2022 Disease Update: Orchard Sanitation and Weather Station Maintenance

As the last apples are being harvested, growers must remember several disease management items before winterizing their equipment for the season. This is a healthy review of what to have on your radar this fall as you put the 2022 season to bed.

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 self-infecting when it comes to apple scab and Marssonina. Even if your fruit are clean of apple scab this season, there is still a possibility of leaves being infected. Reducing leaf litter and the spores they contain 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 the leaf litter. Urea applications will be aided by flail mowing to ensure the complete breakdown of leaf tissue.

Time the urea applications as close to leaf drop as possible. Urea works in breaking down the leaves by the extra nitrogen stimulating the growth of beneficial soil microbes after leaves have fallen on 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 the urea application will reduce inoculum by 95%.

Dissolve 40 pounds of feed-grade urea in 100 gallons of water (5% solution), spraying 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, be sure your nitrogen comes from an ammonium source. Good coverage of the leaves is desired for leaves 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, there is a very low risk of early infections from these diseases.

Comments on defoliating trees

Many growers use copper, nitrogen, or even zinc to speed up the process of defoliating trees in the late fall. Questions about the effect of hardiness have come up. Per communications with Dr. Jim Schupp (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. Also, the tree needs carbohydrate reserves to maintain hardiness throughout the winter. Numerous stories about over-cropped and/or unharvested trees being winter killed bear this out. It follows that 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 to 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, the leaves have little more to do with hardiness. Wait for the first frost before scheduling defoliation. Late-harvested cultivars like Pink Lady should be given a couple of weeks after harvest to accumulate carbohydrates before defoliation."

Cherry Leaf Spot: Leaf Removal Is Key

Cherry leaf spot and apple scab are very similar to infection: fallen diseased leaves are the culprit for creating 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 since the fungus had plenty of 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 off peach trees before treating them to control for 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 enough to encourage bud swell in early varieties, such that late winter fungicide applications were ineffective in successfully controlling peach leaf curl. The following fungicides can be used: copper, ziram, 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 during the season are recommended.
• Keep the solar radiation sensor clean by removing any debris from the top of the sensor and wipe 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 there are issues, it is best to contact the company.
• 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 the Penn State Fruit Research and Extension Center with a nearby NEWA weather station in Adams County.

Additional resources

Check out the Dr. Tree Fruit and Don podcast episode, Fruit Bites 9: 10-18-2022 End of Season Tips and Reminders.

Many resources are available on YouTube for general maintenance guidance and 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.