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Desirable Leaf Drop, Thoughts on Spraying and Pollination Conditions

I’ve had a few calls this week on Desirable leaf drop. While mowing orchards all week, I noticed some of this myself. Upon closer examination, where I was seeing it from the tractor it seemed to be only on trees which had stopped up microsprinklers.

What appears to be going on here is that pecan trees have had adequate moisture all spring from all the rain we’ve had. Over the last week, its turned very dry, temperatures are warming up, and water demand is increasing as well, as the trees approach the nut sizing period. If you were a little late to turn the water on or, as in my case, you have a few trees with stopped up emitters or microsprinklers, those trees have had just enough stress to throw off a few leaves. Its nothing to be too concerned about but make sure you are on an adequate irrigation schedule at this point and be prepared to ramp it up in June. You should be at about 30% of full capacity at this point in the season—I am currently irrigating 6 hours every other day—and you should go on up to 36-40% of full capacity in June.

So far, we are in very good condition regarding scab. I have had very few reports of any scab out there and have not seen any to speak of. We have had very light scab pressure so far. Our spring rains came quickly—usually in one day—and then conditions turned sunny and windy with daytime temps in the 70s mostly and lows in the 40s and 50s. Thus, our spring conditions were not conducive to much scab development. Most growers I have spoken to have two to three sprays on at this point. Our weather conditions have turned dry and temperatures are getting warmer with no rain in the forecast.

As a result, I am of the opinion that you can stretch your spray interval out at this point on everything but Desirable (and similar scabby varieties) if you are clean. I would still keep Desirable, Cunard, Morrill, and anything that normally scabs badly in your orchard on a 2 week interval. Be prepared to stick to a 2 week interval or less (depending on weather) from June to mid August as nuts are sizing. During that period the strongest scab program will be to rotate Miravis Top with Elast/Tin.

I have heard concern from a lot of growers that the cool spring may have caused problems with pollination. To be sure, temperature and humidity play a significant role in the length of the receptive period. But, conditions were actually quite good for pollination this spring. When humidity is low
and winds are warm, the stigma will dry out, which limits receptivity. Additionally, pollen shed is poor when temperatures are above 85 degrees F. High humidity in the form of rain and/or fog may limit pollen shed as well. Our conditions were the exact opposite of this.

While we may think it seemed cooler this spring, our average April high temperature of 77.49 degrees was only 1 degree less than last year. The average low was actually the same as last year at 55 degrees. Our humidity was good, rains moved in and out quickly, and we had lots of sunshine and wind between rains, yet the winds have been cool. I think much of our pollination took place in April this year but the first couple of weeks of May have been about 7 degrees cooler than last year and our average high has been about 80 degrees. So, our pollination conditions were actually pretty good this year. The one thing that does concern me regarding pollination is that I noticed a lot of thrips damage on catkins this year and this can negatively affect pollination.

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Lenny Wells

About Lenny Wells

I am a Professor of Horticulture and Extension Horticulture Specialist for pecans at the University of Georgia. My research and extension programs focus on practical cultural management strategies that help to enhance the economic and environmental sustainability of pecan production in Georgia.