Why can’t we defeat late blight and other fungal diseases

Why can't we defeat late blight and other fungal diseases
Why can’t we defeat late blight and other fungal diseases

Every owner of a garden, large estate, or allotment has probably heard the phrase “fungal plant diseases”. Furthermore, absolutely everyone encounters these diseases in their gardens every year, whether they know it or not.

After all, 80% of all possible plant diseases are caused by plant pathogenic fungi. Many gardeners naively believe that if they just fill a sprayer with the right fungicide preparation and treat their garden, the problem is solved.

But this is not the case. Fungal diseases are difficult to control and cannot be completely defeated. And why not? Let’s try to find out.


Fungal diseases are not only very common but also very destructive. Yield and quality of fruits are reduced, decorative properties become poor and, as a rule, plants remain awake for a long time after the onset of the disease.

For fruit and berry crops, the weakened plant immunity is fraught with severe winter frosts, while for vegetable crops, it is yield loss (plus crop loss in storage).

Usually, we are faced with the external manifestations of fungal diseases: spots and sores (scab, phytophthora, rust), scars (powdery mildew), swelling and cracks in the trunk (cancer), and plant wilt. Let’s first take a closer look at how fungal diseases affect plants.

Powdery mildew

Let’s start with powdery mildew, which is one of the most common fungal diseases. First, a white coating appears on the leaves, on the ends of young shoots, and sometimes on the inflorescences, which thickens over time and becomes felt-like. Naturally, this patch does not allow the plant to develop properly, it produces poor fruit and growth, and may even die. If the humidity and temperature are right, powdery mildew will affect almost all garden and vegetable crops.


Small yellow-orange spots (similar to rust) appear on the upper side of the leaves. These spots gradually increase in size, causing the leaves to shrivel and fall off prematurely. The entire shoot also wilts. Naturally, it is weakened and will not survive the winter.


Dry spots form on the leaves and overtime these spots spread to the plant’s stems, flowers, and fruits, gradually fusing with each other. In midsummer, it will already have lost its leaves. Yield or ornamental value cannot be expected.


Usually, it affects the entire plant. But it starts with small wounds on the bark, where the pathogen penetrates. Brown spots appear on the leaves, the leaves fall off, the fruit rots and mummifies, and swellings, flab and deep cracks form on the trunk and branches. In just a few years, the tree dies.


Every gardener is familiar with it – black spots on the leaves stems, and fruits, on the opposite side of the leaves – white fuzz. Fruits do not have a marketable appearance and are not fit for use, and the plant dies. Not only that but healthy-looking fruit, left in a basement or warehouse, gets infected and rots, infecting its truly healthy counterpart.

I think this is enough of an example. There are many fungal diseases, just as there are many recipes to combat them. Except that every year, they re-attack our plants. There are several reasons for this.


Disease spores overwinter in the soil and fallen leaves

Disease spores usually survive the winter in fallen leaves and in the soil beneath plants. They do not need to survive winter or frost. Therefore, the first suggestion, to dig around the plant bed, does not work at all.

Yes, some of the spores will go deeper and become harmless, but some – which will inevitably remain on or near the surface – will attack your plants with renewed vigor in the spring.

Wind-borne fungal diseases

Most fungal diseases are spread by wind – lightweight spores travel well over long distances in the air. Therefore, even spraying your garden with the latest fungicide will only protect it temporarily.

Within a few weeks, a breeze from an adjacent untreated or abandoned property can bring you a new batch of harmful tenants.

Not the “right” fungicides, or using them incorrectly

Yes, there are fungicides – and this is a special topic because many gardeners use them completely wrong.

They either save money and dilute them at a concentration lower than the instructions, or conversely, just to be sure, they use too high a concentration and harm the plants.

Some modern preparations (also stated in the instructions) work only in the specified temperature range. Their application, for example in early spring or late autumn, is absolutely useless at 41°F (5°C).

Unfortunately, due to the high demand, fake preparations from well-known manufacturers are often sold on the garden market, from which, of course, there is no possible use at all.

There is also the option of inexperienced gardeners buying a preparation that everyone praises without really understanding that this insecticide is used only to control insect pests and not to treat fungal diseases.


A separate topic is folk remedies. Infusion of various herbs (horsetail, garlic), drugs (trichloromethane, manganese, or iodine), even milk whey – can be tried and all seem to produce results.

But the efficacy of such preparations is questionable. If they are effective, they are only one step away from dealing with the disease.

The same is true, for example, of biological agents like “biocides. No, it is effective, but it is not so effective to get rid of phytoplasma epidemics forever. Diseases come back again and again …….


Is it possible to get rid of a biological fungicide forever
Is it possible to get rid of a biological fungicide forever

Well, is there no way to get rid of this scourge once and for all? In fact, there is. All fungal diseases of plants develop and feel good under certain conditions – high humidity and proper temperature.

It is possible to keep a site in dry air at all times and get rid of it from many problems (but many are acquired). But this is not really the way to go.


What we gardeners need to do is to keep the spread of fungal diseases under control and not allow them to significantly weaken the immunity of the plants.

This requires a series of measures from early spring to late fall. Let’s remember which ones.

  1. you should not plant too densely, and the plants themselves need to be thinned – pruned.
  2. Despite this, it is worth recultivating the root zone (there will still be fewer spores surviving). And you can cover it with a thick layer of plant waste (e.g. hay).
  3. Don’t get carried away by nitrogen fertilizers, but focus on phosphorus and potassium fertilizers, which can improve the immunity of the plant. The presence of a full set of micronutrients in the soil is also welcome.
  4. Eliminate all diseased and affected plants or parts thereof. However, it is worth remembering that by removing the top of a potato infected with Phytophthora, for example, you will take it across the plot and safely disperse the spores.
  5. Treat your garden and vegetable garden regularly with fungicides according to the instructions and timing. In the case of flowering and fruiting – use biological agents or folk formulas. By the way, it is worth treating the garden regularly to prevent insect infestations. Often, the wounds they cause are the entry points for diseases.
  6. And – perhaps most importantly! Plant varieties resistant to fungal diseases (there are some). But it must be said that total resistance is a myth, and under certain conditions, they (our resisters!) can also attack.

It is good to provoke your neighbors to implement these measures, and it is better to do it with you. But I guess that’s something other than fantasy.

Good health to you and your plants!

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