Time to Begin Disease Management for the 2026 Season

The 2025 season is one to remember. We broke dormancy a little early in mid-March. We experienced a freeze in early April. April was dry for many, which triggered powdery mildew issues. However, we did experience ideal fire blight conditions for a few vulnerable varieties. Then, the faucet was turned on May 1, and it didn't shut off until the end of July, delivering approximately 1-2 inches of rain per week. These conditions generated a banner year for all of the fungal diseases that give us headaches, especially bitter rot. August arrives, bringing dry conditions most of the month and cool night temperatures during the latter half, which persist for the remainder of the harvest. Although there were some pockets of issues for a few folks, everyone seems to be very pleased with the 2025 apple harvest: lots of apples, decently sized, and beautiful color. As we relish the satisfaction of a great season, there is no rest for the weary. Now is the time to get a jump start on managing diseases for the 2026 season. Since this year has been favorable for many diseases, it is essential to be proactive in reducing pathogen populations in the orchard during the off-season. This review will help you triage your attention and resources as 2025 winds down.

Apple scab and Marssonina blotch: Leaf removal is key

If you notice any scab or Marssonina blotch in your orchard this season, be proactive in mitigating problems for next year. Orchards are susceptible to self-infection when it comes to apple scab and Marssonina. Even if your fruit is clean of apple scab this season, there is still a possibility that your leaves may be infected. Reducing leaf litter and the spores it contains is a vital defense strategy for any excellent scab and Marssonina management program.

Spores need the leaf tissue to survive the winter. To reduce the available spores for next season, growers are encouraged to employ a two-pronged approach this fall: urea applications and flail mowing of the leaf litter. Urea applications will be aided by flail mowing to ensure the complete breakdown of leaf tissue.

 Time the urea applications as closely as possible to leaf drop. Urea helps break down leaves by providing extra nitrogen, stimulating the growth of beneficial soil microbes after leaves have fallen to the ground. If urea is applied too early in the fall season, it can be washed off before the leaves hit the ground. Using urea will reduce inoculum by 50 to 80% for the next season. Flail mowing the leaf litter after urea application will reduce inoculum by 95%.

Dissolve 40 pounds of feed-grade urea in 100 gallons of water (a 5% solution), applying 100 gallons per orchard acre. Feed-grade urea is recommended for the ease of dissolving it in warm water, if available. If you choose not to use urea, ensure that your nitrogen source is derived from ammonium. Good coverage of the leaves is desired to allow them to absorb the urea. If the leaves have already fallen off the tree, urea can also be sprayed on the fallen leaves on the orchard floor. Using an offset flail mower is recommended for shredding leaves. Shredding leaves can be done in the fall or March (or both) before growth starts. When there are no sources of spores on the orchard floor, the risk of early infections from these diseases is very low.

Comments on defoliating trees

Many growers employ the practice of accelerating the defoliation process of trees in late fall by using copper, nitrogen, or even zinc. Questions have arisen about the impact of hardiness. Per communications with Dr. Jim Schupp (retired Penn State Pomologist), this is what he shared:

The leaves sense shortening day length and chilling, which triggers the processes that lead to dormancy. Defoliating too soon could remove the organ that senses and triggers dormancy. Additionally, the tree requires carbohydrate reserves to maintain its hardiness throughout the winter. Numerous stories about over-cropped and/or unharvested trees being winter-killed bear this out. If one defoliates the trees too soon, reserve carbohydrates and hardiness may be lost.

I worked on the effects of fall foliar urea and defoliation on tree hardiness at the Hudson Valley Lab. Sprays were done in late October on Empire trees. Two sprays of urea at 50 lb. per acre did not affect hardiness. Defoliation affected hardiness, but the loss of mid-winter hardiness was slight. Once the leaf has performed the functions of sensing the end of the growing season and producing reserve carbohydrates, it has little more to do with hardiness. Wait for the first frost before scheduling defoliation. Late-harvested cultivars, such as Pink Lady, should be given a couple of weeks after harvest to accumulate carbohydrates before defoliation.

Fruit rots: Remove fruit from trees to prevent mummification

It is essential to harvest all the fruit from the tree at the end of the season to minimize fruit rots for the next season. If fruit remains, it will rot and mummify, becoming great spore factories for the next season. Fruit can be removed by hand; however, this could be a daunting task depending on the number of fruit remaining on the tree. At Penn State FREC, we use Ethephon at 4 pt. per acre plus a surfactant on trees with fruit remaining. It is essential to note that not all varieties respond equally to Ethephon. Gala responds very well and drops fruit easily; Fuji, not so much. Once fruit is on the ground, it will decay and break down due to the natural microbes.

Cherry leaf spot: Leaf removal is key

Cherry leaf spot and apple scab share a similar infection process; fallen diseased leaves are the primary cause of spring infections. Like apple scab, sanitation is critical for effective management. Follow the same sanitation method for managing cherry leaf spot as you would for scab. 

Peach leaf curl: Control is needed when the leaves have all fallen

Some areas experienced a higher incidence of peach leaf curl this year, as the fungus had ample time to cause disease on the leaves. When we have warm springs, the leaves unfurl fast, and the fungus does not have time to do much damage; it is the opposite during a cold spring. You can treat trees in the fall or spring, or both. You must wait until all the leaves have fallen from the peach trees before treating them to control peach curl. Peach leaf curl spores are exposed when the leaves are no longer on the trees. This is your only time to manage the disease. If any remaining leaves are present, these leaves will continue to protect the spores in the buds. If you wait until late dormancy to apply the fungicide, monitor temperatures closely and be mindful of warm spikes (80°F) in temperature during February and March. This warmth has been sufficient to encourage bud swell in early varieties, such that late winter fungicide applications have been ineffective in controlling peach leaf curl. The following fungicides are the best options for managing peach leaf curl: copper, lime sulfur, or chlorothalonil.

Weather Station Maintenance: Now is the time to give it some love

Regardless of the weather station brand you may own, maintenance is essential to ensure the accuracy of the weather data output.  The user can perform some maintenance activity; other work may have to be performed by a trained technician from the company. 

General guidelines to follow

• Remove any debris from the rain gauge that can cause measurement errors. This should be done in the fall and several times during the season. Monthly checks are recommended during the season.
• Keep the solar radiation sensor clean by removing any debris from the top of the sensor and wiping it off using a damp cloth.
• Remove any accumulated dirt and debris from the temperature and humidity sensor. If you notice any data missing or values appearing "off," it is best to contact the company.
• Check the anemometer to see if it is operating correctly. The anemometer and weather vane should move freely in all directions.  Issues occur when dirt accumulates in the bearings.  If you encounter any problems, it is best to contact the company directly.
• Leaf wetness sensors should be observed for damage or corrosion. If there are problems, the leaf wetness sensor should be replaced. 
• To double-check the accuracy of your equipment, it is best to compare it to another weather station nearby to determine if there may be issues with any component. For example, we often compare our weather station at Penn State FREC with a nearby NEWA weather station in Adams County.

Additional resources

Many resources are available on YouTube. for general maintenance guidance and for specific brands.  Just use the search words "weather station maintenance." When in doubt, it is always best to contact the company associated with your weather station for further guidance.