Probably, almost all gardeners encountered the appearance of yellow spots on wide cucumber leaves, after which the plant stopped growing, bearing fruit, and soon died at all. Moreover, such a pattern is observed with the same frequency both in open ground and in a greenhouse protected, it would seem, from most pests. Where does this misfortune come from and can it be overcome? Let's try to consider the reasons why there are yellow spots on the leaves of the cucumber, and at the same time ways to combat them.
If we are talking about an amateur inexperienced in agricultural technology, we can assume a banal burn of leaves. It occurs when water remains on the leaves in hot sunny weather. Rounded droplets create a lens effect, and living tissue beneath them is burned by a focused sunbeam, resulting in the formation of spots on the leaves of cucumbers and their young fruits. That is why all plants, and especially cucumbers, are recommended to be watered either early in the morning or in the evening, so that the plants can dry before the heat sets in. If this is not possible, it is advisable to use the lower spacing between the rows, leaving a relatively dry area around the stem to avoid decay of the roots.
The next factor leading to plant disease is a deficiency of certain minerals in the soil. A
lack of potassium or magnesium can lead to yellowing of greenery, and this usually manifests itself on old leaves. In this case, yellow spots on the leaves of the cucumber usually appear first at the edges, and then gradually capture the space between the veins. If a similar sign is observed in one or more plants, then it is urgent to carry out mineral top dressing in order to protect the rest from premature wilting.
It will be much more difficult to cope with various fungal diseases that affect both very young and formed lashes. Yellow spots on the leaves of cucumbers that are pale in color and have a regular round shape usually indicate infection with anthracnose or ascochitosis. It is caused by a special fungus that prefers a warm, moist environment. It poses a special danger in rainy periods and with abundant dew. With this disease, it is also possible to observe the appearance of dark brown or black depressed spots on the petioles, stems and fruits of the plant. The fungal carriers can be infected seeds and host plants wintering in the soil. As an operative treatment, spraying with phytosporin or a 1% solution of Bordeaux fluid can be used. And damaged plants should never be left for the winter! They need to be burned as soon as possible so that the spores remaining inside the stem can not affect the next plantings.
Another dangerous disease, as a result of which yellow spots appear on the leaves of the cucumber, is considered downy mildew, or peronosporosis. It usually develops during the period of active fruiting - in late July or early August - and manifests itself in the form of small bright yellow dots. Over time, they increase, and then the sheet dies. Under favorable conditions for the fungus (temperature changes, high humidity, etc.), this infection is actively transmitted with water during rains and watering and leads to the death of plants within 1-2 weeks after infection.
In addition to the fungus, yellow spots on the leaves of a cucumber can cause an ordinary mosaic virus. Despite the harmless name, this disease is highly dangerous for plants, especially young ones. Melon aphid wintering in the roots of infected weeds is its carrier. Chemical methods to combat common mosaic do not yet exist, therefore, to prevent it, it is necessary to observe crop rotation and timely get rid of weeds.