The enigma of Yakal disease

Shorea astylosa is generally referred to as yakal, a broad and somehow confusing denomination which encompasses diverse species. The tree appears in the Red List by the International Union for Nature Conservation (IUCN), which classified Shorea astylosa as Critically Endangered. 

Since the assessment by IUCN dates back to 1998, the situation might have worsened further. Actually, Shorea astylosa’s geographic range is limited, being endemic to the Philippines, where its habitat has all but disappeared. In fact, yakal trees are a species of the lowland dipterocarp forest, an ecosystem almost lost in the country. 

In an effort towards in situ conservation of a severely threatened species, we introduced yakals in Luntian Farm. Since August 2014 we have planted seventy trees of this species. However, the introduction of Shorea astylosa in the new habitat has showed mixed results. Albeit a few trees grew fairly well, mortality has been very high: out of seventy, 34 died (49%). 

The identification of factors that may impinge on the successful introduction of this species in habitats different from the lowland primary evergreen dipterocarp forest, where yakals used to grow, is essential to establish successful conservation models. We propose here three hypotheses on possible threats that our yakals may have faced in their new habitat, at the foot of the Sierra Madre range, where Luntian Farm is. 

Swamp buffalo (carabao) for land preparation

The domesticated water buffalo (Bubalus bubalis) is probably the most important draft animal in the world today: both in terms of numbers and for its economic contribution to Asian smallholder agriculture.

For centuries the carabao or kalabaw - as it is known in the Philippines - has been the backbone of rice farming, literally.

Modernization policies have often disregarded the carabao; or they have focused only on milk production. Yet, buffaloes aren’t a remnant of bygone agriculture; nor is the choice of turning these traditional draft animals of Asian smallholder farmers into cogs of dairy production systems always sustainable.

At Luntian Farm, we tried to explore the role of water buffalos in farming processes less dependent on fossil fuels. This would require better understanding of this resource, starting from better designed equipment.

White Lauan (Shorea contorta) trees in Luntian Farm

 

The video presents a profile of the White Lauan (Shorea contorta) trees in Luntian Farm: plant identification, and discussion of the challenges to the establishment of a healthy stand.

The White Lauan is a critically endangered species, endemic to the Philippines. Our attempt at introducing White Lauans in Luntian Farm underwent a few setbacks.

Mortality has been extremely high: 89% of the plants died. All the saplings acquired in 2014 withered and perished in the first 15 months. Out of 18 plants from a second batch in 2015, only 3 survived.

We reckon that most young trees died because of light stress. Most plants did not manage to harden and adjust to the conditions of a reforestation project, where light exposure is inevitably more than under the rain-forest thick canopy.

Windmill before and after repair

Our windmill stopped pumping between May and June 2017: the lack of this critical source of farm water was not particularly felt in Luntian Farm because 2017 was a quite wet year, and rain relatively abundant.

It proved however difficult to come up with a viable strategy to repair it. In November, we reached for Roman who lives in Gapan, the nearby municipality, but has roots in Lambakin. Roman has experience in windmills and recently built one in the province of Nueva Ecija.

In January 2018, after replacing shaft, lubricant case and pinion gear, the windmill wheel began pumping water again.

Replacing the windmill shaft

Roman explains here why a single piece windmill shaft that interlocks with the pinion gear at its end is a preferable option than a three-piece mechanism where the parts are joined by welding.

In order to improve performance Roman manufactured with a lathe (torniyo in Tagalog) a single-piece shaft whose head ends with a toothed head that engages the pinion gear (known sometimes as drive gear).

Avoiding welded joints Roman tries to prevent the shaft from wiggling, and progressively bending until complete failure of the pumping mechanism.

Roman highlights here that his solution is more expensive but potentially more durable.

Why the windmill shaft warped

The crew of farmers and workers who took the wheel down from the windmill examine now the problem that forced us to replace rotor’s shaft and pinion gear.

The issue lies squarely on the flawed connection of shaft, lubricant case and pinion gear. By welding three separate parts, relatively weak joints had been created: eventually, the fast rotation of the wheel warped the shaft.

