Since they were first detected in the blueberry orchards of the country, a few years ago, wood diseases have become one of the main sanitary threats to this crop, because their occurrence is associated with the fall in yield productive of plants.

"Our experience indicates that we can have a negligible loss of productivity or up to 100%, in the most serious cases," says Andrés France, phytopathologist at INIA Quilamapu.

Although the definitive elimination of these pathologies from the orchards is almost impossible, in recent years some strategies have been developed, based on the implementation of various management and the application of chemical and biological treatments, which allow them to live with them, extending the shelf life of plants.

Bet on prevention

The first symptoms of these diseases, mainly caused by fungi and bacteria, usually occur within the branches and twigs, so they are very difficult to detect.

"In fact, growers often discover that plants are being attacked only when the colonization of pathogens is very advanced and, therefore, there is already significant damage at the wood level," says Daina Grinbergs, phytopathologist at INIA Quilamapu.

For this reason, experts agree that the best way to avoid problems is to bet on prevention.

In that sense, they say, the first step to be taken is to make sure that the plants that are going to be established in the garden do not carry any of the pathogens that cause these diseases.

In order to support producers in this management, Andrés France says that at INIA they are working on the development of a kit that will allow, through the analysis of a small sample of material (leaves), whether the plants, especially those that do not have symptoms, are effectively free of silver plating, one of the wood diseases with the highest prevalence in blueberry orchards.

"Our idea in the future is to expand the capacity of this tool to help determine the presence of other diseases of wood and other fruit," he says.

The pruning factor

Once the producer manages to determine that any of these diseases is within his orchard, the best path he can take is to carry out sanitary or cleaning pruning, which consists in eliminating all the branches that show symptomatology.

"Subsequently, all this material must be buried, burned or, ideally, composted," says Daina Grinbergs.

According to Andrés France, the problem is that, in general, sanitary pruning is done in a defective way.

“There are even some producers that only lower the branches so that they rebound from a bud closer to the ground. However, that makes no sense, if we consider that this type of disease usually colonizes the crown of the plant. Thus, the most appropriate is to remove the entire branch by stripping from the base, ”explains Andrés France.

Experts also recommend that pruning be done in late summer or when there is high radiation, in order to minimize the risk of infection.

"Many times the producers do this work in winter, when the fungal fruit bodies release spores that will infect pruning cuts," says Daina Grinbergs.

They also advise that the time elapsing between the completion of the cuts and the painting of the wounds does not exceed four hours.

“I have had to see cases where farmers leave the painting process for the day after pruning, which is negative for the health of the garden, because the pathogens have plenty of time to enter through the wounds,” adds Andrés France .

The two big threats

Although in Chile more than 10 diseases that fall under the categorization of wood pathologies have been detected, there are two that have the highest prevalence in the blueberry orchards of the country: silver, produced by Chondrostereum purpureum; and the neck canker, caused by Neofusicoccum spp.

The canker of the neck, whose presence is extended in almost all the surface of crop of the cranberry in Chile, usually generates chlorosis in the leaves and redness in the leaf lamina, and a fast drying of the foliage.

“In addition, the death of the branches, which is sudden, tends to occur in mid-summer. Thus, without adequate control, the plant will gradually weaken until it perishes, ”warns Andrés France.

For its part, the kicking, a disease that in Chile has been studied since 2005 and that is present in a large part of the blueberry production area, is characterized by showing branches with less vigor and leaves with a coloration between leaden and silver, caused for a toxin

"As the disease progresses, other branches show symptoms until the entire bush is compromised," says Andrés France.

One of the reasons that makes treatment of this disease difficult is that the silver strains that exist in Chile are more aggressive than those in other parts of the world.

"This situation has led to significant damage and loss of yield and quality of fruit, in addition to reducing the longevity of the gardens," says Daina Grinbergs.

Support plants

Wood diseases that usually attack blueberries, in general, are characterized by slow progress. Thus, it is not uncommon for several months - or years - before the affected plants begin to show external symptoms.

At that time, experts say, it is essential that producers do everything possible to prevent plants from stressing.

“The greatest threat that exists today, especially in summer, is high temperatures, so if the producer suspects that these diseases are present in his orchard, the best will be to use any of the tools that are available in the market and which aim to reduce the stress of plants, such as protection meshes, sunscreens and resistance inductors, ”says Andrés France.

Complementary treatments

Although there are various chemical alternatives on the market that promise to effectively combat the various diseases of wood, experts say that none of them is 100% effective, because it is very difficult for them to penetrate the interior of the wood the plant, which is where these pathogens are housed.

Therefore, in addition to performing traditional chemical management, it is recommended to carry out complementary biological treatments. In that sense, one of the ones that has shown the best results to date are the applications of compost tea, a product that arises from the fermentation of organic vegetable matter and the mixture with guano, and that is capable of providing a high microbial load and growth metabolites.

According to Andrés France, it is an effective resistance inducer, which if used frequently, in high doses (minimum 6 thousand liters per hectare per year) and applied from the beginning of sprouting, that is, when the Buds begin to swell, can even reverse the disease.

“We have seen cases of reversal of plants that have healed thanks to the applications of this product. The opposite case has also been seen, of plants that have become ill again after discontinuing the use of compost tea. The best thing is that it is a cheaper treatment than chemical applications, although its use is complementary, ”he warns.

An important aspect in the use of this biological control method is to ensure that compost tea is of good quality, that is, that the compost is stabilized and recent.

“You have to avoid using compost for more than one manufacturing season,” warns Andrés France