Grain fill is one of the most critical and most vulnerable phases of wheat development. Environmental stressors like heat and drought can limit carbohydrate movement into the developing grain, reducing grain weight and yield potential. Research has shown that just 3 days of heat stress during grain fill reduced grain weight by 11–34%, while 10 days of heat stress reduced grain size by 20% on average. Fourteen days of heat stress during grain fill had an even more severe impact, resulting in a 57.3% decrease in grain yield compared to a nearby non-stressed control. GrainStar™ Plant Growth Regulator was developed to help crops navigate these challenges by supporting efficient grain fill when it matters most.
GrainStar is a first-of-its-kind abscisic acid (ABA) formulation, designed specifically for wheat. GrainStar promotes the mobilization of carbohydrates to the developing grain. When applied prior to a stress event, ABA also primes plants to better manage heat and moisture stress, helping protect yield and return on investment.
How GrainStar Works: The Role of ABA
Abscisic acid (ABA) is a naturally occurring plant hormone that plays a key role in how plants respond to stress and manage energy. During grain fill, ABA helps regulate the movement of carbohydrates stored in leaves and stems, triggering their conversion into soluble sugars and transporting them to developing grain.
Once inside the grain, these sugars are converted into starch, contributing directly to grain weight and quality. ABA also supports drought stress mitigation by encouraging stomatal closure, improving internal water regulation, and serving as a source of energy and carbon. Together, these processes help plants maintain grain fill efficiency, even when environmental conditions aren’t ideal.
Proven Performance in Wheat
Across multiple years of university and third-party trials in major wheat-growing regions, GrainStar has demonstrated consistent performance benefits when applied alongside a grower standard fungicide program.
Results from more than 109 trials between 2022 and 2025 indicated that when applied according to label guidelines:
- GrainStar increases grain yield
- GrainStar increases thousand grain weight (TGW)
- GrainStar increases primary seed head length
Yield Results
Twenty replicated trials on wheat in Washington, Oregon, and Idaho, were completed between 2022 and 2025. The trials compared GrainStar to a grower standard treatment. Applications of GrainStar were made between flag leaf and 50% heading in combination with a fungicide. Results from those trials showed that GrainStar improved the wheat yield an average of 4.1 bu/ac compared to the grower standard.
Grain Weight Results
Fifteen replicated trials on wheat in Washington, Idaho, and Montana, were conducted in 2025. Compared to a grower standard fungicide treatment, GrainStar applied in combination with the standard fungicide showed an average of 2.9% greater TGW over those fifteen trials.
Seed Head Length Results
Between 2024 and 2025, seven replicated trials on wheat were completed in Washington, Oregon, Nebraska, and Kansas. Those trials compared GrainStar to a grower standard treatment, and results showed that an application of GrainStar on wheat resulted in 2% longer primary seed head length compared to the grower standard.
GrainStar Application Guidelines
GrainStar is a water-soluble granular formulation containing 8.6% S-abscisic acid. It is designed for foliar application in wheat and is commonly applied between flag leaf and 50% heading, a critical window for grain fill development.
GrainStar is compatible with many common fungicides and insecticides. As with all plant growth regulators, please follow the product label for application timing and rate. Avoid applications if rain is expected within six hours, and do not apply to severely stressed or injured crops, as responses may be reduced.
Supporting Grain Fill When It Counts
When grain fill is compromised, yield potential is lost. GrainStar was developed to support wheat during this high-risk growth stage by improving carbohydrate movement to the developing grain and helping plants respond to heat and moisture stress. With consistent performance demonstrated across key wheat-producing geographies, GrainStar offers growers a practical, research-backed tool to help safeguard grain weight and overall crop performance.
To learn more about GrainStar Plant Growth Regulator and how it fits into a wheat production system, contact your Valent BioSciences representative or visit the GrainStar product page.