How to Grow Potatoes in Zimbabwe: From Planting to Harvest!

Sunday, April 15, 2018


Potato Production in Zimbabwe

Potatoes, also known as Irish Potatoes, are a member of the Solanaceae family which includes tomatoes, peppers, tobacco and eggplants. 

In Zimbabwe, the crop is grown mostly for the fresh and processing markets. The potato is an expensive crop to grow, requiring high variable costs but it does offer high returns per dollar invested if done well. As a result, potato farming in Zimbabwe is practised primarily by large-scale commercial farmers with smallholder (emerging) farmers cultivating smaller hectarages. 

According to AGRITEX, it costs between US$6000 to US$8000 to produce a hectare of potatoes. Potato yields range from 15-40 tonnes per hectare, although national yields are well below 10 tonnes per hectare. There are a number of factors contributing to poor yields especially amongst small-scale farmers. Some of the reasons will be highlighted later, but first, we will focus on general potato agronomy.


Varieties on the Market

Available varieties produced by reputable companies are either early or late maturity.

  • Early maturity varieties on the market:
    • BP1
    • Mnandi
    • Diamond
    • Valor
    • Jasper
    • Sifra
  • Late maturity varieties on the market:
    • Montclaire
    • Amethyst
    • Mondial
    • KY20
    • Emerald
    • Pimpernel
To learn more about the qualities of some of these potato varieties make sure you also check out our previous post The Complete Guide to Growing Potatoes in Zimbabwe.



Choice of variety

Most experienced potato farmers grow varieties that are market specific and quick to mature as well as high yielding. 

Varieties like Mondial are popular in the hospitality industry (fresh chips), whereas Valor and Amethyst potatoes are commonly sold at Mbare Musika because of phenotypic distinguished sizes. Pimpernel is used in the processing of crisp chips. Sifra a new variety has gained popularity because it matures in only 85 days and has good yields. 

However, varieties such as Mondial are indeterminate and need to be regulated in vegetative growth. Successful farmers growing Mondial use growth regulants such as cultar (paclobutrazol) to control vegetative growth at the expense of tuber formation. Prices of the growth regulators packed at US$250 per litre are prohibitive for most smallholder (emerging) farmers.

Soils and pH

Potatoes can be grown on all soil types, although sandy loam soils are the most ideal. On heavy soils, a good structure is needed to avoid misshapen tubers. Potatoes tolerate a soil pH of between 5.5 to 6 and acidic soils must be avoided.

 It is recommended that soils are tested well in advance of planting to correct the soil pH and to get the correct fertilizer recommendations for a good yield. Acidic soils prevent the uptake of nutrients. It is a common practice, especially among smallholder farmers to ignore testing of the soil pH. This negatively impacts overall crop yields. This does not apply only to potato farming but other field crops where yields are currently unsatisfactory.

Climate and Planting Times

The potato crop thrives well in a cool growing season, although warm temperatures are tolerated too. Optimum temperatures range from 15-22⁰C. The crop must be grown during frost-free seasons as the foliage part is easily damaged. In Zimbabwe in Highveld areas, the planting times are November-February, February-May and August – November. 

However recently introduced early maturing varieties such as Sifra that can mature in 85 days have enabled farmers to have quick financial turnovers. A winter potato crop has higher yields and good quality tuber due to limited diseases and pest prevalence.

Sprouting Process

Seed potato is usually unsprouted when bought; hence farmers must use chemicals like gibberelic acid (GA3) at 32ml per 200 litres of water. The tubers are immersed in the solution for 5 minutes then allowed to drain and stored in partial light. Sprouts emerge as from 3 weeks to a month. In the sprouting room, farmers must apply copper-based fungicides and carbaryl to prevent fungal diseases and tuber moth attack on newly formed sprouts. At least five sprouts are recommended to develop on the tuber before planting. If only one sprout (apical dominance), it should be destroyed to allow for appropriate sprouts. To enhance sprouting, tubers can be spread on bedding made of dried grass mulch which improves temperatures. Cold temperatures will greatly delay sprouting.

Planting

If lime is to be applied, this must be applied at least 5 months before planting as early planting will result in potato scab. Land must be deep ploughed and disked to a fine tilth. 

Plant spacing must be 0.3 by 0.9m to achieve a plant population of about 36000 plants per hectare. To prevent nematodes, nematicides such as nemacur, oxamyl, fenamiphos, or salvigo must be applied at least 48 hours before planting in rows. Planting depth should be 15-30cm. 2500kg of seed is required per hectare.

Crop Rotation

A potato crop must not be followed by crops in the same family of Solanaceae like tomatoes, peppers, sweet potatoes, strawberries and tobacco. Such crops tend to host similar diseases in the soil that can adversely affect the crop to follow. It is advisable to rotate the crop with legumes.

