Pineapple diseases in Kasese and the preventive measurements
Research done by Veerle Serlet
Veerle Serlet is a Masters student in Bio Science within the Tropical Agriculture department of the University College Gent in Belgium. She has concluded this research on pineapple diseases within KIIMA Foods, Kasese.
The pineapplefarmers at the Kasese-district who are supported by Kiima Foods have obviously big harvest losses. This losses are different in the three visited area: KUWA and KWC have almost the same losses, the group KWDA from Kinyamaseke has the lowest loss.
Research on the field and microscopical research gave the same result: the fungus Phytophthora cinnamomi is attacking the pineapple plants who are wilting. The symptoms that Rohrbach et al. (2003) describes (chlorose of the heartleaves, wilting of the oldest leaves, curling downwards of the top of the leaves, the leaves that are becoming red and then finally the leaves, the bases of the leave and the stem that rot) could also be seen in the fields at the Kasese-district.
Also mealybugs could often be seen on pineapple plants that are wilting. Typically on these plants were dark green spots at the leaves, especially on the heart leaves. The mealybugs are living at the heart of the plant and often at the bottom of the leaves. At the pineapple plant can live two species of mealybugs: Dysmicoccus brevipes and Dysmicoccus neobrevipes. D. brevipes lives mostly at the bottom of the plant, and D. neobrevipes at the top.
The pathogens Phytophthora cinnamomi and the mealybugs cause wilting of the plant and could be seen together on the same plant. A relationship between these two pathogens could not be found in literature.
Phytophthora cinnamomi is a fungus who is living in the soil and easily spreads itself with the use of water. The three villages that are visited in the Kasese-district receive in August till November a lot of rain, so the fungus can be spread easily with the big amount of water. The maximum temperature for the development of mealybugs is 31 °C.
A big amount of organic material can slow down the rot of the roots. Therefore a possible solution against the rot of the roots is using animal manure, such as chicken and goats manure.
Research of Sether et al. (2002) showed that the PMWaV-2, transported by the mealybugs, is spread easily between the rows and plants, but not between the beds. In the Kasese-district there was a bigger harvest loss when the distance between the plants was less than 45 cm. Sether et al. (2002) suggested the closer the plants, the more affected they are.
So the farmers have to plant the suckers at a certain distance, as far as necessary, to avoid the spread of the fungus. In general the distances are the following: 25-30 cm between the plants, 60 cm between the rows and 75-90 cm between the beds (Scohier et al., 2001).
Most of the farmers at the Kasese-district could not tell which variety they were growing. Smooth Cayenne is a variety that is very sensitive to the fungus P. cinnamomi, as the variety Queen is more resistant. Also Red Spanish has a certain resistance, especially against the mealybugs. Pernambuco is a cultivar resistant to rot of heart and roots. So the best varieties for the farmers are Red Spanish and Pernambuco.
It is very important to know the condition of the original field (where the pineapple suckers come from). The wilt can easily be spread by using attacked suckers. In the Kasese-district it seems that Kinjamaseke has healthy pineapple suckers, so this village could be an ideal place to buy suckers. The place of buying the suckers could be a possible explanation of the differences in harvest losses between the group KWDA from Kinjamaseke and the two other groups KUWA and KWC.
The use of pineapple suckers of the farmers field itself (of adult plants) could also play a role in the spread of the disease. Before using the suckers it is important to control the presence of mealybugs. It is recommended not to use suckers of plants that are growing slowly or growing next to affected plants.
Lots of farmers are not weeding enough at their fields, and old and affected plants are staying too long between the young and healthy plants. It is not enough to take the old and/or affected plants away and lay them down at the edge of the field, because the virus that is spread by the mealybugs is staying alive for a certain time inside the “dead” plant. Therefore it is better to burn the plants that are not needed anymore. Don’t use pineapple leaves as mulch, it can be the cause of spreading the disease.
P. cinnamomi is a fungus that stays for some years alive at the soil, so rotation can not always give a solution, except if farmers decide to wait long enough (for years) before cultivating again pineapples at the same field.
