Kick-back Materials for Last Major Scab Infections 6 & 7 May; Primary Scab Season Is Over But Rusts Continue; Fire Blight Infection 4, 5 or 7 May
1. The primary scab season in Virginia is over as the ascospore reserves have been depleted from the leaf litter below 5%. The 6 and 7 May heavy rain events have triggered the last severe primary scab infection and if you did not cover with a fungicide ahead of it, you can apply DMI fungicides with mancozeb today as DMIs can reach back 96 h and control this scab infection. Regardless of the scab season end, the fungicide coverage needs to be continued on these locations up to 2 weeks after today. This is absolutely needed because you do not know how good your coverage was in the major spring scab infection events and rust infections will warrant these applications ahead. Many of you are using alternate row middle (ARM) spraying that should cease at bloom and you should spray every row from then on. So, if any scab lesions arise now from coverage issues associated with ARM last minute, or due to missed fungicide applications before any rains during early spring, it will be much harder to have perfect looking fruit crop until harvest. Risks from scab are now high in orchards where scab lesions are visible on leaves or, hopefully not on fruit. In those orchards protection from scab scab continues with higher rates of captan as the secondary infections by asexual spores called conidia, which is what is inside of the scab lesions you see, and are now able to infect. If you see scab lesions let em know. Leaves are still expanding now on terminal shoots and can hold much more fungicide residues to protect from diseases, allowing some redistribution during low-amount rains.
2. If not protected by streptomycin, fire blight had caused infection on 4, 5, 6 or 7 May on any stray open flowers by now (most farms are done with bloom, so risk is low unless you have a young orchard). Go and look at the EIP model in NEWA for the nearest station to determine where you protected with streptomycin during the infections positioned between 4-7 May by looking at your spray records. Keep in mind that Apogee or Kudos is a great option used for shoot blight control. Until the terminal bud set is completed on shoots, they are susceptible to fire blight infections from infected flowers. If you missed an application of streptomycin, you can apply Apogee rescue treatment (12 oz/100 gal) that have ability to prevent canker formation from infected shoots: Effective Post-Infection Programs of Prohexadione-calcium for Reducing Shoot Blight and Preventing Fire Blight Canker Initiation on Apple Wood with Cost-Benefit Analysis. Cankers developing on central leader and rootstock can kill trees. In addition to this PGR, you can use Cueva at 2 qts/A in mix withe Double Nickel 1 qt/A to reduce chances for new shoot blight infections. Apogee is used at 6-12 oz/100 gal or 3-6 oz for trees <5 years. Usually, Apogee is applied preventively, first time at 1-3” shoot growth stage (king-bloom to late bloom) and the second time 14-21 days later.
3. Juniper rusts have also had an extremely high infection event from 4 to 7 May, and DMI fungicides plus mancozeb applied for scab should have covered for these infections and can kick-back 96 h to stop these infections on apple. High rust pressure is predicted to continue as almost all cedar galls have emerged at an unprecedented way in the last 7 days (Figure below), and the protection by fungicides will have to continue by applying a DMI plus mancozeb every 14 days.
