Agriculture (Basel), 13(8), 1625. https://doi.org/10.3390/agriculture13081625

14.National Research Council (1985). Plant Diseases and Insect Pests (Chapter 5). In New Directions for Biosciences Research in Agriculture: High-Reward Opportunities. National Research Council, Washington, USA. https://www.ncbi.nlm.nih.gov/books/NBK216440/

15.Rasul, S. A., & Ali, K. A. (2020a). Effect of Radish Aqueous Extract on Germination and Seedling Growth of Wheat, Wild Oat and Wild barley. Journal of Advanced Pharmacy Education & Research, 10–10, 183–189. https://japer.in/storage/models/article/Yx7JWqoRYwGN7JV8IOGrtPpm2PQnyN4z1aQQEBzI8qOKjgRqstL3hrEoe3J7/effect-of-radish-aqueous-extract-on-germination-and-seedling-growth-of-wheat-wild-oat-and-wild-bar.pdf

16.Rasul, S., & Ali, K. A. (2020b). Study the allelopathic effect of radish by incorporate into soil on some poaceae species. Plant Archives 20(2), 3624-3627.

17.Ritchie, H., Rosado, P., Roser, M. (2023). Agricultural production. Our World in Data. https://ourworldindata.org/agricultural-production

18.The Land Connection. (2022, July 27). Radish https://www.thelandconnection.org/il_specialty_crops/radish/

19.University of Saskatchewan. (n.d.). Radishes. https://gardening.usask.ca/gardening-advice/gardenline-nested-pages/food-plant-pages/vegetables/radish.php#top