Latvia is currently seeing one low-temperature record fall after another, and in many parts of the country the air is cooling to as low as -25 °C and -29 °C. Forecasts suggest that such temperatures will persist into part of February as well. On top of that, a thick layer of snow covers the ground in many places, creating a favourable environment for rodents. How will weather of this kind, typical of winter yet almost forgotten in Latvia, affect winter crops, and will it spring any unpleasant surprises on farmers? The question is especially topical right now, because how well winter crops come through the winter will be decisive not only for yield potential in spring, but also for the economic stability of farms in the coming season.

Snow cover acts as a natural insulator

While we are not yet even at the midpoint of the calendar winter, it is too early to draw final conclusions about how the winter will end; nevertheless, judging by the current weather, in most regions of Latvia the winter crops lying under snow are relatively safe at present. Although this winter set in comparatively late, experience from previous years shows that far greater losses to winter crops have been caused by snowless winters with severe frost. Snow cover acts as a natural insulator, shielding plants from the direct effects of the cold.

Although the situation may differ from region to region, on the whole the winter crops under snow are currently in relatively safe conditions. It is precisely snowless winters combined with severe frost that are the most dangerous – in such conditions the frost acts directly on the plants, damaging the root collar and plant tissue, so that winter crops are weakened or fail to survive to spring at all. At the same time, an excessively thick snow cover, especially if it lies for a long period on unfrozen soil, can create additional risks, because plants beneath the snow may become smothered and more susceptible to disease.

Snow cover of up to 40 cm

Successful overwintering depends on a combination of several factors – the depth to which the soil is frozen, the thickness and density of the snow cover, and how often thaws occur. The depth of soil freezing in Latvia currently ranges from 10 cm to as much as 30 cm in some parts of the country, while in places the snow cover has reached as much as 40 cm, according to data from the Latvian Environment, Geology and Meteorology Centre. This situation provides protection against frost, but it also increases the risk of snow mould developing, particularly where the snow has become compacted or where drifts have formed.

If the seed has not been dressed, yield losses can be substantial

Snow mould pathogens thrive in damp conditions with a persistent snow cover. The risk is greatest when temperatures hover around zero for a prolonged period and the snow cover lasts a month or more, especially if it has formed on unfrozen soil. Even in changeable winter conditions, more sensitive varieties can suffer from snow mould, particularly if the seed has not been treated. In such cases plants suffer from root collar rots, overwinter poorly or die off. If conditions favour disease development and the seed has not been dressed, losses can be very considerable. Research shows that in some years, comparing untreated and treated winter wheat fields, yield losses can reach as much as 4 tonnes per hectare. One of the most effective ways to protect seed from disease is seed dressings, especially those containing fludioxonil. They protect plants during the early stages of development in autumn and reduce the impact of pathogens over the winter.

In spring, snow can be a valuable source of moisture

At present, farmers should not be worried about crops lying under snow. Although recent winters have been starkly different – either snowless and mild, or very cold – this year the situation is so far more favourable. Attention should nonetheless be paid to regions where the snow cover is very thick and the soil has not frozen. If there is a great deal of snow but the winter oilseed rape beneath it is still growing, the snow can break its leaves. In spring, however, those leaves are no longer important to the plant; what matters most is that the root collar remains viable. Despite the risks, snow can prove a significant benefit in spring. As it melts gradually, it allows moisture to soak evenly into the soil and helps winter crops resume growth successfully. Snow is rightly called the water of life – it moistens the fields and helps plants recover after winter. This year, though, there is also a risk that a large volume of water may delay spring work and make it harder to get machinery onto the fields.

The risk posed by rodents

A further risk comes from rodents, mice in particular. A thick snow cover gives them ideal conditions – it is warm beneath it, and if the soil is not frozen, rodents dig burrows and damage the crops. Pest control is therefore very important. For now, however, it is not yet possible to predict how quickly the snow will melt or what the situation will be once it has gone.

This winter's weather is at present more of an ally to winter crops than an enemy. The snow cover protects them from sharp frost, while gradual melting in spring will provide valuable moisture for the resumption of growth. The greatest risks lie not in the frost as such, but in a very thick snow cover, unfrozen soil and rodent activity, the consequences of which will only become fully visible once the snow has melted. For now, the most important thing is to follow how the situation develops in spring.