AG RX Newsletter Post Spring 2011

Posted on July 10, 2011

A Word from David Holden of Holden Research and Consulting

Well, looking at the long term forecast, it would appear that we are done with much more winter rain. There may be another .5 to .75 of inch of rain left in the season, but for the most part we are probably going to start our spring watering soon. With that in mind I thought I might lay out a general nutrient strategy plan for citrus and avocado growers for this season. We may have a mild or cool spring this year. That would place our avocado fruit set a little later in the spring with much of it probably occur-ring in May. My observation over the years is that we do not start sticking fruit to avocados until we have average night time temperatures above 50 degrees F. In fact I would say that the 80-20 rule applies to avocado fruit set. That is 80% of the fruit occurs with the last 20% of the bloom. With that in mind I would think about doing bloom sprays to enhance fruit set later than earlier. Watch the night time lows and when they start getting above that 50 degrees F over time then make the bloom sprays. Bloom sprays, according to past information from Dr. Carol Lovett should probably go on prior to 10% open flower for avocados.

From a soil fertilization perspective I would suggest starting out with a phosphate fertilizer if your soil report shows low quantities of P in your soil. For most of you this will not be the case. The next element you need to think about applying then is nitrogen. If soil temperatures are below 50 degrees F, then I would use CAN 17 or AN 20. If the soil temperatures are approaching 55 degrees F, then you can use UAN 32, a more economical source of nitrogen. For you avocado growers, do not go too heavy wit nitrogen, but if your soils are devoid of nitrogen after the winter rains I would not have a problem with you adding 20-30 pounds per acre of nitrogen (about 6-8 gal UAN 32, 10-15 gal of AN 20 or CAN 17). I often hear a concern about adding nitrogen to avocados during bloom. My experience is that this small amount of nitrogen is not deleterious to the set in April or May and to tell the truth I am really convinced that the majority of our set occurs in May (remember the 80-20 rule I mentioned above). As new roots start to grow in both citrus and avocados in late April and May I then like to see the addition of potassium and zinc into the soils as the roots are ready to take these elements up. This would be a good time to include Transit S to this fertilizer application. Those of you that attended AG RX’s recent spring nutrient seminar will remember the data I showed that shows how the Transit S enhances nutrient up-take and efficiency in our soils. 10-20% increases in average nutrient uptake for N-P-K are seen on average though the use of this product in connection with grower’s normal practices. After these applications, it is time to repeat or make some other specialty applications if your are deficient in something else, such as magnesium or iron. Talk to your CCA (Certified Crop Adviser) about their recommendations for the remainder of the year. As an aside, remember that a CCA is different than a PCA. PCA’s are strictly licensed for pest control advice by the state of California. A CCA holds a certificate from the Agronomy Society of America that says he is competent to make both pest control and nutrient recommendations for the crops he advices on.  Happy spring to all!

David Holden

Leave a Reply