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A heatwave during flowering can leave its mark long after temperatures fall. Trees may retain green canopies while impaired fertilization or poor fruit retention reduces the eventual harvest. Assessing the risk means understanding which processes are vulnerable when the heat arrives.
California field trials in avocado and pistachio recorded higher yields from Kelpak programs applied around flowering, fruit set and subsequent development. Avocado yield increased by 96% from an unusually low untreated baseline, while payable pistachio yield rose by approximately 16%. The results give growers a reason to examine how a defined seaweed extract fits into crop support during vulnerable stages.
Kelpak is produced from Ecklonia maxima, a brown kelp species harvested off South Africa's coast. Its proprietary Cold Cellburst technology uses pressure differentials to rupture seaweed cells, releasing their contents without heat-based extraction.
Kelpak is produced from Ecklonia maxima, a brown kelp species harvested off South Africa's coast.
Photo: Kelpak
The physiological cost of heat Crop responses depend on temperature, exposure duration, cultivar, growth stage and water supply. High temperatures can disrupt photosynthetic machinery and membranes, reducing the capacity to capture light energy and produce carbohydrates. Respiration can increase, consuming more of the carbon available for growth and fruit development.
Hot, dry air also increases atmospheric demand for water. Where root uptake cannot keep pace, stomatal closure restricts water loss but also limits carbon dioxide entry and evaporative cooling. Irrigation status therefore influences how a crop experiences heat, although adequate soil moisture cannot prevent every temperature-related injury.
At the cellular level, heat can increase reactive oxygen species. These molecules participate in signaling, but excessive accumulation damages membranes, proteins and other structures. Antioxidant systems help regulate this balance.
Reproduction introduces another set of vulnerabilities. Heat can impair pollen viability, pollen-tube growth and fertilization. Later exposure can affect fruit retention and filling as carbohydrate supply and demand change. The stage at which heat arrives therefore influences its effect on the eventual harvest.
A defined extract and a defined program Seaweed species, extraction method, composition and formulation are important distinctions when interpreting biostimulant evidence. Two products described as seaweed extracts need not contain the same mixture of compounds or elicit identical responses. Results are most useful when tied to the formulation, dose, crop and application program actually tested.
One relevant concept is priming, in which a prior treatment prepares a plant to respond to a later stress. Potential responses include changes in antioxidant activity, membrane stability and metabolism. Establishing these responses requires physiological measurements; establishing commercial value also requires measurements of harvest quantity and quality.
In a 2025 University of Cape Town master's study, tomato plants pretreated with an E. maxima-derived formulation and subsequently exposed to 40°C heat
shock showed better photosynthetic efficiency, less electrolyte leakage and lower lipid peroxidation than heat-shocked plants without pretreatment.
The experiment supports investigation of physiological conditioning before heat exposure. It tested a different formulation from Kelpak and provides background evidence for this research approach.
Avocado during a severely depressed season At Lemon Cove, California, Steve Deitz of Sawtooth Ag Research evaluated Kelpak on Gem avocado using a randomized complete block design with six replicates and three trees per plot. The program comprised three applications at full bloom, petal fall and fruit set in May and June 2024, each at four US pints per acre in 100 US gallons of water per acre.
The report describes the 2025 harvest as severely reduced following excessive heat during fruit formation and poor fruit set. Untreated yield was reported to be approximately one-tenth of normal production for the variety at that location. This unusually low baseline is essential context for the treatment response.
Yield increased from 1,075 to 2,106 lb/acre under the Kelpak program, a reported gain of 96%. Fruit numbers increased from 38.2 to 71.7 per plot. The proportions of fruit in small, medium and large size categories were similar between treatments, and no phytotoxicity was observed.
More harvested fruit contributed to the yield increase during this severely depressed season. The trial did not establish the physiological mechanism behind that response.
At Lemon Cove, California, Steve Deitz of Sawtooth Ag Research evaluated Kelpak on Gem avocado. Yield increased from 1,075 to 2,106 lb/acre under the Kelpak program, a reported gain of 96%.
Pistachio across a longer developmental window The Tipton pistachio trial also used a randomized complete block design with six replicates and three trees per experimental unit. Five applications at three US pints per acre covered early bloom, petal fall, nut set, a reported July heat-stress event and late nut sizing.
Raw yield increased from 6,203 to 7,065 lb/acre, approximately 14%. Payable yield rose from 3,029 to 3,507 lb/acre, approximately 16%, while cluster numbers increasedby about 9%. No phytotoxicitywas recorded.
Quality results add useful detail. Edible yield percentage declined from 50.7% to 48.2%, a reduction of 2.5 percentage points, while the larger crop still delivered higher payable yield. The report records no significant effect on individual nut weight. At the stated price of US$2.25/lb, reported gross returns increased from US$6,816 to US$7,891 per acre, a difference of US$1,075 before treatment costs.
The higher payable yield despite the lower edible percentage shows why growers need both quantity and quality measures when assessing a program. The trial cannot allocate the gain specifically to the spray applied during the heat event.
In Tipton, California pistachio trial, raw yield increased from 6,203 to 7,065 lb/acre, approximately 14%. Payable yield rose from 3,029 to 3,507 lb/acre, approximately 16%, while cluster numbers increased by about 9%
Reading the California results together Read together, the trials show higher harvested output from Kelpak programs spanning reproductive and fruit-development stages. In avocado, the response was accompanied by more fruit and a similar size distribution. In pistachio, cluster numbers and payable yield increased without a significant change in individual nut weight. These observations give growers evidence to examine crop load and payable output when assessing a program's value.
The avocado program covered bloom through fruit set, while the pistachio program extended into nut development. Each trial compared a complete program with an untreated control. Neither isolated the contribution of individual sprays or compared alternative schedules. The results support further evaluation of Kelpak within crop development program under heat risk, with the optimum timing and specific contribution to heat tolerance still to be established.
Both supplier-provided reports used a 10% significance threshold, which
is less stringent than the commonly used 5% level. The pistachio analysis included outlier adjustment. Additional seasons, detailed temperature records and clarification of the outlier criteria would strengthen confidence in the consistency of these responses.
Putting development at the center of heat planning Here, the starting point is to map flowering, fruit set and filling against local heat risk, then evaluate a product-specific program within the orchard's irrigation, nutrition and canopy management. Trial rates describe the experiments; local label directions and crop guidance should determine commercial use.
Monitoring should capture fruit retention, marketable or payable yield and quality, alongside costs and weather conditions. A visibly greener canopy alone cannot establish that the program has protected the processes that determine income.
Across the two California trials, Kelpak programs delivered more harvested avocado fruit and greater payable pistachio yield under the reported conditions. These are commercially relevant findings for growers assessing support around flowering, fruit set and crop development. Their value lies in using product-specific evidence to plan applications alongside irrigation, nutrition and canopy management, then measuring the outcome at harvest. Effective heat planning requires attention to both how the crop is supported and when that support is applied. ●
For crop-specific program information, visit www.kelpak.com.
