Nitrogen is the most frequently needed nutrient applied in tree fruit orchards. Its’ sources include organic matter, the atmosphere, nitrogen fixing soil organisms, recycling, mineralization and fertilizer application. Factors that affect microbial conversion include temperature, oxygen and water supply. Tree fruits generally have a greater demand for nitrogen than most soils can supply, but this does not mean that the soil doesn’t supply some nitrogen. The key is being able to estimate what the soil organic matter is supplying and match that with the additional need with applied nitrogen source. One study showed that in both a 5 year-old and 15 year-old apple trees about 10% of the nitrogen available to the trees was removed with the crop and nearly 90% was either retained within the tree or returned to the soil in the form of leaf litter or pruning cuttings. In comparison to agronomic crops, nitrogen use efficiency was 62% higher in apples than in corn. Therefore there is considerable recycling and reuse of nitrogen in an orchard.
Fruit trees take up nitrogen in both the ammonium (NH4+) and the nitrate (NO3 -) form; with the latter being the more dominant. The ammonium form is usually bound onto the soil cation-exchange complex of the soil. Much of the ammonium form is converted to the nitrate form in a process called nitrification. The level of soil nitrogen is quite variable, changing rapidly. This fact makes the use of nitrogen testing of the soil extremely difficult. Therefore, the most accurate method to monitor the nitrogen status of an orchard is through the use of mid-summer foliar analysis.
Estimation of the nitrogen requirement of an orchard to determine fertilizer requirement is compounded by the fact that trees recycle a good portion of their nitrogen. Nitrogen stored during the season in the leaves can be mobilized and withdrawn from the leaves in the fall before leaf abscission. It has been estimated that somewhere between 23 to 50% of the leaf nitrogen can be mobilized back into the tree. The timing and amount of the withdrawal is probably influenced by a number of factors including available nitrogen, crop load and environmental factors. The nitrogen that is withdrawn from the leaves is usually stored in the woody tissue of the trees. This stored nitrogen is remobilized in the spring to provide nitrogen for early growth in the spring. THIS IS THE REASON I’M SUCH A PROMOTER OF LATE SUMMER UREA SPRAYS! In one study newly planted Golden Delicious/M9 trees had over 50% of the stored nitrogen from the previous growing season recycled out to support new growth. The remobilized nitrogen contributes 90% of the nitrogen in the spur leaves, 50% of the nitrogen in the shoot leaves, and 60% of the nitrogen in the fruit. Early growth, therefore, is largely a function of what is stored and uptake from the soil usually does not occur until the stored nitrogen has been nearly depleted.
Low soil temperatures impact the uptake of N from the soil. At a soil temperature of 46˚F uptake of N occurs very slowly. By contrast, uptake of N in 70˚F soil temperatures is rapid. From experience, 70˚F soil temperatures at CSU OM occur late May to early June. This fact may result in insufficient N levels being available to the trees in the critical post bloom period. Early spring applied N primarily goes to the new and expanding shoots and leaves.
“To preserve the government we must also preserve a correct and energetic tone of morals. After all that can be said, the truth is that liberty consists more in the habits of the people than in anything else. When the public mind becomes vitiated and depraved, every attempt to preserve it (liberty) is vain. Laws are then a nullity, and Constitutions waste paper.”
Daniel Webster, the Fryeburg address. July 1802
Low nitrogen leads to poor tree growth and lower yields due to smaller fruit. In apples low nitrogen manifests itself as small pale green leaves, while in peaches, the leaves may take on a reddish tinge and show some shot holing in the leaves. The best way to determine nitrogen status is a midsummer foliar analysis test. Recent studies also suggest that smaller more frequent applications of nitrogen fertilizers may make uptake by fruit trees more efficient. Usually nitrogen is in overabundance due to overly fertile soils. As a rule of thumb for every 1% organic matter approximately 20 lbs of N per acre are available per year. Somewhere between 25 to 60% of this is absorbed by the trees. Therefore, if you have a soil with 2.0 to 2.5% organic matter it could be providing 40 to 50 lbs of N per acre per year from the organic matter. Excessive nitrogen manifests itself with thick green growth of shoots and leaves. Growth in excess of 24 inches in pome fruit and 36 inches in stone fruit indicate excess nitrogen. The application of foliar nitrogen in the form of urea has been used to overcome short-term deficiencies or to build N levels prior to fall shutdown. Recent work has also looked at late season N applications. A broadcast application preharvest, did not adversely affect current fruit nitrogen concentrations but did result in root uptake and storage of N in the trees and was subsequently remobilized for growth the next spring. The form of nitrogen can have an impact on soil pH. Urea and ammonium sulfate will lower soil pH with extended use.
The peachtree borer (PTB), Synanthedon exitiosa, is a striking clear-winged moth with yellow
and steel-blue body markings. The adults of these insects have from one to four yellow-orange stripes across the abdomen, depending upon species and sex. The PTB enters the tree near soil level and does not require the presence of wounds or breaks in the bark for entry. This species pass the winter as borers (worm like) inside the tree, and in the summer emerge as moths that lay eggs on or in the trunk during the summer. The PTB doesn’t show up until late June early July; and stays active (laying eggs) through September. When the borer stage hatches, the PTB tends to crawl down the tree to soil level and burrow in there. Some PTB larvae take two years to develop, so any control measure a grower would elect will require repeating for at least 2–3 years. Injury is caused by larval feeding on the cambium and inner bark of the trunk close to the soil level. Occasionally, larger roots are also attacked by PTB. Areas attacked often have
masses of gum, mixed with frass, exuding from the bark at or just below the soil level. All ages of trees are injured. Young trees are at times completely girdled. Older trees are often so severely injured that their vitality is lowered and they are rendered especially susceptible to attack by other insects or by diseases. The two forms of control for this pest are trunks sprays applied several times during the season and mating disruption using pheremones. Give me a call if you need help putting a control program together.
Every year at this point in the season I get phone calls from growers wondering if they need to spray a block for codling moth or peach twig borer or, fill in the blank with a pest of your choice. My response always comes in the form of three questions: 1) What does past experience tell you? Is this a problem block that you generally have damage in? 2) Do you see visible signs of damage? Are there stings on the fruit? Do you see flagging on the terminals? 3) WHAT DO YOUR TRAPS TELL YOU?
The first two questions usually generate good discussion, the third brings nothing but silence.
Properly maintained traps can help provide the answer to the question, “Do I need to spray, and when?”
Weekly monitoring (counting) will allow you to track development and size of a pest population. The start of the second generation of codling moth usually is long after the residual from the second cover spray is gone. This means there may be a period when you can back off a bit. What about the second cover for Peach Twig Borer? It’s highly likely that if you were on target with the bloom and first cover sprays that you won’t need the second summer cover. A few traps will help the decision making process. What’s the cost to spray an acre of fruit? Equipment $20/Ac, Labor $10/Ac, Material $20 – 30/Ac Your total cost is in the neighborhood of $50/Ac every time you fire up the tractor! What’s the cost to trap an acre of fruit? NO WHERE CLOSE! Especially if they help you to skip an application. TRAPS DON’T COST…..THEY SAVE!!!
“The longer I live, the more I realize the impact of attitude on life. Attitude, to me, is more important than education, than money, than circumstances, than failures, than success, than what other people think or say or do. It is more important than appearance, giftedness, or skill. It will make or break a company….. a church….. a home. The remarkable thing is we have a choice everyday regarding the attitude we embrace for that day. We cannot change our past….. we cannot change the fact that people act in a certain way. We cannot change the inevitable. The only thing we can do is play on the one string, we have, and that is our attitude…. I am convinced that life is 10% what happens to me and 90% how I react to it. And so it is with you…. We are in charge of our ATTITUDES.” Charles Swindoll
As always THANKS FOR YOUR BUSINESS! And call with any questions.