Term 1 – Week 6 – Disease, Summer Fruit & Propagation

This week we moved on from pests to diseases. Diseases in horticulture are broken down into 3 categories; fungi, bacteria and viruses. In vineyards common diseases are powdery mildew and botrytis.

Just like in humans and animals, preventing disease is obviously a much better idea than trying to cure it. Possible control methods include:

  • Growing disease resistant varieties
  • Increasing airflow around fruit
  • Irrigate under plants (wet and humidity spread disease)
  • Bring in sheep over winter to clear up any rotten/mummified fruit or leaves
  • Spray fungicides from start of first growth (vineyards spray sulfur every 10 days during the growing season)

Disease can also be spread by insects. The damage they do to the fruit can create entry points for disease to get into the plant.

Plants with diseases mainly need to be either removed totally or pruned back to healthy wood.


Powdery mildew

On Wednesday we discussed Summer fruit, basically “stonefruit” has been re-branded as “Summer Fruit”, so it’s cherries, apricots, peaches, nectarines and plums. They all belong to the same genus, Prunus. 

To ripen summer fruit you need at least 800 growing degree days a year. GDDs are added up from 1st Oct – 30 April, average temperature each day minus 10 degrees. So if the daily average temperature was 20 ºC, 10 would be added to the GDD total.

The amount of sun will effect the size, colour and flavour of the fruit.

Summer fruit varieties also need enough cold over winter to break dormancy in spring. For example, apricots need at least 1000 hours of chilling (under 7ºC) over winter. This keeps the trees dormant through winter, even if the temperature warms up slightly for a short time. Once they have had their 1000 hours they will start flowering all at once in spring, which is important so all the trees in the orchard are at the same stage at the same time.

Dry conditions are also good for summer fruit. It helps to reduce diseases like brown rot and bacterial blast.

In the afternoon we went out to the cherry trees we planted last winter and did some tree training. This just involves pruning off any unwanted branches and clipping up the rest to the wire to ensure upright growth.

In propagation class we packed up the seed from last week that had been processed and was now finished drying.


We also sowed some Sophora microphylla seeds (kowhai). They need to be scarified before being planted because they have a thick, hard seed coat. Scarification involves damaging the seed coat so they can absorb moisture and start all the chemical processes involved in germination. We used sand paper to rough up one little spot on each seed, only a little bit is needed otherwise you could end up damaging the embryo as well as the seed coat. To check if you have done enough you can soak them in water for a few hours and see if they puff up a bit.


The kowhai seed we used is from a really old kowhai tree at Northburn. It seems to flower earlier than other kowhai so it would cool if these seedlings end up taking after its parent. I think kowhai take about 7 years to flower from seed so it will be a bit of a wait to find out.

Last week’s weather:

The evapotranspiration numbers have really dropped now, so not much irrigation is needed at this stage.



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