Black coffee twig borer, Xylosandrus compactus (Eichhoff) on robusta coffee in Uganda

The Black Coffee Twig Borer (BCTB), (Xylosandrus compactus (Eichhoff)) is a devastating pest on robusta coffee in Uganda. The coffee in Uganda grows mostly in agroforestry systems where trees and crops are combined and interact with each other. Farmers believe they have to cut down other trees in order to reduce the problem of the BCTB, because they think the trees increase the risk of receiving the pest on their farm. This is against the vision of Vi Agroforestry, who plant and preserve trees in order to increase stability within the farming systems. This study investigated if abundance of the BCTB increases with increased amount of shade on robusta coffee. Another aim of the study was to investigate if the knowledge level and opinion about BCTB and shade for coffee, vary between farmers, officers and researchers. The study was mostly conducted in Kalungu and in Bukomansimbi districts in the central region of Uganda. This included the observational field study as well as interviews with the farmers and officers working in these districts. Other interviews with researchers and officers working with the whole country were conducted in the surroundings of the capital, Kampala. We measured amount of shade in relation to degree of infestation by the BCTB by counting their entrance/exit holes on coffee trees in each farmer’s coffee plantation. The opinions and knowledge between the three groups of people (farmers, officers and researchers) differed in some questions. One question that resulted in various answers, especially among the officers and researchers, was if shaded or sun-exposed coffee is most affected by the BCTB. Most of the farmers said it is the shaded coffee that is most affected by the BCTB. Our observational study showed a significant (P<0.05) increase of infestation by the BCTB between two categories of shade, from 0-20 % to 41-60 % shade. The increase of infestation was close to significant (p=0.075) also between two other shade categories 0-20 % and 61-80 % shade. The shade by trees may not be the only reason for more infestation close to other trees, since they can be alternative host trees for the BCTB. However, there were different opinions among farmers, officers and researchers about possible host trees and this disagreement can be explained by a lack of research or that new information has not reached out. There is literature supporting that A. chinensis is a host for BCTB, but no such evidence is found for F. natalensis. These findings are interesting for future design of coffee agroforestry systems, but still more research is needed to be able to take the right measurements when it comes to BCTB, shade and effects of possible host trees intercropped with coffee. The interview results indicate that officers need more training so that they can provide consistent and relevant advice regarding shade. An interesting approach for further research would be to investigate if there is a host tree that is more attractive than coffee and thus could work as an attractant (trap crop) for BCTB. The infested twigs of this host tree could then be harvested and used as cooking fuel. As an extension of our study it would be interesting to sample more coffee trees within the three higher shade categories (41-60 %, 61-80 % and 81-100 %), to see if there is a significant increase of BCTB even for these higher shade categories.