Kelpak news
California Mandarin Trial
Fruit set and retention show 11% increase in box yield
In the world of citrus, yield is determined by how much fruit a tree sets and by how much of that fruit stays on the tree long enough to be harvested, packed and sold. That is especially important in mandarins, where fruit drop can erode returns. A certain level of drop is expected in citrus production, but when losses increase during key stages of fruit development, the result is fewer marketable fruit and lower packout.
Recent California mandarin trial data by Kelpak suggests that targeted plant support during bloom and early fruit development can help address this challenge.
In a 2025/26 field trial in Elderwood, California, conducted by Steve Deitz, a four-application Kelpak foliar spray program was evaluated on Tango mandarin trees with a known fruit drop challenge. During the program, the product is applied to the leaves and canopy, allowing the plant to absorb it during important growth stages.
The trial used four applications at petal fall, 32 days after petal fall, 60 days after petal fall and 81 days after petal fall, at a rate of 1.6 pints per acre. The design followed a randomized complete block structure, with nine replications of three trees each. This type of trial design helps compare treated and untreated plots more fairly by reducing the effect of natural differences in the orchard.
The Kelpak treatment reduced fruit drop by 35%, increased fruit number by 7%, and improved production of 5-pound boxes by 11%. This means that the treated plots produced 91.75-pound boxes compared with 82.6 boxes in the untreated control. Yield increased from 16,610.2 pounds per acre in the control to 18,457.7 pounds per acre in the treated plots.
Based on market conditions at the time of the trial, this translated into an additional return of approximately $590 per acre.
The treatment did not significantly affect the percentage of fruit in different size categories, Brix levels or average fruit weight. This suggests that the yield gain was mainly driven by better fruit retention rather than by changes in fruit size distribution.
A separate W. Murcott mandarin trial in Elderwood during the 2024 to 2025 season gives further context. Conducted on the same trees as the previous year, the trial evaluated a four-spray Kelpak program from full bloom through early fruit development. The season itself was a high-yielding year, with the grower standard producing more than 25% above the previous harvest.
Even under these conditions, the Kelpak treatment increased fruit number and 5-pound box production by 8%, enhanced overall yield by 6%, and added approximately $340 per acre in returns.
The W. Murcott data also points to another issue citrus growers know well: alternate bearing, when trees produce a heavy crop one year and a lighter crop the next. While one trial does not solve alternate bearing, results across two consecutive seasons indicated that well-timed plant support may help reduce some of its impact in citrus production.
Kelpak is a liquid seaweed concentrate produced from Ecklonia maxima harvested off the South African coast. Rather than replacing fertilizer inputs, it is designed to support natural plant processes during key crop development stages.
“As production costs remain high and growers continue to look for ways to protect and improve returns without expanding acreage, trial work like this offers a practical solution,” says Linda Greyling, Head of Technical support at Kelpak. “Better fruit retention, higher box counts and measurable per-acre return are the kinds of outcomes growers can evaluate against their own production systems.”
The California data does not remove the need for sound nutrition, irrigation, pest management or cultivar-specific planning. But it does show that targeted interventions during sensitive crop stages may help growers improve the amount of marketable fruit carried through to harvest.
Kelpak support
For more information on how Kelpak can improve crop health, resilience and marketable yields or for nearest distributor information, please contact one of the phone numbers or email addresses below:
KELP PRODUCTS INTERNATIONAL
Head Office - South Africa
Tel: +27 21 786 2090
Fax: +27 21 786 3274
Email: info@kelpak.com
TECHNICAL SUPPORT
Contact: Linda Greyling
Email: linda.greyling@kelpak.com
or
Paul Hills
Email: paul.hills@kelpak.com
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