Season Crop disease Loss (US$) Livestock disease Loss (US$) 1 Maize smut 1 200 Tick-borne diseases 3 500 2 Maize smut 2 800 Foot-and-mouth disease 12 000 3 ...

(a) Livestock disease caused the greatest total economic loss over the three seasons [1].

Livestock disease losses ($17,700) were more than double the crop disease losses ($8,500).

(b) Two reasons why maize smut losses increased from Season 1 ($1,200) to Season 3 ($4,500) (any two for [2]):

1. The farmer may not have practised crop rotation, so smut spores accumulated in the soil year after year, increasing the inoculum level available to infect each successive crop [1].
2. Infected plant debris was not removed or destroyed after harvest, allowing spores to persist in the soil and on the surface, infecting the next season's crop at progressively higher rates [1].

Also acceptable: repeated planting of the same susceptible variety; weather conditions increasingly favourable for the fungus.

(c) Symptoms of maize smut for field identification (3 marks):

1. Large, swollen, grey or black galls (tumour-like growths) develop on the ears, tassels, stems or leaves of the maize plant [1].
2. The galls are initially covered by a silvery-white membrane. When this membrane ruptures, it releases masses of dark, powdery teliospores [1].
3. Affected ears are deformed and produce little or no grain, reducing yield from those plants to nearly zero [1].

(d) How crop rotation reduces maize smut incidence (3 marks):

1. Growing a non-host crop (e.g. a legume or root crop) in the season following maize breaks the disease cycle because the smut fungus cannot infect the alternative crop [1].
2. Without a susceptible host, the spore population in the soil declines over time through natural degradation and the activity of antagonistic soil microorganisms [1].
3. After two or three seasons of rotation, maize can be replanted with a significantly reduced risk of infection because the soil inoculum has been depleted [1].

(e)(i) Two symptoms of foot-and-mouth disease in cattle (any two for [2]):

1. Blisters (vesicles) on the tongue, gums, lips, dental pad and around the hooves, which burst to leave painful ulcers [1].
2. Excessive salivation and drooling, often with strings of saliva hanging from the mouth [1].

Also acceptable: lameness; reluctance to eat; fever; drop in milk yield.

(e)(ii) Why the government imposes movement restrictions (2 marks):

1. Foot-and-mouth disease is highly contagious and spreads rapidly through direct contact, airborne droplets and contaminated vehicles. Restricting animal movements prevents infected animals from being transported to markets or other farms [1].
2. Movement restrictions contain the outbreak geographically, protecting the wider national livestock industry and international trade status, since FMD is a notifiable disease with major economic consequences [1].

(e)(iii) Two immediate actions if FMD is suspected (any two for [2]):

1. Isolate the suspected animals from the rest of the herd immediately to limit direct contact spread [1].
2. Report the suspected case to the veterinary authorities, as FMD is a notifiable disease that requires official intervention [1].

Also acceptable: stop all livestock movements on and off the farm; disinfect boots, equipment and vehicles.