Two major post-harvest diseases have been found in New Zealand avocados (Persea americana Miller): anthracnose, associated with Colletotrichum species, and stem-end rots, associated with Botryosphaeria andPhomopsis species. Several Fusarium species have been also isolated from fruit rots. Scab (Sphaceloma perseae Jenkins) is recorded for the frrst time on New Zealand avocados.

Species of Colletotrichum, Botryosphaeria, and Phomopsis causing postharvest rots in avocado (Persea americana Miller) fruits are present in the living and dead branches and twigs of avocado trees, and in the living pedicels. They dominate the fungal population within the extra-cambial tissues but are less common within the xylem elements. There is no evidence that invasion of these tissues is pathogenic. With the possible exception of C. gloeosporioides they appear to be discontinuously present and are more properly termed phellophytes rather than endophytes. There was a higher incidence of stem-end rots than of body rots in untreated (control) 'Hass' avocados in New Zealand experiments and most of these stem-end rots were associated with B. parva and Phomopsis spp. A high proportion of stem-end infections appeared to be initiated during harvesting. Picking the fruit by snapping the pedicels instead of clipping, as in commercial practice, resulted in an unusually high level of stem-end rots caused by C. acutatum. Frequently sterilising the clippers used to harvest the fruits reduced the incidence of stem-end infections, in particular those caused by B. parva, indicating that contamination of the clippers is an important source of infection. It is suggested that this contamination is probably present as fragments of infected extracambial tissue.

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The seasonal abundance of ascos'pore~of Sclerotinia sclerotiorum (Lib.) de Bary m the au depended~n ramfall rnotstenmg the soil sufficiently for apothecia to devt:l~p. No otherclimatic factors were found to be related to the trapping pattern.Conidia of Botrytis ctnerea Pers, ex Fr. were released in large numbers if the preVIOUS day was calm and the night wal"Ill;, or when rain was falling. Few conidia wer~released~t night unless ram was falhng. Ascospores of S. sclerotiorum and conidia of B. ctnerea both showed markedly diurnal distribution patterns.

The time required for potato late blight lesions, caused by Phytophthora infestans (Mont.) de Bary, to produce sporangia during periods of continuous leaf wetness, and for inoculations to produce lesions bearing sporangia, was determined over a temperature range of 5-24°C. Equations were derived relating time to sporulate with temperature. A 2-h break in leaf wetness, initiated at any time within the first 3 h of incubation after inoculation, markedly reduced lesion numbers. When the break was initiated later it had less effect, except at the lowest temperature tested (9°C).