A pecan seminar presented by LSU AgCenter Pecan Research/Extension Station faculty was held Wednesday March 28 at the Pecan Research-Extension Station in Shreveport.
[Here are the notes I took – SHN]
Dr. Jere McBride gave welcoming comments and went on to talk about the problem of the proposed I-69 coming through the research station. Any members with ideas about how to change the route should contact Dr. McBride or Ben Littlepage.
Next Charlie Graham spoke on “Pecan Nutrients and How They Interact”. He made the point that if we are beginning to see symptoms of nutritional deficiency then we are already in an advanced state of trouble. And he pointed out that the most important element is whichever one happens to be in short supply in a given orchard. He listed the macronutrients (nitrogen, phosphorus, potassium, calcium, sulfur and magnesium) and the micronutrients (zinc, iron, manganese, copper, boron, chlorine and molybdenum). Micronutrients are not less important, just needed in smaller amounts. For example, only one nickel atom is needed for every one million nitrogen atoms.
Briefly, nitrogen is needed by the tree for producing all organic compounds. Sulfur is needed for certain amino acids. Phosphorus is needed for a variety of energy transfer reactions. Calcium, boron, and silica are needed for structural compounds. Magnesium, iron, and manganese are necessary for certain enzymatic reactions. Sulfur, calcium, molybdenum, and nickel are needed for the proper utilization of nitrogen. Nickel is particularly important if you are using urea for a nitrogen source. If using ammonium nitrate, molybdenum is more important.
A deficiency of nitrogen can cause the tree to have pale chlorotic leaves. A deficiency of sulfur can cause the same appearance, as nitrogen and sulfur assimilation is linked at several different levels. Sulfur deficiency is more common now that we have less “acid rain” than in the past.
Soil pH can be altered depending on what fertilizer we apply. Ammonium nitrate has both alkalizing and acidifying qualities. Ammonium sulfate tends to decrease the pH, as does any sulfate.
Potassium deficiency is rare; calcium deficiency is rare unless the pH is very low. Calcic liming with calcium oxide can lead to calcium/magnesium imbalance; use dolomite instead. Boron deficiency is rare; toxicity is increasing, and made worse if soil pH is high. Manganese is usually not deficient in Louisiana, but may see toxicity (liming can help if you have manganese toxicity). Zinc is needed for leaf size. Copper can be a problem in very sandy areas.
Next, John Pyzner spoke on “Fertilizer Applications”. [I didn’t take any notes but I have reprinted here John’s article on fertilizers – SHN]
“Cost of nitrogen has become a major expense in growing pecans. It is time to think about the most efficient and cheapest way to put out fertilizer. A split fertilizer application would probably be a good choice. Half of the nitrogen fertilizer should be put out in March and the second half can be put out in May if a good pecan crop develops. Eliminating the second half of the nitrogen application if a light crop is present can reduce production cost and also reduce the potential of a very large nut crop being produced the following year which often results in poorly filled nuts and severe alternate bearing in following years.
A producing pecan orchard normally needs 100 to 150 units of nitrogen per acre. Traditionally, 100 units of nitrogen per acre are applied when leaf samples indicate nitrogen levels of 2.5% to 2.75%. For each 0.1% unit below 2.5%, an additional 10 pounds of nitrogen is added per acre.
Ammonium nitrate has been the traditional nitrogen source for pecan orchards in Louisiana. It loses little nitrogen to the air under Louisiana conditions and has been easily obtained and has usually been competitive in price. Ammonium nitrate is 33-34% nitrogen. There have been some concerns about the availability of ammonium nitrate this year. Conversations with eight fertilizer suppliers in North and Central Louisiana indicated that ammonium nitrate in bulk was available and these suppliers had not received any word on new regulations or restriction for handling ammonium nitrate. Ammonium nitrate sold in bags may be less available.
Urea (45-46% nitrogen), anhydrous ammonia (82% nitrogen) and ammonium sulfate (21% nitrogen) are possible alternative nitrogen sources, however they have some disadvantages. Urea can volatilize (lose nitrogen to the air) when applied to the soil surface if it is not incorporated by tillage or rainfall within a few days. Volatilization occurs most rapidly with higher soil temperatures, higher soil pH, surface plant residues and moist soils. Urea is best used before expected rainfall with soil temperatures below 70 degrees and soil pH below 6.5. Do not apply urea to wet soils.
Anhydrous ammonia is a compressed gas that has to be knifed below the soil surface. The soil must be moist enough to retain the gas but not wet enough to form cracks in the soil that allows the gas to escape. Knifing the ammonia into the soil can cut surface roots. The knifing operation also produces soft areas in the soil that can cause equipment to become stuck following rains.
Ammonium sulfate is best used on higher pH soils. The soil acidity produced by ammonium sulfate is three times the acidity produced by ammonium nitrate. It would take 535 pounds of pure calcium carbonate to neutralize the acidity produced by the ammonium sulfate used to supply 100 pounds of nitrogen per acre.
