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Effective Measures To Control Powdery Mildew On Fruit Crops

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Fruit crops, in addition to pests, are often affected by various kinds of diseases. One such disease is powdery mildew. On the surface it seems harmless, but in fact it is a rather dangerous fungal infection. Powdery mildew - perhaps the most common fungal disease, which occurs literally on all crops: flowers, vegetables, berries and even fruits. The disease is caused by powdery mildew fungi (Erysiphales). In fruit crops, this fungus infection mainly affects leaf blades, but also occurs on shoots, flowers, and even fruits. This article is about it.

Effective measures to control powdery mildew on fruit crops
Gooseberry powdery mildew. © Which?"

Content:

  • Mildew on fruit trees - what is it?
  • Causes of powdery mildew
  • Symptoms of powdery mildew
  • Spread of powdery mildew
  • Multiplicity of powdery mildew
  • Preventive measures against powdery mildew
  • Effective measures of powdery mildew control

Powdery mildew on fruit - what is it?

At the very beginning of development, the marsupial fungus begins to form a fungus, it attaches itself to a leaf (shoot, fruit and so on) by appressoria and launches haustoria into its tissues. Further, as it develops, the powdery mildew fungus on affected leaf blades (shoots, etc.) of fruit crops begins to develop rather abundant conidial sporulation and eventually forms cleistothecia with bags and sacospores.

The most interesting thing is that even after natural death of a leaf blade (fruit), the powdery mildew fungus often does not die, it is well preserved in soil, in plant debris or under old bark. With the arrival of warmth, the fungus comes to life and spreads quite actively through the plants with its conidia, infecting them. Usually, four to ten days pass from the moment of powdery mildew infection to appearance of a whitish plaque containing conidia on leaf plate surface.

The speed of infection depends on weather, soil and air humidity, plant age and its general condition. Spores usually develop to full maturity within a month and a half or two to three months, very rarely longer. It has been noted that in warm weather with plenty of moisture in the soil and air, powdery mildew develops much more actively, and fruit crops in such seasons are less resistant to it.

Causes of powdery mildew

The powdery mildew is an infection that is easily transmitted through the air. In fact, it is present in the air in varying degrees almost constantly, but in order for the infection to begin to develop on the leaf plate (fruit, shoot, etc.), you need to put together several factors.

For example, the most active powdery mildew develops in the temperature corridor from +16 to +27 degrees, if the humidity is within 65-85%.

Multiple powdery mildew appears en masse on fruit crops at:

  • frequent and abrupt fluctuations in temperature;
  • strong rejuvenation pruning of fruit crops that weakens their immunity;
  • excessive doses of nitrogen fertilizers that dramatically increase the nitrogen concentration in the soil;
  • crowded plantings of fruit crops, which do not allow free circulation of air masses and prevent the natural evaporation of moisture from the leaves and soil surface
  • of irrigation regime violations, when the soil is moistened too much or, conversely, watered very rarely.
Effective measures to control powdery mildew on fruit crops
Apple fruit powdery mildew. © Jay W. Pscheidt

Symptoms of powdery mildew

Usually on fruit crops powdery mildew appears in the spring and very early summer, that is, in the first half of the warm season. The first affected leaflets (shoots) on fruit crops can be found already in the phase of bud formation. As we have already mentioned, powdery mildew appears most often in fruit crops on leaf blades, but it is often found on shoots as well.

In some years, when outbreaks of fungal infection are particularly strong, powdery mildew can be found on inflorescences as well, where a close examination reveals a very dense, whitish-blue film, which leads to significant deformation of inflorescences, their wilting and partial or complete fall off.

A whitish plaque is also formed on shoots at first, but with time, when the volatile powdery mildew spores mature, it turns brownish-gray in color, darkening with formation of fungus cleistothecia, looking like black dots on it. The development of powdery mildew fungus on leaf leaves leads to leaf growth retardation, curling, usually along the central vein, withering and falling off much earlier than it should.

