How are your CLR management plans going?
Submitted by Education and Protection Committee, July 30, 2022
Last year the invasion of coffee leaf rust (CLR) was a surprise and added another element to management that was unwanted. There was an assortment of impacts experienced by Kona Coffee Farmers. Some farmers faced no ill effects while others had severe defoliation and tree death. It is difficult to pinpoint the variability between farms causing such an extreme range in responses to the infection. The KCFA Protection Committee was asked to assemble highlights of management practices that can influence the extent of CLR symptoms that occurs on farms in the Kona District. At the time of this writing, there is not a definitive Pest Management Plan available for farmers to use for sustainable production in the presence of CLR. Therefore, the concepts discussed here should be thought of as a menu outline that can be selected from for further exploration for application on your farm.
Hawaii was the last coffee growing location on the planet to develop CLR. Other regions have a head start and have already dedicated many resources to research developing remedies, assessing effectiveness, and fine-tuning management practices to modernize reactions to a CLR attack. The emphasis by the international coffee researchers and the global grower community seems to be the cultivation of CLR resistant varieties. While the time span needed for resistant varieties to be available to us is unclear (maybe 2 or 3 years), the Kona Coffee Industry will have the choice to replace susceptible trees currently in our orchards with locally tested resistant varieties. This transition will require present trees be replaced or grafted with resistant fruit stock. For most coffee growing regions of the world, this approach has been acceptable and popular although it required considerable resources and nonproductive time to complete the transition. Resistance to CLR in those new varieties is not complete but reduces susceptibility to the virus and has been used successfully in Africa and Central and South America (Filho, 2019).
In Kona deciding to replace Kona typica trees with another resistant variety may not be an easy decision. That is for the reason that in Kona, the grower’s business and marketing and stories are tied to Kona typica, a coffee variety we know is susceptible to CLR. If a resistant variety replaces Kona typica trees, then the grower’s story will change, the coffee will change and the assumption about our businesses will change too. Which leads to the question: Are coffees that are not Kona typica but grown in the Kona District still Kona coffee? Likewise, if a farmer chooses not to grow newly introduced resistant varieties but wants to manage CLR in their current Kona typica trees, what tools might be available to sustainably carry out that goal?
Conditions leading to CLR spread
Coffee leaf rust attacks the leaves of the plant, preventing them from photosynthesizing light into energy. As the disease progresses, the leaves fall off, as well as flowers or cherries. The result is a much reduced or destroyed harvest and sickly plants.
Environmental conditions favorable to coffee leaf rust are the same as coffee. Temperatures between 59 to 86°F and high humidity prompts spore sprouting. If you have thriving coffee plants, then you also have an ideal situation for coffee leaf rust. Knowing that, we are now aware that we will always have to contend with rust (Talhinhas, 2017).
A big obstacle in managing coffee leaf rust is how easily it disperses. Because the spores are small and light weight, they are effortlessly moved by wind and rain and attach to clothes and tools of workers and skin of animals. Alvaro Gaitan Ph.D. (Plant Pathologist from Cornell University), and the Head of Plant Pathology at Cenicafé, the National Center for Coffee Research in Colombia explains that as rain hits infected leaves, the spores are released into the air and easily transfer onto new plants. Rain paired with a wind is an extremely efficient delivery system for coffee leaf rust spores. In addition, when the tree is in fruit, it has partitioned more of its energy to fruit production, leaving less to fight a disease which then leads leading to increased vulnerability during this period of flower and cherry development.
Planned pathways. On many farms, there are different workers, family members, neighbors, and other visitors. Implementing bio-control measures attempting to restrict introduction of spores to a farm by limiting vehicles and other sources of CLR transportation CLR may be of use. It can be hard to control the way that people move through your farm and even more difficult to ensure that they follow defined paths and avoid brushing against plants. You might create paths through your farm which could be bordered with non-coffee trees to create a barrier. In addition, if you border a traveled road, you may also consider whether planting non-coffee borders to reduce risk to your coffee.
Health and nutrition. Coffee plants that are off color, weak, old, or already stressed by other diseases or pests are more predisposed to CLR. Keep your trees vigorous with timely soil heath practices, plant nutrition targeted methods and pest control. Balanced proportions of nitrogen (N) and potassium (K+) reduced the rust severity in coffee seedlings [Pérez et. al., 2019]. That work showed that increasing the dose of N caused a reduction in the disease severity, with even better results with at higher doses of K+. The effect of different doses of boron, zinc (Zn), and manganese on the severity of coffee leaf rust was evaluated by Pérez et al. in 2020. The three nutrients influenced the disease severity, with a distinct reduction seen with a dose of Zn. Consider soil and/or leaf analysis to pinpoint tree nutrition and to develop plans to remediate any deficiencies. If you find your trees lacking one or more nutrients, make extra efforts to regularly check and record nutrient status of young and old coffee plants.
