Experts suspect the problems stem from cultivation practices rather than pathogens, but they are not ruling anything out.

Technicians from La Unió de Llauradors show researchers from the Ministry of Agriculture multiple cases in the Plana Baixa region

Alarm has begun to spread among farmers in the Plana Baixa region, as well as in other citrus-growing areas where problems of yellowing and defoliation of trees are occurring, the causes of which are still unknown.

Given the scale of the problem in the plantations of various municipalities in Castellón, La Unió de Llauradors has called on the Ministry of Agriculture and the Valencian Institute of Agricultural Research to take action and study with special dedication what is happening.

The representatives of La Unió have shown several affected plots to Vicent Dalmau, technical manager of Plant Health of the conselleria, and Antoni Vicent, expert in mycology and citrus pests of IVIA.

According to Carles Peris, head of citrus at La Unió, the visited plots are suffering from severe defoliation, which was already noticeable last year but worsened since last spring. They are mostly located within the municipalities of Vall d'Uixó, Vila-real, and Burriana, although the affected areas extend further afield. The purpose of this initial visit was to raise awareness of the problem, examine trees, and collect leaves for analysis.

The symptoms of decline and defoliation are varied and do not always coincide in adjacent areas. Sometimes leaves appear with necrotic tips, which is usually a clear indication of salinization, but analyses of the irrigation water and the salt content of the leaves themselves reveal that this is not the cause. Fungal attacks also commonly occur, although most of the time these are saprophytic species that take advantage of weakened plants, but they are not the pathogens that initiate such weakness.

Peris indicated that in La Plana, the predominant cases of yellowing and decline don't begin with an abundance of necrotic leaves, like those shown in the photo below, but rather with the widespread appearance of trees like those in the image above. He noted that "they lost their spring growth and the twigs were left leafless.".

Based on the initial findings of the researchers, Dalmau and Vicent are more inclined to believe that the ailments could be related to physiological disorders or culture patterns rather than to pathogens, although these may be present, but they believe only incidentally. However, they are not ruling anything out, as the investigations have only just begun.

It is true that salt-related issues can be ruled out initially, because the problems appear both in areas irrigated with potentially more saline water and where concentrations are well below problematic thresholds. Occasional salinization due to excessive fertilization in the root zones where drip irrigation is used is also ruled out; or at least it is not a definitive cause, because the same symptoms appear in the same areas, using the same water, but with flood irrigation and without recent fertilization.

Vicent and Dalmau proceeded to carry out small tests in root zones, to see if there was root hair (the absorbent roots of the trees) and verified that it had not been lost, so they also ruled out that the cause could be there.

The existence of widespread Phytophthora and Mycosphaerella fungal infestations was discussed among them and the technicians from La Unió, but they believe these are not the root cause of the problem. A higher incidence was also observed in the Clemenules, Clemenvilla, and extra-early Clementine varieties (although it is also seen in orange trees), and the Carrizo rootstock was found to be the most susceptible, while the Citrumelo was the least.

VICENTE LLADRÓ

http://www.lasprovincias.es/economia/agricultura/201607/04/ivia-estudia-decaen-naranjos-20160703235724-v.html