It's time once again to mention a program that I'm a big believer in: fall foliar fertilization. I started 35 years ago injecting UN32 into my overhead sprinkler system on apples. My first attempt opened my eyes. I overdid the rate and fried all the leaves. I never slept well the entire winter wondering how my trees would come out the following spring. As it turned out I had the biggest strongest buds and bloom I’d ever seen! Research on foliar application of urea dates back to the 1940’s in California. 1990’s work 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 a soil application. (If you're trying to cut back on your annual fertilizer expense this is a program that will get more N in the tree for fewer dollars!) This nitrogen is mobilized and moved into other plant parts such as shoots and buds within one week. Trees move nutrients from the leaves back into the buds and wood prior to leaf drop. It remains there until spring when it is available for early use during cell division (more cells = larger fruit)! Peach fruits have three fairly discrete stages of growth. The first stage (Stage I) lasts from full bloom until about 50 days after bloom. During this time the fruits grow fairly rapidly and growth is primarily due to cell division. Most of the cell division occurs during the first 30 days after bloom, but the length of stage I may be influenced by temperature. There is an increase in both fruit size and fruit dry weight. During stage I, shoot growth begins but there is too little foliage on the tree to support the growth of the fruit and shoots. Therefore much of the carbohydrates for early fruit and shoot growth come from reserves stored in the tree during the previous season. Urea is known to enhance the uptake of other micronutrients when sprayed in combination. 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. Now is a great window of opportunity to put a bit of fuel back in the tank for next year.
Along the same note, this just came to my email box from Lynn Long at Oregon State:
Dr. Greg Lang of Michigan State University has found that late summer or autumn urea sprays increased the shoot hardiness of the cherries that he tested and produced up to 20% larger spur leaves in the spring. As a whole, throughout the growing season, the spur leaves are the most important leaves for supplying nutrients to developing fruit. Greg speculates that if the spur leaves are larger, than photosynthesis is increased and there are more carbohydrates being exported to the developing fruit.
In his trials Greg applied two applications of low biurate urea as a foliar spray. An application on August 31 and a second application about one week later actually gave the best uptake of N into spur tissues and provided earlier acquisition of cold hardiness in the year that it was treated. However, application can be made up to leaf fall.
Each application should consist of 15 to 20 pounds of N/acre. In the past I stated that this was 15 to 20 pounds of actual N/acre, however, last year Greg corrected me and stated that he used 15-20 pounds of urea product per acre. After I made that correction I got feedback from several growers saying that they had used the higher rates with good effect and no phytotoxicity. I would encourage you to use the rate that you are most comfortable with.
In Greg’s trials he mentioned that dilute sprays of 250 gallons/acre are possible, but some leaf burn at the leaf margin could be possible with these dilute sprays. Concentrated sprays ranging from 25 to 75 gallons/acre showed less phytotoxicity when applied with a curtain-type sprayer (small volume, small droplet size). The reduced toxicity which was noted with the concentrated sprays is probably due to less pooling of the material along leaf margins and therefore less burning of the foliage.
It is also a good idea to apply boron in the fall. Studies show that there is greater boron uptake in the fall while leaves are still on the tree than during a delayed dormant application in the spring.
Should you be concerned about hot afternoon temperatures?
Dr. Eric Hanson, MSU nutrition expert stated that the majority of the uptake takes place in the first 6 hours after application. So, as long as the application is made first thing in the morning, the late afternoon heat and volatilization probably doesn't affect the total amount that is likely to be taken up.
With the repeated rain storms we had this season it gives us a bit of insight into what eastern U.S. growers face every year. Combating disease issues in Colorado’s desert climate is a “walk in the park” compared to back east. On peaches we typically apply fungicides twice in a season. I had a conversation with a pathologist from Michigan earlier this summer. He stated that they applied fungicides all season long. They use a 10 to 14 day efficacy interval for most of the products.
If you were fortunate to have a peach crop this year it probably showed up at the packing house with some Coryneum blight on the fruit. So what’s your plan to have clean fruit next year? An ounce of prevention is worth a pound of cure! It’s hard to wrap our minds around the attitude of being proactive, not reactive. The materials we have available are protectants not curatives. The following is taken from the UC IPM website – “Shot hole is managed primarily with fungicide treatments to protect buds and twigs from infection.” The key word in successful blight control is “prevention.”
The first autumn rains can start the spread of the disease. Infection can take place in the dormant season if proper moisture and temperature conditions occur. Spores, spread primarily by splashing water, can remain viable several months. Establishing a protective barrier with copper is vital to keep Coryneum from germinating and spreading. Good spray coverage is important! The disease usually starts low inside the tree where moisture persists, so be sure to target this area. The most common application timing is at 50% leaf fall. It’s not necessary to wait for that to happen. 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. A fieldman friend in Washington state mentioned that he has his growers add a sticker to all their Fall copper sprays. He said it's easy to still see the copper on the tree in February.
Sanitation is a key component of any disease control program. In orchards where twig infections are prevalent, the efficacy of the dormant treatment can be improved by pruning out and destroying infected wood. A conscientious annual program of removing infected wood is necessary over multiple years to alleviate the problem. The following quote comes from the 1996 Colorado Tree Fruits crop management guide. “Once established in an orchard, Coryneum blight is difficult to eradicate. Infected buds and twigs may produce spores for 2 to 3 years. ”
How aggressive you need to be next Spring depends on the level of infection you have now, the “clean up” program you undertake with pruning and the weather conditions next season. We may be back to our normal two fungicide season, but if it rains……..
Here’s a link to a great article on Fire blight. I know that you’ve put that problem on the shelf until bloom, but once again sanitation is a key part of control. It should impact how you prune.
If you’ve read this newsletter for very long you know I like quotes that are thought provoking commentaries on our society. I know they strike home because over the years I often get comments on the quote I inserted….. not the horticultural information I put hours into… So here’s a few of my favorites.
"When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant."
"Orchards are a form of autobiography."
“The democracy will cease to exist when you take away from those who are willing to work and give to those who would not.” Thomas Jefferson
“Man despite his artistic pretentions, his sophistication, and many accomplishments, owes the fact of his existence to a six-inch layer of top soil – and the fact that it rains.”
“And if we think that laws designed to prevent crime can indeed make the world a safer place, we should ask ourselves this: How exactly, is the world made a safer place by making self-control and responsibility irrelevant?”
~Jeff Snyder (Nation of Cowards)
“You can tell the ideals of a nation by it’s advertisements”
The average age of the world's greatest civilizations has been two hundred years. These nations have progressed through this sequence: From bondage to spiritual faith; from spiritual faith to great courage; from courage to liberty; from liberty to abundance; from abundance to complacency; from complacency to apathy; from apathy to dependence; from dependence back again into bondage.”
~Penned by Alexander Tyler over 200 years ago while we were still a British Colony!
“Thus the metric system did not really catch on in the States, unless you count the increasing popularity of the nine-millimeter bullet”
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