Community Gardening Blog 3. The Nitty Gritty: Basics of Crop Rotation, Weed and Pest Management
by Barbora Stankova, Kollie Tokpah, and Anam Riaz
So, you have found yourself stuck in quarantine with nothing to do but watch Tiger King and reluctantly do your readings? If your days are slowly becoming one long, never ending Tuesday,and leaving for your state-mandated walk seems like a chore by now, learning a new hobby might be the answer to getting your morale up, just like everyone constantly recommends.
Why not start gardening? Whether you start with a grown plant or try your luck at starting your plants from seeds, watching your flowery friend grow and prosper gives you a sense of accomplishment and calm that might just bring you some peace of mind. And if you are already a seasoned expert in keeping your plants alive, learning how to grow crops could expand your horizons, give you a new skill and make you a valuable asset in the apocalypse!
In this article, we will skip all the easy-peasy basics (but see garden blogs 1 and 2 for these!) and get right to the super complicated bits – crop rotation, weed and pest management.
I. Crop Rotation
Why should we rotate the crops we plant, we hear you ask! Well, my friend, there are many answers to this question. First of all, different crops deplete or supply different nutrients into the soil. For example, take the wonderful legumes – not only do they provide a healthy source of nutrients for you, they also supply the soil with very important nitrogen. They do not produce Nitrogen on their own – in fact, a very specific type of bacteria, rhizobia, creates nodules on the roots of these plants, which not only uptake nutrients from the soil into the plant, but also participate in a process called nitrogen fixation in which they take nitrogen from the air and turn it into nitrogen compounds which can be used by plants. This way, there is no need to add artificial fertilizer in order to supply nitrogen. On the other hand, root crops are, unsurprisingly, a little bit more demanding when it comes to nutrients. However, as we can see, legumes are pretty self-sufficient in supplying some of their ownnutrients. Therefore, if we plant legumes after root crops, we should still get some quality produce. This is the basic principle of crop rotation – different plants interact in different ways with the soil – some supply certain important nutrients, so that other, more demanding, crops can use these.
Second, crop rotation is extremely valuable in preventing pests and diseases of your crops. Large monocultures that we can see today are quite susceptible to crop failures, and one factor is disease or pest that is specific to that crop. For example, if we keep planting cabbage year by year, we might get cabbage flies which are attracted by this specific crop. And because every year we end up planting cabbage, we have to end up spending more resources on prevention and protection from this pest. However, if we mix it up and plant a different crop after cabbage, for example corn (since it is generally not affected by preceding crops), cabbage flies will not be attracted by this crop and we will get better results. Crop rotation also helps with reduction in weeds and pests – it is truly a gift that keeps on giving!
Third, crop rotation overall improves the soil. As we already saw, with smart crop rotation, we can add certain nutrients to the soil in order to feed the subsequent crops. However, different crops interact with the soil in different ways based on their roots as well. Depending on their length, roots take water and nutrients from different layers of the soil, interact with different microorganisms and break down and enrich the soil in different ways. Moreover, one of the big problems of today’s industrial-sized agriculture is soil degradation – from water erosion, decline in organic matter, increased salinity, and jut general decline in the quality of the soil, these are all problems facing current food security. Crop rotation can greatly improve all of these factors.
So now comes the fun part – actually figuring out how to rotate. If you have just a tiny garden or even a small balcony with a few pots of vegetables, crop rotation is a no-brainer. Just switch your crops in the pots and add a bit of compost every season, so that there is enough variety.
However, if you are operating on a larger scale where you have the opportunity to plant your crops in a higher number of plant beds, it can (and does) get quite complicated. Probably the best way is to write down all the crops you want to plant and visualize. And with all the free time you now have, you can get creative with it – learn how to draw a cauliflower, colour in those tomatoes, cut out some strawberries from packaging and use them. Later, you can repurpose these and learn a new language (for example, corn in Russian is кукуру́за)!
