Nematodes,the silent enemy

September, 19, 2017. Many ornamental growers in Kenya have reported increasing nematode infestations under greenhouse production. According to crop protection experts, many growers do not diagnose the problem of nematodes early, but only realize later when the crop is already damaged and they are incurring losses in yield and quality.

Different levels of successes in the management of nematodes have been achieved through pre-plant fumigation, water-filtration and UV treatment of irrigation water, biological control and chemical control. While we appreciate these efforts, farmers need to understand the economic impact of nematodes in order to prevent introduction and spread to avoid crop losses.
Nematodes are long, thin round worms, so tiny they can usually only be seen under the microscope. They are found in diverse habitats and different area, but the ones of most concern to farmers is those found in the soil and feed on plant roots. These are commonly called plant parasitic nematodes. They damage plant roots and slow down or block absorption of water and nutrient by the plant.

Signs in affected plants are usually not uniform in the greenhouse but occur in patches along the beds. Above-ground symptoms often resemble nutrient deficiency or drought stress and farmers almost always mistaken to nutritional and water deficiencies. These signs include yellowing, wilting, stunting, thinning and flower injuries.

To confirm the presence of nematodes, soil and root analysis is recommended. A visual examination of roots is done and depending on the types of nematodes present, there will be galls or knots on the roots.

Once introduced, it is highly unlikely that nematodes will be totally eradicated because they have several host plants. These include the most commonly cultivated vegetable crops such as tomato, carrots, spinach and several weeds. In addition nematodes have a sophisticated adaptation to survive harsh conditions for months or years as eggs or juveniles in the soil or within root fragments.

POINT OF CAUTION. Nematode infestation has led to breakdown of resistance to crop pathogens, making the plants to become more susceptible to other disease such as Fusarium wilt and Bacteria wilt. When nematode population in the greenhouse is not managed, they significantly reduce crop yield and quality. Root damage caused often leads to secondary infection resulting to a rapid crop health decline and losses in yield.