My Mango Yields are dropping
I planted 20 mango trees on two acres in Malindi and had a good harvest in the first season, but recently, my yields dropped. I want to know:
1. What part of the mango tree needs pruning most?
2. What manure and fertiliser should I use, and how frequently?
3. How frequently should I water a mature tree?
4. What chemicals do I use to spray trees?
The phenomenon of good harvest in one season and a drop in the next one is referred to as biannual or alternate bearing/fruiting.
It is influenced by many factors including environmental (humidity, water, temperature and diseases), genetic and cultural (soil fertility). The problem can be managed by avoiding cultivars which are known alternate bearers or managing the environment and optimising cultural practices like:
In mango growing, the most critical pruning is the frame formation or formative pruning to produce a spreading framework or canopy which forms the fruit bearing surface (dense canopy). In the first year, when the trees have grown to over 1m above the ground, trim at 0.90-1.0m from ground to encourage side branches. In year two, leave four to five well-spread branches to be future scaffolds on which the bearing surface will develop.
Any laterals below this head or graft union should be pruned off. Further pruning is not required other than normal removal of dead, diseased, broken wood or parasitic plants. Mango requires dense foliage, which is important in fruit development.
The nutrient requirements of mango trees are dependent on the stage of growth. Fertilisers are recommended after the establishment of a root system (about three to six months after planting).
Mango trees require a good supply of nutrients during the active growth stage until after about four years when they start fruit production and, thereafter, more nutrients are required, especially during flowering and fruit formation.
Excess nitrogen fertilisation in initial stages injures mango roots. The following general nutrient supply guidelines are suggested but a soil, tissue analysis report or both should be the best indicators for mineral element supplementation.
• Year 1: 50 to 100g Calcium Ammonium Nitrate (CAN) per tree per year.
• Year 2: 200 to 200g CAN per tree, per year.
• Year 3: 150 to 300g CAN per tree, per year.
In subsequent years, apply 200 to 400g CAN per tree, per year depending on the crop potential. Apply rates in two to four splits to avoid losses due to leaching or scorching of roots.
Phosphorus (P) and Potassium (K) general fertilisation based on tree age in g/tree/year (in absence of leaf and soil analyses) are as follows.
Year P K
1 25 200
2-3 50 200
4-6 75 250
6-7 100 375
8-9 125 500
10 > 150 650
During the early development of the mango tree (in the first four years), a regular supply of compost and green manure can be provided to improve the foliar development.
During flowering, application of organic fertilisers (compost made of farmyard manure or other organic material) should be applied so that enough nutrients are available for fruit formation and fruit development.
Some 10kg of farmyard manure per tree, per year is beneficial.
In mature orchards (established fruiting trees), water is normally withheld from the end of the wet season until flowering. This period of low soil moisture is believed to encourage earlier and more synchronous flowering.
Watering mature trees
Irrigation is highly recommended from flowering until late fruit maturity. Some growers prefer to start irrigating after 50 per cent of the tree is in flower and at least 50 per cent of the flowers are open.
Other growers will start irrigating from the commencement of visible flower panicle development in an attempt to speed up the flowering and fruit setting process. The amount of water will depend on tree size (canopy cover), evaporation rates and evaporation replacement rate. Irrigation frequency will depend on soil type (water-holding capacity) and effective root depth.
You should cease irrigating a few weeks prior to harvest and it is not recommenced until flowering in the following season.
Use of chemicals
Although mangoes are spread throughout all feasible agro-climatic zones, they have relatively few major problems with pests and diseases. The chemicals, for example, insecticides and fungicides used to spray mango trees will depend on the problem.
Chemicals should be used as little as possible but as much as necessary. Base your spray decisions on pest and disease monitoring and choose products depending on the pests/diseases present, state of the crop and resistance management strategies.
• Horticultural spray oils (petroleum or paraffinic oils) are also effective against whiteflies, aphids, scales, mealybugs and mites,
• Potassium soaps are soft options for small pests such as thrips, mealybugs, scales and whiteflies
• Dimethoate, fenthion, malathion and labaycid are for fruit flies.
