Early cultivars in Southern Wisconsin will be at petal fall by early next week, when we reach about 100-125 growing degree days from bloom. This is the time to start looking at the NEWA carbohydrate model to adjust your chemical thinner rate (i.e., NAA and Maxcel). Looking at the weather forecast for next week and the projected carbohydrate model, it doesn’t look we will be in a severe carbohydrate deficit (< -60) for petal fall sprays. This means that for growers that have heavy bloom, no frost damage, and have not done a blossom thinner spray, you should do a petal fall spray if you want to ensure a good return bloom for next year. For growers that have some cold damage but is less than 20% of kings I would still recommend you do a petal fall spray, since petal fall thinners have a mild effect and there is little risk of over-thinning. For growers with more than 50% frost damage, you should wait until 10-13 mm to thin.

Here’s a list of alternatives for petal fall thinning sprays:

Fruits at 5-6 mm

1. Sevin (1pt/100 gallons) very mild thinner.
2. Maxcel (64 oz/100) plus Sevin (1pt/100 gallons), this is a great option for Gala.
3. NAA (3-4 oz) plus Maxcel (64 oz/100).
4. NAA + Sevin

Consideration for petal fall sprays:

Are bees present? Caution if you are using Sevin.

You need a period of at least 8 hrs with no rain after the thinning spray.

Finally, how do you know how much thinning you have achieved with bloom and petal fall spray? You need to use the Fruit Growth Rate model.

This article was posted in Apples and tagged Amaya Atucha, Apples, Petal Fall, thinning.