Even when a tomato crop is not intended for pruning, there are occasions when some pruning is justified. This excludes processor-type tomatoes which remain on the ground throughout their life cycle. Outdoor, staked tomatoes whether determinate or indeterminate can benefit from limited lower pruning. One usually doesn’t prune determinate varieties as they only reach a certain height and then stop growing. What actually happens is that at a certain point, instead of another shoot growing from a leaf axis, a flowering truss develops ending further vegetative growth. We thus need the side shoots in determinate varieties to give us yield. Removing a few shoots and leaves near the ground would have little or no effect on yield as the plant compensates with enough vegetation to do the job. There is a tendency not to prune indeterminate varieties due to the high cost of labour. But there can be benefits to removing the shoots below the natural fork, which develops about 30cm above the ground.
It’s an undisputed fact that disease affects plants surrounding infected plants. We can often clearly see the pattern of infection in a few rows that may have been missed by the sprayer or when there is a younger planting next to an old, diseased land. Bearing this in mind we can appreciate that the lower leaves that touch the ground are both more difficult to effectively spray and are also subject to a moister microclimate. The leaves are therefore more prone to become diseased and create a high level of inoculum that infects the leaves above. Such leaves can also trap moisture at the base of the plant increasing the incidence of catface. Air movement and more effective spraying delay the onset of disease. Clearly, addressing these problems can justify the labour for the job. The lower leaves sustained the plant during the initial growth stages but when there are sufficient leaves above, the plant loses interest in them. Lower pruning can also be justified if the crop is to be on the land for a longer period, making it even more important to delay the onset of foliar diseases. Once foliar diseases set in, the cost of spraying increases. Lower pruning is a neglected practice, but can create benefits that far outweigh the cost. – Bill Kerr (e-mail [email protected] or call (016) 366 0616)