(a) Ways ways By Which Diseases Spread On A Crop Farm: (i) rain splash (ii) use of contaminated tools and equipment. (iii) use of infected planting materials. (iv) wind blowing pathogens to other crops. (v) animals, especially predators during feeding. (vi) insect vectors (vii) visitors (viii) weeds harbour pathogens (ix) through irrigation water.
(b)(i) Symptoms of Onion Twister: (i) Twisting and curling of the leaves and the pseudostem. (ii) The twisted leaves later change from the normal darkgreen colour to yellowish green. (iii) The neck of the affected onion plant becomes abnormally long. (iv) the bulbs are narrow and elongated. (v) The bulbs rot quickly when stored. Control Measures of Onion Twister: (i) Early Planting (ii) Removal and destruction of infected plants. (ill) By spraying fungicides. (iv) Practising good farm sanitation.
(b)(ii) Symptons of Root-Knot Disease of Tomato: (i) Formation of galls or knots on the roots of infected plants. (ii) Stunted plants. (iii) The leaves turn yellow. (iv) Production of many secondary roots. (v) Death of plants. Control Measures of Root-Knot Disease of Tomato: (I) Planting resistant varieties of tomatoes. (ii) Soil treatment with nematicides. (iii) Soil sterilisation/ burning of crop residue and weeds. (iv) Practising crop rotation. (v) Removal of crop residues from the field. (vi) Weed control.