Research on coffee growing

Research on coffee growing

Coffee leaf rust: a complex disease

Coffee leaf rust in Bolivia. Photo by Neil Palmer (CIAT).

Coffee rust (Hemileia vastatrix) is fungus that is one of the most devastating coffee diseases in the world. Native to Africa, it is now present in every coffee-growing nation. Infected leaves drop off, weakening the plant. Copper-based fungicides can be effective against coffee rust. However, it must be on the leaf surface to prevent infection, and copper can build up in soils, eventually reaching toxic levels.

The spores of coffee rust are spread by wind or rain, and will only germinate when exposed to one to two days of continuous wetness. Usually humidity is not enough; rain provides the necessary conditions.  Latin America has suffered through more frequent and prolonged rainy periods in recent years as have parts of Asia, thought to be due to climate change. As a result, coffee rust has been having increasing detrimental effects on coffee production.

Aside from fungicide application, there are two lines of defense against coffee rust: planting resistant hybrids, and modifying cultivation methods.

When coffee rust first arrived in the New World, around 1970 in Brazil, nearly all coffee being grown commercially was genetically nearly identical and very susceptible to rust. Thus, the development of rust-resistant hybrids has been an important element in battling this disease. Rust fights back, of course; there are over 40 strains of coffee rust, some of which now attack previously-resistant hybrids.

Colombia has made a large investment in “renovating” the nation’s coffee farms by swapping out older coffee varieties with rust-resistant types. This has been accomplished on a third of Colombia’s coffee lands so far. Some of the resistant varieties include Castillo, Tabi, and Colombia. One thing they all have in common is parentage that includes Hibrido de Timor, which in itself is a natural hybrid between arabica coffee (Coffea arabica) and robusta coffee (C. canephora).

Reliance on selective breeding and fungicides have more or less dominated the fight against rust, because there is debate about which cultivation method, sun or shade, helps mitigate this disease. This is in large part because the various factors that influence the severity of coffee rust outbreaks can be influenced, sometimes dramatically, by microclimate. This makes farm-wide management decisions tricky. Some examples of the quandary:

  • In full sun, plants dry out faster, hindering the germination and spread of rust, and sun may kill the fungus. However, pores (stoma) on the surface of leaves open up at high levels of light intensity, allowing more frequent and deep penetration of rust spores that are present.
  • Coffee grown in sun (especially if generously fertilized, as is usually the case) produces heavy yields. This over-bearing stresses the plants and makes them more apt to succumb to rust and other diseases.
  • Shade increases the life of leaves and their size, so rust spores have more leaf area to colonize and time to be dispersed.
  • Coffee types that are less genetically resistant to rust show lower levels of infection at lower levels of light intensity.
  • Shade trees intercept raindrops in gentle rains, so spores are not dispersed. In heavier rains, however, larger drops of rain accumulate and splash on the coffee, releasing many spores.

One very interesting bit of research suggests that growing coffee under shade can facilitate complex ecological connections that help fight coffee rust in Latin America. Green coffee scale (Coccus viridus) is a small insect that has many hosts, including coffee (on which it is usually more of a nuisance than a pest). Like many scale insects, it has a mutalistic relationship with some species of ants. The ants feed on “honeydew,” a sweet substance exuded by the scale insects. In exchange, the ants defend the scale insects from predators.  Meanwhile, green coffee scale can be infected with a fungus (Lecanicillium [Cephalosporium] lecanii) …which also attacks coffee leaf rust. Researchers have found that where green coffee scales are protected by a particular common species of ant (Azteca instabilis) which nests primarily in the shade trees, the scale insects reach localized population levels that enable the Lecanicillium fungus to attack the coffee rust.

Although not conclusive, this study suggests that shade coffee systems may provide some level of biological control over coffee leaf rust, and in fact this ant-scale-fungi relationship may be one reason rust was not as devastating in the New World as it was in the Old World. (The ants, scales, and fungi are only part of this very complicated system, which also includes a decapitating fly, wasps, and a lady beetle; see Vandermeer et al. 2010 for more fascinating details.)