In the beginning of fruit formation powdery mildew may appear on them, there you can also see a whitish film, which, however, disappears quite quickly, leaving behind a rusty net, which is very similar to that of hail or other mechanical influences on the fruit.

It is interesting that at the beginning of its development powdery mildew from any plant organs can be removed without a trace with a simple cloth or other means, but in just a few days in the same place the spots appear again and are already more serious in size. If no action is taken, the fungus will eventually become more dense and brown in color. Fruiting crops affected by powdery mildew severely stop their growth and development or these processes are strongly retarded, leaf blades wither and fall off before their proper time, echoing the flowers and buds.

Spread of powdery mildew

The powdery mildew is widely spread in Russia, its nearest neighboring countries, and the Baltic States. Powdery mildew is most active in Alma-Ata, Central Asia, Kazakhstan, Transcaucasia, as well as Armenia and Moldavia. There, the degree of infestation of fruit-cultures by this plague reaches 90%. In Krasnodar Territory, Georgia, Kyrgyzstan and Transcarpathia, the degree of infestation of fruit crops by powdery mildew does not usually exceed 60%; in the countries of Baltic Region, Volga Region and Black Earth zone, the extent of infestation by powdery mildew reaches 40%.

Effective measures to control powdery mildew on fruit crops
Vine powdery mildew. © The Ohio State University

Mildly developed powdery mildew

Harm from it can be almost unnoticeable, but when it develops strongly, the harmfulness can be very substantial and noticeable. As we have already pointed out, powdery mildew has a negative effect on the whole plant. A tree affected by powdery mildew is weakened, its immunity is depleted, growth and development are impaired, or growth ceases altogether. Affected leaf blades fall off considerably early, and affected flowers and ovaries also fall off.

If shoots are affected by powdery mildew in their initial stages of development, their tops begin to shrivel or become deformed. Depending on the degree of development, the crop may be reduced from 10-15% to 60%.

Most of the negative symptoms of powdery mildew are invisible to the eye. Thus, powdery mildew-affected plants greatly decrease winter hardiness, and usually the tips of young shoots and flower buds become extinct.

Mildew is especially dangerous in nurseries where seedlings grow quite close to each other and the disease actively spreads through neighboring plants.

Preventive measures against powdery mildew

As you know, any disease is much easier to prevent than to cure, powdery mildew is no exception here. To minimize the risk of powdery mildew in fruit crops, it is necessary to follow the scheme of planting, not to overgrow plantings, to water moderately - only as needed, not overwatering the soil.

To prevent powdery mildew, pruning with crown thinning and aimed at not allowing its densification can also help. In addition, you need to maintain order in the root zone: remove trash and plant debris, loosen the soil, remove weeds. Do not allow weeds to develop near fruit crops, in this case it is necessary to mow them or treat weeds with herbicides.

To prevent powdery mildew, it is necessary to treat fruit crops with chemical preparations, these can be fungicides, i.e. preparations for preventing and combating fungal infection, and more environmentally friendly preparations containing copper - copper sulfate, bordeaux liquid, copper chloride and the like.

Preventive treatments against powdery mildew must be carried out at least three times per season, starting in early spring and ending in late autumn.

Fertilizers also help to increase the immunity of fruit crops and strengthen resistance to powdery mildew. Thus, it is advisable to add potassium salt and superphosphate to the soil (usually 15-20 g per tree).

Effective measures to control powdery mildew on fruit crops Effective measures to control powdery mildew on fruit crops
Muddew on dogwood leaves. © Ric Bessin

Effective measures of powdery mildew control

If powdery mildew has attacked fruit crops, you should not delay the fight against it, it should be started as soon as you notice the appearance of a characteristic powdery mildew scum. It is important to focus on the period of fruit ripening, if it is less than three weeks before the ripening period, chemical preparations must not be used because harmful substances contained in fungicides can accumulate in fruits as well.

