Assessment of production and dispersal of inoculum ofAlternaria Macrospora in various parts of the cotton canopy
Morning and evening counts of spores ofAlternaria macrospora in a cotton (Gossypium barbadense) field were assessed for the number of spores (a) produced on the last night, (b) dispersed during the day, and (c) retained in the spore reserve on leaves. Throughout the season, 1 m2 of the field produced (P) and dispersed (D) approximately 163 x 106 and 137 x 106 spores, respectively. The 16% discrepancy between P and D values reflects experimental errors. Most spores were produced on shed leaves on the ground, fewer on leaves in the lower part of the canopy, and least on leaves in the upper canopy. The contribution to total D decreased from leaves in the lower part of the canopy, to shed leaves, and to leaves in the upper canopy. In tests with potted plants with spore-bearing lesions attached to various heights of the canopy under various conditions of weather, dispersal of spores at these heights was conditioned mainly by wind velocity, which decreased from the upper to the lower part of the canopy. In leaves close to the ground, approximately 29% of the released spores were removed by sedimentation to the ground. On any one day, the daily rate of D differed from the daily rate of P. On days in which D was higher than P, the difference was due to a reserve of spores remaining on lesions after dispersal during the previous days. In weather adverse for production of new spores, the reserve was depleted within 4 and 6 days in the top and bottom leaves, respectively, but remained relatively high in the shed leaves on the ground; a similar number of days was needed to restore the depleted reserve in sporulation-favorable weather.
Quantitative Assessment of Inoculum Production, Dispersal, Deposition, Survival and Infectiousness in Airborne Diseases
The integrated effects of production, dispersal, deposition, survival and infectiousness of inoculum are manifest in the disease severity it is able to cause under the specific conditions of environmental and host factors. Evaluation of these components and of their integrated effects is often so difficult that they constitute the “black boxes” in many epidemiological analyses. There are no research techniques that will eliminate completely these black boxes. However, there are some direct and indirect approaches that may improve quantitative assessment of the individual components and their integrated action.
Purple blotch (Alternaria porri) of Onion In Kenya.
SUMMARY 
In 1961 an epidemic attack by Alternaria porri occurred on irrigated onions at Baringo in the Rift Valley, Kenya. Two distinct lesion types appeared: (1) typical purple or brown blotches; (2) white, irregular spots or flecks. These were present in varying proportion, depending on the duration of conditions favourable to infection, and subsequent relative humidity. High R.H. favoured the development of purple blotches; low R.H. for prolonged periods after infection usually resulted in white flecking only. These flecks were often sterile, making diagnosis difficult. 
 
Germination, appressorial and lesion formation displayed a broad optimum temperature (21–30° C). Resistance to the disease shown by a number of American hybrid onions was governed by cuticle thickness; this resistance was reduced by wounding—such as is associated with sand-storm blast—or by incubation after infection for prolonged periods at high R.H. 
 
Two fungicides, mancozeb and dicloran, effectively controlled the disease in the field.