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Precious Manomano
Herald Reporter
Tobacco growers have been urged to implement cultural practices to mitigate effects of the anticipated dry weather conditions to improve the quality of their crop and ensure that they survive adverse conditions
Recommended practices include planting potential high leaf varieties, drought tolerant varieties, using quality seed and delaying nitrogen top dressing.
Preliminary weather forecasts indicate a transition into an El Niño state in the second half of 2023 and Zimbabwe is among the countries at risk of dry conditions.
In a normal season, transplanting of the dryland tobacco crop commences in early October. When adequate water is applied in the planting hole, this allows the crop to survive until the arrival of the rains, four to five weeks later.
In a statement Kutsaga Tobacco Research Board said when using animal draught power, ensure deep ploughing, up to 25 cm while with a tractor drawn plough, aim for a depth of up to 40cm to 45 cm.
“Land preparation is also important in removing weeds that will deplete soil residual moisture that is needed for good establishment of the transplanted seedlings,’’ he said.
The board added that quality seed is an essential starting point for climate-smart crop production with careful selection of quality seed of well-adapted varieties.
Growers are therefore urged to get authentic seed of approved varieties from reputable sources.
Recently the Board has introduced drought tolerant varieties including varieties KRK71 and K RK75 which have a remarkable capacity to rebound and give high yields and maintain leaf quality after a debilitating drought growing season compared to others.
The varieties KRK71 and K RK75 should be the varieties of choice in drought prone areas and also when drought is forecast.
It is recommended that in a drought year, growers select high leaf potential, slow maturing cultivars, that can withstand drought stress without bolting prematurely, that is before attaining 18 or 19 leaves.
Cultivars with a low leaf potential such as K RK26R, K RK22 and K RK23 may flower early when exposed to a prolonged period of drought stress.
In the 2023-24 season, Kutsaga placed on limited release new climate proofed tobacco hybrids bred for cultivation in marginal areas. These new varieties (T78, T79, T80, and T81) were bred for a generally short growth duration that allows them to mature early and escape drought especially in situations where the crop is predicted to suffer a late-season drought stress.
Early maturity also enables the reduction of total seasonal evaporation and transpiration because of the crop’s short duration in the field
“Use disease and pest free seedlings that are uniform and healthy. For seedlings produced using the conventional system, an ideal seedling should have a stem 15-17 cm long and 6-10 mm thick. It must be well-hardened, have 8-10 leaves and must have a strong, vigorous root system.
To get the ideal seedling farmers are urged to sow seedbeds 90 days before the intended planting date.
Finger rolling is also encouraged to check if a tobacco seedling is well hardened.
Beds have the advantage that the total surface area exposed to evaporation is less that when single ridges are used.
Farmers are encouraged to avoid re-ridging during the drought period as this causes moisture to be lost from the soil.
In a season when the rains have been delayed, establishment and survival can be improved by the application of additional water in potholes made between plants on the bed or ridge, after planting.
It is also recommended that this be done within two weeks of planting.
This is because less water is applied after pre-watering as the soil in the planting hole is already at field capacity.
Research at Kutsaga has shown that once the seedlings have taken off and have adequate moisture, they will survive for up to six weeks of dry weather without significant yield losses.
‘’Ensure that seedlings are planted in the centre of the planting hole, straight down and not layered in the soil. This will ensure that the roots are placed in a zone of soil that will not dry out completely, even when rain is delayed for seven to eight weeks,’’said the board.
Farmers are urged to delay the nitrogen top dressing in a period when the dry conditions have been prolonged, growers must think very carefully before applying a top-dressing fertiliser to their crop.
‘’No nitrogen either applied through the basal or residual will have been lost through leaching and will thus still be in the soil. It is therefore unlikely that the crop will benefit from topdressing and in most cases it will be harmful.
“When the rains eventually fall, the plants will make maximum use of soil nitrogen. In fact, the hotter and drier the conditions before the start of the rains, the greater the release of mineralised nitrogen.
“The uptake of this nitrogen will be enhanced by the fact that during the dry period, roots would have continued to grow. Well planted seedlings planted downwards into subsoil moisture, and good root systems would have developed. However, soil mineralized nitrogen availability is higher in early ploughed lands,’’ said the board.
It is essential to remove weeds early and keep crops weed-free during their period of major growth in order to reduce evapotranspiration. Weeds can be managed by herbicide use or manually.
Additionally, good sucker control is recommended as this reduces moisture consumption. Preventative pest and disease management is important. It is a well-known fact that healthy, actively growing plants have better capacity to withstand pest infestations and disease infections than their stressed counterparts.
Insecticides such as imidacloprid or thiamethoxam applied in the planting hole will ensure that the crop is protected against aphid infestations.
These insecticides are also effective against a wide array of soil pests such as white grubs and wire worms that if left uncontrolled will damage plant roots, further weakening the plants
Other insecticides such as lambda-cyhalothrin and other pyrethroids for cutworm prevention will be applied around the base of each transplant immediately after transplanting, to protect against stand loss.
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