2026 Disease Update: Begin Scouting for Fire Blight Infections

Begin scouting your orchards for fire blight infections. You will want to look closely at blossom clusters for blackening of the midveins of spur leaves, as well as browning of pedicels. Given the severity of the infection conditions occurring during the week of April 13th, the plant regulator Prohexadione calcium (ProCa; Kudos or Apogee) is highly recommended to help slow infections. ProCa is a plant growth regulator that thickens plant cell walls and hardens off the shoots. It takes 10-14 days for the effect to occur in the tree, and repeated applications may be necessary to help control potential shoot blight that may arise from blossom infections, or leftover cankers in the trees (i.e. canker blight).

Although we are on the downside of mature apple scab spores being released from overwintering leaves, the risk of infection remains. Currently, the forecast indicates an apple scab infection period for April 29–30. Rust infection is also a risk during this time, as galls remain active. Even if you have a low to no apple crop, apple scab and rust still need to be managed. In these cases, growers can be conservative with their management by focusing on broad-spectrum fungicides, such as mancozeb, captan, and sulfur. Mancozeb (3 lb/A) and captan (2.5–3 lb/A) can be tank mixed, and mancozeb and sulfur (8–15 lb/A, depending on the sulfur formulation) can be tank mixed. Do not tank mix captan and sulfur. If you still have ziram around, this is also acceptable. Conversely, these products can be used alone. Mancozeb is the only broad-spectrum product to control rust.  For those who have fruit on their trees, there are additional fungicide options. More information about protecting apple trees during this period can be found in the 2026 Disease Update from April 16, 2026. 

Marssonina blotch is a problem in apple and pear orchards, regardless of whether there is a crop, as this disease can severely defoliate trees. Marssonina spores are being released right now; however, the temperatures are too cool for infection. Marssonina infections favor warm temperatures (upper 60s and higher) and wet conditions (at least 4 leaf wetness hours). Warmer temperatures are forecasted for the week of May 5, 2026, and growers should be on alert if rain occurs. Marssonina blotch control will be necessary through early June.

Additional Resources

Dr. Tree Fruit and Don Podcast 

Penn State 2026 - 2027 Tree Fruit Production Guide

For commercial fruit growers, please note: When controlling for disease, weather, and tree growth conditions need to be monitored at a local level within one's own orchard. To support management decisions (especially during infection events), growers can use the NEWA website, which has weather stations across Pennsylvania.  Before applying chemical products, be sure to comply with current use regulations and read the product label. Product information can easily be obtained from CDMS, Agrian, or Greenbook.