3 Diagnostics of Palms

In the Oct 2017 edition of "Detective Dendro, the diagnostic sleuth", a park manager called up the detectives because one variety of palm at her park seemed to be green and healthy, and another variety of palm had some fronds that looked yellow even with what was claimed to be optimal maintenance. Phoenix dactylifera (date palm) is dioecious (having male and female parts on seperate trees) and the healthy variety is only male. However the variety in question is female, and they had allocated magnesium to their developing fruits, and there were insufficient amount for the leaves. Solution was to prune off inflorescence stalks before fruits start to develop, or increase fertilisation rate for female palms. Use a balance, palm-specific fertiliser at a rate specified on the label, and avoid overdosing, which could induce deficiencies in other nutrients.

In the Feb 2014 edition, the detectives were called over during winter, to look at a  palm (Archontophoenix cunninghamiana) with frizzled fronds, looking like there were withered and burnt. At first, one detective thought that it was obviously due to frost damage. But the park manager shared that the skateboard area near that palm was fairly new, and another detective asked where the construction workers washed out their cement trunk. After digging around the base of the palm for a bit, chuncks of concrete were revealed. The washed out concrete raised the pH to make a more alkaline soil, and that would generally tie up manganese and iron leading to deficiency. Manganese deficiency leads to frizzling and that is commonly referred to as frizzle top. That detective asked the park manager to try a palm-specific fertiliser with at least 2% manganese in sulphate form. She suggested to fertilise the rest of the plantings with general fertiliser to lower the pH.

'Frizzle top'

In the Aug 2013 edition, the detectives were at a beach and noticed a Phoenix canariensis (Canary Island date palm) at the roadside with lots of dead fronds in the crown. The palms showed signs of being maintained as their leaf bases were pruned. However, the same palm in a private backyard does not have browning fronds. Upon closer inspection of the fronds, one-half is dead and brown while the other half is still alive and green. One detective postulated that if one of the petioles was sliced open, the vascular tissue would be dark brown with a pink blush in the surrounding tissues, indicating the presence of Fusarium oxysporum. To be sure, the detective suggested to the city arborist to send a sample to a diagnostics lab. He also postulated that the arboriculture contractor, which city arborist said quoted him low prices, was the culprit. He further shared that Canary Island date palms are very susceptible to Fusarium wilt, which is frequently transmitted through contaminated sawdust and tree sap on saws. The spots that remain on the saw between cuts are easily transmitted onto another palm. Therefore with these palms, hand saws (blades can be sterilised) should be used and not chain saws. Nothing could be done for the palms now that it was infected with Fusarium wilt, as it is nearly 100% lethal. New date palms should not be replaced on the same spot, as they would likely be contracted with Fusarium wilt from the infected soil. The detective suggests to the city arborist that he replace the palms with any other kind of palm that is not Phoenix spp., as Fusarium oxysporum is fairly host-specific.