The cooler temperatures and dry weather this week hopefully gave you a breather from streptomycin sprays and other disease management tasks. However, as we transition into petal fall (1st cover for some areas) in most cultivars and with the warmer temperatures it's time to gear up for an "exciting" weekend and week ahead. At this point in the season and looking at the forecast, temperatures during the day and even some evening will be warm enough for infection by the Colletotrichum fungi causing bitter rot and Glomerella leaf spot. Further, blossom blight risk is high across all major production regions through the weekend and through early next week. Shoots are starting to elongate quite rapidly in our research orchards, so there's shoot blight to worry about. Of course, Marssonina leaf blotch should also be managed during this time. For this week's post let's take a bit of a closer look regarding shoot blight management and GLS/bitter rot management, as MLB was handled in my bloom update. However first some blossom blight risk updates....

Polk County and Morganton area: According to the EIP model, there is a High Risk of blossom blight from April 11-14, 2026. If you have open flowers remaining or rattail bloom, EIP population levels well exceed 100 on these days and a wetting event is the only condition not met for infection to occur. If you are making a pesticide application on any of these days consider adding streptomycin to the tank (100 ppm rate). If you tend to get a heavy dew in these orchards also consider a strep application.

Alexander, Wilkes, and Henderson Counties: According to the EIP model, there is a High Risk of blossom blight from April 12-14, 2026. If you have open flowers remaining or rattail bloom, EIP population levels well exceed 100 on these days and a wetting event is the only condition not met for infection to occur. If you are making a pesticide application on any of these days consider adding streptomycin to the tank (100 ppm rate). If you tend to get a heavy dew in these orchards also consider a strep application.

In addition to blossom blight, around the petal fall timing (or even slightly before) is when you want to start thinking about your first application of prohexadione calcium, formulated as Kudos. In order for shoot blight to occur, their must be inoculum present within or near an orchard (i.e. there must be a local inoculum source). Thus, even just a few blossom blight infections can serve as a strong catalyst for shoot blight infection. Shoot blight is the result of infection to young, emerging leaf tissue. Injury to this susceptible leaf tissue provides the means for bacteria to invade and progress down young shoots. Insects with sucking or piercing mouth parts, or other types of wounds created from environmental conditions (e.g. hail, wind, soil abrasion, etc).

At least two applications of Kudos should be applied during the season for shoot blight management. For mature trees a 12 oz/100 gal rate is recommended between the period of petal fall and 1-3" shoot growth. You'll want to follow up with a second application 14 days later. For trees less than 5 years old in which you are trying to fill the canopy, consider applications at the same timings but at a reduced rate of 2-3 oz Kudos plus 1 oz Actigard/100 gal OR 6 oz/100 gal Kudos. Make sure to follow label guidelines on the addition of water softeners and penetrating adjuvant when making an application. Also, do not apply calcium in tank mixture with ProCa. For her dissertation with Tom Kon, Annie Vogel (now Assistant Professor at UT-Knoxville) conducted the impacts of Kudos and Actigard in young high density orchards for both shoot blight control and impacts on tree growth and production. Last years she contributed to our Portal Posts with FAQs About Kudos. I encourage you to check this out!

Anytime from now through early next week I would consider your first application targeting Glomerella leaf spot and bitter rot. What exactly does that mean? Continue with mancozeb as your backbone fungicide for resistance management and broad spectrum disease control, but also add a strobilurin containing fungicide such as Cabrio, Merivon, Pristine, Flint Extra, or Luna Sensation. In our trials and those of my colleagues, Sovran has really not performed as well as other strobilurins. When making an application, I would use the highest labeled rate for apple.

Now do I have a preference of which of the 5 other strobilurins to use? It really depends on the situation:

1. Cabrio EG and Flint Extra: Cabrio (pyraclostrobin) was re-registered for apple this year and Flint Extra is the newer liquid formulation of trifloxystrobin. What is attractive about both of these options is that they are single a.i. products. This will give you more flexibility in regards to incorporating SDHI fungicides (FRAC 7) into other spray timings. The downside of applying just a strobilurin fungicide at this timing is that they have demonstrated high efficacy in our Marssonina trials. That said, mancozeb should help some, and I would highly encourage you to rotate to a newer DMI like Cevya or Indar next spray or fluxapyroxad (Tesaris) if you can get your hands on it.... One reason you may want to choose Cabrio over Flint Extra, is that it may have better "kick-back" activity against the Colletotrichum species causing Glomerella. In lab trials, trifloxystrobin (a.i. of Flint) demonstrated no activity in the mycelial growth stage compared to pyraclostrobin (Cabrio). To be fair, we haven't tested kickback activity in the field or in the immediate stages after an infection.
2. Merivon: Merivon is a formulated pre-mixed product of pyraclostrobin (Cabrio) and sercadis (Tesaris; FRAC 7). It is only the pyraclostrobin component in Merivon that provides activity against GLS and bitter rot. Thus, if you're strictly going after GLS and bitter rot, Cabrio may be the better option to provide more flexibility with using SDHIs in other sprays. If you are concerned about Marssonina and GLS in your block, Merivon could be the better choice.
3. Pristine: Similar comments in regard to Merivon; however the boscalid (FRAC 7) component does not have the activity that fluxapyroad does against Marssonina leaf blotch.
4. Luna Sensation: Luna Sensation contains trifloxystrobin (FRAC 11) + fluopyram (FRAC 7). Again, trifloxystrobin performed similarly to pyraclostrobin (Cabrio) against Colletotrichum spore germination in lab trials. In field trials, this translates to a protectant application prior to a spore landing on a leaf or fruit. It's the questionable post-infection activity that makes me a little gunshy and this season we will attempt to evaluate both strobilurins for their activity immediately following an infection event using detached fruit and leaf assays. In the one year of field trials that we conducted against Marssonina, Luna Sensation had weak disease suppression compared to Merivon.

• Blossom Blight: Keep an eye out for heavy dew or any pop up showers not in the forecast as a wetting event is the only condition not met for a blossom blight infection in blocks that still have open flowers. This risk remains from Saturday or Sunday through Tuesday (NEWA does not forecast beyond that as of this evening) so if you decided to make a pesticide application during this period, consider including streptomycin
• Get Kudos out in all blocks; particularly those with a history of fire blight
• Including a strobilurin (FRAC 11) in tank mixture with 3 lb/A mancozeb within the next 5 or so days for management of GLS and bitter rot.