Protecting Your Remaining Pecans After the June Drop
We need to temper the optimism with which we view the spring crop of female flowers with a realistic view of something anyone who has been growing pecans for a very long should recognize. Pecans will drop from the trees in June! This fact is especially true of ‘Desirable.’ Yes, your ‘Desirable’ trees burst out of spring with cluster sizes of three to five flowers, and later, nuts per cluster. But those threes, fours, and fives you see on ‘Desirable’ will be thinned down to zeroes, ones, and twos this month. I can almost guarantee it.
Pecan trees of almost all cultivars undergo four natural fruit abortions or “nut drops” per season. The severity of these nut drops varies by cultivar and sometimes by year within a single variety. The first drop occurs in May, shortly after pollination, and results from weak flowers and/or low energy reserves within the tree. This drop is inversely related to shoot length or the stress level imposed on the tree in the previous season. Often the first drop goes unnoticed in many orchards.
The second drop, occurring in June, is the most commonly recognized drop. The June drop is brought on primarily by a lack of egg fertilization. Certain varieties such as ‘Desirable’ undergo a noticeable June drop each year. For such varieties, trees at least partially control the drop, which cannot be wholly prevented. There are, however, positive aspects to shedding fruit at this time, which enables ‘Desirable’ to bear consistently from one season to the next. Most ‘Desirable’ trees can consistently bear a crop of 1,000 to 1,500 pounds per acre, solely because they naturally shed nuts. Usually, you won’t get 2,000 to 2,500 pounds per acre crops of ‘Desirable’; the tree just isn’t made that way, which is why it was never very popular in the West. It just won’t produce the yields of ‘Wichita’ and ‘Western Schley.’
Here in the Southeast, yield expectations have not historically been above 2,000 pounds per acre. Typical yields below this amount are the result of a combination of lack of sunlight (too much cloud cover in the Southeast) and wider tree spacings to optimize the available sunlight. As hedging catches on, tree spacings are growing tighter, and yield expectations have risen. But most of these situations do not involve ‘Desirable,’ as its scab susceptibility has pushed growers to other cultivars.
I have seen growers achieve ‘Desirable’ yields of 2,000 to 2,500 pounds per acre or more, but these yields are not very common and will not likely happen consistently. I think as far as ‘Desirable’ yields go, Dr. George Ray McEachern has it right when he informs us all of the 11th Commandment: “Thou shall not want more than 1,500 pounds per acre.”
We have demonstrated in the past that foliar boron (B) sprays applied up until pollination can reduce the severity of the June drop and enhance nut retention. Yet, it only increases nut retention by anywhere from 2 to 12 percent, and the June nut drop will still occur.
The third drop occurs in July and results from problems with endosperm development. A fourth drop resulting from problems with embryo development may occur in August. The endosperm provides nourishment for the developing embryo. If the endosperm fails to develop properly, the embryo may be weak and the tree may abort the nut.
Most natural fruit abortion occurs during the first and second drops. Other factors may lead to nut drop throughout the season. These include poor pollination, self-pollination, nutritional deficiencies, pecan scab, mechanical injury, and water stage fruit split. A variety of insects may also result in nut drop throughout the season, including spittlebug, pecan nut casebearer, hickory shuckworm, and pecan weevil.
I do expect what will seem like a large nut drop on ‘Desirable’ this year because the crop load on most ‘Desirable’ trees looks very good as I write this at the end of April. Usually, the greater the crop load, the heavier the drop appears. Under normal conditions, ‘Desirable’ experiences an average fruit abortion of 40 to 60 percent during the second drop. If kept free of scab, these trees generally still make yields in the range of 1,000 to 1,500 pounds.
So, when you see those threes, fours, and fives thinned down to zeroes, ones, and twos, don’t get too alarmed. That’s just ‘Desirable’ doing its thing. You’re not going to change it. Focus on the percentage of terminals bearing nuts and not on the number of nuts per cluster. Trees with a fruiting terminal percentage over 70 percent are overloaded. As long as you have a fruiting terminal percentage of 50 to 65 percent, you will likely produce a good yield and have a strong likelihood of a good return crop.
We may also see a significant drop on other cultivars. This potential drop will depend on how well the trees have recovered from Hurricane Michael. However, I am hopeful these trees will be able to carry these nuts to maturity. In the meantime, growers will need to focus on their scab program for susceptible cultivars—‘Desirable,’ ‘Pawnee,’ ‘Cunard,’ and ‘Morrill.’ We are in the nut sizing period—the most critical period for protecting those nuts from scab. At this point, producers need to pay close attention to their spray interval and choice of fungicides.
During the rest of the season, growers will get maximum protection from scab by rotating Miravis Top with the Elast/Tin combo. These chemicals are the best nut scab materials out there for high-pressure situations. Stay at a minimum 14-day spray interval until mid-August. If you get more than two rains within the 14 days, tighten that interval to 10 days. If you have moderately susceptible cultivars, I recommend using the same intervals; you can also rotate in other products like a full rate of Tin alone or a DMI fungicide combined with Tin to reduce expenses. But be wary of spraying the same chemical classes back to back. Rotation of chemistries is key to avoiding resistance.
I know the crop won’t look as good at harvest as it does now, but we are off to a great start, and it should be the best crop we’ve had in three years. I hope everyone can have a good year and make a profit after two tough seasons back to back.