Forewarned is Forearmed

Check list:

~Indiana Disease management program for apples for 2018 is available at: https://www.extension.purdue.edu/extmedia/BP/BP-201-W.pdf
This information is identical to the Midwest fruit pest management guide, but provided in a table format and includes Fungicide Resistance Action Committee (FRAC) Codes, REI, PHI and efficacy information for each product (Fig. 1).

~Reducing overwintering inoculum for apple scab:
For orchards with less than stellar scab control last year, inoculum reduction before the growing season begins is an integral component of scab control. In the spring, two approaches can be used to reduce overwintering scab:

• An application of a urea spray (42 lb/A in 100 gal of water/A) sometime before green tip with a penetrant surfactant like LI700 or Wet Betty, and/or
• Shredding leaf litter with a flail mower
  • Rake or vacuum up leaves, and remove them from the orchard (home orchard only)

For growers in southern Indiana who may be already experiencing green tip: Apply the urea with a boom sprayer rather than with an airblast sprayer. Urea applied via airblast sprayer after green tissue is present on trees may result in urea uptake, making the tissue more susceptible to damage by any later application of oil, copper, sulfur, or Captan sprays that are applied within a week of the urea application.
For more information see: Adjuvants to Improve Disease Control in Apples

The second tactic, shredding the leaf litter, uses a mechanical approach to break down leaf debris. It is important to note that in the spring, effective leaf shredding requires that the flail mower be set low enough to contact the wet, matted leaf litter on the orchard floor. This may require that leaf litter beneath trees to be blown or raked into the row middles so the flail mower can effectively shred the leaves. Most rotary mowers will not be able to shred overwintering leaf litter. Take care that low flail mowing doesn’t damage the overwintering grassy strips that are essential for pesticide applications later in the season!

Using either of these tactics in the spring (urea sprays or flail chopping leaves) can reduce ascospore production by 70–80% (Sutton et al., 2000). It is important to note that urea fertilizer contains 46% actual nitrogen that will provide nitrogen fertilization to the trees. As such, nitrogen fertilizer rates should be adjusted accordingly for orchards where urea applications are used for scab control. If the addition of nitrogen is undesirable, leaf shredding with a flail mower may be a better option.

Incorporating either of these sanitation tactics (urea spray or leaf shredding) prior to bud break will not eliminate the need for protectant sprays beginning at green tip but should be regarded as an essential component of integrated scab management. Although not many infections are likely to occur, any infection has the potential to rapidly develop devastating levels of inoculum (See Figure 1). In orchards where SI resistance is known, or suspected, extra care must be taken to ensure that trees are protected early in the growing season with mancozeb, Polyram, captan, Scala or Vanguard, prior to repeated rain events, as the SI fungicides will not effectively eradicate newly developing infections.

Finally, urea sprays or flail shredding are unnecessary in orchards that did not have issues with apple scab last year. By using an integrated approach that includes sanitation by chemical or mechanical means WITH a timely and tight schedule of fungicides from green tip through first cover, scab problems should be reined-in in a single season.

Literature cited: Sutton, D.K., Mac Hardy, W.E., and Lord, W.G. 2000. Effects of shredding or treating apple leaf litter with urea on ascospore dose of Venturia inaequalis and disease buildup. Plant Dis. 84:1319-1326.
Beckerman, J. 2016. Adjuvants to Improve Disease Control in Apples. At http://www.hort.cornell.edu/expo/proceedings/2016/TreeFruit.Adjuvants%20to%20improve%20disease%20control%20in%20apples.Beckerman.pdf