Avelino, J., Willocquet, L., & Savary, S. (2004). Effects of crop management patterns on coffee rust epidemics Plant Pathology, 53 (5), 541-547 DOI: 10.1111/j.1365-3059.2004.01067.x

Vandermeer, J., Perfecto, I., & Liere, H. (2009). Evidence for hyperparasitism of coffee rust (Hemileia vastatrix) by the entomogenous fungus, Lecanicillium lecanii, through a complex ecological web Plant Pathology, 58 (4), 636-641 DOI: 10.1111/j.1365-3059.2009.02067.x

Vandermeer, J., Perfecto, I., & Philpott, S. (2010). Ecological Complexity and Pest Control in Organic Coffee Production: Uncovering an Autonomous Ecosystem Service BioScience, 60 (7), 527-537.

Research on coffee growing

Research: Farmers, prices, and shade coffee

Why shade coffee does not guarantee biodiversity conservation. 2010. Tejada-Cruz, C., E. Silva-Rivera, J. R. Barton, and W. J. Sutherland. Ecology and Society 15: [online] http://www.ecologyandsociety.org/vol15/iss1/art13/.

The title of this paper should probably be “Does promoting shade coffee encourage forest conversion?” This question is perfectly legitimate, and has been debated in the literature before [1,2]. I’m not sure, due to methodological and other weaknesses, this paper adds a lot to this debate. It addresses, hypothetically, what coffee farmers might do if coffee prices increased, theoretically due to increased demand created by promotion of shade coffee to consumers.

The authors interviewed 57 coffee farmers inside and outside the buffer zone of El Triunfo Biosphere Reserve in Chiapas, Mexico. Farmers were chosen by the “snowball technique” in which one farmer refers the authors to the next person to be interviewed and so on, so a linkage is assumed between respondents. The authors did not address how this may have biased responses, e.g., shared attitudes regarding forest conservation, risk perception, or coffee production; mutual membership in cooperatives with an organizational slant towards particular farming methods; or similar economic pressures.

The salient question in the interviews for this paper was whether the farmers would convert forested areas on their property to “shade coffee” (not defined) if coffee prices increased. The authors did not specify in their interviews how much of an price increase or how long it would need to continue to influence farmer behavior.

About half of the respondents within the buffer zone said they would be likely to convert forest remnants into shade coffee if prices increased, while this figure was around a third for those outside the buffer zone (where less forest remained to be converted).

This might be instructive, but is missing critical elements. For example: even if the farmers wanted to convert forest, could they? The introduction states that this paper sheds light on “how small-scale coffee growers make decisions on land use when confronted with the choice to switch from conventional to eco-friendly’ labeled coffee.” The authors did not make this explicit in the Methods or survey questions, but given the context of the paper, “eco-friendly labeled coffee” presumably means certified by some agency with environmental standards.

All “eco-friendly” certifying agencies have restrictions on clearing of forest or cultivation in forested areas in their standards, a fact noted in the introduction of the paper. This includes one of the major coffee purchasers in the area, Starbucks. Their C.A.F.E. Practices is not a certification, but a sourcing guideline. One of their mandatory requirements is that there is no conversion of natural forest to agricultural production. Non-compliance would make it difficult if not impossible to become a Starbucks supplier. If farmers were unable to gain “eco-friendly” certification or status, they would be unable to access the increased prices being offered, and the question becomes, in practice, a moot point.

The authors acknowledge conversion is generally not allowed, but that they observed conversion occurring anyway. The circumstances and details were not explained, and it’s unclear from this paper what was going on — whether these farmers were doing so outside a certification system, if they were just not being audited, etc. Without more facts, it’s difficult to ascertain the extent of the problem and what would remedy it.

Within the buffer zone of the reserve, only certain activities are permitted [3]. This includes organic coffee production (which typically requires at least some shade) but not “traditional coffee production” except under certain conditions. It’s worth noting that if coffee prices fell or remained stagnant, farmers might turn to other permitted activities which might not be so eco-friendly, including palm cultivation, organic corn, or cattle management. Some discussion of this would have been helpful in the paper.

