I have a few palm trees that look like this. Advice appreciated

 

I'm not sure without knowing more about the growing conditions, soil and water management, but this is common with water issues and sometimes made worse with nutrient deficiencies and salts. 

 

Contributing factors can be water deficit/drought stress, or radical changes in water availability sometimes due to irregular irrigation, or wet during rainy season and then left to dry out too much without watering during dry season. Mulching the soil surface during the dry season and establishing a good watering program is important. 

 

Looking at the photo, is that white material a rock/gravel on the soil surface? If so, it can reflect heat onto the palm trunks. Mulch with organic matter may be a better ground cover. 

 

It can also be compounded by calcium deficiency. Most commercial NPK chemical fertilizers don't have a Ca component. Agricultural gypsum is one way to provide Ca without altering the pH (acid/alkaline balance). 

 

August 29, 2014 by Permakulturnik

The importance of Calcium for health and proper functioning of the plant

Calcium is one of the elements, which are essential for plants. They need it in very large quantities – in Good soil, giving the highest value of fruits and vegetables, calcium is more than all the other necessary elements combined plants. It performs many functions in the plant (Calcium functions):

§  Regulates the absorption of other minerals by plants

§  It stimulates the correct elongation of plant cells

§  Strengthens the structure of the cell wall, which are responsible for the proper form and shape of plants

§  Participates in the process of enzymatic and hormonal

§  It helps to protect plants from heat stress

§  Protects the plant by diseases – many fungi and bacteria secretes enzymes, that attack the cell walls of plants. Strong and rich in calcium, cell walls are better able to resist the invasion of pathogens

§  Affects the quality of the fruit

§  It is needed for the proper functioning of stomata

 

Trunk splits/cracks – Small vertical cracks on the trunk of a palm are commonly caused by too much or too little water or planting the palm too deep. Large vertical cracks are usually caused by too much water or damage during the planting or transporting of palms.

The palms are there for 9 years already, and don't get watered, but it has rained virtually without stopping for the past 3 weeks and a lot in the weeks before as well.

 

Is this a symptom that can appear in such a short timespan, like lets say too much water for 5 weeks, and will it recover afterwards or do I have to cut those trunks?

You would have to answer that question, if the cracks appeared in such a short timespan. I suspect that the condition was there, but maybe accelerated with the heavy rainy period. It could be from a rapid growth response, or there is a possibility of a fungal infection with the wet weather. But all the cracked palm stems that I have seen have been related to water and nutrition issues. 

 

As far as removing the affected stems, you have to be the judge. If the green fronds have dried up then yes, that stem may be dead.  But surface cracking may not affect the uptake of water and nutrients. If the foliar growth appears normal then there may be no need to remove that portion. Palms have vascular bundles/conductive tissue throughout the stem and not just around the outside circumference like other woody trees. So even with superficial damage, the uptake can continue. 

 

What Causes Cracks In My Palm Tree Trunk? (gardenersyards.com)