This 2018 growing season thus far is proving to be one of the more severe apple scab seasons. As of today, June 19, we have had eight apple scab infection periods and have had several of those infection periods last for more than 36 hours and two of them lasting more than 48 hours. That has made it nearly impossible to control primary scab outbreaks. With that being the case, we are at a point of now having to protect fruit from secondary scab.
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| Fig. 1 |
Season-long control is difficult if primary infections develop, like those in Fig. 1, which produce secondary inoculum placing fruit at risk for secondary, conidial infections. With primary ascospores possibly depleted, we will have to continue to monitor scab infection events and maintain spray coverage accordingly for at least two more weeks, if not longer, since we have found primary lesions, like those in Fig. 2 on McIntosh and McIntosh hybrids like Cortland and Empire. If you have seen lesions like those in Fig. 2, on your trees, then you will need to protect your fruit from secondary lesions.
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| Fig. 2 |
The best product for protecting your fruit is Captan, a protectant, so that means that your trees will need to be sprayed with Captan at the full labelled rate prior to any rain event to protect your fruit. If there are no rain events between sprays, a single protectant spray will last at least 10 days but not more than 14 days, based on the product's labeled directions. You will need to make sure that your trees and fruit are protected prior to any rain event if when using only a protectant. But, a protectant can lose its effectivness after 2" of rain, so you also want to keep an eradicant on hand like myclobutanil, which is available as Spectracide Immunox. A protectant like Captan has to be applied prior to a rain event. If no protection is available during the wetting event, then only an eradicant like Immunox can be applied that has a reach back of at least 48 hours. That means that it can still have an effect on the scab pathogen for up to 48 hours after a wetting event. A good option is to actually use both a protectant and an erdicant at the same time, like Captan mixed with Immunox, which will give you both protection and eradicant action after a wetting event.
As always, be sure to follow the label directions on any spray product you may use. For further information on control of apple scab, refer to:
