Irish Potato (Solanum turberosum L.) Production in Zimbabwe
Introduction
•Potato is one of the most popular food crops in Zimbabwe.
•Unfortunately many small scale growers do not produce this wonderful crop.
•Potatoes were well established in Zimbabwe in the early 20th century
•Seed production and breeding activities are concentrated in the eastern highlands
•In these notes we will assist you to have a sound knowledge on how and when to produce a good potato crop.
Why growing potatoes
•Potatoes have high return per dollar invested
•Potato is one of the few crops which can be used in a variety of ways ie Potato chips, mashed potato, boll with skin, mixed with other vegetables
•Potatoes are rich source of Vitamin A, Vitamin C, Carbohydrates and potatoes.
Climatic requirements for potato production
–Potatoes should be grown in areas where temperatures do not exceed 320c.
•Temperatures above 320c results in poor yields
•Potatoes are susceptible to frosts
•Optimum temperatures for potato production are between 15 – 200c
Soils best for potatoes
•Potato can grow on a wide range of soils
•The best soils are medium textured loam soils with good drainage and high organic matter content
•Heavy soils that may become hard can affect the shape of the tubers, however yield can be very high
•Soil ph of 5-5.5 (cacl2) are favourable)
•Avoid water logging conditions
•Do not lime ptatoes directly but apply before planting to avoid a disease called potato scab
Planting times
•Summer crop. (November to March)
•Plant in November with first rains. It is not recommended to plant into hot dry soil prior to the rains.
•Planting can be done earlier under irrigation.
•In marginal areas supplementary irrigation is essential for good crops.
•This plant is subject to late blight.
•In areas where farmers have irrigation and where frost does not occur potato can be grown three times in Zimbabwe
•First winter crop (February to June)
•Plant in February
•This is an irrigated crop
•The chance of late blight is less and susceptible varieties may be used
•Second winter crop (August to November)
•Second irrigated crop for areas in the high veld
•In the low veld temperatures will be too high during this period (above 320c)
•The chances for late blight is less and susceptible varieties may be used
How to treat potato seeds before planting
•It is recommended to plant certified seeds from a well-known seed dealer or potato seed producer (Any other seeds may give you problems)
•Spread tubers on a dry ground under direct sunlight
•Protect them only when the sun becomes too hot
•Rain does not damage as long as it drains off the tubers
•When tubers and sprouts turn green it makes them both tough and less liable to damage, during planting
•Shoots should not be too long before planting the tubers in the field, about 5 cm
Varieties
•Four varieties are grown commercially in Zimbabwe
•Amethyst, average sized bulbs a locally bred variety ocuppies the greatest area follwed by
•BPI early maturing medium sized bulbs originally from South Africa
•Mont-Claire large flattish tubers good for making chips (Locally bred)
•Jacaranda average sized bulbs
•Pimpernel, a yellow fleshed variety originally from Hollad is grown under contract for crisp manufacturers
Planting
•Rows should be spaced at 90 cm apart
•Inside rows plants should spaced at 30 cm apart
•Potatoes are intiataly planted on flat ground
•Planting depth is determined by the soil type, the moisure it contains, the size and condtion of seed
•Plant tubers 7 to 10 cm deep under irrigation and upto 15 cm deep as a dryland crop
•Make sure the whole potato seed is covered by soil
•Tractor mounted ridger can be used for making furrows: seed is planted by hand.
Fertiliser and lime
•Ferliser application is based on
•1. Soil analysis -considers residual soil nutrients, soil ph, avoid excess fertiliser expense
•2. Foliar analysis -verifies quality of soil test recommendations and confirms status of N, S and boron
•3 Blanket fertiliser recommendations (600 – 1000kg Cpd S -Fails to account of residual soil nutrients, causes greater expense than needed, can result in excess fertiliser
•Crop-removal-based rate -Supplies nutrients in needed ratio, but fails to account for residual soil nutrients, which might be sufficient for crops needs
Fertilisation
•Depending on soil type and history initial application of 1000 to 2000 kg/ha of compound S is required
•Where soil analysis show potasium to be low compound C should be used.
•The best method is to prepare the rows and mark the planting station by digging a hole. Place Compound fertiliser at the rate of 16 – 30 g/station or palnting hole and cover it a bit with soil before placing the tubers.
