3. Pests and Pest management

Plantations in West Africa have several pests and diseases that are prone to affect the Cocoa plants.
Two insects that affect the cocoa trees very often are Mirids (Distantiella theobrama or Sahlbergella singularis) and so called stink bugs (Bathycoelia thalassina).

Figure 1: Mirid

Figure 2: Stink bug

Figure 3: Damage after punctures

An infestation with either of these two insects has severe consequences for the trees. They feed and inject their saliva into the plant leaves. The resulting punctures in the plant tissue make it possible for fungal pathogens to enter. This so-called "secondary invasion" results in dieback disease. Additionally, stink bugs causes premature ripening and also often deformations of the cocoa fruits.

The main pest management practice against Mirids is the application of insecticides. Stink bugs can also be controlled through this indirectly.
There has been very little research on breeding cocoa varities that are resistant against those two pests.

Starting in 1940, insecticides like endrin, heptachlor, lindane and dieldrin were sprayed on the cocoa plantations in West Africa. However, the insecticides were not used in the correct manner. Either they were sprayed prophylatically or when it was already too late and the plants were infected.
Since 2000, major developments have been introduced to the pest control of cocoa trees. There has been a lot of research and monitoring of the two most important pests, mirids and stink bugs. Additionally, the concerns about protecting the natural environment and the wildlife became more influential in pest management.
Major issues in the spraying of insecticides are that pest populations are very hard to predict, therefore it is difficult to say when thy have to be applied. Secondly, most farmers do not have the ability to spray large areas at short notice. That means it could already be too late for the application of insecticides.
Another very important concern when sprayng insecticides are the effects on the natural environment and animals .
Lastly, most of the farmers are smallholder farmers that simply cannot afford the chemicals or the needed equipment for a safe spraying of insecticides.

Another possible pest management practice is the use of aggregation pheromones. They are hormones which effect and confuse the insects in their mating behaviour. However, this method is not very established yet and needs further research.

Clearly, the pest management sector in West Africa still needs to develop further. More research about alternative practices such as pruning, agro-forestry, etc. has to be implemented. Furthermore, breeding and finding resistant cocoa varieties have to be emphasized.

Well-planned integrated pest management would include the use of resistant varieties, pheromones, alternative cultural practices and the use of chemicals when necessary. As already mentioned, this sector needs more research in order to establish best management practices for the crops, the people, as well as the natural environment.

References

Dropdata. (n.d.). The World's Worst Cocoa Problems. Retrieved 09 2018, from http://www.dropdata.org/cocoa/cocoa_prob.htm

Richard Adu-Acheampong1*, J. E. (2015). Strategy for Insect Pest Control in Cocoa. American Journal of Experimental Agriculture. Retrieved 09 2018

Skillman, V. (2016). Damage caused by Mirids. Retrieved 09 2018, from http://skillmav.wixsite.com/cocoapest/damage

pictures:

Figure 1: http://skillmav.wixsite.com/cocoapest/general-description

Figure 2: http://www.dropdata.org/cocoa/cocoa_prob.htm

Figure 3: http://gsbpestcontrol.com/img/cms/stink-bug.jpg

2. Cocoa Production Stages and Plant Development

Theobroma Cacao is a C3-plant like the vast majority of plants.
 It is classified as a perennial tree crop that can grow up to 8-12 metres. Cocoa trees prefer a humid and hot climate. That is the reason why they grow best in countries near the equator. In fact, the region between 0 and 20 degrees south and north of the equator is also referred to as the "Cocoa Belt".
Cocoa likes to be grown along with other tropical forest plants. This means it is not a typical plant that is cultivated in monocultures, but rather in biologically diverse environments.

Stages of Crop Development:

Figure 1

Cocoa trees are planted by either sowing the seeds that have been extracted from the pods or by planting grafted plants.
10-18 months after planting, the stem of the Cocoa tree grows up to a height of about 1-1,5 metres. Then it curls into a whorl of 3-4 horizontal branches and one or more vertical shoots, also referred to as suckers. The suckers initiated the next phase in growth of the plant.
Flowers grow between 18 months and three years after planting, depending on the variety. The flowers grow at the bottom of the tree or on thick branches throughout the whole year. However, flowering increases druing the rainy season which lasts from the beginning of April and reaches its peak in July. One tree can have up to 50 000-100 000 flowers every year, but only 6% of the growers are naturally pollinated. That means that often, gowers have to assist this process manually. If pollination was successful, the pods start to develop and take up to 6 months to mature. Fruit production starts April and is highest in August.What is unusual about the cocoa plant is that it can have flowers and fruits at the same time at different stages of maturity.

Figure 2

A tree bears around 20-30 pods annually.  The color of the cocoa pods indicates the stage of maturity. It either changes from green to yellow in the case of a Forastero plant or from yellow to red in the case of Criollo plants.







Is flowering affected by photoperiod?

Daylength in tropical regions where cocoa is mostly grown is about the same throught the year. This and the fact that flowering increases during the rainy season, indicates that the flower production of the cocoa plant is dependend on the stimulus of water rather than the photoperiod. (= the period of time each day during which an organism receives illumination; day length)

References

Adjaloo, M. K., Oduro, W., & Banful, B. (2012). Floral Phenology of Upper Amazon Cocoa Trees: Implications for Reproduction and Productivity of Cocoa. Retrieved 09 2018, from https://www.hindawi.com/journals/isrn/2012/461674/

Pohlan, H. A., & Perez , V. D. (n.d.). GROWTH AND PRODUCTION OF CACAO. Retrieved 09 2018

Ritter Sport. (2018). Ritter Sport GmbH. Retrieved 09 2018, from The Cocoa Tree: https://www.ritter-sport.de/en/cultivation_preparation/Cultivation-preparation-The-cacao-tree-RITTER-SPORT/

Tamil Nadu Agricultural University. (2013). Cocoa (Theobroma cacao L.). Retrieved 09 2018, from TNAU Agritech Portal: http://agritech.tnau.ac.in/horticulture/horti_plantation%20crops_cocoa.html

 Pictures:

Figure 1: https://onthecocoatrail.files.wordpress.com/2012/09/s1500037.jpg

Figure 2: https://www.edenproject.com/sites/default/files/styles/image_carousel_full/public/image-carousel/theobroma-cacao-trunk-2.jpg?itok=3-vhslDI&c=ab024485c7c9b3493b62ace8588e266c