What to do if you have Ethrel damage?
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
A lot of Ethrel damage has been showing up in the past few weeks in the northwest (view images). This injury has come as a result of highly stressed trees, most from drought stress. However, we have seen San Jose scale on some sweet cherries in certain areas, and these insects have put more stress on trees. This stress is then compounded when we apply Ethrel, especially under hot temperatures. Injured trees have lots of leaf yellowing and leaf drop, and there is excess gummosis in affected trees. The gummosis is often clear, and it can be anywhere on the tree – branches, trunks and branch angles.
Since the damage has already happened, we need to have a plan on how to keep these trees as healthy as possible. First, growers should avoid pruning until dormancy. We need to make sure these trees have all possible resources heading into winter, and pruning off any branches and leaves at this time will reduce the trees’ ability to make these resources. Therefore, growers should save pruning efforts until trees are in dormancy. When growers do prune in dormancy, they should be sure to give the trees an extra hard pruning. This method will remove some of next year’s fruiting area, and it will place the resources into fewer fruiting points and keep the majority of resources in the tree rather than fruit.
We also want to make sure to reduce any potential stress on the trees. We want to maintain good weed control, and we need to have good cherry leaf spot control as we do not want any premature leaf drop this season. Even though we have had little rain and very low disease pressure, a post-harvest Bravo application is warranted if trees are showing Ethrel damage. Another reason a disease spray should be used is due to a long post-harvest period, as harvest ended so early this year. Also, mite thresholds have dropped in situations where trees are showing Ethrel damage and drought related symptoms. Trees that have been damaged by Ethrel cannot tolerate high mite populations. The threshold for mites on sweet cherries is usually around 30 mites per leaf in normal years, but sweet cherries suffering from Ethrel damage have had their thresholds decrease to five to seven mites per leaf. If this threshold is reached, a miticide is needed.
Lastly, a fertilizer application may be warranted in orchards where nutrients are needed. Growers should not apply any extra nitrogen this fall, except where it is needed. The rates suggested at this time are 100-120 lbs. actual nitrogen in spring or a split application in spring and fall of 50-60 lbs. We also need a good dose of potash this fall if potassium levels are low.