•Lime should not be applied direct to the potato crop but in the rotation
•Potatoes are very sensitive to boron toxicity. So avoid land that has received large quantities of compound L or fertiliser borate
Ridging
•First ridging-When the crop has grown to a height of 20 – 30cm apply top dressing preferably per station. After applying top then ridge up the plants covering the plant upto a ridge level of 20-25 cm
•Do not cover the tops of the plants
•This is also a way of weeding your crop
•Ridges can be made using a hoe, ox-drawn plough and or tractor drawn ridger
•Second ridging is done when the tubers are cracking the ridges and some of them will be seen protruding out of the ridges. These should be covered to prevent them turning green protect them from potato tuber moth and late blight. Care should be taken not to damage roots.
Irrigation
•Potatoes require 500 – 700 mm of water
•Irrigation requirements
Soil class
Hot months (Interval
Cold Months (Interval
Irrigation required
Light soils
3-4 days
5-7 days
25-30mm
Heavy soils
5-7 days
10-12 days
30-35 mm
Weed management
•Herbicides suitable for potatoes
•Dual preemrgence herbicides for control annual grasses and some broadleaf weeds suppresses nutsegde
•Lasso preemrgence herbicides for control annual grasses and some broadleaf weeds suppresses nutsegde
•Sencor preemrgence herbicides for control broadleaf weeds and some annual grasses
•Afalon preemrgence herbicides for control broadleaf weeds and some annual grasses
•Late weeds shuld be pulled by hand
Pest control
•Aphids-small pear black bodied sucking pests often grouped in colonies.
•Aphids are vectors of viral diseases
•Control should be based on scouting
•Recommended chemicals are Azodrin, Diamethoate, Malathion. The sprays can be incorperated with the routine sprays against blight.
Potato tuber moth
•Larvae make tunnels or holes inside the tuber
•Signs are wilting and drying tops
•Control is by covering the tubers well or spray Azodrin 40 at 15 ml/10litres of water once a week after first ridging in areas where this problem occurs
Root knot nematodes
•Maladogyne spp are a serious pest of potatoes especially on light texture soils.
•Control is by observing a rotation of 4 years with out growing potatoes, tomatoes or paprika.
•Fumigation is also encouraged
Production constraints
•Late blight
•Virus diseases include PVY, PVX, PVS and PVM
•Insect pests eg aphids, tuber moths and root knot nematode
•Baboons
Diseases control
•Late blight is a problem, particularly during the summer ware crop in the highveld
•It is most prevalent when the temperatures and humidity are high.
•Signs of disease are brown patches at end of leaves with white mycelium underside, brown black spots on stems
•Early blight
•Spread slowly when temperatures are around 250c
•Common during wet and dry season
•Signs are concentric necrotic spots
Control of late and early blight
•Spraying with fungicides
•The fungicides are grouped into preventive and currative
•Preventative is used before infestation eg Dithane M45, Copper oxchloride,
•Curative is used when the crop is already infested eg Folicur, Ridomil
Harvesting
•When 90% of the tops have dried or have changed colour to pale yellow
•Stop irrigating the crop
•Cut and remove the tops (when tops are completely dry, burn them to control diseases)
•Leave the tubers in the ground to cure for 10 – 15 days
•Lift after curing with a garden fork to avoid damaging the tubers
Grading and packaging
•Harvested tubers should not be left in the sun for too long
•Tubers must be move to cool, dark place as soon as soon as possible after digging
•Curing under this environment for a few days will allow cuts to heal
•Grading can be done in the field and pack straight to pockets
•Grade by size of tubers
•Pack into ventilated 10 to 15 kg pockets
•Store at temperatures between 30c and 50c.
•Store and dress tubers with 1% malathion dust
Storage
•storage of seed and ware potatoes in Zimbabwe is remarkably, perhaps uniquely, unproblematic
•In the eastern highlands cool temperatures, dry soils, and isolation from viruses allow harvest of seed to be spread out from March to July without loss of yield or seed quality
•The tubers are stored well ventilated sheds without refrigeration, allowing rising temperatures in August and September to break dormancy
•Such tubers are well-sprouted and in excellent condition for planting in November
•With year round production ware potatoes spend little time in storage.
Marketing
•Marketing of potatoes is free from government controls other than a small tax levied on the sale of ware potatoes
•Large-scale farmers belong to a marketing organization though which they sell their crop to private wholesalers
•The five major wholesalers set prices once a week
•Potatoes are sold in 15 kg pockets
•Seed potatoes are sold are sold in 30 kg pockets
•If sold on the open market allow for auctioneer fees ranging from 10 to 12.5% of realisation
•Presentation
Marketing
•Presentation for sale is important, as having spent considerable effort in growing the potato, it is wastefgul to lose the maximum price advantages for top quality produce, the potato is badly presented through poor grading, inconstant weights or poor packaging.