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nafex - Re: [NAFEX] chemical thinning question

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  • From: <dmnorton@royaloakfarmorchard.com>
  • To: "North American Fruit Explorers" <nafex@lists.ibiblio.org>
  • Subject: Re: [NAFEX] chemical thinning question
  • Date: Thu, 7 Jun 2007 08:51:31 -0500

Steve,

It seems thinning is more of an art than a science and timing is critical. The temperature plays a large part in how well a chemical thinner works. Here is a quick synopsis from Cornell on the weather factors that can affect thinning. It is the best thinning guide I have found and we follow the recommended guidelines here at Royal Oak Farm. You can find it at http://ipmguidelines.org/TreeFruit/CH10/CH10-04.asp along with a temperature chart giving you what temperature ranges have what affect on the mode of action of the chemical.
Frost. Frost before application of thinners can greatly increase the amount of thinning obtained from chemical thinners. Frost at bloom can damage fruitlets and reduce seed set, which can result in increased natural drop and greater chemical thinning response. Frost can also damage spur leaves, resulting in greater chemical uptake and thus greater thinning response. Wherever flowers and leaves have been damaged by frost, extreme caution should be used with chemical thinners. Typically, lower rates would be used in such cases.

Sunlight Levels before Application. The amount of sunlight for the 3-5 days preceding application of chemical thinners has an important effect on chemical uptake and response. Intense cloudy weather before application of thinners can result in increased chemical uptake and greater thinning response, due to greater succulence of the leaves and a thin wax cuticle. In addition, intense cloudy weather results in reduced carbohydrate supply for fruit growth and reduced fruit growth rate. This results in increased natural drop and greater chemical thinning response. Growers should reduce the rate of thinner used, if intense cloudy weather precedes application.

Temperature at Time of Application. The uptake of chemical thinners is greater at higher temperatures than at lower temperatures. The optimum is between 70-80° F. Above 80° F, uptake is substantially greater than below 80° F. The time of day applications are made appears to be unimportant. Applications made in the morning or evening when it is cool have a longer drying time on the leaf, resulting in a slow but sustained uptake of chemical, while at higher temperatures during mid-day, drying times are shorter, resulting in a short but rapid uptake of chemical. Thus, the total amount of chemical taken into the plant appears to be very similar regardless of the time of day. Recent research results also indicate that similar thinning is achieved regardless of the time of day applications are made.

Weather After Application. Temperature and sunlight levels for the 5-day period after application of thinners are the predominant weather factors affecting chemical thinning response. The interaction of temperature and sunlight with the chemical thinner creates stress in the tree, which is necessary to make some fruit drop off. Warmer temperatures increase thinning response, while greater light levels decrease thinning response.

Night temperatures are also an important factor to consider. Warm night temperatures (>60° F) give greater thinning response. With high night temperatures, fruits use up the carbohydrates that were produced during the day at a fast rate, resulting in a deficit of resources for fruit growth and causing the weakest fruits to drop. The greatest thinning can result if warm night temperatures are combined with intense cloudy/warm daytime weather. Under these conditions, the tree produces little reserves during the day and at night the fruits use up all of the reserves produced during the day, making the fruits very susceptible to the stress caused by chemical thinners. Under these conditions, excessive fruit drop can result. The least effective thinning is achieved when bright, warm daytime weather is accompanied by low night temperatures. Under these conditions, the tree produces large amounts of carbohydrates during the day and the fruits use them up at a slow rate during the night. Under these conditions, there is little stress created by chemical thinners and the thinning response is poor. Growers should critically examine the weather forecast for the 3-7-day period following application of thinners and adjust rates of chemical thinners up or down 50% based on forecasted temperatures and sunlight levels.

Then of course there is the size of the fruit and how much NAA or Sevin to use based on the size of the fruit and how many of your trees have fruit that is the same size, the variety of the apple and so on and so on..........

Most of the thinning results will be seen at June drop.

Dennis Norton
Royal Oak Farm Orchard
http://www.royaloakfarmorchard.com
http://www.theorchardkeeper.blogspot.com
http://www.revivalhymn.com
----- Original Message ----- From: <sjkeipert@highstream.net>
To: <nafex@lists.ibiblio.org>
Sent: Thursday, June 07, 2007 6:54 AM
Subject: [NAFEX] chemical thinning question



Some of my apple trees that have a tendency to be bienial bearers are getting to
the size where hand thinning is a pain. This year I tried thinning with a spray
of 10 ppm NAA along with a spreader/sticker to improve wetout. I sprayed about
12-14 days after petal drop, so its been about 3 weeks now. So far I have not
noticed any difference in drop, just the usual loosening of stem connections in
the undersized apples. Having never done this before, what should I be looking
for? When should I expect thinning, at the normal June drop? Any advice would
be appreciated. - Steve









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