Nov 29, 2021
Don’t overlook orchard sanitation and weather station maintenance

After several weeks of summer trying to keep a firm grip on us, fall weather is finally here. As the leaves are falling from the trees, there are few disease management items on the to-do list before growers winterize their equipment for the season.

This is a healthy review of what to have on your radar this fall as you are putting the 2021 season to bed.

Apple scab and Marssonina blotch

Leaf removal is key

If you noticed 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 an important defense strategy for any good scab and Marssonina management program.

Spores need the leaf tissue to survive the winter. Growers are encouraged to reduce the available spores for next season by employing 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 breaks 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 due to 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. Shred leaves in the fall or in March (or both times) 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 employ the practice of speeding up the process of defoliating trees in the late fall using copper and nitrogen, or even zinc. Questions about the effect of hardiness have come up. Per communications with 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, then reserve carbohydrates and hardiness may be lost.

I worked on the effects of fall foliar urea and of defoliation on tree hardiness when I was at the Hudson Valley Lab. Sprays were done in late October to Empire trees. Two sprays of urea at 50 lb per acre had no effect on hardiness. Defoliation had some effect on hardiness, but the loss of mid-winter hardiness was small. Once the leaf has performed the functions of sensing the end of growing season and of producing reserve carbohydrate, then the leaves have 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 carbohydrate before defoliation.”

Cherry leaf spot

Leaf removal is key

Cherry leaf spot and apple scab are very similar when it comes 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

This year, some areas experienced a higher incidence of peach leaf curl 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 to control for peach curl. When the leaves are no longer on the trees, peach leaf curl spores are exposed. 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 choose to 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 not only be done in the fall but several times during the season. Monthly checks during the season are recommended.
  • Keep the solar radiation sensor clean by removing debris from the sensor’s top 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 appear “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.
  • Observe leaf wetness sensors for damage or corrosion. If there are problems, the leaf wetness sensor should be replaced.
  • Double-check the accuracy of your equipment. It is best to compare 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 Fruit Research and Extension Center in Biglerville with a nearby NEWA weather station in Adams County.

Additional resources

There are a lot of resources available on YouTube for maintenance guidance in general and specific brands. Just use the search words “weather station maintenance.” It is always best to contact the company associated with your weather station for further guidance when in doubt.

Kari A. Peter, associate research professor, tree fruit pathology
apple and pear diseases peach, cherry, other stone fruit diseases. Tree fruit disease management.

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