Fertilization

Farmers must be guided by the soil test results for fertilizer application for their potato crop. However, as a general recommendation, potatoes need 1200-1400kg of potato blends (6:19:25). Tobacco fert or Compound C or S may work but at higher rates, if the former is not available. 

3 weeks after emergence farmers must top dress with potato top (23:0:23) or potassium nitrate split applied at 400kg per hectare. After topdressing, it is advised to earth up or ridge the crop. Earthing up is done to avoid direct sunlight contact with tubers that will turn green and subsequent pest attacks.

Watering Potatoes

There are certain stages of growth where water management is most critical: that is to promote emergence, at tuber set (flowering), tuber bulking up, final crop watering and pre-harvest irrigation. Potatoes are very sensitive to irrigation. Correct irrigation gives yield responses of around 0.2 tonnes/ha/mm water which makes it highly profitable. 

The method of irrigation includes drip, overhead or centre pivots. However, use of drip irrigation minimizes fungal diseases occurring. Flood irrigation must be avoided at all costs.

Disease, Pest and Weed Control

Early blight and late blight are the most important diseases in potatoes. It is necessary to apply preventative fungicides before noticing the disease which appears as brown lesions and dark spots on the leaves and stems. Such fungicides include copper based, Dithane M45, bravo etc. In the event of noticing the diseases apply Amistar, Folio gold or Revus at recommended rates. Where soil-borne diseases such as Common scab and black rot are prevalent fumigate the soil using Amistar Top.

Common pests include cutworms, white grubs, tuber moth, aphids and nematodes which can be controlled by karate, ampligo, chess and nematicides mentioned earlier. Local companies have developed broad-spectrum pesticides such as thunder that work effectively against a number of pests.

Herbicides such as Dual magnum and Sencor /metribuzin can be applied to control grass or broad leaf weeds as compared to a mechanical approach which can be costly.

Physiological disorders in potatoes

These are not diseases but conditions that occur as a result of the environment:

1) Greening: this is when tubers are exposed to direct sunlight thereby turning green. As a result, the tubers become unmarketable. This can be controlled by ridging the plants as from the third week.

2) Cracking: this is when potato tubers develop severe cracks on tuber surfaces. This is caused by uneven water distribution and supply or when the plant receives water after moisture stress.

3) Hollow heart: this is when tubers develop large holes at the centre. This is common on large tubers as a result of uneven fertilizer applications and moisture management.

Harvesting and Yields

Depending on the variety, crop matures from 85 to 140 days. It is recommended to harvest when 95% of the leaves reach senescence. The haulms should be destroyed at least ten days prior to harvesting to improve tuber shelf life. Harvesting can be done using a potato reaper on a large scale and hoes on a smaller scale. Tubers are graded into extra large, large, medium, small and charts before being stored in a well-ventilated shed. Small and charts may be used as retained seed depending on the generation.

 15 Dos and Don’ts for Potato Farming

1) Always take your soils for analysis before planting.

2) Apply lime if your soil is acidic.

3) Know your market needs before making a choice of which variety to grow.

4) Never buy seed from unreputable seed suppliers

5) Never used recurring seed generations or seed retained for longer generations.

6) Never plant unsprouted seed.

7) Always use appropriate fertilizers at planting and not cheap ones to cut costs.

8) Never apply lime at planting.

9) Prevention is better than cure; apply nematicides before planting to control nematodes.

10) Irrigate to field capacity only once to allow for emergence.

11) Rotate both preventative and curative fungicides as some diseases may be at incubation periods.

12) Never leave tubers exposed, always ridge plants at least once.

13) Always apply sufficient water at flowering and tuber bulking stages.

14) Never harvest potatoes before clipping the foliage.

15) Always grade your potatoes before packaging.

 Common Problems facing Local Potato Growers

There are a number of problems associated with growing potatoes in Zimbabwe but the major one being low yields especially amongst smallholder farmers due to:

1) High Input Costs

The cost of inputs such as seed US$2500, fertilizers US$1450, chemicals US$1200 and other salient costs per hectare are highly prohibitive for most smallholder (emerging) farmers. As a result, farmers end up cutting costs therefore significantly reducing potential yields.

2) Limited Seed Suppliers and Breeders

The country has a limited number of reputable seed suppliers and breeders with only two in the capital and a few in Manicaland (Nyanga).

3) Outdated agronomic practices

Limited attention has been paid to agricultural research through limited funding. Not much has been done to update agronomic practices being implemented by farmers.

4) No Soil Analysis

Most farmers especially smallholder farmers take soil analysis for granted, hence ending up planting potatoes with very little knowledge on the soil pH and fertilizer needs.

About the Author

Joshua Nyamowa is a Senior Research Officer at the Horticulture Research Institute (HRI) in Marondera, Zimbabwe. He is also a Senior Agronomist at Greens Agricultural Consultancy. You can reach him at  +263 772965151 or by email at joenyamowa (at) gmail.com.

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