We are in the third week of April, and hopefully the threat for a freeze has left us for the year. I have had a few calls in the past few weeks regarding concern for frost damage, as seen below, to some of our younger pecan trees. In general, it takes relatively low temperatures for an extended period of time in areas with poor air circulation (mid to high 20’s for several hours) to cause long-term or crop damaging injury to our trees. Also, injury is dependent on how far along the pecan trees bud break and foliage development is when the freeze occurs. Buds on pecans can withstand colder temperatures, whereas new foliage and the cambium layer under the thin bark layer is most susceptible to freeze injury.
As of now, our pecans are finally leafing out and beginning to parachute, so now is the time to consider the initiation of a fungicide program for your pecan trees. Below you will find the 2021 fungicide spray recommendations and comments from our pecan specialist Lenny Wells.
Due to the variability in scab susceptibility from one variety to the next, spray programs are formed around three main cultivar categories: low input, medium input, and high input requirements. A fourth category, medium/high input, includes varieties that could, under normal conditions, be successfully managed by a regular spray program. However, in certain locations (below highway 280, low elevation areas, crowded orchards, etc.), these medium/high input varieties may require a more intensive program to produce a successful crop.
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 sprays. If excessive rainfall is occurring throughout the nut sizing period, you can shorten your interval and extend the program out further than 7 sprays 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 Miravis Top and Elast/Tin. Bear in mind that some cultivars listed in the moderate category may fall into the high category in some locations.
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
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 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)
With the late foliage development this year, crop maturity could potentially be later than normal which means the need for these sprays in the medium to high input category could extend out beyond mid-August. Fungicide sprays should continue through shell hardening.