of the rust.
The central puzzle was, as it had been with Morris, to determine the full life cycle of H. vastatrix. The phases internal to the coffee leaf were, by that point, reasonably well understood, but the phases external to the leaf had still not been settled. Morris had argued that the fungus’s life cycle included an external phase in which the fungus covered the surface of the coffee plants in a microscopic mycelial web for several months. Ward quickly cast doubt on Morris’s model. He collected samples of these mycelial threads in the field and studied them under a microscope. He concluded that these filaments were produced by four species of fungi, none of which bore any relation to H. vastatrix.57 Furthermore, none of these external mycelia connected with the internal mycelia that were definitely H. vastatrix. Based on this, Ward discarded Morris’s model and the control methods on which it was based.
To clarify the rust’s life cycle, Ward conducted experiments on living plants under tightly controlled conditions. He collected rust spores from a lesion on an infected leaf. He then placed them in droplets of water on the leaf of a healthy coffee plant housed in a Wardian case. This glass case reduced the risk that the plant could be contaminated by other fungi. He found that the spores germinated in as little as twelve hours after contact with water, and the mycelium started forming inside the leaf two or three days after that. Within two weeks, this mycelium would produce a lesion visible to the naked eye. Roughly a week after that point—three weeks after the initial infection—the lesion would start producing and releasing new spores. Under ideal conditions, the lesion could continue producing spores for five to six weeks.58 He calculated that a single lesion, produced by a single spore, could produce 150,000 new spores at a time. And a badly infected leaf could contain many lesions, which could cause the leaves to drop prematurely. Each individual spore thus carried the potential to cause tremendous damage.59 As Darwin had done on a much larger scale, Ward demonstrated the tremendous cumulative power of small biological events.
Ward’s field research shed new light on the rust’s ecology. He showed how all the seemingly mysterious phenomena of the disease could be explained by the fungus’s life cycle. To determine how the spores spread in the field, he placed sterile glass slides in various parts of the farm, on the ground and attached to trees. In a single water droplet collected this way, he found spores of fifty-one species of fungi (including H. vastatrix). His experiments with slides suggested that spores could travel up to 50 feet in a single journey. He carried out other experiments that showed how outbreaks of the rust were connected to wind and rain patterns. He had placed potted coffee trees around the veranda of his house and noted that “the plants placed on the side of the house more exposed to the wind suffered more than those that had been sheltered”60 Extending these observations to the coffee estates, he argued that “a sudden appearance of the disease is closely connected with the wind and this connection is of exactly the same nature as what we should expect if the wind blows spores about.”61 Similarly, the veranda experiment showed that water was also important to the development of the disease: plants “placed on the edges of the verandah, and kept wetter on the whole (from drip, driving rain, etc) appeared to become more diseased than the sheltered ones,” an observation that he later confirmed experimentally using coffee plants in Wardian cases.62
Using the pathogenic model of disease, Ward explained the patterns of rust outbreaks in Ceylon. He described a field that had been apparently free of the rust in April but was badly infected by June. Using temperature and rainfall records, Ward showed how rains in mid-May would have caused spores across the farm to start germinating. As expected, the first lesions in the field were observed two weeks after the rain. Ward’s report discussed a number of real-life examples, showing how each outbreak could be explained mainly in terms of how wind and water shaped the fungus’s dispersal and development. He argued that the connection between the fungus and its conditions of existence “were no more mysterious than that between the life of any organism and its environment: sow the spores of Hemileia on a proper nidus, and give them air, water, and warmth, and they germinate and flourish as do the seeds of coffee or an similar plant in damp, warm, aerated soil.”63
Based on this, Ward’s recommendations for rust control differed from the ones Morris had made. Ward argued that chemical control would only be effective under limited circumstances. The fungus was only vulnerable during the few hours after it had germinated but before it had penetrated the leaf tissues. To control the rust, then, the chemical had to be applied before the spores germinated. It needed to coat the leaf and stick to it. It had to be soluble so that it could be sprayed, yet it also had stick to the leaf during the heavy monsoon rains. It would need to be toxic to the fungus but not to the coffee plant or the soil. These stringent criteria eliminated most of the chemicals that planters had been trying. Ward enlisted a number of eminent planters in a series of spraying experiments, using various measures (weight of leaves and fruit produced) to assess how farms treated with chemicals fared in comparison to untreated farms. At the time, only sulfur compounds and particularly sulfur of lime met the criteria. In fact, planters found that the lime also acted as a manure, improving the life of the tree. Ward struggled to quantify the amount of benefit that applications of sulfur would give, but most experiments suggested that it offered planters at least some benefit if it was applied at the right time.64
Ward argued that the rust could best be controlled through preventive measures. “The problem of combating this disease,” he argued, “is not a mere matter of quantity of chemicals and their efficacy in killing the fungus, but also in maintaining the strength of the tree and preventing reinfection.”65 Like some planters, Ward called for the careful cultivation of coffee—judicious pruning and manuring as well as the systematic elimination of infected leaves and trees. A few years before, planters had argued that manuring actually cured the rust. Ward argued that it did not; in fact, paradoxically, “of every basket of manure placed at the foot of the tree, a certain proportion must be looked upon as serving the mycelium of Hemileia for food.”66 Even so, careful manuring was still worthwhile because it would help the trees produce their leaves sooner and retain them longer, allowing the fruit and branches to develop more fully, which would mitigate the rust’s effects. Outbreaks could also be controlled by planting windbreaks that would slow the dispersal of spores.
Ward’s research was a scientific success, but it was a practical failure—at least as far as Ceylon’s planters were concerned. The planters accepted the basic premise of fungal pathogenicity and Ward’s account of the epidemic; most quietly abandoned their earlier models of disease. But from their perspective, Ward had failed to accomplish his main purpose: he did not offer them any tools to effectively manage the rust. He had shown them why most of their treatments would not work, but he had given little guidance as to what would. So the planters continued to innovate on their own. “We have now,” wrote the planter G. A. Talbot, “all that can be taught us by scientific men about Hemileia, and it is for practical planters, in working their coffee, to study the disease. I must say, I think there is a good deal to be found out yet.”67
In 1880, the planters of Ceylon founded a horticultural journal, the Tropical Agriculturist, that published reports summaries of horticultural research as well as reports from European planters across the tropics. In this sense, the Tropical Agriculturist was a tropical version of The Gardeners’ Chronicle, which published horticultural pieces from both professionals and amateurs.68 In the field, some planters continued to experiment with new methods of controlling the disease. One of the most widely reported of these involved the experiments of a planter named Eugene Schrottky who developed what he described as a “vaporization” technique that involved covering his coffee plants with a powder containing carbolic acid. In the local press, however, coffee planters argued heatedly about whether or not Schrottky’s method did much to control the disease. In the end, it was never adopted on a large scale.69
