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Winter treatments for fruit trees: where to start?

When to treat and prevent diseases and parasites

Whereas people use clocks and calendars to measure the passage of time, the life of plants is instead dictated by hours of daylight, temperature and water availability. Based on these environmental variables, deciduous trees – which include almost all fruit trees – lose their leaves in autumn and germinate in spring. During the coldest months, plants reduce their metabolism to the bare minimum in order to withstand ambient conditions that offer them scant resources.

In winter the sun is low on the horizon, so it heats less and hours of darkness exceed those of daylight: here in Italy, December is the month with the shortest days (or rather, with the fewest hours of daylight), while January is the coldest month on average. In February the days become noticeably longer and the sun's heat gets a littler warmer. But it is from autumn onwards that you can get a head start on diseases and parasites, to limit the chances of them reappearing in the warm season: read on to find out how...

Fruit trees and winter treatments

Winter is the prime season for pruning: we are talking about winter pruning or dry pruning. Prune fruit trees during the vegetative dormancy period, ideally around February. The aim is to thin out the canopy of the plants so that the leaves and fruits receive abundant sunlight, to reinvigorate the fruit-bearing branches, and to ensure that the vegetation doesn’t become too thick and remains at a comfortable height.

Depending on the size of the plants, the thickness of the branches, the hardness of the wood and the number of trees to be pruned, you can use pruning shears, a handsaw, lopper, telescopic saw and telescopic lopper or a chainsaw – which can be a pruning chainsaw – or a telescopic pruner. When using pruning tools, always wear suitable protective clothing: protective glasses, utility gloves and safety shoes are sufficient in the case of manual tools, but if you are working with a chainsaw or pruner, wear chain-resistant clothing, ear defenders or ear plugs and, when necessary, a helmet.

A fruit tree that is well looked after and properly pruned is likely to be healthier, less vulnerable to diseases and parasites, and more resilient if it does come under attack. Although most trees in the garden and countryside are bare during winter and everything seems still, in reality fungal spores and parasites still survive. They spend the coldest months nestled in the bark of tree trunks and branches, in hanging fruit, or hibernating hidden among fallen leaves on the ground and even in the soil, ready to torment plants when spring arrives and temperatures begin to rise.

On the other hand, in autumn/winter, plants can show signs of diseases that attacked them during the summer, such as dry branches, wood lesions and mummies (infected fruits with a characteristic woody consistency). Therefore, at this time of year it is good practice to inspect trees; it is also useful to consult plant health bulletins, which are typically issued by regional authorities to notify the agricultural sector about problems that have occurred in the area.

Even if there is no news of infection or infestation at the current time, it is advisable to treat your fruit trees nevertheless. Here in Italy, these autumn and winter interventions are called brown treatments (“trattamenti al bruno” or “sul bruno”), because they are applied directly to the brown, leafless branches rather than to the foliage. This process effectively suppresses many pathogens, lowering what is known as the inoculum potential. It basically means that you are reducing the risk of the disease or infestation reappearing the following season, along with the need to treat any affected trees. In practice, winter treatments on fruit trees are a preventive action.

Winter treatments should be applied two or three times on individual trees and in the orchard: once after the leaves fall (such as in November), again after dry pruning (in February) and ideally once more before the end of March, i.e. before vegetative activity restarts.

Winter treatments and prevention

After the leaves fall and before carrying out winter treatments on fruit trees, prune all parts that were infected during the previous spring-summer; otherwise, dry and damaged branches, mummified fruits and their attached branches may become sources of infection the following year. Don’t leave the cuttings on the ground; instead dispose of them away from the garden or orchard.

Some winter pruning tasks that we recommend bringing forward to the late autumn include removing broken and badly positioned branches from the fruit trees, and also cutting off suckers and water sprouts. The aim is to make the foliage more airy, thus avoiding conditions that favour infections and parasites. Remember to disinfect the pruning tools that you use to work on infected or previously diseased plants (bleach is fine for this purpose).

Clear the area at the base of the plants, not only of pruning debris but also of fallen fruit, dry leaves and tall weeds (for the latter use a brushcutter, or even a multifunction brushcutter, which can then be converted into a pruner using the dedicated accessory). Brush the trunk and thicker branches (limbs) to smooth the bark, so that they don’t become a refuge for adult parasites or their eggs and larvae.

Winter treatments on fruit trees: what action to take

We mentioned that winter treatments on fruit trees are preventive interventions, to lower the risk of trees developing new diseases and infestations that already occurred in the previous spring-summer. In fact, it is not advisable to treat plants by sticking rigidly to fixed deadlines or certain stages of their life cycle.

If you grow pome fruits such as apples and pears, treat these trees with Bordeaux mixture to prevent typical fungal diseases like scab and cankers of the wood. Bordeaux mixture is also effective against brown spot, a serious cryptogamic disease that affects pear trees.

Bordeaux mixture is a traditional fungicide based on copper sulphate and hydrated lime. It is a powder that you dissolve in water and apply with a mistblower or sprayer pump (wear protective glasses and a face mask when doing so). You can buy ready-made Bordeaux mixture, or prepare it yourself by weighing and mixing the components to adapt it to your specific needs (instead of having a neutral pH, you can make it more acidic or alkaline). Follow the doses prescribed on the label or – if preparing it yourself – the correct proportions, because copper can be toxic to plants and accumulate in soil. Spray the Bordeaux mixture evenly over the entire trunk and all the branches, both large and small, without neglecting the least accessible bits. This fungicide forms a chemical barrier that acts on the surface, so take into account the weather forecast, to avoid the rain washing it away before it has time to take effect.

 

You can also protect pome fruits against mealybugs by spraying white oil, an insecticide used in organic and conventional agriculture that is derived from petroleum distillates and is effective against insects at all stages of their life cycle (from eggs to adults). It is water-soluble and must be diluted with water according to the dosage indicated on the bottle, before being applied with a mistblower or sprayer pump. It is not compatible with several fungicides – including copper-based products such as Bordeaux mixture – so such treatments should be spaced 2-3 weeks apart. Also as regards pests of pome fruits, you can ward off attacks by codling moths and tingidae by brushing the trunks and keeping the area under the tree clear of fallen fruit, dry leaves etc.

For stone fruit trees – like apricot, cherry, peach and plum – the main problem is brown rot or moniliosis, a fungal disease: prevent it from reactivating by treating peach trees with sulphur and other stone fruit trees with Bordeaux mixture. In addition to preventive winter treatments, other measures are important against brown rot, such as removing mummies, applying fertiliser sparingly, and pruning in order to aerate the foliage. Another common disease of stone fruits is coryneum, which you can also prevent using Bordeaux mixture. This fungicide is equally effective in stopping the recurrence of leaf curl and cankers which affect apricot and plum trees, and the fearsome peach leaf curl and cherry leaf spot. Prevent mealybug infestations on stone fruit trees with white oil, together with careful fertilisation and pruning so as not to create conditions that favour recurring outbreaks.

Do you have a vineyard? Here's how to prevent and treat mealybugs and powdery mildew, which are among the main enemies of vines. One job that needs doing in the vineyard in autumn is the annual production fertilisation. The arrival of colder temperatures is also a reminder that you need to protect garden plants and vegetables on your winter allotment. If you don't already have one, here are our guidelines for planting an orchard.

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