I am leaving for a research conference for the next week, so I am getting out a preemptive notice of things to watch for while I am away. So, while I am discussing disease management, remember to check NEWA to assess actual disease conditions before applying prophylactic sprays in your orchards.
Bud stages have moved pretty rapidly in the past ten days, and we are a good 7-10 days ahead of ‘normal’. In many years I start spraying the orchard on or around earth day. This year I started April 13, and put a second spray on this morning to buy some protection while I’m gone for a week. If you have the notion, you can report your bud stage dates at this link (https://go.uvm.edu/23applebudstage) to help me keep an eye on things around the state.
Orchards are at or around the tight cluster bud stage in Champlain Valley of Vermont, which means that there is plenty of tissue out there for apple scab to infect, and the disease is in a critical management phase. Orchards should be covered with an effective contact fungicide (mancozeb, captan, sulfur if organic) going into any expected wetting periods. If coverage is questionable going into a wetting event, a postinfection material may be used- Vangard is effective prebloom and during relatively cool weather. There are several others, too- see the New England Tree Fruit Management Guide apple spray table for details. Note that these post-infection materials, including DMIs, SDHIs, Strobilurins, and Anilinopyrimidines, have high potential for the fungus developing resistance to them, so always mix with a protectant and rotate fungicide classes every application. Organic growers have fewer options for postinfection materials. I am not recommending liquid lime sulfur anymore, as it is just too caustic and dangerous to applicators, trees, and equipment. Some materials such as the peroxide (e.g., Oxidate) and bicarbonate (e.g. Armicarb) based fungicides have shown efficacy when applied during infection, as the spores are germinating on wet leaves, but are pretty limited in providing any real control after cuticle penetration has occurred. Bottom line: keep the orchard covered.
There is still time to apply oil to manage mites and scale. I am a proponent for putting oil on as late as possible, up to tight cluster or even pink. The rate should be adjusted down as buds open more: 2-3 gallons per 100 gallons water (straight % in tank, not adjusted for tree for volume or per acre) is good from dormant through green tip; 2 % GT-tight cluster; and 1% as you approach pink. Oil should be put on dilute- slow down and open up your nozzles if you can. For most orchards, 100 gallons of water per acre should be the minimum for applying oil. That means recalibrating your sprayer in many cases.
Trees are approaching their peak energy needs as bloom approaches. Now is a good time to get your first soil-applied nitrogen fertilizer down. In many cases, split applications are more useful than a single application, timed at tight cluster to pink and a second application at petal fall. Without a foliar analysis (which is always the gold standard for developing fertilizer recommendations), growers should err on applying a total of 30-40 pounds of actual nitrogen per acre whether in one or two applications. This is also a good time to apply the foliar tonic of urea (3#/100 gallons), boron (1# solubor or 0.1-0.2 lb actual B/100 gal) and zinc (many materials, use label rates). I wouldn’t mix this tonic with oil, do one and then the other in this next spray or two if needed.