Understanding the causes of this failure is essential to optimize windmill technology, which has been recently introduced in the village. Increased reliance on wind energy depends on its adaptation to the village context, and broader local know-how about construction, maintenance and repair.

Getting the fan off the windmill

The windmill tower is 50 feet tall. It carries the fan on its top: a multi-blade wheel sitting above the canopy formed by the crowns of old mango trees. Our fan has 20 blades – also known as “sails” – in galvanized iron (1.4mm gauge), and a diameter of almost 3.5 metres. The fan is attached to a shaft: the shaft rotates, as the fan revolves pushed by its ‘sails; and this motion turns a pinion gear inside a gearbox on the opposite side of the shaft. The uppermost tip of the rotating fan reaches a height of 55 feet.

Even with minimal wind, the fan and its 20 “sails” make up a very heavy frisbee.

To replace shaft and pinion gear we had no other option than getting the wheel off the tower. Not an easy job: it took eight people to take it down, dismounting the fan from its shaft above the tree crowns and descending it 55 feet below.

birth of a carabao

Riding a domestic swamp buffalo (kalabaw)

The complex and mysterious game behind the health of our trees

Pests are a contentious issue. Their fright and scare are biblical, no doubt. Yet the emotions their very appearance stirs have allowed the agro-chemical complex to introduce final solutions, whose impact on human health is ambiguous while their economic benefits for the farmers have proved elusive.

A stem borer

A common stance on pests situates them in a linear relationship between a cause – the pest -, and an effect, - the plant disease -. Pests cause diseases among trees, such as those in Luntian Farm, as well as annual crops, such as the rice we grew in the past and we intend to grow again. In the linear presentation of the problem, pests cause death of plants and loss of crops. Hence, the solution is just to remove the cause: kill the pest, the plant will thrive.

If we look at the stem borers burrowing through our cacao trees or digging into our marang (Artocarpus odoratissimus) saplings, we cannot but agree that here we have the agent behind a plant disease. Indeed we do

So why we didn’t cure it with powerful biocides? Is a green ideology blinding us to the harm inflicted by this “monster”?

Eulophonotus myrmeleon (cocoa stem borer)

Hard to say: ideologies and faiths play a role we cannot discount. Even in our own work in the farm. And, for sure, those stem borers have harmed the cacao.

But the cacao tree, even if heavily infested, did not die. So far it has resisted the invasion. 

Cacao tree (Theobroma cacao) resisting a stem borers' assault

Borers have exacted their toll from marang saplings, as well. They hollowed out completely the upper stems of a few marang’s – known sometimes as Johey Oak -, leaving just the lower trunks and their roots.  

This marang lost the whole upper stem to the borers

A few died. But several survived developing lateral stems.

A lateral stem has grown to replace the portion lost to the borers

Recovering marang tree

New shoots on a cashew

The causal relationship between pest and plant disease at least implicitly assumes a permanent and severe damage to the tree and its functions: generally its death. But this assumptions is hardly evident walking across the fields and working with trees and plants. On the contrary: trees have a large arrays of strategies to fend off malicious pests.

And, even under the fiercest attack, we should not take for granted the death of the plant.

The cashew in the pictures beside and below underwent a severe aggression by a major pathogen, a fungus (Lasiodiplodia theobromae) that generally leads to gummosis, a serious fruit tree disease. 

We thought the tree was bound to die, as the gummy patches had spread and the plant profusely discharged exudates from its wounds. It did not die, as these pictures show

 

Recovering from gummosis

So what? Are we here proposing an acquittal from murder for lack of consistent evidence?

Not really. The idea instead is to question the linear sequence pest-plant disease-death, and replace it with a model where pests interplay with many other factors in determining the health of a tree. The interplay among those factors explains why a marang might be killed by the borers and another not, why a cashew may succumb to gummosis while another survives. Soil, water, weather, tillage, harvesting practices and the tree’s own adjustment to its surroundings are all contributing factors, in the interplay that causes health and disease. Other living organisms, animals and plants that share the same space, are factors too.

Thus, there is no final solution: a biocide to kill off the individual, malevolent pest. Only strengthening the positive interplay among multiple agents, some obvious others not, we can treat the tree. This positive and complex synergy is probably a good way to present organic agriculture.