"You see this one," he says, waving in the direction of a majestic but diseased olive tree on his property near Gallipoli on the Salento peninsula on Italy's heel.
"It is over one thousand years old. Fires and wars failed to kill it, but that's what xylella is doing."
Manni's wedding pictures were taken underneath this particular tree. And he is filled with dread at the prospect of its imminent demise at the hands of a bacterial infection thought to be behind an outbreak of dessication ravaging the olive groves of this fertile corner of southern Italy.
"I am very pessimistic," the young spokesman for producers organisation "La Voce dell'Ulivo" (The Olive's Voice), tells AFP. "I feel like we have no weapons with which to fight back."
The reason for Manni's despair is xylella fastidiosa, a deadly bacterial pathogen that has no known cure and, for reasons experts have so far been unable to explain, began infesting olive trees in Salento at the end of 2013.
More than a million trees, 10 percent of Salento's total, are estimated to have been infected in a region where abundant olive groves are synonomous with the timeless landscape.
Most of those that have been infected have or will soon become stunted, leafless and ultimately lifeless.
How many trees will ultimately suffer that fate is unclear, as is the extent to which the bacteria has spread to other parts of Italy.
What is clear is that the potential damage is huge: xylella does not harm humans but can kill over 200 types of plant, including fruit trees and grape vines. "It is an environmental disaster," says Manni.
Under pressure from the European Union, the Italian government last year approved the felling of some 3,000 trees under a plan to create a sanitary buffer zone between affected and non-affected areas, thereby hopefully containing the problem in Salento.
- 'Very worrying situation' -
But a legal challenge from producers succeeded in halting the implementation of the scheme.
"Our expert told us that there it was not absolutely sure that xylella was the only reason for the dessication of the trees," explained Cattaldo Mota, a magistrate in the city of Lecce who ordered the halt.
"The identity of the landscape of the Salento is linked to the olive tree, we wanted to prevent it from being destroyed without an opportunity to look into the problem more deeply," Mota added.
To complicate matters further, 10 officials involved in tackling the disease have been placed under investigation on suspicion of misrepresenting the scientific evidence and acting in a way that threatened the environment in an area of outstanding natural beauty.
The local ruling was revised last week by Italy's Council of State. The culling of trees is once again authorised but it has to be done in agreement with growers who must be allowed time to carry out their own tests and evaluations.
The Italian authorities have also lifted a "xylella state of emergency" which gave them powers to enforce felling.
The situation however remains "very worrying", according to Gianni Cantele, regional president of the national farmers' organisation Coldiretti.
"The (insect-born) disease is continuing to spread," he said.
Pantaleo Piccinno's 270-hectare estate at Caprarica di Lecce is among those to have been infected. But he said he was still able to produce his oil.
"The progressive nature of the disease means an affected tree can continue to produce olives from the parts of it where the leaves are still green and there is no impact on the quality of the oil," he says.
Production also continues in parts of Puglia that are little or not at all affected by the epidemic.
But lost output has already had an impact on wholesale oil prices. A recent study in seven EU countries attributed a 20 percent hike over 2015 to the impact of the xylella crisis.
Coldiretti's Gianni Cantele warns that the disease could spread across olive growing areas across the northern Mediterranean with cases of xylella having already been detected on the island of Corsica and in southeastern France.
"The problem is that once xylella gets a foothold in an environment, it is very difficult to eradicate," he said. That's why, he explains, replanting in contaminated areas is currently banned.
Cantele said he was hopeful a compromise could be agreed with the European Commission under which older trees would be reprieved, younger diseased ones culled and producers authorised to replant.
But above all the Salento's olive growers are hoping that science will come up with a treatment for xylella sooner rather than later.