P. cinnamomi needs water to be spread, but also stress-situations as extremely drought or wet soils can make the plant more sensitive. By the use of irrigation it is important that the water can not run freely, to avoid the spread of the disease. The farmers can make some holes where the water can stay in.
As the farmers has to cultivate the pineapples on an organic way, it is impossible to use chemicals. Therefore the use of the wasp Anagyrus ananatis can be used. It is important to be aware of the food the wasp needs.
The fact that pineapple plants are wilting and mostly also dying before fruiting is not only a problem in the Kasese-district. All over the world where pineapples are cultivated it has been mentioned. There has been already lots of studies about it, but it is not such an easy case. Researchers and farmers are trying to find out what kind of disease is killing the plants.
As I compared the symptoms I have seen at the fields in the Kasese-district with these described in papers and books, and also after the microscopical research in Kampala and Belgium, I could conclude that there are two pathogens: the fungus Phytophthora cinnamomi and the mealybugs Dysmicoccus brevipes and Dysmicoccus neobrevipes.
Lots of researchers all over the world has tried to kill this two pathogens. For the farmers at the Kasese-district I can propose the following organic measures:
- A first very important preventive measure is the use of healthy suckers. The use of crowns, slips or suckers from affected plants should be avoided. I could conclude that at the Kasese-district lots of affected plants were bought at the same place. It is important to inform yourself if the fields of the suppliers are healthy. I would like to mention that the farmergroup KWDA from Kinjamaseke has the lowest harvest losses, so probably they are receiving healthier suckers than the other groups.
- Cultivating resistant varieties is also a preventive measure against the wilt. The cultivar Red Spanish is likely resistant to mealybugs, and the variety Pernambuco is resistant to heart- and rootrot (Phytophthora).
- One of the most important measures is to plant the suckers on beds. If an affected plant grows on a bed and it is raining, the water is running of the bed and can’t touch another plant, because the other plant also grows on a bed. As the fungus P. cinnamomi is spread by water, this is a very important preventive measure.
- The distance between the plants is very important. It is not good to place them too cloose to eachother, because than the mealybugs can go easily from one plant to another and so transport the virus (mealybugs are the vector of a virus). If the plants are too cloose it is also more easy for the fungus Phytophthora cinnamomi to be spread, for example by the water when it is raining. In general the distances are the following: 25-30 cm between the plants, 60 cm between the rows and 75-90 cm between the beds.
- Look after your field is also very important: weeding between the plants can be a preventive measure against the survival of mealybugs, because some weeds are food for the mealybugs too.
- Affected and old plants should be taken away from the field. They must not been used as mulch, as they can help to transport the virus (it is proved that the virus is still alive for some days in the dead material of pineapple plants). Affected plants should be taken immediately out of the field and be burned or buried.
- Rotation can be a solution to destroy P. cinnamomi, if the farmer decide for not cultivating pineapples for a long time at the same field. The fungus can survive for a long period inside the soil, and can attack again after some years.
- If irrigation is used, farmers should take care of running off water: it is not good that the water can flow easily from one part of the field to another, because the fungus is spread by water. So if an irrigation canal is made, it would be good to construct also some little beds crossing the canal, so that the water can’t run off.
- Take care of transporting machines and tools from one field to another, because the fungus P. cinnamomi can be spread by affected soil.
- As mealybugs are living together with ants, it is an advice to kill the ants. Ants can be tempted by using a mixture of maize and soya beans, or creamed milk with pollards or flour. If the ants are killed, about 75% of the mealybugs will die too, because they need the ants to survive.
- Using an extract of the neemtree (Azadirachta indica) could destroy the mealybugs. The oil should be mixed with water in an proportion of 2 to 5/100 and with a kind of soap, for example castillesoap.
- The natural ennemies Anagyrus ananatis and Cryptolaemus montrouzieri can be brought into the field to destroy the mealybugs (these two species of insects eat mealybugs). Cryptolaemus montrouzieri can be bought under the international name CRYPTOBUG.
- Another solution is not organic, but with chemicals: before planting the suckers it is useful to dip the foot of the suckers in a solution of parathion and diazinon. Also ants can be destroyed with parathion.