The authors report that, according to the farmers interviewed, there has been an increase in the cultivation area, “allegedly at the expense of forest,” although there is no external corroboration.  An accompanying figure graphs the increase in acreage in coffee and decrease in forest patches based on the farmers’ answers; the decade covered was 1991-2001. There is no correlation with coffee prices to provide a link to the theme of the paper. That decade, in fact, was the run-up and commencement of the world coffee crisis, one of (if not the) most volatile periods in modern coffee history. Prices went from a high of nearly $3.00/lb in the mid-1990s to a low of less than $0.50/lb in 2001.

The paper states that there was a “steady increase in cultivation area” for this period, which seems unlikely — when prices began to fall after the peak, many farmers didn’t continue to expand their plots, they abandoned them. Perhaps the 2001 end-point was too soon to reflect this. If these interviews were really done around 2001 (the date is not given), when prices were at 30-year lows and farmers were literally starving, it’s hard to imagine farmers not saying they’d convert forest for higher prices. Is this really indicative of what farmer would do in a more stable market? One of the major lessons learned from the coffee crisis is that prices drop when there is an oversupply and this type of overplanting is generally now discouraged.

Without some discussion of what actually happened in this area during this period to these farmers, using this graph as support for the argument that they will convert forest to coffee during an increase in prices makes little sense. There was a follow up question on the survey asking farmers to explain why they would or would not convert their forest to shade coffee. That would surely shed some light on their motivations and experiences, but it was not discussed in the paper.

Some of the discussion surrounding the theme in this paper is worthwhile. But the title of this paper makes quite a definitive negative statement. It is no doubt true under various circumstances,  but the facts in the paper don’t quite back up the claim. Shade coffee, grown under diverse shade — especially when organic and certified using strong, verified standards — is still one of the most environmentally-friendly agricultural alternatives for biodiversity conservation available.

[1] Philpott, S. and T. Dietsch. 2003. Coffee and conservation: A global context and the value of farmer involvement. Conservation Biology 117(6):1844-1846.

[2] Rappole, J. H., D. I. King, and J. H. Vega Rivera. 2003. Coffee and conservation. Conservation Biology 17:334-336.

[3] Castro Hernandez, J. C., R. Hernandez Janapa, S. Nanuez Jimenez, S.R. Rodriquez Alcazar, C. Tejeda Cruz, A. Vazquez Vazquez, K. Batchelder, A.Z. Maldonado Fonseca. 2003. Community-based Conservation Participatory Conservation in Buffer Zone Communities in the Natural Protected Areas of Chiapas, Mexico. The Nature Conservancy, Arlington, VA. 65. pp.

C. Tejada-Cruz, E. Silva-Rivera, J. R. Barton, & W. J. Sutherland (2010). Why shade coffee does not guarantee biodiversity conservation Ecology and Society, 15 (1)

Coffee and the environment / Research on coffee growing

Research: Shade coffee conserves bee diversity

Impacts of coffee agroforestry management on tropical bee communities. 2010. Jha, S. and J. H. Vandermeer. Biological Conservation 143:1423-1431.

Most people are aware of the importance of bees and other pollinators to functioning ecosystems and agriculture. This study took place in Sococusco, Chiapas, Mexico, and looked at what habitat variables were most important to the abundance and diversity of insect pollinators (bees, in this case). It looked at a number of variables — number of tree species, how many were in flower, canopy cover, etc. — and how important they were at different scales (100 m, 500 m, and 1 km). The study took place in small forest fragments and many small shade coffee farms (13 to 70% shade).

Researchers trapped 46 different bee species in these sites, including both social and solitary bees, and cavity-, wood-, and ground-nesting species. They found that habitat management on farms was more predictive of bee abundance than the forest cover in the surrounding landscape at all the three scales. On these farms, tree diversity — the number of tree species — was the best predictor of bee abundance and diversity. The number of tree species flowering and canopy cover were next.

