Amid-Thin W® Is Now Labeled for Thinning Apples at Full Bloom

Full bloom is good timing for thinning apple cultivars that have small fruit size, or which have a tendency towards biennial bearing. Early removal of excess fruits on the tree results in less competition for the remaining fruits and for next year’s flower buds at this critical stage of development.

A recent change to the Amid-Thin W® label now allows for application at full bloom. Its active ingredient is NAD. It is an amide salt formulation of NAA, a familiar post-bloom thinner. It is a milder form of NAA, and the activity of 50 ppm NAD is roughly equivalent to 5 ppm of NAA. Milder refers to both its lower thinning activity as well as its side effects on the trees. Historically NAD was recommended for summer ripening cultivars which needed to be thinned as early as possible but had foliage that was sensitive to NAA. Although many summer varieties are no longer grown commercially, NAD would be a good choice for cultivars such as Lodi, Rambo, or Ginger Gold.

NAD is best used on cultivars that are easy to thin or moderately easy to thin with NAA. Its mild efficacy makes it a less desirable choice for cultivars that are hard to thin with NAA, such as Golden Delicious, Gala, or Fuji.

Perhaps the most interesting opportunity for a bloom spray of NAD is with Honeycrisp. Honeycrisp return bloom benefits greatly from early thinning and it is moderately easy to thin with NAA. Blossom timing with NAD is applied early enough that its thinning effects may be clearly visible by the 12 mm fruit diameter growth stage. By applying the first thinner at bloom, the grower has an opportunity to accurately assess its effects, with time to make a follow-up thinner application in the usual post-bloom window. Furthermore, the milder effect of NAD, combined with the milder effect of early thinning timing reduces the risk of over-thinning.

Forty to fifty ppm (6.4 oz. - 8 oz. per 100 gallons) has been an effective range of NAD for thinning Honeycrisp. In some instances, this has provided sufficient thinning for the season, but in other cases, some mild follow-up thinning with NAA or carbaryl was called for.

Since this label change is recent, it is possible that you may have older stocks of Amid-Thin W® available to you which don’t have a label with the bloom timing update. Make sure you have an updated label in your possession when making a full bloom application.

Updated Amid-Thin W® label