Now that you have a visual representation of your crops, you should try and order them into your rotations. Think about factors such as how many plant beds you will have, whether you want to plant each crop separately or try companion planting, how much space each plant needs and whether some plants need more or less sunshine (you can plant taller plants in front of crops that do not need that much sun). Then it is necessary to think about the different ways your crops will interact. Some tips from Eliot Coleman include: legumes (e.g. beans) are a good preceding crops and they are usually not affected by any negative effects a preceding crop might have. On the other hand, cabbages can have detrimental effects on subsequent crops – unlike legumes, onions, lettuces and squashes, which are beneficial. Potato yields better if it is preceded by corn, whereas if it is preceded by peas, oats or barley, it can have problems with diseases. It can seem quite daunting at first, and believe me, it does not get much easier with time.
However, to help you visualize what crop rotation might look like, here is a 3-plot rotation example from the Royal Horticultural Society:
Table 1: Sample Three Year Crop Rotation (Source: https://www.rhs.org.uk/advice/profile?PID=124)
Legumes, onions and root vegetables
Legumes, onions and root vegetables
Legumes, onions and root vegetables
The more plots you have, the more years the full rotation will take. Just to illustrate how the system works in different configurations, the same source provides us with a 4-plot plan:
Table 2: Sample Four Year Crop Rotation (Source: https://www.rhs.org.uk/advice/profile?PID=124)
Onions and roots
Onions and roots
Onions and roots
Onions and roots
So, there you have it, folks. These are just a small number of factors that can help you decide your ideal crop rotation pattern. However, do not expect to find the perfect one straight away. There will be other elements to your success, from soil type and richness in organic matter, weather and climate or weeds and pests. Figuring out crop rotation is most definitely a learning experience, so do not get discouraged if your seemingly perfect plan does not work as well as you had hoped for!
II. Weed and Pest Management
Now that you’ve planned and planted your garden, what to do if unwanted guests arrive?
Weeds can be a serious threat to cropyields, even when gardeners and farmers spend time removing them from gardening systems (Kumar 2016; Barberi 2002). The composition and competition of weeds are part of the overall dynamics of the organic system, and they are found in different ecosystems based on the crops grown, bioticand abiotic factors, as well as environmental conditions and management practices (Kumar 2001).
A few common weeds from the grass family and their scientific names are listed in Table 3. For more information on other common garden weeds, their habits, and even some of their potential uses, see here.
Table 3: Some Common Garden Weeds (Source: https://www2.ipm.ucanr.edu)
Seasons and type
Summer annual grass
Winter annual grass
Summer annual grass
Fig. 1. Witchgrass (Source: ipm.ucanr.edu/PMG/WEEDS/witchgrass.html)
Fig. 2. Barnyardgrass (Source: ipm.ucanr.edu/PMG/WEEDS/barnyardgrass.html)
Yet it is important not to view the management of weeds only from a reductionist perspective, that is - separating weed control from the overall context of organic systems management. This conventional approach does not significantly improve the immunity of crops in agro-ecosystems. In this regard, it would be appropriate to consider weed management from a systems perspective, using and an integrated approach that aims to improve the whole cropping system. Depending on weed population dynamics, in addition to the crop rotation discussed above, farmers might integrate cover crops, mulching, intercropping, and other direct, cultural and biological methods in a mutually supportive manner to manage weeds (Bond and Grundy 2001; Barberi 2002).
Cover crops (e.g. velvet bean, Sudan grass, berseem clover) are non-crop species grown in the garden to cover the soil. These crops have the competitive ability to suppress weeds and inhibit weeds by allelopathy. In so doing, they control soil pathogens and increase the presence of beneficial organisms. Mulch, such as straw, wood chips, or chopped leaves, can also be applied to discourage the emergence of weeds.
