Mildew

By : | 0 Comments | On : March 10, 2016 | Category : Gardening

Mildew is a fungal disease which occurs in damp conditions, sometimes decimating a crop almost overnight, and is one of those things where prevention is better than cure.

Mildew got its name from the Old English for honeydew. This is a sweet substance covering the leaves and stems of plants which are heavily infested by aphids. When the aphid pierces the sugar-rich tubes inside the plant, the sweet liquid, under pressure, gushes out of the aphid and covers everything behind. The sugar becomes food for all sorts of fungi and almost invariably the plant becomes infected by fungi.

You don’t necessarily need honeydew or aphids to get mildew however, it’s a term which covers a large number of infections. There is usually a combination of blotchy staining or powdery growths, and a very distinctive smell. Most mildew thrives in damp, warm conditions and can be very troublesome in polytunnels and greenhouses, especially in the early stages of seedling growth or in plants nearing harvest.

It can be found in hot weather where damping takes place with a lot of water without adequate ventilation. Fungal spores are spread by draughts but also by water splashes.
With most mildews you might not notice the fungal spores, and spore-bearing bodies, all you might notice is the partial yellowing of leaves. There is usually a distinctive, earthy musty aroma, which should give you a clue.

Other symptoms
Apart from decaying leaves, plant growth is usually stunted. Flowering and fruiting are affected and the plant can wilt because the fungal mycelium cause restriction in the vascular tissues. Fruit, such as grapes, can be completely ruined and you might smell alcohol as well as the mustiness.

Cure
There is no real cure for mildews, especially for the amateur gardener. The best policy is to avoid the problem in the first place.
The main problems occur when the plant has been under water tension – in dry conditions. All herbaceous plants are held together by hydraulic tubes which become increasingly taut as the plant tries to stay upright in dry conditions. Suddenly the tubes snap one by one, and the tissues around the tubules are damaged. These sites become the perfect centre for infection by fungal spores, so prevention is largely a measure of making sure the plant is well watered, which seems paradoxical when you consider that water is one of the promoters of the disease.

Keep plants well watered.

Mulch to preserve soil moisture.

Reduce humidity by weeding, pruning and greater spacing between plants.

Make sure the plants are as well fed as they need to be, without having too much soft growth.

You can buy varieties which are more resistant.

Saving the day
If you notice mildew you can prune it out and use the plant quickly. Make sure the affected parts do not touch the soil and don’t compost them – burn and then add the ash to the heap. After this you can give a spray of Bordeaux Mixture so long as there is plenty of ventilation too. You can also dust with sulphur, especially on the soil and on any cut areas.

There is usually a distinctive, earthy musty aroma…
Most mildew thrives in damp, warm conditions…
You can buy varieties which are more resistant.




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