Southeast Michigan fruit update

An update for apple growers making apple thinning decisions and strawberry growers concerning slugs in strawberries.

Our rollercoaster weather ride that we have been on this spring seems as if it just won’t end. With cold temperatures, excessive precipitation and cloudy weather, these factors will all have a great impact on apple thinning decisions. As of this morning (May 27), warmer temperatures are still predicted for Sunday (May 28), Monday and even into Tuesday. Hopefully we will receive sufficient sunshine and some wind, except when you are trying to spray, to dry soils out across the region.

For apple growers who are considering thinning decisions, it is going to be even more of a difficult decision than it typically is. Here are some things to consider and then I will share my advice. With warmer temperatures expected over the weekend and early next week, and with apples now at fruit set in many blocks, it looks like we have a perfect window for applying thinners.

My fine colleague, Phil Schwallier from the Grand Rapids area, has been working with colleagues across the country on developing a carbohydrate model to help growers thin fruit more effectively and to make the process more predictable. In this model, weather forecasts are used to determine when trees are under stress – trees under stress will thin easier. Schwallier presented this model to growers at our Spring Tree Fruit meeting in March. According to Schwallier’s most recent model, it appears that apples are approaching a period of great stress over the next four or five days, meaning that fruit will thin easier. Also, with the amount of cloudy weather that we have had and questionable pollination periods in many blocks, there may be additional fruit drop due to these factors.

Schwallier’s advice is to use 50 percent less thinners on moderate appearing crops and 25 percent less on heavy appearing fruit sets. He goes on to say to “exercise a bit of caution with thinning over the coming weekend.”

Here are my two cents or opinion on thinning apples this season. I encourage you to consider being conservative in your thinning as I feel that we will have a fair amount of natural fruit drop, and with this period of stress, trees will be undergoing that fruit will thin easier than normal. This is a dangerous time of year for apple growers on a very difficult decision. Good luck with it and stay in touch with your email over the weekend if I have further updates on the matter.

Also for apple growers, a word of caution about primary apple scab season: I am still catching spores with each rain event, although the number of apple scab spores that I am catching is declining. Therefore, we are not at the end of primary apple scab season and you need to continue to be on top of apple scab control with each wetting event.

Now for a word of caution for strawberry growers: be on the lookout for slugs in strawberries. Based on several visits I have made to strawberry farms across the region and on the amount of moisture that we have received, I am seeing very high numbers of slugs in most strawberry fields. Slugs are immature at this time, but will be reaching maturity and able to reproduce fairly quickly. My advice for strawberry growers is to scout fields closely by pulling back the straw and carefully checking the soil surface for slug populations. If you find populations in your strawberries high as well, I would consider an immediate application of a slug bait. For some specific information on strawberry slug control, read MSU Department of Entomology’s Rufus Isaacs article, Slug control in strawberry.

Look for my next report on Tuesday (May 31), unless things change in the meantime.

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