Probably, almost all truck farmers faced the appearance of yellow spots on the broad cucumber leaves, after which the plant ceased to grow, bear fruit, and soon died. Moreover, this pattern is observed with the same periodicity both in the open ground and in the greenhouse, which is protected from the majority of pests. Where does this attack come from and can it be overcome? Let's try to consider the reasons for which there are yellow spots on the leaves of the cucumber, and at the same time and ways to deal with them.
If we are talking about an amateur inexperienced in agrotechnics, we can assume a banal burn of leaves. It occurs when the water remains on the leaves in hot sunny weather. Rounded droplets create a lens effect, and the living tissue underneath them is burned by a focused sunlight, resulting in spots on the leaves of cucumbers and their young fruits. That is why all plants, and especially cucumbers, are recommended to water either early in the morning or in the evening, so that before the heat, the plants can dry out. If this is not possible, it is advisable to use lower irrigation in the aisles, leaving a relatively dry area around the stem to avoid decaying the roots.
The next factor leading to the disease of the plant is the deficit of some minerals in the soil. To yellowing green can lead to a lack of potassium or magnesium, and this manifests itself usually on old leaves. In this case, the yellow spots on the leaves of the cucumber usually appear first along the edges, and then gradually seize the space between the streaks. If such a sign is observed in one or several plants, then it is necessary to urgently 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 affecting both very young and formed whips. Yellow patches of pale yellow color and regular rounded forms on the leaves of cucumbers usually indicate infection with anthracnose or ascochitis. It is caused by a special fungus, preferring a warm moist environment. He presents a special danger in rainy periods and with abundant fall of dew. In this disease, it is also possible to observe the appearance of dark brown or black dented spots on the petioles, stems and fruits of the plant. Carriers of the fungus can be infected seeds and plant carriers that winter in the soil. As an operative treatment can be used spraying with phytosporin or 1% solution of Bordeaux fluid. And in no case should the damaged plants be left for winter! They must be burned as soon as possible so that the spores left inside the stem can not affect the next planting.
Another dangerous disease, which results in yellow spots on the leaves of the cucumber, is considered to be downy mildew, or peronosporosis. It usually develops in 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 leaf dies. Under favorable conditions for fungus (temperature drops, high humidity, etc.), this infection is actively transmitted with water in rains and watering and leads to plant deaths within 1-2 weeks after infection.
In addition to the fungus, yellow spots on the leaves of the cucumber can cause a virus of ordinary mosaic. Despite the innocuous name, this disease is very dangerous for plants, especially young ones. Its carrier is the melon aphid, which hibernates in the roots of infected weeds. Chemical methods of combating mosaic ordinary do not exist yet, therefore, to prevent it, it is necessary to observe a crop rotation and to get rid of weeds in a timely manner.