Rain, Rain, and more Rain in the 10 day forecast. The recent weather conditions and the projected forecasts are highly favorable for disease development in Pecan. With the weather conditions we are having I wanted to provide pecan producers with a few notes to assist them in their current pecan management decisions in regards to irrigation and fungicide applications, find those further in this newsletter. I also wanted to touch on a few questions I have received the past couple of weeks and give a quick update of the pecan crop in Appling County. Visiting orchards in the county we are currently still holding on to the crop the trees have set, this is good. As mentioned in last months update we have a better crop this year across the county than we expected to have, with this being said lets manage orchards accordingly to their crop load. Also, I am starting to see a good bit of pecan scab developing on trees, especially our more susceptible varieties, and have seen a fair amount of Pecan Nut Case Bearer damage as well.
Recent Rains and More Showers to Come: Decrease Irrigation and Tighten Spray Intervals.
According to the UGA Weather Station in Baxley, GA. We have already received over a 3.5 inches of rain in the first 10 days of June. With this amount of rain it is obvious that we can cut back on our irrigation, but how much? Below are comments from Dr. Lenny in August of 2023 when the state was also receiving a good amount of rain. As you read his comment do note that this was written in August and it is currently mid-June. Our Pecan trees are not in Peak Water Use Demand until August. Right now we definitely do not want to over irrigate because if we do over-water now and size the nuts too large, we are setting ourself up for problems with kernel filling in August/September. Also, as mentioned earlier, with these rain showers and the humidity we are in extreme Scab conditions, with that being said I have also dropped in another few point from Dr. Lenny Wells in 2023 on managing scab in extreme conditions. His main points are rotate your MOAs (rotate miravis with elast mixes), tighten spray intervals, surfactants, and drying time.
Water Management – Dr. Lenny Wells (August 2023)
Its tricky to manage irrigation when it is raining frequently but you are at peak water demand for the crop. You want to rely on the rain as much as possible but you don’t want the trees to get water stressed. This can affect not only the current crop quality but also, next year’s crop load. If the ground stays too wet and you get some wind in one of these afternoon thunderstorms, you could find yourself propping up or cutting out fallen trees. So, where’s the balance?
As I said, its tricky and there is no one answer because the needs on each soil type and in each orchard will vary. Tree age, hedging, variety, and crop load all play into the equation as well. The best advice I can give you is to pay very close attention to your soil moisture in the orchard. Our recommended irrigation schedule for pecans from mid August to mid September is to run at full capacity, especially if you have a good crop load. Trees with little to no crop load will require less water. As a general rule of thumb we recommend irrigating daily and turning the water off for 3 days only when you get a 2″ rain during this period. However, as wet as the soil is this year, and as frequent as the rains have been, you may want to modify that based on your situation. Perhaps turning off the irrigation for 3 days when you get a 1″ rain if you have been wet leading up to this period. If you get a 1/4 inch or 1/2 inch within that 3 day period, maybe leave it off a day or 2 longer. Examine your orchard soil and make a judgement call based on how long that soil moisture appears to persist.
Managing Scab in Extreme Conditions – Dr. Lenny Wells (June 2023)
There are a few things to keep in mind when trying to control scab in the apocalyptic scab conditions we are dealing with.
- The best options for scab control during the nut sizing period from June-August will be Miravis Top, Miravis Prime or Dodine (Elast). Growers should rotate either Miravis Top or Miravis Prime with some form of Dodine, whether you use dodine alone or tank mix it with Tin. Under regular conditions, you likely won’t see a lot of difference in Miravis Top and Miravis Prime. Under the extreme conditions we are experiencing, I would say that if there is a scenario where the use of Miravis Prime would be justified, this is it. However, both products are excellent on nut scab. But DO NOT FAIL TO ROTATE these products with a Dodine application of some sort. If you use one of the Miravis products back to back to back, you are going to abuse this excellent product and at some point we will not get the benefit from it that we currently enjoy. I know growers will be tempted to want to use “the best possible product” every time but I cannto over-emphasize the need to be good stewards of the chemistry we have for scab control. The dodine chemistry remains excellent and growers should not be afraid to rotate this with the Miravis products.
