Managing Fruit Rots This Season

Fungicide re-applications are necessary since several inches of rain have fallen the last few days. Management considerations are discussed for mitigating pome and stone fruit rots.
Managing Fruit Rots This Season - News


Hail damaged fruit need protection from fruit rots. Photo: T. Ford, Penn State

We are in the middle of a delicious peach harvest and apples aren't far away. Consequently, preventing fruit rots is now the priority. Significant rain has occurred in the region over the last 48 hours and is forecasted to continue this week. Monitor your area for rainfall: If more than 2 inches of rain falls and you have already applied fungicides this week, another application will be needed to keep the rots at bay since there is a good chance the protection will have washed off. This is especially important for peaches and nectarines nearing harvest. Some nuggets of wisdom to keep in mind:

Peaches and Nectarines

A review of brown rot management strategies

Peaches and nectarines are ripening, which means 'tis the season for brown rot. The fungus causing brown rot is quite opportunistic: it can kill blossoms and it can also ruin the fruit you've worked hard all season to grow. Brown rot disease is favored by warm, wet weather conditions. Under optimum temperature conditions, fruit infections can occur with only three hours of wetness when inoculum levels are high. Longer wet periods during infection result in shorter incubation times so symptoms develop more rapidly. It's not uncommon to have brown rot appear "overnight" on fruit.

Spores produced on early maturing cultivars can fuel a continuing outbreak on late-maturing cultivars - this is especially important for those who have battled rot infections already this season. To add another headache to the issue, insects can be important vectors of the fungal spores during fruit ripening: they can carry spores to injury sites produced by oriental fruit moth, Japanese beetle, green June beetle, and other insects that can injure fruit. Wounded fruit are much more susceptible to brown rot than unwounded fruit. It's critical to be on top of insect management. Another concern to worry about is split pit. Unfortunately, these fruit are quite prone to rot problems. Keep in mind: under the right conditions, "healthy" fruit harvested can be contaminated and may decay later during storage.

Research at Rutgers has shown that timing brown rot sprays 18 days, 9 days, and 1 day before harvest provided greater than 95 percent control under heavy disease pressure. When following this regime, be sure to rotate chemistries by FRAC group for resistance management. For example, one could spray the following, provided the maximum number of sprays has not been exceeded for that chemistry:

  • 18 days: Fontelis (FRAC Group 7; 0-day PHI)
  • 9 days: Indar (FRAC Group 3; 0-day PHI)
  • 1 day: Merivon (FRAC Group 7 +11; 0 day PHI)

Other options to rotate:

  • Luna Sensation (FRAC Group 7 + 11; 1 day PHI)
  • Luna Experience (FRAC Group 7 + 3; 0 day PHI)
  • Topsin M (FRAC Group 1; 1 day PHI)
  • Inspire Super (FRAC Groups 3 + 9; 2-day PHI)
  • Orius (FRAC Group 3; 0-day PHI)
  • Tilt (FRAC Group 3; 0-day PHI)
  • Quash (FRAC Group Code 3; 14-day PHI)
  • Flint Extra (FRAC Group 11; 1 day PHI)
  • Captan (FRAC Group M4; 0-day PHI)

Keeping in mind products that were used to control blossom blight, be sure to comply by obtaining the current usage regulations and reading the product label. Depending on the number of sprays needed and what you may have used during bloom time, be sure to practice fungicide resistance management and rotate chemistries by FRAC group ("Spray by the Numbers").

Bitter rot symptoms on young fruit: the apple on the left shows advanced symptoms, including salmon-colored spores on the lesion surface; the apple on the right shows small red lesions, which are early symptoms. Photo: P. Martin, Penn State

Alternative options for rot management

The key for growers who farm organically or prefer using alternative products is to spray as often as possible as disease conditions persist, manage insects, scout often, and prompt removal of infected fruit as soon as you see it. Spraying often ensures you have continuous protection; removing infected fruit from the trees ensures you are decreasing the number of spores available to cause disease and hopefully minimizing an epidemic. Knocking infected fruit to the ground will be enough to limit spread. Vigilance is important, and this may translate spraying every few days, especially if rain washes off products. According to studies at Rutgers, sulfur is not effective for controlling brown rot. Some organic options labeled for brown rot control are Cueva, Double Nickel, Serenade Opti (or Serenade ASO), and Regalia.


Protecting fruit from rots

We are nearing the home stretch of the apple season and folks will want to be considering sprays to keep their apples free of rot, especially while in storage. Not only a headache in the field, but the fungi causing fruit rots can be quite stealthy since spores will land on the fruit and cause symptoms only after the fruit have been in storage. This is especially significant if your apples are headed for a packinghouse or even fresh market.

Mother Nature often throws curveballs this time of year, particularly when unexpected thunderstorms produce hail. Hail damaged fruit is often destined for juicing, as a result. Protection from rot fungi is critical for these damaged fruit since they are now more susceptible. Since these fruit are especially vulnerable, growers will want to consider using complete sprays.

The most problematic fruit rot this year may be bitter rot. There have been several reports of growers already observing bitter rot on some of their immature fruit. The optimum conditions for disease development include rainfall, relative humidity of 80 to 100 percent, and warm temperatures (80 – 90ºF). Unlike other fungi causing rot, the bitter rot fungus does not require fruit wounding to establish an infection and can directly penetrate the fruit skin. Rot spots usually appear on the side of the apple directly exposed to the sun as small, circular brown lesions and change to sunken, dark brown lesions as they enlarge. During humid conditions, large numbers of creamy to salmon colored spores are produced. Fruiting bodies visible to the naked eye appear after the lesion is one inch in diameter and are arranged in a concentric circle pattern in the center of the lesion (see picture). These spores are spread through the tree canopy via rain splashing. This is problematic now with the frequent rain events we have been experiencing, and it is important to maintain vigilance with protection, especially when the high amount of rain falling this week is most likely washing off fungicides.

I highly encourage growers to use Merivon (FRAC Groups 7 + 11; 0-day PHI) or Luna Sensation (FRAC Groups 7 + 11; 14-day PHI) as their last one or two sprays before harvest since these products do show efficacy keeping rots in check while in storage. This recommendation is both for fresh market and juicing apples: the pack houses and processors will thank you! There are a couple of sprays up to that point, and the following are additional options for control (be mindful of the maximum limit for sprays for each product/FRAC Group):

  • Flint Extra (FRAC Group 11; 14-day PHI)
  • Sovran (FRAC Group 11; 30-day PHI)
  • Indar (FRAC Grop 3; 14-day PHI)
  • Topsin M (FRAC Group 1; 1-day PHI)
  • Captan (FRAC Group M4; 0-day PHI - used alone or tank mixed with a single mode of action product)
  • Ziram (FRAC Group M3; 14-day PHI)
  • Serenade Opti (biofungicide - B. subtilus; 0 PHI)

We evaluated Serenade Opti the last few seasons for summer disease control at 16 oz/A as the last two cover sprays, with a conventional program up to these sprays. We observed minimal fruit rot diseases in the field and storage, at least on Golden Delicious. These results may vary with other cultivars, depending on their susceptibility to certain rot diseases, as well as the severity of disease conditions.