<p>Cashew is one of the leading export crops in Tanzania in terms of foreign exchange earnings. It is also the main source of cash income to over 2.5 m people in Mtwara and Lindi regions in southern Tanzania. Cashew is also traditionally grown in other regions of Ruvuma Coast, Tanga and recently in non-traditional cashew growing areas like Dodoma, Singida, Iringa, Mbeya and others.</p> <p>In early 1990s many cashew orchards were abandoned because of low productivity due to a number of factors, among them was outbreak of diseases and low farm gate prices, which made cashew farming to be uneconomical to poor resource farmers. However, the development of cost effective socially acceptable disease control strategies and introduction of appropriate agronomic practices in cashew, helped to revive cashew production through rehabilitation of the abandoned orchards. The development and release of new high yielding cashew varieties allowed upgrading of existing unproductive cashew orchards.</p> <p><strong>Cashew rehabilitation and upgrading</strong></p> <p>Rehabilitation is a process of bringing abandoned cashew farm into production. Essentially it consists of bush clearing, weeding and thinning of overcrowded trees, control of diseases such as powdery mildew disease (PMD) and leaf and nut blight ; control of insect pests and inter-cropping with high value annual crops. Rehabilitation gives substantial economic return starting from the second year of operation. Inter-cropping is recommended from first year of rehabilitation onwards to cut down initial investment costs.</p> <p>Overcrowding in Tanzania, like in many other African countries has demonstrated to be the biggest problem in farmers’ fields. This is due to the fact that most cashew trees were planted randomly at a close spacing and some of the cashew trees were self-sown without any proper spacing. Apart from low yield, overcrowding of cashew trees in farmers field have shown to create an environment, which is conducive for the development of PMD. In order to overcome this problem, thinning need to take place to optimum recommended density (12mx12m for common cashew types and 10mx10m for dwarf cashew types). However, it is sometimes not possible to do this with any precision due to irregular planting in farmers’ fields, which have many gaps. Tree densities in farmers’ fields are very much variable even in the same field and also yield is highly variable from one cashew tree to another. In view of this problem, it is logical to do selective thinning by removing low yielding and unproductive trees. Equally, where possible (depending on position and size of the tree) stumping can be done and sprouting shoots can be grafted using scions of improved cashew clones. This method is the cheapest and has quick economic return as top-worked trees produce in the same year.</p> <p>Usually if thinning is done properly, the average yield of the farm does not decrease even in the first year of operation because only unproductive ones are removed. This allows the remaining cashew trees to have less competition for light, moisture and nutrients. Observations on cashew rehabilitation trials at Agricultural Research Institute Naliendele showed a considerable increase in yield in the first year upgrading, and two folds increase in yield in the second year. During rehabilitation, the control of insect pests and diseases is necessary in order to increase yield as well as quality of the raw cashew nuts.</p> <p><strong>Upgrading</strong></p> <p>Upgrading is a method of increasing cashew nut production in an existing cashew farm using different agronomic practices, which include top-working, new planting, inter cropping and diseases and control of insect pests. As it is known, after planting, cashew trees, and cashew nut production in farms increase from one year to another until a certain stage when canopies overlap, then the production starts to decline. The age at which this happens depends on the type of planting materials used, type of clones planted, the spacing used, soil types and soil fertility. Cashew usually bears fruit on the periphery, which requires a lot of light for good production. Shaded areas produce few nuts or nothing at all.Upgrading need to be accompanied with inter cropping (annual crops), in open areas, where trees have been thinned or stumped for top working. This will increase farmers’ income; therefore it is important that farmers are provided with improved seeds and methods of their cultivation.</p> <p><strong>Top working</strong></p> <p>Top working is a quick standard horticultural practice used to convert or upgrade inferior cashew clones to better clone without up-rooting the original tree. This is implemented by stumping cashew trees at a height between 1-2 m. The cut is finished on the stump with a sloping cut (around 30o) to allow water to drain freely from the cut surface and new shoots are allowed to come up. It usually takes between 6 and 8 weeks. The new shoots are then grafted using scions of high yielding cashew tree/clone.</p> <p><strong>Control of Cashew diseases and insect pests</strong></p> <p><strong>Insect pests</strong></p> <p>There are several insect-pests of cashew but the most devastating ones are Helopeltis spp and coconut bugs (pseudotheraptus wayi). Nymphs and adults infest young and tender tissues including tender leaves, tender shoots, young buds, panicles, receptacles, and young tender apples and nuts. Tender shoots when infested produce translucent resin exudates from the affected site, which harden gradually. The infested tender shoots turn black and dry up gradually, and new tender shoots emerging from the infested branches will also be infested if the bug is not properly controlled. Tender leaves when infested will shrivel with polygonal water soaked spots, and dry out finally. Panicles when infested will dry up and drop. Infested receptacles show brown scars, and at heavy infestation numerous scars coalesce into a group of brown scars, ultimately leading to drying up of the whole panicle. Young tender nuts show papillose spots when infested, and shrivel and drop finally. Both pests can easily be controlled using pyrethrum insecticides like Lambda cyhalothrin at a rate of 5 mls/litre of water. The applications of the insecticide are undertaken when there are symptoms of attack. The control of insect pests is not a common practice, however, the diseases particularly the powdery mildew (PMD) and cashew leaf and nut blight disease (CLNDB) must be controlled in order to get desired yield and good nut quality.