Gray mold disease in capsicums and other horticultural crops

Gray mold in capsicums is usually characterized by dark grey “flour-like” spots in its late stages. In its early stages, it appears as water-soaked and slimy substance in sections of the capsicum fruit, on petals or leaves. Consequently, this leads to plant death at more advanced stages due to stem infections.

Gray mold is caused by a fungus scientifically called Botrytis cinerea and research has shown that it can be treated either by biological, chemical or physical means. The fungus is stimulated by moderate temperature and high humidity i.e humid and warm conditions. It affects a wide variety of crops including strawberries tomatoes, potatoes, capsicum, carrots, peas, cucurbits, citrus, mangoes, onions, wheat family among others.

Physical approaches

The physical approach ensures that a combination of humid and warm conditions are reduced during crop cultivation. This is done in several ways:

1. Through good air movement and a high light interception to ensure that free water dries as soon as possible especially in greenhouses and,
2. Avoiding rainfall during the blossom period by covering crops in open fields. Research has shown that this can reduce the disease by 90% especially in strawberries.
3. Avoid over fertilization with nitrogen
4. Removing plant remains from previous seasons to avoid spread of remnant fungi
5. At post harvest, research has shown that the fruits can be dipped in warm water about 50 degrees celsius for three minutes to inhibit the spread of the disease at post harvest.

Chemical approaches

Chemical methods for gray mold involve the use of fungicides and is not highly advocated for due to effects on human health. It can be avoided by using of either physical or chemical means. However, if chemical means have to be used, any of the following chemical control methods can be used and should be alternated as a disease management strategy.

Biological approaches

Biological approaches to treatment of gray mold are not common in Kenya due to complexity in use. However, they have potential for use especially by organic farmers who target chemical free products for both local and export consumption. They involve introduction of biopesticides such as Trichoderma Viride Biopesticide, certain types of yeasts among others. Basically, they are living organisms introduced to the affected areas and work in the following ways. The biopesticides:

1. Compete for nutrients with fungi that causes gray mold but do not harm the plant.
2. Discharge substances that are harmful to the fungi that cause gray mold
3. Weaken the fungi that cause gray mold’s defense mechanisms

Recent insights from research

Insights from recent research form University of Adelaide have shown that the fungi that causes gray mold disease infects the fruits in the pre-harvest period and the effects of the disease are experienced at post harvest. They recommend sufficient levels of calcium and boron should be present to minimize the development of the fungi at the pre-harvest and post harvest period. Therefore, fertilizers rich in those nutrients are essential to avoid gray mold.