Randy Sanderlin covered “Disease Control Update”. He talked mostly about scab control, and suggested that I reprint his article on this topic:
Importance of Scab Control in the Spring
For pecan growers spring is the time to start efforts to control scab disease for the entire growing season. It is critical to avoid early season infection of nuts. Because of near drought conditions last year, scab disease pressure was at a low intensity and control was easy. However, because the disease can increase very rapidly, a low level of disease last year does not provide any insurance against rapid disease build up this year if rainfall is frequent in the spring.
One of the primary determinants of the severity of scab disease development is rainfall. Amount, frequency, and time of rainfall all have important effects on the development of scab. A single scab lesion left from the previous year can produce thousands of spores as the fungus becomes active in the spring. Spores can infect growing leaf and stem tissue when it stays wet for several hours following rainfall. Thus, a small amount of rain that occurs late in the evening , at night, or with heavy cloud cover may result in more scab spore germination than a larger amount of rainfall that occurs during midday and quickly dries from pecan tissue surfaces. Factors that reduce drying time such as air movement, good tree spacing, and orchard site elevation can help reduce the amount of infection that occurs during a rainfall period.
To prevent infection, fungicides have to be on the trees before a rainfall occurs. Pecan scab control is preventative control. There is often concern about rainfall removing fungicide from trees. It is true that some wash-off can occur with some fungicides (many fungicides now are absorbed into tissue and can’t be washed-off) but enough usually stays on to prevent infection if the tissue was well covered before the rain and it has not been more than two to three weeks since the application (new tissue grown is not protected). The approach of trying to apply fungicide following a rain period to stop infection will usually not work well. It is difficult to get fungicide applied in time to stop an infection after spores have begun to germinate in wet weather.
Even though preventative application of fungicide is necessary for successful scab control, and early disease control is important; I think that we sometimes tend to spray too much in the early spring. Just as frequent rainfall can quickly result in a severe level of scab, no rainfall means no scab disease. This is something we can take advantage of, especially if the orchard cultivars are not extremely susceptible to scab. In most years and on most of our common cultivars, the level of scab observed on foliage during April and May is limited. The primary goal is to keep scab off of the nuts which are not present until mid May. Depending on the orchard location, cultivars, disease history, and rainfall pattern, it may be possible to make just one preventative fungicide application before pollination and save most of the fungicide for protection of the nuts. It is of course impossible to put into print exactly when any fungicide application should be made or delayed because of all the variables that affect scab development. Because of this, fungicide spray schedules for pecan scab control are written on the conservative side and it is often possible to adjust these schedules to better fit a particular orchard situation.
All of the fungicides in the list below do a good job of scab control. Some of the fungicide groups are more subject to development of pathogen resistance problems than other groups. Fungicides in Groups 3 and 11 and those with products from these two groups are particularly subject to resistance occurrence. It may be best to use fungicides in these groups when there is a low level of disease in the orchard such as in early in the season or in the summer if little disease development has occurred.
Pecan Fungicides List By Activity Group*
FRAC GROUP PRODUCT RATE / ACRE
Group 30 Agri-Tin 7.5 oz
Organotin Super-Tin 7.5 oz
__________________________________________________________________
Group 3 Enable 8 fl oz
DMIs Propimax 6-8 fl oz
__________________________________________________________________
Group M Syllit 2 lbs
Guanidine Acetate Elast 51 fl oz
(Dodine)
__________________________________________________________________
Group 11 Abound 9.5 fl oz
Strobilurin Sovran 3.2 oz
Headline 7.0 fl oz
__________________________________________________________________
Group 3 & 30 Orbit/Super Tin 4 oz & 3.75 oz
DMI + Organotin Enable/Agri-Tin 1.3 oz & 3.74 oz
__________________________________________________________________
Group 6: Mix of Stratego 10 fl oz
Groups 3 & 11 Quilt 14 fl oz
*To obtain the best control and reduce the chances of pathogen resistance, use a rotation of fungicides from different FRAC Activity Groups, or a mixture of
fungicides from different groups. The Fungicide Resistance Action Committee (FRAC) groups fungicides by their mode of biological activity. Development of resistance to one fungicide in a group generally means a pathogen will be resistance to all of the fungicides in that group.
Randy made an important point regarding fungicide use. The fungicides from Group 30 (organotins) and Group M (dodine) have relatively low risk of resistance forming compared to Group 3 (DMIs) and Group 11 (strobilurin). It is a good idea to use Groups 3 and 11 early in the season when there is not so much fungus in the orchard. This may help to prevent the occurrence of resistance.
There were a couple of questions related to the use of surfactants and buffers. A surfactant is probably not necessary, and buffer is not needed unless an insecticide is also being applied.
