Peter Cundall: Guru’s advice for foiling fungal problems
Recent heavy rainfalls are causing many problems for gardeners from leafcurl in nectarines to more serious fungal diseases such as apple and pear scab, writes PETER CUNDALL
Fungal diseases of every kind are now causing serious problems in all parts of our Tasmanian gardens
Let’s face it, this spring’s persistent rains have produced positive results. Farm dams are now brim full, the growth in most gardens has been phenomenal and many moisture-loving fruit trees, especially pear, apple, plum, cherry and apricot have clearly been thriving because of extra moisture in the soil.
Unfortunately many negative aspects of heavy rains and saturated soils are also appearing and the results can be devastating. Fungal diseases of every kind are now causing serious problems in all parts of our Tasmanian gardens.
Anyone growing peach or nectarine trees will already be seeing the destruction caused by leafcurl. Once foliage has been infected it is too late to spray for control. All we can do is pick off all distorted leaves on which the leafcurl fungus has started to bloom, leaving the youngest, healthy leaves untouched.
Other serious fungal diseases now infecting some fruit trees have been encouraged by rainfalls late in the day or at night. They cause leaves to remain wet for hours, allowing disease organisms to gain access to fruit and even young shoots.
Apple and pear scab are serious fungal diseases and both operate the same way. Parasitic spores arise from the diseased remains of last summer’s leaf and fruit debris, still lying beneath trees.
The spores settle on leaf surfaces but cannot penetrate unless conditions remain wet for several hours. That’s why evening and night rainfalls can be so deadly. Later the disease organisms move on to immature, developing fruit causing unsightly scabs, which in turn make apples or pears become distorted and inedible.
During the day, even an odd shower does little harm because leaves dry off
during warm, sunny periods making it difficult for the disease to penetrate.
Disease control is also why we prune trees, shrubs and roses to open up overcrowded canopies to allow drying air to circulate freely, preventing infection.
Scab diseases prefer the slightly acidic surface of leaves in order to survive and thrive. I’ve found reasonable control can be achieved by making leaf surfaces alkaline and unattractive to scab organisms.
I do this by spraying all the foliage with lime water – nothing more than a big, double-handful of fine, white builders’ lime mixed into a large bucket of water.
When sprayed over the trees, the mixture dries off so leaves become heavily spotted with white lime. To get the spray over the tops of large tree canopies I slide a 2m long piece of conduit over part of a hose to stiffen it. A spraying device is then attached with a tube linked to the bucket of lime water. This allows me to use normal water pressure from a tap which also sucks up the lime mixture to effectively cover all leaves.
The builders’ lime does no harm to the trees, but even provides calcium while also helping control pear and cherry slug, also a serious pest of hawthorn, quince and Japanese plums,
The other fungal disease spread by rain is quince ‘fleck’. This too results from spores arising from last autumn’s debris. The fungus first shrivels leaves, then attacks the fruit causing it to turn black and split.
Quince trees prefer acidic soils so I avoid using lime water. Instead I prune off all leaves and small branches showing early signs of infection. It also helps to prevent the disease spores from rising if thick layers of overlapping newsprint are spread beneath quince trees, extending from the trunks to well beyond drip-lines.
The newsprint is wetted and weighed down with sheep manure, blood and bone or pelletised poultry droppings.
Finally they are covered with a heavy mulch of straw. This organic material seals in moisture, then gradually rots away during summer to gradually enrich the soil.