Bitter rot on apple and pear fruit is caused by the pathogenic fungi Colletrotrichum gloeosporioides and C. acutatum. Photo: Kari Peter, Penn State
This might very well be the “Year of Bitter Rot.” Reports have been rolling in about the high incidence of bitter rot in apple orchards. The conditions this season have favored this explosion of disease activity. Consequently, we want to take advantage of this situation.
We are interested in obtaining apple fruit infected with the bitter rot fungus from around Pennsylvania to understand what species occur in Pennsylvania. We also want to test these fungal isolates for fungicide resistance to the most commonly used fungicides.
This research ultimately will lead to better bitter rot management strategies. Our goal is to collect bitter rot apples from as many PA counties as possible. Pennsylvania is a big state, so we need your help!
What to look for in the orchard (See photos below)
- Apples exhibiting bitter rot will have circular brown lesions with spores on the surface.
- Spores are often orange-salmon colored and in a concentric ring pattern.
- Depending on fruit variety, there may be a red halo around the rot lesion (this lesion also will have spores on the surface).
- If you cut through the center of the rot lesion, a “V”-shaped rot will be evident in the flesh.
All apple varieties are susceptible; however, Honey Crisp is one of the most susceptible varieties.
If the pictures of bitter rot below hit close to home and you are interested in participating, please contact Kari Peter, firstname.lastname@example.org or 717-677-6116 Ext 223 to receive instructions for sampling and sending the fruit to Penn State FREC.
Our request is for fruit rot from commercial orchards only. We are not collecting fruit rot from homeowners with backyard fruit trees at this time.
Figure 1. V-shaped rot in the flesh of a cut apple. Photo: Kari Peter, Penn State
Figure 2. Photo: Kari Peter, Penn State
Figure 3. Photo: Kari Peter, Penn State
Figure 4. Photo: Kari Peter, Penn State
Figure 5. Photo: Kari Peter, Penn State
Figure 6. Photo: Kari Peter, Penn State
Figure 7. Photo: Kari Peter, Penn State