Urganly diseased fruit crops are treated against powdery mildew when it appears three or four times a season. As we have already mentioned, copper-containing preparations or more effective fungicides such as Topaz can be used for this purpose. Treatment with this preparation or other approved fungicide should be started as soon as the first fruit plant organs affected by powdery mildew appear, alternating once every 7-11 days, until symptoms of fungal infection have completely disappeared.

In addition to chemical preparations harmful to the environment, there are many completely safe, but therefore no less effective folk remedies against powdery mildew. These remedies are especially effective if the plants are still small, so that the entire vegetative mass can be treated as thoroughly as possible. Besides, folk remedies against powdery mildew can be used even during the period when the use of fungicides is prohibited for safety reasons.

The most common means of powdery mildew control is probably a solution of soda and soap. To obtain it, you must dissolve 60 g of ordinary table soda and 30 g of antibacterial soap in a bucket of water at room temperature. After that, the solution obtained must be applied three times to fruit crops affected by powdery mildew at intervals of 7-8 days.

Proven as a solution against powdery mildew solution of whey. To obtain it, dissolve a liter of whey in a bucket of water at room temperature, then stir well the resulting solution and treat the affected plants exclusively in dry weather four times at intervals of three days.

Effective measures to control powdery mildew on fruit crops
Mildew on the leaves of black currant. © Mariluna

A kefir solution also helps to deal with powdery mildew. To obtain this solution, take a liter of yogurt or well fermented kefir and dissolve in a bucket of water, then the resulting solution should be treated plants three times at intervals of four days.

To cope with powdery mildew, especially on young trees, and decoction of horsetail. You need to take 150 g of horsetail and pour 1.5 liters of water, let stand for 30 hours, then boil over low heat for 15 minutes. It remains to cool the broth, strain it, dilute it five times with water and you can carry out them up to five treatments at intervals of 3-4 days. It is worth remembering that this decoction can be stored in a cool place without access to light for no more than ten days.

In case of slight damage to fruit crops by powdery mildew, a mustard solution is a good way to cope with it. To prepare it, take two tablespoons of mustard powder and dissolve it in a bucket of water at room temperature. Then you can treat plants with this solution until the powdery mildew disappears.

Manganese solution will also help to exterminate powdery mildew, if it is not much on the plants. It is necessary to take 6-7 g of ordinary pharmaceutical manganese and dilute it in a bucket of water. With this solution, in addition to shoots and leaf plates, you can also treat ripening fruits affected by powdery mildew.

The ash solution is most effective on young plants with minor powdery mildew. It is also a good foliar feeding with potassium fertilizers and trace elements. To prepare the solution, dissolve about 800 g of wood ash in a bucket of water at room temperature, then let stand for five days. After this time, add 30 g of liquid antibacterial soap to the solution, strain the solution and start treating the affected plants.

Another infusion serving as both foliar feeding and powdery mildew control is cowpea infusion. To obtain it, 1 kg of cowpea, pour 10 liters of water and allow to stand for three days. Then the infusion should be filtered, diluted twice and you can treat the affected plants. This infusion is most effective against powdery mildew before flowering.

Effective measures to control powdery mildew on fruit crops
Mildew on the leaves of honeysuckle. © Steve Willson

The onion husk, its infusion is also both a fertilizer and a cure for powdery mildew. It is necessary to take 300 grams of the onion husk and pour 10 liters of boiling water over it. After that, the container should be tightly covered with a lid and allowed to infuse for 48 hours. After this time, the solution should be strained and used to combat powdery mildew. Such treatments are especially effective before and after flowering and in autumn, before the leaves fall off.

In general, powdery mildew is not such a dangerous disease, if a person with a certain level of knowledge about this disease follows the garden. The material provided in this article is quite sufficient to detect the disease and eradicate it, or, using preventive measures, to prevent the appearance of powdery mildew on your fruit crops.

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