1. IN FALL 2022 YOU CAN REDUCE INOCULUM FROM APPLE SCAB & MARSSONINA BLOTCH; 2. PLAN DORMANT ZIRAM, COPPER, CHLOROTHALONIL IN PEACH
1. Apple Scab and Marssonina Leaf Blotch were visible in the Shenandoah Valley apple orchards this year. As the fungi that cause these diseases overwinter in the dead leaf litter on the orchard floor, you can reduce apple scab ascospore inoculum dose by 50-70% and thus increase the future efficacy of your spring fungicides by using practices and materials that quicken degradation of the leaf litter. The best time to spray the leaves with these materials is in fall, just before the major leaf drop. You can also spray the leaf litter on the ground in fall or spring, but the application in fall allows better leaf coverage with the material than after it is on the ground. If there is no snow cover and mud is not preventing you to get into the orchard with the tractor, use flail mower to shred the leaves on the ground to smaller pieces – that will speed up the degradation of dead leaves by microorganisms and worms on and in the soil. In smaller orchards, you can rake the leaves from under the trees into the row middles and remove leaf piles with flail mower mode for scalping the sod. The most used practice is to spray urea to apple leaves on the trees in fall, just before the major leaf drop. If you miss to do it in the fall, you can spray the leaves on the ground late winter but before bud break. Use rate of 40 lbs of urea / A in 100 gals of water. Once done with the application, wash and rinse well your spray equipment since urea can wear up any rubber parts, washers, and gaskets in the sprayer, especially the sprayer pump diaphragm. If you are an all organic grower urea is not to be used use. Use dolomitic lime instead and at a rate of 2.5 tons / A, which also can be used in conventional orchards. Lime is best used after leaf drop in fall or early in the winter. Lime increases the pH or basicity (opposite to acidity) of soil surface promoting microbial activity and thus apple leaf litter breakdown. You can use powdered lime spreaders as the most efficacious way of applying it.
2. Leaf curl of peach. Copper for leaf curl should be applied while trees are dormant, i.e. wait for the leaves to drop if you want to apply early winter. Most of the times the best is to apply late in winter and up to and during bud swell (bud break). Use at least 4 to 8 lb of metallic copper per acre. Ziram for leaf curl should be used during dormancy, after leaf drop in fall, and prior to bud swell. You can combine Ziram and copper or copper and Bravo (chlorothalonil), but do not apply Ziram and copper during bud swell (bud break). Copper aims to reduce the leaf curl fungus spores that overwinter on the tree. Infections take place in the spring as the buds open. This fungal pathogen infects buds during rain events from bud swell to bud opening. Very long cool wet periods during bud burst slow bud development and thus lead to severe peach curl infections. Copper products also give some suppression of bacterial spot. In spring, if you missed the window for late winter copper application, and you suspect based on cool and wet weather that infection has already occurred, Bravo or Ziram are better than copper as they have efficacy after infection and Bravo redistributes during rain.