Biotic stresses such as viruses, fungi, bacteria, weeds, insects and other pests and pathogens are a major constraint to agricultural productivity from fields to markets in the developing world. With few resources to combat or prevent infection and infestation, people farming small plots of land in developing countries are most vulnerable to these stresses and can experience devastating crop losses before and after harvests.Currently, most crop protection strategies involve genetic improvement of plants to resist pests and pathogens and/or the application of chemical deterrents. In areas of high disease pressure, like tropical sub-Saharan Africa, new crop varieties that are released with single sources of genetic resistance are frequently overcome either before or soon after poor farmers gain access to the improved varieties. Although some farmers do apply chemical herbicides and pesticides, access is limited and not always accompanied with training, which results in ineffective and unsafe use.Pests and pathogens that affect crop plants after harvest can be equally difficult for smallholder farmers to combat. Post-harvest losses mean surplus crops do not reach market, affecting the livelihoods of farming families, and too often these families are left with no other option than to eat contaminated stored food. These constraints impact the food security of these farming families as well as the communities and countries in which they live.