If weeds do appear, hand-weeding or using a garden hoe to remove weeds between crop rows before they have a chance to fully establish are good tools for home gardeners. For larger spaces, or larger weeds, farmers may find that a mechanical weed chipper or portable string trimmer are effective in eradicating weeds (with the latter, be sure to cut before the weeds establish seeds that can spread throughout the garden). Overall, it is crucial to monitor and manage weeds throughout the year – fall, winter, spring, summer.However, it is also important to know that some weeds areedible! Permaculture followers have been known to say that a weed is only a plant whose uses we do not fully take advantage of! For example, the yellow petals and young leaves of dandelions can be used in salads, and the roots can be used as a coffee substitute. For more edible weed suggestions, see here.
Fig. 3. Dandelions (Source: https://www.abc.net.au/news/health/2016-05-12/edible-weeds-and-how-you-can-use-them/7406004)
Other unwanted guests may include pests, which are organisms that damage desirable crops in your ecological garden. Pests can be vertebrates (birds, rodents, deer, etc), invertebrates (insects), or pathogens (virus, bacteria, or fungus) that cause diseases that are harmful to crops and the entire ecosystem. They transmit diseases via direct feeding orlaying their eggs on plant parts (accidental transmission), transferring disease from an infected crop to a healthy one (active transmission), or transferring disease through mouthparts to healthy crops (passive transmission).
Table 4: Some common crop pests (Source: https://www2.ipm.ucanr.edu)
Insects and mites
Bacterial soft rot, corn stunt, charcoal rot, maize dwarf mosaic
Corn leafhopper, corn leafminer, flea beetles, aphids
Anthracnose, bacterial leaf spot, Cladosporium leaf spot
Caterpillars, leafminers, spinach crown mite
Black mold, anthracnose
Tomato bug, loopers, cutworms
Some of these diseases can be prevented by mechanical controls. This method includes checking the bottom of leaves for pest eggs and removing the insect by hand. It is also appropriate to cover the crops with agricultural mesh.
Fig. 5. Caterpillars can be removed by hand (Source: https://www2.ipm.ucanr.edu/agriculture/spinach/Caterpillars-Lepidopterous-Pests/)
Fig. 6. Fabric mesh (re-usable) used to cover crops to avoid pest damage (Source: China-Agriculture-Crop-Garden-Mesh-Frosted-Cover-PP-Spunbond-Agro-Fabric.html)
Planting times can also help evade pests. Early planting and maintenance of a corn-free period over the winter months, for example, is an effective way to avoid damage from leafhopper and emergence of corn stunt. The use of reflective mulches is also feasible in managing insect pests (though the use of plastic has its own environmental cost to be considered).
Fig. 7: Reflective mulch repels insects (Source: https://www.flickr.com/photos/8773704@N06/3030768322)
Finally, you could also use companion planting of flowers and aromatic herbs to confuse pests in your garden, at the same time increasing biodiversity and attracting pollinators and other beneficial insects, as detailed below.
Enhancing biological diversity and promoting natural enemies of insect pests
In dealing with pests, as with weeds, a more holistic approach will be more beneficial than a reductionist one. By enhancing diversity in your garden or crop fields, the natural predators of pests can be increased. Intercropping of cash crops with insectary plants ortrap crops can be beneficial. Insectary plants are those which attract beneficial predatory insects through pollens and nectars. Trap crops are crops planted in the vicinity of your crops that will attract the pests and thus keep them away from your crops. As opposed to conventional farming, agroecological systems rely on predatory beneficial insects to create beneficial insect allies (Wang and Uchida 2014).
Table 5: Beneficial plants (insectary plants) that attract natural enemies of pests (Source: Wang and Uchida 2014).
Insectary plants should be planted in advance, so that their flowering and attraction of beneficial insects coincides with the arrival of the pests. This will help to attract and maintain population densities of predatory insects or parasitoids(who feed on or lay eggs on the insect pests) that can help to reduce transmission of viral diseases from insects. Some criteria to select insectary plants are (Wang and Uchida 2014):
- Low potential to host plant virus diseases
- Attractiveness to beneficial insects
- Low potential to become a weed
- Low cost of seed and establishment
- Low attractiveness to pest species
- Early and long blooming period
Cover crops can also provide beneficial functions in your garden in relation to pests. Many studies conducted in the tropics have shown positive results of using cover crops to manage risks of disease transmission from viruses. Hence integration of cover crops provides many benefits to farmers such as enhancing various beneficial organisms like natural enemies of vector insects.Different approaches to integrate cover crops with cash crops include:sowing ground cover in orchards; planting border or barrier crops;inter-cropping living mulch plants (that you cut and leave in place as mulch) with cash crops; and planting trap crops to attract pests (Wang and Uchida 2014).