• Carbaryl, fenthion and thiamethoxam for mango seed weevil.
• Dicafol for mites
• Anthracol and Kocide DF before and after flowering for anthracnose.
Spray Benlate before flowering and again three weeks later mango powdery mildew
Prof Joseph Wolukau is horticulture expert at Egerton University.
Why chicks die in second week
What could be the cause of death for chicks in the brooder which are in their second week after hatching? Mine become weak and throughout that week, they die about 10 of them per day. Then they stabilise after the second week. I have observed this pattern for the third time now and it is worrying me.
Johnson from Athi River
Mortality during the first two week of chicks’ life is often related to the quality of hatched birds. Chicks must be active, clean and dry with open, bright and alert eyes. Check for navel infection which comes due to unabsorbed yolk. Environmental conditions are likely to pre-dispose the chicks to high stress levels making them dull and inactive.
To minimise losses, ensure the brooder is pre-heated prior to chick transfer into the facility to avoid cold from stress; provide warm water mixed with glucose and chick formula (contains vitamins and anti-biotics) to provide energy and boost appetite and immunity.
Sophie Miyumo, Department of Animal Science, Egerton University.
I want to Start Growing wheat
I am in the process of growing wheat for the first time in Kianduva, Nyandarua County. From the requirements outlined on the seeds packet, 1kg of copper mineral is needed. Please advice on the purpose of applying the mineral and at what stage is it applied. I would also wish to know at what stage CAN is applied.
Copper (Cu) is a micronutrient and, therefore, it is required in very small amounts for protein and enzyme production. Copper is involved in the following ways:-
• It promotes seed production and formation.
• It plays an essential role in chlorophyll formation.
• It is essential for proper enzyme activity.
If wheat is grown in deficient soils, the plant leaves become yellow, they later twist and die. Seed/grain formation is inhibited and crop can die in severe deficiencies.
Application: The rate of 1kg is usually a general recommendation for Kenyan soils that are deficient in Cu. Its application is, therefore, intended to correct deficiencies and should be incorporated before planting, (along with other fertilisers), or as foliar application (on leaves).
Foliar application of Cu is most-effective at tillering, which occurs between 30 to 50 days after sowing. Copper sulfate (CuSO4) is the most common used material for foliar.
Calcium Ammonium Nitrate (CAN) can also be applied just before sowing (basal) or broadcast (top dressing) at tillering and at boot stage, that is, just before the panicles (heads that bear flowers) emerge. It supplies Nitrogen (N), a major nutrient deficient in most soils. For enhancing nitrogen uptake by plants, applying in splits of two to three times (depending on labour availability and weather – avoid heavy rains or drought), is preferred.
Prof Anthony Kibe is an expert at Crops and Soils Science department, Egerton University.
Kindly assist me with the contact of farmer Paul Ruga from Nyeri who has kept his farm mole-free.
EDITOR: Ruga can be reached through our reporter on 0701480038.
I hope this letter finds you well. My name is Margaret Maina from Kiambu County. I appreciate Seeds of Gold for carrying my advert on an incubator that I wanted to sell. I sold the incubator the same day it was advertised. May God bless the team that works on Seeds of Gold.
Editor: Thank you and keep reading.
Jack of all value adddition
Please pass me the contacts of the farmer from Kakamega you featured on March 21 who makes soap from palm oil.
EDITOR: Kindly contact William Simiyu on 0704827806.
I am in need of the contact of Livingstone Waithaka who was featured October 24 last year. I want to buy an incubator.
EDITOR: Talk to Waithaka on 0722766728.
My name is Risper. I would like to contact Mbeere’s Mwangaza Farmers Society.
EDITOR: Please talk to the group through our writer on 0722624621.
Send me the contact of Justin Njoka, the bee farmer featured recently.
EDITOR: Reach the farmer through his trainer Karuga on 0724424400
Copies of Seeds of Gold
The Denise Hogan Library in Zimmerman Estate, Nairobi keeps a special file on all back issues of Seed of Gold. It is the most popular corner in the community library with people coming to read various aspects of farming for free. Please get in touch if you missed anything in the magazine.