The Honeycrisp 'Yellows'

July 31, 2000

Many growers are reporting yellowing/browning of Honeycrisp foliage this growing season. This is not a new observation, having been quite frequently reported nationwide as more and more Honeycrisp trees go in the ground. Unfortunately, there is no proven explanation why the Honeycrisp 'yellows' occurs, although several 'theories' have been put forth, including: potato leafhopper injury; nitrogen deficiency; latent virus from propagating stock; and carbohydrate partitioning. Fortunately, most agree it is not a serious problem, and growers are continuing to plant Honeycrisp to capitalize on it's remarkable fruit quality and marketability. Researchers, however, are continuing to study the problem hoping that indeed it is as benign as it appears.

Young Honeycrisp trees on M.9 rootstock. The yellowing foliage is characteristic of the cultivar, but observed in varying degrees. It's cause is unknown, as well as it's impact on tree vigor and fruit. Click on the picture for a close-up of the 'yellows.'

A Honeycrisp on B.9 rootstock in the row next to the Honeycrisp/M.9 pictured above. Note there is some slight yellowing, but in general the foliage is much greener. Looking down the two rows -- side-by-side, M.9 vs. B.9 -- the B.9's exhibited far less yellowing of the foliage than the Honeycrisp/M.9. (The red fruit at the bottom of the picture is actually B.9 fruit on a shoot originating from the rootstock shank.)

Some have noted that the yellowing does seem to express itself more on weaker growing trees on more dwarfing rootstocks. (This alone might suggest a nitrogen issue?) Recently I did observe a block of young Honeycrisp trees where a row of M.9 and a row of B.9 rootstock trees were planted side-by-side. The B.9 trees were larger and more vigorous (which in itself is an interesting observation) and perhaps not coincidentally, were much 'greener' than the M.9's which suffered from a rather severe case of the Honeycrisp 'yellows.' Note that neither of the trees appeared to be under any particular stress from lack of moisture, pest injury, etc. (Although potato leafhopper has been prevalent in Massachusetts during the 2000 growing season.) And crop load appeared to be comparable between the Honeycrisp on the two rootstocks. My casual observation was also that fruit size was smaller on the more seriously yellowed Honeycrisp/M.9 compared to fruit on the B.9's. Very interesting.