</p> <p><strong>Powdery mildew disease</strong></p> <p>The powdery mildew disease infests all tender tissues of the cashew tree, mainly the tender leaf and inflorescence including the part not well unfolded. The disease seldom attacks old and mature leaves. A white powdery growth is formed on the infested fruit bearing branches and inflorescence. The lesions of the infected parts turn from green to brown and after 2-3 weeks they shrink gradually and become dry and shed, leading to drying out and drop of numerous flowers and tender fruits.Infected apples turn dull and their skin becomes much coarser. The apples when heavily infected show deep cracks on the surface and gradually shrivel and dry up.</p> <p>Tender nuts when infected are deformed on the shell. Infected nuts when they mature, the nut quality deteriorates. The lesions turn grey on infected tender apples and nuts. Infested nuts deteriorate in quality during storage, decays easily and produce poor quality kernels when processed. The PMD if not controlled it can cause a crop loss of more than 70% for tolerant cashew varieties and close to zero for local varieties.</p> <p>In Tanzania PMD are controlled using Sulphur dusts or wettable sulphurs. The rate of application of Sulphur dust is 250 g/tree at an interval of two weeks repeated five times in a season. Wettable sulphur application is 85.5g per tree/litre of water at the same intervals and rounds mentioned above. However, Sulphur dusts are protective and not curative though highly acceptable in organic food chain. The most effective fungicides to control PMD are organic fungicides (Triadimenol, Hexaconazole and Penconazole). They are sprayed on the trees canopies using boom sprayers or motorized blowers. The rate of application is 10-15 ml/litre of water per tree at an interval of 14 days and rarely 21 days depending on the disease severity. Three to four rounds of application are adequate for the control of the disease. On the other hand, the cultural control measures e.g. pruning, thinning and sanitation can delay outbreak of the PMD. In southern Tanzania the disease control starts last week of June, which is the time when cashew flowering starts. In Eastern zone the disease control can delay for one month until last week of July.</p> <table align="left" cellspacing="0" style="width:466pt"> <tbody> <tr> <td style="width:187.05pt"> <p><img alt="" src="../upload/1025270627.png" style="height:224px; width:184px" /></p> </td> <td style="width:146.1pt"> <p><img alt="" src="../upload/732155312.png" style="height:229px; width:142px" /></p> </td> <td style="width:132.85pt"> <p><img alt="" src="../upload/61888529.png" style="height:238px; width:128px" /></p> </td> </tr> </tbody> </table> <p> </p> <p><strong>Leaf and nut blight disease </strong></p> <p>Leaf and nut blight (LNBD) caused by Cryptosporiopsis spp is among the diseases affecting cashew nut production in Tanzania. The disease was reported attacking cashew for the first in Southern Tanzania, in 2003; however, of late it has become the second important disease of cashew in the country. The LNBD attacks tender leaves and young fruits. The leaves infected produce lesions with black brown or dark red margins, and the lesions are expanded but limited by the leaf vein, and then enlarge gradually to form a large patch of lesions, leading to drying out and drop of the infected leaves. The old lesions are thin like paper, silver gray, fragile, and the leaves are finally full of bullet-like holes. This disease can also infect young tender nuts, which will turn black rapidly and drop, leading to loss of yield. The mature nut infected will show typical black spots that look like the colour of asphalt and are slightly depressed.</p> <p> </p> <p>In Tanzania the disease is controlled by spraying fungicides as follows:- Trifloxystrobin 10% SC (2-4g/litre), Difenaconazole WG (water dispersible granule 14 g/litre), Picoxystrobin (10 ml/litre) and Trifloxistrobin + Tebuconazole (14 ml/litre). Disease control commences when first symptoms occurs particularly during fruiting season. LNBD can cause crop loss of more than 70%.</p> <p> </p> <p><strong>Severity of LNBD</strong></p> <p><img alt="" src="../upload/84561776.png" style="height:94px; width:142px" /><img alt="" src="../upload/1089679898.png" style="height:94px; width:126px" /><img alt="" src="../upload/1089615634.png" style="height:98px; width:132px" /></p> <p>Anthracnose is a disease caused by fungus Colletotrichum gloeosporioides Penz. The fungus infects leaves, tender shoots, inflorescence, young and mature fruits and apples. The leaves and young fruits when infected will dry out completely while mature fruit will dry and remains hanging on the tree. Under favourable conditions anthracnose can reduce cashew nut yields greater than 50% and give serious impact on the quality of apples and nuts. Affected nuts and apples starts to decay followed by dry-out, shrivel and remain on the infected shoots as hanging nuts that remains on the shoots and may act as next source of inoculum during the next season. Anthracnose occurs in all cashew growing countries in the world. It is the most important disease in cashew plantations in Brazil but only third or fourth to powdery mildew disease in East Africa. The disease is highly accelerated by rain showers during fruiting season. In Tanzania there are no disease control measures as Anthracnose is yet to be a disease of economic importance though it is increasingly noted in farmers’ fields. It is on many occasions misinterpreted as LNBD because it has more or less similar characteristics on leaves.</p> <p><strong>Anthracnose on mature apples/nuts</strong></p> <p><strong><img alt="" src="../upload/264249753.png" style="height:155px; width:207px" /></strong></p> <p> </p>