- Tighten spray intervals. If you do not tighten your interval during extreme wet weather, it will not matter what fungicide you use. I know this is hard to do when it is raining daily but you have to keep the nuts covered and they are growing very rapidly. If you spray today there will be tissue there in 5 days that was not covered by today’s spray so in wet weather, frequent applications (every 7-10 days) are required for effective scab control on susceptible varieties.
- Use a surfactant with certain products. Under dry or even normal conditions, I don’t think you get any economic benefit from using a surfactant. However, in wet weather, a surfactant can be a big help with products like Miravis Top or Miravis Prime because they may help the fungicide to stick on the nut surface better, spread over the nut surface better, or move into the nut tissue faster (depending on the surfactant used). All of this can help under wet conditions . The Miravis products should ideally have at least 5-6 hours of drying time before a rain. A surfactant may possibly give you a little room for error and speed that up. Dodine has surfactant properties itself, so a surfactant is not necessary with Dodine, however since it is a pure protectant, dodine (and tin) need 24 hrs for maximum rain-fastness. With any product, if you get rain within an hour of spraying, you need to re-spray eveything you put out in the last hour as soon as you can.
Why are leaves dropping from my trees?
There are several reasons leaves could be dropping from trees this time of year, such as Phyloxerra damage, stress (drought, hurricane), or disease. I believe that most of the leaf drop incidences I have been asked about this year are due to some sort of stress on the tree, maybe broken roots from wind damage by hurricane Helene, we do not know for sure though. But we have been able to cross off some of the important causes of leaf drop incidences like disease and phyloxerra damage. If we have leaf drop due to phyloxerra or disease we can take notes now and make plans for next year.
Here is a link to Dr. Barmans newsletter from last year on phylloxera: https://site.extension.uga.edu/pecan/2024/03/impact-of-phylloxera-on-pecan-crop-maybe-more-than-what-we-see/. The main points you need to take now is to learn the identification of phylloxera damage and understand how to treat the pest. So, see Barmans newsletter for pictures of the damage and note that treatment will have to occur in the spring. Once the galls form, the insecticide cannot penetrate the gall to kill the phylloxera. Imidacloprid is effective at controlling phylloxera, but the timing is critical. The application must be made at budbreak, once green tissue has emerged. You may need to treat twice if the timing of budbreak is different among varieties.
Now lets discuss the diseases that can cause leaf drop Anthracnose and Neofusicoccum. Mr. Andrew Sawyer wrote a very well written newsletter a few years back on Anthracnose, here is the link to that: https://site.extension.uga.edu/pecan/2022/09/anthracnose/. And here are comments from Dr. Lenny Wells and Dr. Tim Brenneman on Neofusicoccum: Neofussicoccum likely infected the leaves a month or more ago but it usually takes that long after infection for symptoms to appear. Neofusicoccum will begin at the terminal end of the leaflets and compound leaves, moving toward the base. The leaves often stick in the trees for a while and are starkly obvious as brown patches among the green. Eventually they will fall. Sometimes we see Neofusicoccum associated with phylloxera galls as well. Anecdotal observation suggests that this fungus can be somewhat opportunistic in possibly entering through the wound of the gall but it by no means requires such a wound to establish. Dr. Brenneman suggests use of a strobilurin or a DMI/strobilurin mix like Absolute or Quadris Top when conditions favor infection (usually prolonged cool and wet conditions). Even if a grower has used these materials their timing may have been off enough to allow infection, especially if they were stretching sprays when the conditions occurred. Once you see the symptoms its too late to do anything about it. If you see this disease this year and conditions are favorable next year, be sure and use a DMI/Strobilurin combo during susceptible periods (cool, wet conditions).
Leaf Anthracnose
Neofusicoccum