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Once harvest is over and as leaf fall begins, we come into an important period for control of diseases which enter the plant through the leaf scar tissue, carry over on fallen leaves, or become active in the cooler autumn conditions.
Leaf scar invaders:
- European Canker (pipfruit)
- Bacterial Blast (summerfruit, pears)
- Bacterial Spot (summerfruit)
Leaf carry over:
Cooler autumn activity:
Control measures are as follows.
Leaf Scar Invaders
Pre leaf fall and leaf fall copper sprays. For best results formulations with strong residue persistence will give the best results. Bordeaux mixture made from copper sulphate, hydrated lime is generally considered the most persistent form of copper spray. At the beginning of leaf fall, the 600 g copper sulphate to 800 g hydrated lime per 100 l concentration is used. For end of leaf fall sprays, the copper sulphate is increased to 1 kg/100 l, but the hydrated lime remains at 800 g/100 l. Substitute ready mix Bordeaux and copper oxychloride formulations are also suitable.
The objective of these copper sprays are to maintain sufficient copper in rain splash to protect leaf scar tissue from invasion by disease.
Black Spot
Where black spot has been seen in the crop, there will be many leaf infections for carry over of the disease into next year.
A pre-leaf spray of urea at 5 % concentration (5 kg/100 l) just as the leaves are falling will reduce ascospore release next spring. The urea enriches the leaves with nitrogen, which will hasten their breakdown. In addition to enhancing leaf breakdown, this high rate of urea also has an inhibitory effect on ascospore development. For this effect, urea concentration is quite critical.
Phytophthera
With the autumn rains and cooler soil temperatures, phytophthera root rots become active. Orchard blocks with a history of phytophthera problem, particularly replant orchards on MM106 need preventative sprays of a phosphorous acid based product as soon as the crop has been harvested, while there is still good leaf activity for uptake.
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