Greetings NC apple community. First, my apologies for not updating often this season. I had several personal challenges, including the death of my remaining parent for whom I served as caretaker and well it was a struggle to get through the season to say the least. That said, I appreciate all of your kind words, thoughts, and patience as I navigated through this and other unexpected losses. That all said, my head seems to be in a decent spot and let’s discuss this year’s Spot and Rot issue, the rain, and how you should prepare for the remainder of this season and to ensure you get on the right foot next season!

As far as a growing season for apples goes, this has been among the strangest and most challenging that I’ve experienced since I’ve been at NC State. From April 1-June 30th, 14.7 inches of rain fell in the apple production area of Henderson County. Contrast that to the month of July, when 15 inches of rain fell, 11.2 inches of that over a 16 day period (July 16-31). During and after this period I’ve contacted a number of colleagues who unfortunately agree with me that not even the most diligent fungicide programs could have led to GLS and bitter rot free trees. In addition to the rain, leaf wetting hours during this period averaged 14.4 hours per day, with an accumulation of 216 hours total.

That said, the environment, particularly the late-July timing of the rains, played a crucial role in the severity of GLS, bitter rot, and Bot rots that we’ve observed throughout the region. Looking at both disease control at MHCREC, speaking with growers throughout the region, and speaking with growers in other production areas I’m still feeling good that fungicide applications on 7 to 10 day intervals is still the correct practice. However, I’ll again stress that these intervals really are critical starting around the bloom/early petal fall period through harvest. Regardless of the drought conditions we faced from mid-April-June, there were still 430 accumulated leaf wetness hours with an average of 5.6 hours per day. Remember, rain is not ideal for disease management as it aids in spreading fungal spores, causes leaf wetness, and depletes fungicides (amongst other downstream consequences). However once a spore lands on susceptible tissue, it really just cares about wetness, temperature, and to some extent humidity. Thus, even with the lack of rain during the late spring/early summer, infections were still occurring.

That said, given that apples are a perennial crop, this year’s inoculum load from disease can certainly be next year’s issue. I would suggest the following tips as you continue through and following harvest:

1. Keep spraying if you still have clean apples on the trees. The majority of conidia (spores) of Colletotrichum pathogens (Colletorichum fructicola and Colletotrichum chrysophilum ) causing GLS and Glomerella fruit rot cause infection when temperatures are between 59 F – 86 F and if free water (e.g. dew or rain) is available on leaf tissue. Despite the cooler weather, there have been 7 days since the beginning of September where the temperatures and leaf wetness hours have lined up to create a possible infection event. For cultivars that are a week out from picking, consider a Merivon + Captan application as the Merivon will have longer activity then captan following harvest. For other cultivars, continue with captan cover sprays, but don’t shy away from including Ziram (4 lb) + a spreader sticker if you still have Ziram remaining. Just remember the 14 day PHI. For those that are 30+ days out (perhaps Pink Lady?), Aprovia or Omega have demonstrated good efficacy against GLS and bitter rot in NC and/or other production regions.
2. Consider removing rotting apples from trees still needing to be harvested. If you have a high value cultivar that is susceptible to bitter or Bot rots (white or black rot), it may be worth removing fruit with rots and throwing them in the row middles (ok) or removing them from the orchard and destroying (best). This should reduce local inoculum- particularly if rains continue.
3. Clean up your trash more than once. What’s been particularly puzzling this year is that orchards that are supposedly utilizing similar fungicide programs and application intervals are seeing stark differences in spot and rot control. Normally I’d turn to microenvironments, but many of these orchard blocks in which varying levels of control are observed are only 100s of yards away with no significant elevation change. One thought I have is the degree of leaf, fruit, and mummy “clean up” occurring between different sites. Given the high inoculum load going into the fall and winter, it is IMPERATIVE that leaf and fruit litter (which can harbor pathogen spores) is destroyed. My suggestion is to i) flail mow to increase leaf surface area and then ii) Apply 40 lb urea/a on a day above 50 F. The flail mowing increases the leaf surface area for microbes to break down leaf litter and in return destroys fungal structures. While early results from our mummy studies suggest that the Bot Rot fungi are recovered more frequently from mummies than Colletotrichum fungi, removing mummies if possible is also helpful for disease control.
4. Consider spraying a fungicide every 14 days or so on GLS susceptible  cultivars. This should keep inoculum down.

LASTLY……Resistance to FRAC 11 (strobilurin) fungicides may have also played a role in the increased incidence of GLS and bitter rot this year. My program has been working with some growers to screen for strobilurin resistance but we need more samples! Next Wednesday (Sept 25), Terry Kelley and myself are headed out to the county to collect samples for resistance screening. We’d love to swing by your orchard and will head out on more days if needed to collect for anyone interested in participating. We are also putting together a survey to tease out possible cultural control practices that could be associated with different levels of disease severity. A survey will be sent in the coming weeks, but if you have any thoughts/questions that should be added to the survey please let me know! If you’d like screening for resistance, please send me a quick email: smvillan@ncsu.edu, include your phone number and we will get you on the list!