Scab disease development requires the host and pathogen to be present and the conditions to be suitable for the pathogen to grow. The conditions required for scab development is a temperature range of 59-95 degrees F (optimal temp is 59-77) in the presence of moisture for at least 12 hrs. For the next 12 days we have 6 days with a 50% or greater chance of rain with average low and high temperatures between 46 and 87 degrees. It’s time to spray.
Be sure to calibrate sprayers! Link below is a guide for calibrating:
As Dr. Lenny Wells has done in the past, a spray example is provided based on different varieties susceptibility to scab. These schedules are simply to be used as a framework on which to base your program. They incorporate what we know about the best use of each fungicide. Some fungicides like Phosphite and the group 3 + group 11 materials have better activity on leaf scab. Others, like Elast, Tin, and Miravis Top offer the highest degree of nut scab protection. There are also other labeled materials that could be worked into the schedule. The following is simply an example.
Low input cultivars are those with a very high degree of scab resistance –think Elliot, Excel, Lakota. These require a bare minimum of sprays–3 applications at most–primarily to help manage minor diseases aside from scab like powdery mildew, anthracnose, downy spot, etc. and to assist in maintaining scab resistance.
Spray 1: Phosphite ~ mid-late April
Spray 2: Phosphite ~ mid-to-late May
Spray 3: 11 + 3 mix ~ early-mid June
These are cultivars that will require fungicide sprays to manage the disease but on which scab is usually easily managed without an intensive spray program in most locations. Some of these cultivars can fall into the high susceptibility category in locations with a history of scab on these particular cultivars or under situations of low elevation, poor air flow, or frequent rainfall. Use your best judgement with regard to where these cultivars fit for your own location.
Scab on these cultivars should be controlled with 7-8 sprays. If excessive rainfall is occurring throughout the nut sizing period, you can shorten your interval and extend the program out further by continuing to rotate Miravis Top and Elast/Tin in the example below.
Spray 1: Phosphite ~ mid-late April
Spray 2: Phosphite OR 11+3 ~ mid May
Spray 3: Miravis Top ~ early-mid June
Spray 4: Elast+Tin OR phosphite ~ mid-late June
Spray 5: Miravis Top ~ early-mid July
Spray 6: Tin OR Elast+Tin ~ mid-late July
Spray 7: Miravis Top ~ early-mid August
These are cultivars that we know must be sprayed intensively in order to produce the crop. They will require at least 10 fungicide sprays and likely more in many locations. If you need to extend beyond spray 10, continue rotating with Elast/Tin but consider substituting a group 3 + group 11 for Miravis Top since no more than 4 sprays with Miravis Top are advised in a given year. Miravis Prime may also be an option for rotation with Elast/Tin if available.
Spray 1: phosphite
Spray 2: phosphite
Spray 3: 11 + 3 mix
Spray 4: Miravis Top + phosphite
Spray 5: Elast + Tin
Spray 6: Miravis Top
Spray 7: Elast + Tin
Spray 8: Miravis Top
Spray 9: Elast + Tin
Spray 10: Miravis Top
As mentioned previously, there are certainly more fungicides labeled for pecans than what you see listed in the examples above. Their exclusion from these examples does not mean they do not control scab. To the contrary, many are very good fungicides and could be rotated into a program just as easily as what you see above. But, based on Dr. Tim Brenneman’s data, we feel that these chemistries applied at the stage the crop will be in during the times shown above will offer maximum protection from leaf and nut scab. Group 3 and Group 11 fungicides are those containing both a Triazole and a Strobilurin fungicide chemistry (think Absolute, Stratego, Quadris Top, Amistar Top, Quilt, Brixen, Custodia, TopGuard EQ, and others).
Pecan Commercial Spray Guide: