This is pecan leaf sample time – July 7 through August 7. In addition to leaf samples, UGA Extension Horticulturalist Dr. Lenny Wells has information on soil testing, particularly in row middles.
Many have found that pH in the herbicide strip is lower than that found in the middles. When we were doing the work on fertilizer placement and comparing broadcast band applications of dry N fertilizers with broadcasting over the whole orchard area, herbicide sprayer application of N, and injecting N through the irrigation system, we observed that soil pH is always lower in the herbicide strip regardless of the fertilization method you use (Pecan Response to Nitrogen Fertilizer Placement). We do have the potential to drop the pH faster in some situations where you concentrate fertilizer N in the strip, but its always lower in the strip. This is because the vegetation growing in the middles keeps the organic matter levels up, which helps to buffer soil pH, allowing it to remain a little more stable than areas free of vegetation.
Managing soil chemistry in the herbicide strip is vitally important because that is where the tree’s feeder roots are located around irrigation emitters. After their transformation to nitrate-N, both ammonium and urea fertilizers have an acidifying effect on the soil to which they area applied. In order to manage this, growers should take their soil samples within the herbicide strip and lime based on this reading. Because the vegetation in the middles helps to buffer the pH, you probably won’t need as much lime in those locations. It would be wise to check pH in the middles every few years and make an additional lime application to the middles when pH drops below 6.0.
It is time for us to take leaf tissue samples in pecans. UGA Extension Pecan Specialist Dr. Lenny Wells has this information:
The general recommended period for leaf sampling is July 7-August 7.
Why does it matter when you sample?
Concentrations of N, P, and Zn on a leaf dry weight basis start off relatively high early in the season, decline rapidly, reach a fairly steady state after mid-June, and then decline near leaf fall. K tends to start high, then decreases and plateaus at about the same time as N, P, and Zn. Most of the P and Zn that accumulates in the leaves have done so by the time the leaves reach full size. Calcium (Ca) accumulates in the leaves as the season progresses, peaking in August-September. Magnesium (Mg) Manganese (Mn), and Boron (B) also tend to increase as the season progresses, but to a lesser extent than Ca.
Collect middle-pair leafleats
How do we sample?
- Collect 50- 100 middle-pair of leaflets from the middle leaf of this year’s growth (right). Use terminal shoots exposed to the sun. Avoid twigs from the interior of the tree. Collect leaflets from all sides of the tree. Avoid leaflets damaged by insects and diseases.
- Abnormal trees or trees not representative of the area should be sampled separately. A complete and accurate description of abnormalities should accompany these samples.
- Sample trees of the predominant variety in a given block. If Schley is the main variety, sample Schley; etc.
- Immediately upon collection, wipe leaves (entire surface, both top and bottom) with a damp cellulose sponge or cheese cloth to remove dust and spray residue. Do not allow the leaves to come into contact with rubber or galvanized containers. Partially air dry and place in the large envelope of the mailing kit.
- If recent soil test data is not available, it would be advisable to collect a soil sample and have it sent to a soil testing laboratory. By sampling the same trees each year, growers can more readily see the results of any changes to their nutritional programs.
**Some growers have taken leaf samples throughout the growing season to determine the fertility needs of the tree. This is really unnecessary. Leaf analysis does not necessarily reflect the actual use pattern of mineral nutrients, but instead indicates concentrations of those elements in the leaf at the time of sampling. The tree knows what it needs and when it needs it.
Concentrations of mineral nutrients in the leaves change as leaves emerge, expand, and finally senesce in the fall. For many elements, the least change in concentration occurs from early July-early August.
Mouse ear is a growth abnormality from a nickel deficiency in pecan trees. This disorder occurs mostly on newly transplanted trees in established orchards. This is the first time I’ve seen it, but it is close to the text book pictures and easy to ID. Mouse ear first appears on the spring growth flush. The most common symptom of mouse ear is a rounded or blunt leaflet tip. Other symptoms include dwarfing of tree organs and necrosis of leaflet tips. The degree of severity with the tree canopy typically increases with canopy height.
Mouse ear symptoms, rounded or blunt tip
Necrotic leaf tips due to build-up of lactic acid from Ni deficiency.
There are 4,000 seedling trees in this nursery and probably half are affected by the Ni deficiency. At this point we need to spray a foliar application of nickel now and again in one month. UGA Pecan Horticulturalist Dr. Lenny Wells says mouse ear may consistently reappear from year to year, or appear on occasion. For mouse ear prone sites, it is recommended to have a foliar spray of nickel in med-late April when leaves are in the parachute stage. (Ni is not absorbed in the plant until leaves are in parachute stage.) We follow up with an additional application in late September or early October to prevent mouse in the following spring.
Long-term Management (From Southeast Pecan Grower’s Handbook)
- Monitor leaf and soil samples for availability of Ni to trees.
- Don’t make excessive applications of zinc. Zn competes with and inhibits uptake of Ni. Foliar Zn should only be applied when Zn leaf levels are less than 50 ppm or when visual Zn deficiency symptoms are present. Do not allow soil to become acidic (making Zn more available.)
- Maintain good soil moisture at budbreak. Ni is relatively low in the soil in most orchards, and it is absorbed by the tree in the lowest of many nutrients.
- Maintain soil pH at 6.5.
- Do not give late applications of N, to ensure that senescing foliage can translocate to shoot and bud storage prior to defoliation.
- Manage phosphorus, iron, and copper levels in soils. These nutrients affect uptake of Ni. They may also alter the availability of Ni within the leaf.
Rosetting and necrotic tips from Ni deficiency.
With Friday’s heavy rain and the arrival of budbreak, pecan growers are anxious to get their first fungicide spray on for scab protection. Infection has historically been bad in our area, and growers like to get started early. Here are some points from UGA Extension Horticulturalist Dr. Lenny Wells:
At this point, the only pecan variety growers should be concerned about is ‘Desirable’. Most varieties that have budded out far to this point are less susceptible to scab and is less of an urgency to get those covered. If ‘Desirable’ is to the point where the leaves are unfolding, and you are located in a scab prone area (below 300′ elevation or surrounded by woods), it may not be a bad idea to spray this week. If the leaves are still tightly enclosed in the form of a swollen bud or you are in an area with good air flow, I would hold off at this point.
For most other varieties, especially Stuart – which is further behind in its progression of bud break – there is no need to spray just yet. While we had significant rain Friday and there is a chance of rain one night this week, low temperatures are forecast to remain in the mid to low 40’s, especially toward the end of the week. The optimum temperature range for scab infection is 59-77 degrees F and a leaf wetness of about 12 hours. If the cooler weather this and last week slows down budbreak, it will likely slow down scab as well. Except for ‘Desirable’ in the situation described above, I would plan on waiting until next week to begin scab sprays in most areas of the state.
For an example of a proven fungicide program to consider see a previous blog post on: Example of Fungicide Program to Manage Scab.
Filed under Disease, Pecans
Bud break of pecan has arrived in south Georgia. If you have problems with phylloxera, UGA Extension Pecan Horticulturalist Dr. Lenny Wells says it is time to consider making an application for this pest. The southern pecan leaf phylloxera, is a tiny aphid-like insect that feeds on the foliage of pecan trees. The insects are rarely seen, but the galls that they cause are prominent. The southern pecan leaf phylloxera is primarily a pest on mature pecan trees, but it can be found on nursery and young trees.
Some products are taken up by the plant systemically, and this may provide an easier control option. Last season, we put out a trial to test drenching Admire at different times. After rating, we found no difference in drenching from December through March. We are thinking of other ways to test this theory. Until then, foliar spraying is our best option. The timing is critical.
Overwintering eggs hatch beginning the first week of April and continue until the first of May. The newly hatched stem mothers crawl to the expanding leaves where they settle down and begin feeding. Feeding causes rapidly growing gall tissue which encloses the immature stem mother within a few days. Stem mothers mature by mid-April at which time they lay eggs within the gall.
Phylloxera inside gall
Light populations are most probably of little consequence. However, each gall results in dead leaf tissue and numerous galls can cause premature leaf shedding. Hickory shuckworm uses phylloxera galls for first generation larval food.