Record-Keeping. You may want to keep records on first sightings of CLR and outbreaks every year that include time of year, extent of first leaf lesions and the weather conditions at the time first occurrence. This should help in understanding patterns associated with your farm and better prepare for future infections. In Central and South America, it has been reported that the infection rate varies by year and farmers may become complacent during years of minor infestation. When an aggressive infection gets started, it is not something new but needs to be addressed consistently. We can learn from these occurrences that we must pay attention to the weather conditions and understand and review our records after an infection lull as sometime in the future we may have another epidemic.
Importance of monitoring. Although it may be difficult to prevent infection, you can reduce harm by carefully monitoring your trees to anticipate management techniques to implement before uncontrollable infectious lesions are found. Research shows that timing and awareness of the weather are important in preventing spread. Remove leaves and hold them in the light so you can observe small spots that are a sign of an oncoming infection. Approximately two weeks after the infection of the leaf by the rust spores, the infection becomes obvious when you hold the leaves up into sunlight. The spots are formed due to the green pigment of the leaves disappearing and eventually turning yellow. These are the first symptoms of coffee leaf rust. After a development time, these chlorotic spots give rise to the first spores, and you can see the fungus on the underside of the leaf. Currently, there is no farm-based diagnostic method for detecting coffee leaf rust, so you must be on the farms every day inspecting the plants constantly to determine if you have an infection. You may want to be recording what you see. Your records can be written or photographic.
Pruning. Since high moisture conditions are very favorable for CLR growth and transmission, you may want to manage your trees to allow for high air flow between trees and to accommodate higher exposure of sunlight thru pruning. This strategy indicates that fewer leaders are kept after pruning. For example, rather than pruning for 3 to 5 leaders, prune so that only 2 to 3 are kept. Shorter intervals to reenter the orchard to remove suckers and ancillary leaders to minimize obstruction of air circulation and shading may contribute to prevention success. A highly infected tree can be severely pruned or stumped to minimize its potential role as a reservoir of CLR that can infect adjacent trees.
Chemical Agents. Chemical controls widely used around the world are based on the spray of a knock down agent, biological competitor and/or systemic fungicides on the foliage (Zambolim et al. 2005). Among knock down fungicides are copper-based and oxidases, (Zambolim et al. 2005b). The activity of these class of treatments is short lived but it kills the rust on contact when sprayed. Long term use of copper sprays should be used with caution since copper build up in the soil can lead to toxicity and sick trees. An example of a biological competitor is the product Serenade™. The active ingredient in Serenade ASO fungicide, Bacillus subtilis strain QST 713, is a beneficial soil bacterium (Serenade ASO Fungicide | Crop Science US – Bayer). These agents would be considered a preventative treatment to stop infection before it starts but would not be considered curative. Among trans-laminar fungicides, there are two that are available: Priaxor™ and Pro Blad Verde™. Both agents are absorbed into plant tissues to fight the fungal infection. These two products will reduce an already existing infection and their activity is comparatively long-lived for at least 2 weeks. It is recommended that these products be used in combination with others to minimize development of resistance to CLR. Hawaii does not currently have legal access to the true “systemic” fungicides found in other regions. These are currently under review by EPA but will likely not be released before 2024.
The control of coffee leaf rust is a combined management effort made up of cultural practices and chemical controls. With the benefit of planned management practices, farmers can create conditions unfavorable to CLR which should result in less or no reliance on chemical control. This outcome is compatible with most farmers’ management goals that promote coffee production while helping to protect the environment, support healthy for conditions plants and animals and the farm’s bottom line.
Filho, Elias de Melo Virginio and Carlos Astorga Domian. Prevention and control of coffee leaf rust. Handbook of best practices for extension agents and facilitators. 2019. © Tropical Agricultural Research and Higher Education Center (CATIE), 1st ed. ISBN: 978-9977-57-704- Costa Rica.
Pérez, C.D.P.; Pozza, E.A.; Pozza, A.A.A.; de Freitas, A.S.; Silva, M.G.; da Silva Gomes Guimarães, D. Impact of Nitrogen and Potassium on Coffee Rust. Eur. J. Plant Pathol. 2019, 155, 219–229.
Pérez, C.D.P.; Pozza, E.A.; Pozza, A.A.A.; Elmer, W.H.; Pereira, A.B.; da Guimarães, D.S.G.; Monteiro, A.C.A.; de Rezende, M.L.V. Boron, Zinc and Manganese Suppress Rust on Coffee Plants Grown in a Nutrient Solution. Eur. J. Plant Pathol. 2020, 156, 727–738
Talhinhas P, Batista D, Diniz I, Vieira A, Silva DN, Loureiro A, Tavares S, Pereira AP, Azinheira HG, Guerra-Guimarães L, Várzea V, Silva MDC. “The coffee leaf rust pathogen Hemileia vastatrix: one and a half centuries around the tropics.” (“The coffee leaf rust pathogen Hemileia vastatrix – PubMed Central (PMC)”) Mol Plant Pathol. 2017 Oct;18(8):1039-1051. doi: 10.1111/mpp.12512. Epub 2017 Jan 25. PMID: 27885775; PMCID: PMC6638270.