Monitoring Risk for Bitter Rot and Apple Scab Kirk Broders Assistant Professor Dept. of Biological Sciences, COLSA University of New Hampshire Matt Wallhead PhD Candidate Dept. of Biological Sciences, COLSA University of New Hampshire

Venturia inaequalis epidemiology V. inaequalis has coevolved to eject spores at same time as the tree flowers “The catch” – ascospores will not eject until a significant rain event Old model used degree day accumulation from 50% Mac green tip Weather patterns were more consistent year to year

RIMpro (Relative Infection Measure) Infection period Discharged ascospores Germinating spores Infections Rain Wetness Kickback Fungicide Inoculum

4 + 4

Total # of Sprays During Primary Scab Season 5 Unsprayed Captan Calendar- Based Captan according to RIMpro KBC+S according to RIMpro 0859* *KBC+S costs ~50% less than Captan

Bitter rot & Glomerella leaf spot Increased frequency in 2011 & 2012 Historically, a bigger problem in the southern and mid-Atlantic states Same organism causing leaf and fruit lesions? Where is the inoculum coming from? – Infected leaves? – Latent infections? – Other orchards – Other crops (strawberry, cherry, blueberry, etc)

Inoculations

Differences in virulence & resistance

Average % Disease 6-Weeks Post-Harvest 9 ABC AB

Phylogenetic analysis of Colletotrichum from apple in New Hampshire All 20 isolates were C. fioriniae Included leaf and fruit strains C. fioriniae is likely made up of two distinct species

Implications What we knew about C. acutatum and C. gloeosporioides may not hold true for C. fioriniae What is the distribution of C. fioriniae in NE & NA? Is C. fioriniae the dominant species in NE? Is there variability in virulence? When does infection occur?

Apple Blossom Inoculation Study Investigate the rates of Bitter Rot infection in apple trees inoculated at blossom with Colletotrichum 83% of fruit on trees inoculated at flower developed bitter rot 5% of fruit on trees that were not inoculated developed bitter rot 12

Future Plans Second year of RIMPro Second year of Apple blossom inoculations Colletotrichum on fruit in the Northeast – Fungicide sensitivity and virulence – Host specificity and genetic diversity