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September 2005


I saw more Coryneum blight this season than I have for several years.   Think about the winter and spring we had.  Lots of precipitation.    Between the Coryneum blight, powdery mildew and hail that wet seasons bring,  I kind of prefer drought!  If you found blight marked fruit in your bins, starting your clean up program this fall will go a long way towards a clean crop next year.  The first autumn rains can start the spread of the disease.  Infection can also take place in the dormant season if proper moisture and temperature conditions occur.  Spores, spread primarily by splashing water can remain viable several months.  The key to control is PREVENTION.  This is especially true if you’re farming with organic methods.  Establishing a protective barrier with copper is vital to keep Coryneum from germinating and spreading.  Good sprayer coverage is important! The disease usually starts low inside the tree where moisture persists, so be sure and target this area.  The most common application timing is at 50% leaf fall.  It’s not necessary to wait for that to happen.  If we have a wet September you could be behind by the time leaf fall occurs.  How aggressive you need to be with rates and applications depends on if you need to clean up a problem or are just performing routine maintenance.   When you purchase a copper material, look at the percentage of copper in the product.  With some materials you can spend a lot for not much copper.  My preference is still COCS.  It provides you with the most actual copper for the least dollars.


We’re in a great window to help build next years crop.  Here’s a couple of repeats from last years letters.  Late summer nitrogen.  The idea is to apply N just after the tree’s response to shortening day length has stopped terminal growth but the daily temps are still high enough to keep tree transpiration high.  An application of fertilizer will be pulled into the tree to be stored for use at next Spring’s bud break.


Soil Fertilization

The most common approach to fertilizer timing has been to make an application in the late fall.  Research has shown that uptake and movement into the tree of a dormant application is greatly reduced and subject to winter leaching (recovery of soil-applied N by fruit trees typically ranges from 25-35%, Khemira, 1995).  Moreover, a late fall (winter) application will not be available till late, (too late) in the spring, past the cell division period when soil temps warm up.  A dormant application contributes most toward summer vegetative growth.  Consider a different timing.  Mid-August to mid-September most terminal growth has ceased, the temps are still warm and the tree is maintaining a high rate of respiration.  Fertilizer applied at this time, followed by a light irrigation will quickly be moved up into the tree.  It’s then stored, ready for cell division the next spring.   The “sweet spot” to aim for is the period when the tree is between it’s summer work and winter sleep.  Be cautious about late maturing varieties, they stay active later in the season.


Fall Foliar

Trees move nutrients from the leaves back into the buds and wood prior to leaf drop.  Research in California shows that a foliar spray of urea on peach begins to move into the leaf within two hours, with over 80% of the applied N moving into the leaves within 24 hours.  The efficiency of N recovery through a foliar urea application is four-fold greater than through soil application.   This nitrogen is mobilized and moved into other plant parts such as shoots and buds within one week. It remains there until spring when it is available for early use during cell division!  Give me a call to talk about rates.  Urea is known to enhance the uptake of other micronutrients when sprayed in combination.  Adding zinc, iron, manganese or any other element your tree requires will help boost bud strength.  No detrimental effects have been found on winter hardiness, quite the opposite, research has shown that healthy buds with good nutrient reserves are the most winter hardy.


Want to know what the price of nitrogen is going to be?  A friend in the fertilizer industry passed this along.  Whatever the price of regular gas is at the pump, add .30 cents and move the decimal over two spots. Here’s an example.  If gas is $2.24 per gallon, add .30 = 2.54, that means that nitrogen will run about $254 per ton. So why the connection? Nitrogen products are made from ammonia (the most concentrated form on N) which is synthesized from natural gas, steam and air.  Ammonia is then upgraded to produce other nitrogen products.  The largest cost (70 –90%) of nitrogen production is natural gas which as you know has a close tie to the gas pump.


If you’re not on Harold Larsen’s e-mail list, here’s the latetest on Guthion.  The EPA announced their decision to terminate Guthion use on peaches and nectarine.  The ruling states that existing supplies can be used on these crops through September 30th , 2006.  In other words, next year look for another choice on peaches.  Apple and pear use remain the same.

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