May 1, 2015

Amid-Thin (NAD) might be a useful bloom/petal fall thinner

Preliminary trials with Amid-Thin (NAD) indicate it may be a useful thinning tool on Honeycrisp and Pink Lady at bloom and/or petal fall. Growers are cautioned to not spray pigmy-prone cultivars and not to spray past petal fall, as there is an increased risk of inducing small fruit to stick at later timings. Conduct your own trials with this product – including unsprayed checks – prior to deciding whether this is a good thinning tool for you.

In a recent email exchange, instigated by a note from Jim Schupp, that Amid-Thin (NAD) is now being sold in Pennsylvania after its price was reduced, I contacted Duane Greene in Massachusetts and Greg Peck in Virginia because they have been looking at this material again.

Both Duane and Greg have been looking at applications of Amid-Thin as a bloom thinner. Duane has specifically been looking at it as a bloom and petal fall thinner on Macoun. Greg has looked at NAD as a bloom thinner on Honeycrisp and Pink Lady based on the pollen tube growth model with two applications.

Duane was looking for a thinner that could be applied at bloom and/or petal fall to reduce the initial fruit set. He applied the NAD at 40 and 50 ppm at either bloom or petal fall or both. The least effective treatment was a single application of 40 ppm at bloom, with 50 ppm being slightly better. He also noted that two applications at either rate did not seem to result in an additive affect. Treatments of 50 ppm and treatments of 40 ppm twice and 50 ppm twice increased fruit weight and reduced the number of spurs having 2 fruit per spur. He noted that an advantage of using NAD over NAA at the bloom/petal fall timing is that NAD is less susceptible to the over-response of NAA to high temperatures. In a communication to me he does not want to use NAD after petal fall for fear of inducing small fruit to stick (mummies).

Greg indicated he had success with NAD at 25 to 50 ppm for Honeycrisp in 2013 and Pink Lady in 2014. He made two applications per season and felt they were a much stronger bloom thinner than 6-BA or NAA with similar levels to lime-sulfur and oil, but no russet or phytotoxicity problems. Greg also cautioned that pygmy prone cultivars should be avoided. Finally he indicated that Amid-Thin in Virginia was less expensive than NAA or 6-BA.

– Robert Crassweller, Penn State University