The cider industry continues to remain strong for craft beverage drinkers – and for those who grow and harvest the apples that are fermented into that tasty drinkable treat. However, just like any other horticultural crop, disease pressure remains an issue.

Looking into “Phenology, Infection Risk and Fruit Rot Susceptibility of Cider Cultivars” are a research team comprising Vera Soucy, Kristi Gdanetz MacCready, Katherine Olive and George W. Sundin, all within the Department of Plant, Soil & Microbial Sciences at Michigan State University.

That team explained that cider cultivars tend to break dormancy later in the growing season compared to dessert cultivars, which causes a significant lag in development between the two tree types.

The Michigan State group used bitter and black rot studies to inform growers which cultivars have high susceptibility rates to these pathogens. Figures relating to infection rates and cultivar susceptibility for apple scab (Venturia inaequalis) and fire blight (Erwinia amylovora) were also included. (You can never have enough tools in your toolbox.)

The purpose of these studies were four-fold: To quantify the phenological differences between the different cider apple cultivars from silver tip to fruit production; to determine post-harvest fruit susceptibility rates of said cultivars to bitter rot (Colletotrichum species) and black rot (Botryosphaeria obtusa); and to be able to determine cultivar susceptibility to apple scab relating to bloom development stage.

This project took place in a block of cider apples at the Michigan State University Plant Pathology Farm in East Lansing, MI. The orchard block was planted in 2016 and consists of 32 cultivars. The average growth stage lengths were recorded by the team for one month.

The cultivars in the orchard were Ashton Bitter, Bedan, Binet Rouge, Brown’s Apple, Brown Snout, Bulmer’s Norman, Chisel Jersey, Dabinett, Ellis Bitter, Foxwhelp, Frequin Rouge, Goldrush, Harrison, Harry Master’s Jersey, Herefordshire Redstreak, Honeycrisp, Kingston Black, Liberty, Michelin, Muscat de Bernay, Nehou, Porter’s Perfection, Red Mac, Somerset Redstreak, Spitzenburg Esopus, Stembridge Cluster, Stoke Red, Tremlett’s Bitter, Vilberie, Virginia Crab and Yarlington Mills. (Those who make cider all have their preferences, just as consumers who eat apples do.)

This Harrison cider apple specimen originated in Sussex County, NJ. Image courtesy of USDA Pomological Watercolor Collection

For the experiment, three replicates of eight apples from each cultivar were inoculated with both bitter and black rot in separate trials. Over the course of 10 days, each batch of replicates was monitored for lesion size and symptom development.

A few cultivars performed very well against fire blight: Liberty, Goldrush, Frequin Rouge, Virginia Crab, Ginger Gold and Harris, all exhibiting less than 40% fire blight infection. Every other cultivar experienced infection rates of 75% or higher.

Ashton Bitter, Chisel Jersey and Liberty saw zero apple scab infection, and another 21 cultivars had an infection rate of lower than 5%. Porter’s Perfection and Spitzenburg Esopus fared well enough, with lower than 25% infection, but Frequin Rouge, Harrison, Red Mac, Stembridge Cluster and Virginia Crab all had apple scab infection rates of 40% or higher.

When it came to the rots, certain cultivars had an edge over others. Those with low susceptibility to black rot included (from lowest susceptibility upward) Stembridge Cluster, Harrison, Frequin Rouge, Porter’s Perfection, Herefordshire Redstreak and Tremlett’s Bitter. (On the flip side, Bulmer’s Norman ended up sporting huge lesions – nearly 90 mm in diameter).

Similarly showing low susceptibility to bitter rot were Harrison, Vilberie, Frequin Rouge, Spitzenburg Esopus, Goldrush, Muscat de Bernay, Stoke Red and Porter’s Perfection. Faring the worst against bitter rot was Herefordshire Redstreak.

The silver lining to these studies is that since most cider cultivars bloomed at a later date compared to the dessert cultivars, they might escape apple scab infection due to their later development. For example, when Red Mac and Ginger Gold were at first pink, some cider cultivars were still in silver tip.

A strong contender for best fighter is Harrison, due to its low susceptibility to black rot, bitter rot and fire blight. Its only kryptonite was apple scab.

by Courtney Llewellyn