Of much greater concern than leaf phylloxera, a separate species, stem phylloxera can be much more damaging. They produce a hard swelling or tumor like galls, one tenth to one inch in diameter on leaves, leafstalks, succulent shoots, catkins, and nuts of new growth. Heavy infestations can completely destroy an entire nut crop and the accompanying malformed and weakened, infested shoots reduce tree vitality to such an extent that damage may reduce the following years production. This is rarely seen in managed orchards but where it does occur it needs attention.
Imidacloprid is a good, inexpensive, systemic choice for phylloxera control. Phylloxera sprays should be applied just after bud break or no later than when the leaves are one-third grown. Once galls are observed it is too late to spray until next year.
There are reports of budbreak in the state. Many growers are in the process of getting out herbicide strip applications. There are many herbicide options for pecan growers to choose based on weeds, pre and post emergence, and herbicide activity. UGA Extension Pecan Horticulturalist Dr. Lenny Wells has these thoughts on herbicide choice:
- Glufosinate and Paraquat would be better selections for burndown than glyphosate under newly planted and young trees because they are contact materials and any potential drift would cause very limited and only temporary damage unlike the systemic glyphosate. Just be sure to protect the bark from any herbicide.
- Burn down herbicides should include glyphosate where grass is a major issue. Just be careful about drift where using this material under young trees. Paraquat and Glufosinate normally will not give long term control on a thick covering of Bermuda grass.
- Include pre-emergent herbicides in your program. Again, we have many options here. Alion is an excellent pre-emergence material that gives long lasting control. It has a high price tag, but will significantly cut down on the number of applications you need to make, which offsets the cost. Use the 5 oz/A rate in the first year that you use Alion. After that, you can drop down to the 3.5 oz/A rate. Previously Alion was only labeled for trees 3 yrs of age or older. I was recently told by Bayer representatives that this has changed and can be used on 1st year trees and older. We have tested it for a number of years on 1st year trees at high rates and have never seen a problem.
- Flumioxazin (Chateau) is also an excellent pre-emergence herbicide for use on trees 1 year and up. Its residual is not quite as long as Alion, but it’s close. Even if you are using Alion, rotation between Alion and Flumioxazin from one year to the next is a good idea to manage resistance and limit the over-use and buildup of indaziflam (Alion) in the orchard.
- We have many other options for pre-emergence which can be utilized in pecan orchards. These include Surflan, Simazine, Prowl, and Diuron. Isoxaben (Trellis) and rimsulfuron (Metric, Solida, and Pruvin) are recent additions to this arsenal. Of these, Surflan, Prowl, Isoxaben and Rimsulfuron can be used on 1st year trees and up. Trees must be 2 yrs old for Simazine and 3 years old for Diuron. Also, do not use Diuron on sandy soils. Consult the current UGA Pecan Spray guide here for a complete list of herbicides available for pecan and their uses.
- Tank mixing burndown and pre-emergent herbicides will reduce the number of trips made over the orchard but be sure to have at least 75-80% bare ground when using a pre-emergence material. Most of them need good soil contact to be effective.
Ambrosia beetle toothpicks
UGA Extension Pecan Entomologist Dr. Will Hudson confirmed the first ambrosia beetle flight reported yesterday in southern Grady County. ABB initial flight usually occurs when temperatures go over 70 degrees. A few days ago, Dr. Hudson said they will likely fly this week. Growers with young pecan trees, especially under 5 years, need to check their traps. Remember, we are looking for the “toothpicks” on the wood. This is the frass from the beetles as they bore into the tree.
Once we see AAB attacking the traps, we need to spray. Trunks of young trees should be sprayed with a pyrethroid. Barrier sprays of Lorsban will not work for AAB. The beetles are particularly attracted to stressed trees (although they will attack non-stressed trees.) Pay close attention to trees planted in poorly drained soil. Once a flight is observed with the traps, it is advisable to spray each week in problem areas until the trees have leafed out.
Dr. Hudson speaks at 2016 Thomas County Pecan Update in Thomasville