Clean seed replacement timing on-farm

The guide at this link provides more details about the points below.

Seed health and seed degeneration. Pathogens and pests can accumulate when seed is saved on farm. This is the case for most crops, and especially for vegetatively-propagated crops like banana, cassava, potato, sweetpotato, yam, and cocoyam. Buying quality-declared seed benefits farmers by giving them healthier crops, at least at the beginning of the season.  Pathogens and pests may still find the crop, but the crop gets off to a good start.

Use of informal seed. Informal seed saved on-farm, or obtained from friends and neighbors, may be sufficiently pathogen- and pest-free for use in the coming season. If disease and pest pressure was low, the seed may be fine. Farmers may also select for symptomless plants to be their sources of seed, to reduce risk. But over time, pathogens and pests tend to build up.

How frequently should external clean seed be obtained? If farmers can afford it, buying quality-declared seed every year is often a worthwhile investment. At the same time, farmers can invest in improved varieties. In cases where quality-declared seed is too expensive to buy every year or is not always available, farmers need to decide how frequently to buy seed.

Developing decision support for frequency of clean seed replacement. To support farmer decision-making about how frequently to purchase seed, it is helpful to have a general guideline about the costs and benefits of purchase. This might be adapted to particular environments in a region. An example of a recommendation might be the following.  ‘For farms above X m, it is best to buy seed every 5 years. For farms below X m, it is best to buy seed every 3 years.’ There is also the potential to adjust decision making for varieties that are resistant versus susceptible to the most important diseases and pests.

Data needs for developing decision support. To develop useful decision support, data are needed to understand at least three types of relationships. First is the relationship between time and the level of disease in seed that is saved on-farm. Second is the relationship between disease level and economic loss. Third is the effect of environment (and/or variety or other management factor) on these relationships. Combining models of these relationships, we can look at likely yield loss over time in the set of environments (and/or varieties or other management factors) being considered and see at which time point yield loss is more expensive than the cost of purchasing quality-declared seed, i.e., when yield loss is likely to exceed an economic threshold.

Testing decision support. Decision support rules can be tested on experiment stations or in farmers’ fields. New data collected in these tests can also be used to improve the decision support recommendations.

The potential for decision support to benefit farmers. Good decision support can help farmers maximize their yield. If farmers use informal seed, they will save the cost of purchase but have higher risk of loss to disease and pests. Decision support can help farmers anticipate when the risk of loss is high enough to motivate seed purchase.

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