2022 Bloom Considerations

Weather is always a consideration when almonds begin to flower. Flowers are one of the most susceptible parts of plants to disease, and environmental conditions that favor disease could lead to crop loss. These conditions include periods of rain and warm temperatures. Protecting these flowers through the conditions is therefore important to maintaining yields and tree health.The forecast at the time of writing for the next few weeks is suggesting dry weather. If dry, warm weather persists, the risk of disease is very low and a different fungicide program should be considered. In this situation, early fungicide treatments can be withheld without too much risk. This is not just due to the dry conditions, but also the warmer temperatures increase the rate in which the tree progresses through bloom. Treatments within this scenario may skip the early and full bloom stages, and focus on an application timed to the petal fall of Nonpareil.If the weather forecast changes and rain is predicted, the plan should change. Rainy conditions over 59F/15C favor brown rot and other spring diseases. If wet, mild conditions persist for over 24 hours, a spray is warranted. This spray should be made prior to the rain event for best coverage. If utilizing FRAC 3, 11, newer 7 fungicides, and 9, this window can extend to 24-48 hours after the rain. Re-application should occur within 10-14 days depending on the frequency and amount of rain received. Fungicides should be applied 30-45 minutes before to provide enough time for them to dry.Although earlier stages of flowering may not require fungicide treatment, an application at petal fall should be considered. This stage of the flower/fruit development is very sensitive to diseases due to the dying flower petals, and amount of dead plant material aggregating within the fruiting clusters. This material is the perfect home for fungi. Materials at this point should provide protection for brown rot, botrytis, anthracnose, and shot-hole. Keep in mind that FRAC 3 and 11 do not provide great control of botrytis, and a tank mixture or product containing of another class of fungicides should be utilized. If the orchard has a history of bacterial spot, this is a very effective timing in reducing the spread of the disease, and copper (at low rates), biological products, or antibiotics should be considered.Springtime disease control will need to continue through May. Rainy conditions will increase the frequency of cover-sprays to every 10-14 days. Wet conditions during this period can flare several diseases, including anthracnose, scab, botrytis, rust, bacterial spot, and Alternaria. If wet conditions persist, rotate modes of action (i.e. FRAC groups) to help decreases resistance and increase the life of fungicide products.Withholding fungicide applications until the forecast dictates rain is a reasonable means to reduce operational cost without impacting productivity. This is only feasible if the fungicide product planned to be used is available and the operation has the capacity to mobilize spray rigs with enough time to make the treatment. Some strategies for this are covered in this article. The risk of this, however, is that when a spray is needed based on the weather, nearly all operations will be wanting to perform the action, reducing availability of fungicide and custom operators. If utilizing this strategy, it is best to be prepared by having the fungicide on hand and any equipment planned for used prepared for service (e.g. maintenance performed, custom operators on stand-by, diesel available, etc.).Fungicides are chemicals and are toxic to certain living things. This should go without saying, but it is just a reminder that fungicides, additional surfactants, and tank mixing of insecticides during bloom have been shown to reduce honeybee health and increase colony die-offs. Adding products to the fungicide spray other than basic foliar nutrients should be avoided. Fungicides should be sprayed when bee activity is low, and the rig operators should be aware of hive placement to avoid spraying them or their water supply directly.For further information on what fungicides to consider to manage bloom and spring time diseases, please refer to the 2021 Fungicide Efficacy Publication by the University of California, as well as your pest control advisor. Additional articles on almond flowering can be found here (Fungicide considerations, 2021), and here (2020 bloom considerations), and on FRAC groups here.