These results are different than many other similar studies. Often, biodiversity in agricultural areas is dependent on the quality and extent of the surrounding landscape, which acts as a source and provides resources for fauna found on farms. Two factors could be influencing the results of the current study. First, this shade coffee region has farms with high structural diversity, and
low regional forest cover, so resources may be more available on farms
than in forests. Second, bee communities in the study area are small-bodied and thus have shorter foraging ranges. They may react more strongly to local resources.

This study indicates that coffee farmers in Chiapas — and in similar landscapes — can attract pollinators and bolster biodiversity by using diverse shade tree species, allowing trees to mature, creating
light gaps, and creating patches of flowering herbaceous plants. Farmers will also benefit from the ecosystem services provided by the bees which will pollinate supplementary crops on the farm in addition to promoting cross-pollination of their coffee (which improves yield).

The authors conclude that coffee farmers don’t need to rely just on the presence of landscape-level forests to provide pollinator resources. They note, “…most coffee cultivators can only implement land-use changes within their own farms… Our study indicates that local habitat factors, managed within agroforestry systems, can have strong impacts on local bee abundance and diversity.”

Augochlora bee, one of the common genera found in this study, by graftedno1 under a Creative Commons license.

Jha, S., & Vandermeer, J. (2010). Impacts of coffee agroforestry management on tropical bee communities Biological Conservation, 143 (6), 1423-1431 DOI: 10.1016/j.biocon.2010.03.017

Birds and other biodiversity / Research on coffee growing

Research: Birds reduce coffee pests in Jamaica, take 2

Pest reduction services by birds in shade and sun coffee in Jamaica. 2010. Johnson, M. D., J. L. Kellermann, and A. M. Stercho. Animal Conservation 13:140-147.

Matt Johnson’s team from Humboldt State University (CA) continues its excellent research on birds and ecosystem services on coffee farms in Jamaica. This study, similar to others, looked at pest reduction on a 18 ha farm, Kew Park Coffee. This farm is about 70% shaded; the other 30% has shade trees too young to provide shade yet. The farm also has one side bordered by dense second growth forest.

Exclosures were placed on some coffee trees to prevent birds (but not insects) from accessing them, and the number of insects on these and control trees were examined. The authors found that on trees where birds had access, there was a 40 to 58% reduction in the coffee berry borer (CBB), or broca (Hypothenemus hampei), the world’s most serious coffee pest.

The most common means of controlling CBB are the nasty pesticide endosulfan (although some are developing resistance), or scent traps. Traps are most effective when female CBBs leave coffee cherries to lay eggs in other cherries; the birds in these studies usually attacked the CBBs as they were entering new cherries. Thus, the birds can provide an extra layer of control even on farms that use traps. The authors determined that the pest reduction by the birds on this small farm amounted to 12% of the value of the crop.

This study did not find that birds were more effective at controlling pests in shade than in sun, but it may have been due to the small size of the farm and the proximity of adjacent forested area. A previous study on four different Jamaican farms by some of the same researchers found that the birds consuming CBBs declined dramatically in abundance as distance from forest patches increased. Birds may have made use of the unshaded portions of the farm in the current study because of the amount of forest and shaded coffee surrounding it. I saw a presentation by another member of this research team at a recent ornithological conference that indicated some of the bird species in question foraged in coffee during the day, but retreated to forest patches to roost at night.

Bird species found in the shaded portion of the farm in good numbers, but not at all in the sun portions, included the national bird of Jamaica, the Red-billed Streamertail (Trochilus polytmus), a hummingbird also known as “Doctorbird”, shown above); another resident hummingbird, the Jamaican Mango (Anthracothorax mango); and the North American migrants the Black-and-white Warbler (Mniotilta varia) and Prairie Warbler (Dendroica discolor), which winter on the island.

Johnson, M., Kellermann, J., & Stercho, A. (2010). Pest reduction services by birds in shade and sun coffee in Jamaica Animal Conservation, 13 (2), 140-147 DOI: 10.1111/j.1469-1795.2009.00310.x