With these tips, hopefully you can enjoy more of the bounty from your garden!
This is the last of the Earth Day 2020 Community Garden Blog Series. Happy gardening!
Additional resources and bibliography:
Barberi, P. 2002. Weed Management in organic agriculture: are we addressing the right issues. Weed Research 42: 177 – 193.
Barzman, M., Barberi, P., Birch, N.E., Bonekamp, P., Dachbrodt-Saaydeh, S., Graf, B., Hommel, B., Jensen, J.E., Kiss, J., Kudsk, P., Lamichhane, J.R., Messean, A., Moonen, A.C., Ratnadss, A., Ricci, P., Sarah, J.C., and Sattin, M. 2015. Eight Principles of integrated pest management. Agronomy for Sustainable Development 35: 1199 – 1215.
Coleman, Eliot. 1995. The new organic grower: A master's manual of tools and techniques for the home and market gardener. Chelsea Green Publishing.
Crop Rotation – Guide (2020) | E-agrovision – https://www.eagrovision.com/crop-rotation/
Eat that Weed. Melbourne, Australia. 2019. The weed foragers handbook. URL: https://www.eatthatweed.com/
Grundy, A.C. and Bond, W. 2001. Nonchemical weed management in organic farming systems.Weed Research 41: 383 – 405.
Hemenway, T.2009. Gaia's garden: a guide to home-scale permaculture. Chelsea Green Publishing.
Kumar, V. 2016. Weed in tropics: problems and prospects. India: Tropical Forest Research Institute.
Liebman, M., and Dyck, E. 1993. Crop rotation and intercropping strategies for weed management. Ecological Applications 3 (1): 92 – 122.
Norris, R.F., Kogan, M., and Caswell-Chu, E. 2003. Concepts in integrated pest management. USA: Prentice Hall.
Weerarathne, L.V.Y., Marambe, B., and Chauhan, B.S. 2016. Does intercropping play a role in alleviating weed in cassava as a nonchemical tool of weed management. Crop Protection 95: 81 – 88.
Zehnder, G., Gurr, G.M., Kuhne, S., Wade, M.R., Wratten, S.D., and Wyss, E. 2007. Arthropod pest management in organic crops. Annual Review of Entomology 52: 57 – 80.
Statewide integrated pest management program. University of California Agriculture and Natural Resources. 2019. URL: http://ipm.ucanr.edu/PMG/weeds_intro.html.
Wang K.H. and Uchida J. 2014. Plant Disease Prevention and Management in Sustainable Agricultural Systems InSustainable Horticulture Systems.DOI: 10.1007/978-3-319-06904-3_16
Community Gardening Blogs
Each year CEU students and community members have the opportunity to participate in the Agroecology and Organic Gardening Systems (AOGS) course offered at the Department of Environmental Sciences and Policy. The course provides participants with a theoretical and practical introduction to agroecology and to organic farming techniques. Course participants are assisted in developing a comprehensive permaculture, agroecology and organic agriculture inspired plan for a garden which they could implement in a tangible location, while also coming up with their own ideas for gardening educational outreach materials which the students could help disseminate in the University community.
'Soil Degradation' (NSW Environment, Energy and Science, 2019) <https://www.environment.nsw.gov.au/topics/land-and-soil/soil-degradation> accessed 5 April 2020.
Coleman, Eliot. 1995. The new organic grower: A master's manual of tools and techniques for the home and market gardener. Chelsea Green Publishing, pp. 56 – 57.