Cashewnut farmers find it tough to battle against new biotic disease

16Aug 2016
Gerald Kitabu
The Guardian
Cashewnut farmers find it tough to battle against new biotic disease

For several years, Cashew nuts grown mainly in the southern eastern regions of Lindi and Mtwara have battled against several biotic factors such as insects, pests and diseases.

Farmers show mealy bug attacks on cashew crop at Kisongo village in Lindi Region. Left is Dr Wilson Nene:

Our Correspondent GERALD KITABU visited the affected farmers at Kisongo village in Lindi Region who are struggling against one of the diseases - Leaf and Nut Blight.

He also talked to reserchers from Naliendele Agriculture Research Institute at the recent Nanenane exhibitions on the measures being taken to smoke out the disease.

MACHOROKO Hassan (36) has earned a living from Cashew nuts agriculture. Through cashew growing and selling, he has been able to pay school fees for his children, gradually expanding his farm and venturing into other income generating projects like poultry.

However, with the outbreak of Leaf and Nut Blight disease in his village and the ward in general, Machoroko feels a blind future due to the devastating effects on the crops.

The village Executive officer Mwalimu Naise (58) says that the disease started gradually but as time passed on, it has spread in many farms, reducing production of the crop to many farmers.

“When the nut start coming out of the flowers, it starts wilting and after a short time it turns black. We are struggling to stop it using our own means such as spraying insecticides but all in vein,” he says.

The village Chairman, Abeid Seleman (46) explains that the efforts to stamp out the disease are going on and currently the farmers are working with scientists from Naliendele Agriculture Research Institute to rescue the crop from the diseases.

According to the crop protection scientist, Dr Wilson Nene, from Naliendele Agriculture Research Institute, the cashew which is an important crop in terms of foreign exchange earnings especially for Lindi and Mtwara regions has been constrained by several factors that often result into yield fluctuations.

Biotic factors such as insects and pests and diseases are among those largely contributing to yield fluctuations. For example, he says, failure to control powdery mildew disease might cause yield loss of between 70 and 100 percent.

Leaf and Nut Blight

Commenting on the Leaf and Nut Blight disease, he says, that this is a fungi disease caused by Cryptosporiopsis sp. He further explains that it is a new devastating disease which was recorded on cashew for the first time in the Southern regions in 2002.

The disease attacks young tissues on leaves, flowers, nuts and apples. Its symptoms are dark tan angular lesions with dark reddish brown margins.

The lesions subsequently enlarge and coalesce causing blighting and defoliation. Older lesions become papery, silver or grey in colour, he explains.

He further says that the disease was initially observed at Nanyanga Cashew Development Centre (CDC), Mtopwa sub-station and Chiwindi village, in Newala District, Southern Tanzania.

“This disease started earlier in other neighbouring countries for example, it was also observed at Itoculo in Monapo District, Nampula, in Mozambique in 2000,” he says.

During fruit setting, infection on young nuts causes rapid blackening and abscission, resulting in significant yield losses.
The infections of older nuts results in a characteristic dark, slightly sunken, “tar spot” like lesions that frequently extend onto the apples.

Most young infected nuts fall down prematurely. The disease is severe when there are leaf flushes, nut setting and rainfall.
According to Nene, generally the disease has an incubation period of about seven days and the pathogens is water loving and can be spread by rain splashes and wind.

Control Measures

Dr Nene explains that the disease is best controlled by a combination of approaches such as cultural, resistance and use of fungicides.

Cultural control involves removal of heavily infected tissues including leaves and nuts and either bury them in the soil or burn them.The practice is intended to reduce the level of inoculums and thus delay onset of the epidemic.

There are two types of cashew genotypes which appear to show a good level of tolerance or resistance, which are AZA 2 and AZA 17. However, it is advisable to plant more than one cashew genotype in a farm.

According to Nene, the following fungicides; Rav (Chlorothalonil), Flint (Trifloxistrobin), Nativo (Trifloxistrobin+Tebuconazole), Score (Difenaconazole) and Acanto (Picoxystrobin) are recommended for control of the blight in Tanzania.


Dr Nene explains that spraying should be done soon after first disease symptoms appear. Normal spraying interval should be two weeks depending on the existence of favourable conditions for disease development.

He said that majority of farmers are aware of the major types of cashew insect pests and diseases. However, the famers namely Juma Nammocho and Polu Omary explained that untimely and inadequate availability of subsidised pesticides have accelerated the problem.

They cited other problems as poor knowledge on pesticide and cost of inputs such as Motorised blowers saying they are major factors that constrain adoption of recommended technologies in the Cashew growing areas among many farmers in Lindi and Mtwara regions.

Dr Nene therefore recommended that policy makers should take steps to streamline and strengthen the linkages between the farmers and the service providers and purchasers.

For his part, the Coordinator of Open Forum on Agricultural Biotechnology (OFAB) Nyinondi Philbert says that the forum has received several calls from farmers in Lihimalyao ward, particularly Kisongo village, who reported the emergence of new cashew nut pest, which they call ‘Sangara’.

He says after receiving the calls on thwarting the diseases, the Commission for Science and Technology (COSTECH) through the Open Forum for Agricultural Biotechnology (OFAB) has responded.

COSTECH consulted researchers from Naliendele and agreed to visit the ward for a quick assessment and hold meetings with concerned farmers, he says.

“We are here to learn with and from you. We want to find out how unique are the challenges in crop production in this village and give our advice,” Nyinondi told the affected villagers.

He adds: “We (OFAB) talk to farmers about the crops they want to grow and eat or trade; we facilitate conversation that will bring innovative technologies to smallholder farmers who are struggling.

In this case, he says: “We see farmers in Kisongo village to be un-aware of the crazy ants (Anoplolepis spp.), which they call ‘Sangara’ while researchers know the problem and had developed temporary solutions to reduce its negative impact. We hope more effective solutions will be available soon to help the farmers,”.

He said that COSTECH through the forum has witnessed new varieties of cashew nut that are resistant to some of the diseases and have higher yields.

He advises stakeholders including the government, civil societies, business companies and donor communities to make such that varieties are accessible and affordable to smallholder farmers.

“Unless we take collective actions, farmers like those in Kisongo village will not benefit from expensive investments in developing innovations and technologies in the agricultural sector, says Philbert Nyinondi.