Almond Fungicides and Bloom: Plan Your Work, Work Your Plan

Planning your fungicide program has multiple benefits, and now is a good time to start doing so. Time can be taken to identify fungicides and respective modes of action to develop a proper rotation strategy. It allows the ability to price and compare differing options that may swap materials at specific points. Finally, it gives the opportunity to review the labels of the materials to determine application requirements, and the need to include (or most likely exclude) additional materials.

To determine the year’s spray program, several things need to be considered. These include anticipated weather during flowering, disease history, materials available, operational tolerance to disease, and the ability to spray (budget constraints). Dry weather during flowering will reduce the need to spray, while free moisture from rainfall or humidity/fog can increase disease pressure. If dry conditions are present, fungicide sprays can be withheld until conditions change. In these types of years, bloom typically progresses rapidly, making it difficult to spray due to the shorter duration. As the flowering period ends and petal fall begins, it may make sense to consider a “clean-up” spray for any infections that might have occurred.

Having a history of disease increases the presence of the given disease’s inoculum. This means that as soon as any rain event occurs, this disease will begin to spread at a higher rate. If dealing with a previous outbreak of a disease, especially diseases that form wood cankers (e.g. Anthracnose, Monolinia, Phomopsis, etc), fungicide applications should occur prior to going into any wet period, and re-application should be considered for any rain events that occur 10-14 days after the previous application. This may mean multiple sprays during wet years to reduce disease inoculum. As incidence decreases in future years, the spray program can be gradually reduced.

Available chemistries for disease control are becoming a greater concern. In-country regulations, EU regulations on maximum residue limits (MRLs), bee health, and other considerations are reducing the number of chemistries that can be applied. If unaware of the various pesticide regulations or trade conditions, check with the country’s pesticide regulations, a handler, or pest control adviser to determine if a material can be applied without impacting the ability to market or export. Within CA, the ABC does a good job in keeping the industry up to date on emerging fungicide issues, but it does not hurt to double check as these regulations move quickly.

The operation’s tolerance for disease is another primary driver in determining the number of fungicide sprays. If “zero-tolerance” is the goal, then more sprays will be needed. If some disease is tolerable – which may mean some crop loss – reducing the sprays during bloom may be considered. There are operations in the San Joaquin Valley located in areas with very low rainfall that do not apply or rarely apply fungicides during the flowering period. They do, however, have occasional years in which they experience crop loss, but feel that the reward of operational savings is greater than the risk. In contrast, growers in wetter areas tend to be more “conservative,” and make applications that may not be needed in anticipation of wet weather patterns. Many operations settle somewhere in between, attempting to “spray before the rain” to maximize disease control.

Budget constraints vary by operation and are an important factor in years with uncertain commodity pricing. Every application has multiple realized and unrealized expenses. These include the fungicide, any fertilizers or surfactants, the application, as well as the opportunity cost of that time and money which could be redirected to other activities. The most expensive spray is the one that is not needed. If needing to reduce expenses, try to be timelier with fungicide sprays by applying only when weather conditions favor disease. Furthermore, consider reducing or eliminating various additives instead of reducing sprays. These additional products have been shown to have limited success in replicated trials. They also may not be required based on the fungicide being used and the costs add up with multiple sprays. Spray only when and what is needed to protect the crop, and the budget will take care of itself.

Below are some bloom spray programs to help guide the decision-making process. These suggestions utilize FRAC numbers, which identify the mode of action of the chemistry. Further details on the other alternatives and trade names can be found in the “Fungicide, Bactericides, and Biologicals…” document produced by the University of California. Please consult with local support services for site-specific recommendations. Further details about the diseases can be found at the UC IPM website for almonds.

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