Community Gardening Blog 3. The Nitty Gritty: Basics of Crop Rotation, Weed and Pest Management

Table 1: Sample Three Year Crop Rotation (Source: https://www.rhs.org.uk/advice/profile?PID=124)

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)

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

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)

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) 

Pests

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)

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).

The good news is that you can include beneficial plants even on your balcony or in your backyard garden. See here and here for more information on companion planting recommendations for your garden.

With these tips, hopefully you can enjoy more of the bounty from your garden!

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This is the last of the Earth Day 2020 Community Garden Blog Series. Happy gardening!

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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.