As fall progresses across California’s citrus-growing regions, growers begin watching the forecast more closely. The first significant rain events can mark the beginning of a costly challenge: rind disorders.

Rain, prolonged canopy moisture, extended periods of fog and temperature swings can create conditions that increase the risk of rind disorders, including rind breakdown and decay. What may begin as water-soaked areas on the rind can develop into brown, necrotic lesions, reducing fruit quality and, in more severe cases, contributing to premature fruit drop and losses before harvest. For growers focused on maximizing premium packout, protecting fruit through this period is an important part of a management strategy.

The Weather-Driven Risk

Rind disorders associated with wet weather are not a new concern for California citrus growers. The challenge is that several environmental factors can occur together during the fall and winter, making it difficult to predict exactly when fruit will be most vulnerable.

Rain is an important trigger, particularly when fruit has reached color break and is approaching maturity. Wet conditions combined with a sudden decrease in temperature can disrupt the rind and cause cells beneath the cuticle to collapse. The resulting damage can leave fruit more susceptible to secondary decay from pathogens associated with diseases such as brown and clear rot.

The University of California characterizes mandarin rind breakdown as primarily a physiological, abiotic disorder rather than a conventional fungal disease. Fungi can then colonize damaged, water-soaked tissue, adding to decay and fruit-quality concerns. For growers, this difference is important. Fungicides remain an important component of a citrus disease management program, but they do not address the underlying environmental stress that initiates rind breakdown.

“Warmer, wetter conditions are increasing the pressure on citrus rind quality and fruit retention,” said Jacob Dominguez, Cultiva technical sales agronomist in Southern California. “When fruit can’t dry down, disease pressure and rind breakdown become bigger concerns.”

In high-value citrus, those concerns can quickly translate into lost revenue. Rind appearance is a major component of marketability, and fruit with significant blemishing or decay may be downgraded or lost before it reaches the packinghouse. 

Why the Fall Window Matters

Fall marks a transition in California citrus production. Rain and fog become more frequent in many growing regions, while temperatures can fluctuate significantly from day to day. A block can move from relatively dry conditions to a period of rain, fog and high humidity in a matter of days. When moisture remains on the fruit and temperatures fluctuate, the rind can experience increased environmental stress.

The 2025 season illustrated how quickly those conditions can become challenging. In parts of the Central Valley, persistent tule fog combined with record rainfall and warm temperatures limited opportunities for fruit to dry naturally. Citrus was dropping off the trees, and much of the crop was left damaged with blemishes. The prolonged moisture contributed to rind-quality issues and heightened risk of fruit drop, leading to high percentages of unmarketable fruit and significant crop losses.

It doesn’t take an extreme weather event to create rind-quality challenges in citrus. Even routine periods of rain, fog and temperature fluctuations can put fruit at risk, making the fall window an important opportunity to evaluate strategies that help protect fruit, maintain quality and maximize marketable yield.

Protecting the Cuticle Before Conditions Turn

As weather patterns shift, a proactive approach to citrus rind protection can help growers prepare fruit before those conditions occur. One approach is to focus on the fruit cuticle, the outer protective layer of the rind that serves as the first line of defense between the fruit and the external environment. It also helps regulate water movement at the fruit surface.

Maintaining cuticle integrity can therefore be an important part of a broader strategy for managing rind quality as fruit moves into the fall and winter window. This is where Parka^® can fit into a fall citrus management program.

Powered by SureSeal^™ technology, Parka is a cuticle supplement designed to provide a protective layer over the fruit and leaf surface. This technology is designed to seal microfractures in the existing cuticle while creating a hydrophobic barrier that helps repel water.

The goal is to establish protection before prolonged wet conditions occur. “When we know we’re moving into a period of rain, we want to have protection established on the fruit before those conditions arrive,” said Dominguez.

Depending on the region, variety and seasonal conditions, growers may consider beginning applications in September or earlier when conditions warrant. October and November can represent an important application window in many California citrus-growing regions as fall rains become more frequent.

“Timing is especially important for varieties approaching color break and maturity during the winter months,” said Dominguez. “As fruit moves closer to harvest, protecting rind integrity becomes increasingly important because the rind becomes more susceptible to breakdown under prolonged wet conditions.”

Building a Comprehensive Program

Parka can serve as an additional tool within an integrated program focused on maintaining fruit quality and protecting the crop through challenging weather. Fungicides remain an important component of disease management while Parka adds a cuticle-focused approach to help establish another layer of protection against the environmental conditions that contribute to rind disorders.

Parka is compatible with most foliar nutrients and fungicides, making it a convenient addition to regularly planned fall sprays. Application quality remains important, with complete coverage of the crop recommended for best results.

“Parka isn’t replacing a fungicide program,” said Dominguez. “It’s addressing another part of the problem by helping protect the cuticle and reduce the amount of moisture reaching the rind.”

For growers and PCAs, incorporating Parka into an existing program can provide a way to address rind protection without treating it as a stand-alone practice.

“Parka is a great cuticle enhancer that we are able to incorporate into citrus to protect against weather conditions,” said Alex Del Rio, PCA for Nutrien Ag Solutions. “Incorporating Parka with a fungicide program in the fall and reapplying it helped prevent fruit drop during the challenging conditions last season.”

Research has demonstrated Parka’s ability to improve rind quality. In California trials on Sumo citrus, a fall Parka program consisting of two applications at 30-day intervals in October and November reduced rind rot by an average of 43.6% compared with untreated.

The economic value of rind protection is ultimately tied to what reaches the packinghouse. Fruit that remains on the tree and maintains rind quality has a greater opportunity to contribute to premium packout. That makes fruit retention and rind integrity important considerations when developing a fall program.

Del Rio has seen that difference in the field.

“Using Parka in my program, I’m able to see better fruit quality and better fruit retention,” Del Rio said. “Parka covers the outside layer of the fruit, helping maintain that rind integrity, so my packout becomes better because I have more premium fruit at the end and I don’t have the fruit drop that a lot of farmers encounter.”

The objective isn’t to rely on a single product or practice. It is to build a program that considers the different factors contributing to fruit loss during challenging weather.

Preparing for the Seasons Ahead

Weather variability is one challenge California citrus growers face every season. Properly timed Parka applications can help establish a protective barrier on the fruit before prolonged wet conditions arrive, complementing fungicide and cultural practices as part of a comprehensive citrus protection program.

“Every piece of fruit is profit,” Del Rio said. “We want to retain that profit in the tree. With Parka, growers can experience better packout, more retention of fruit and better rind quality.”

Talk with your Cultiva representative about incorporating Parka into your citrus management program.