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What About Using Oil This Year?

By: ray.perry : January 29, 2015

By Robert Beede, U.C. Farm Advisor, Emeritus

The decision depends on the value of harvesting four to five days sooner, the degree of alternate bearing, the condition and age of the orchard, and how deficient you are in chilling. My oil tests show that six gallons of the 415 oil applied between late January and mid-February worked as well as Volck® (a 476 oil no longer available) in years with sufficient chilling. I would use at least a 440 oil when chill portions are marginal (estimated 53 portions). In areas with less than 46 chill portions (estimated to be about 550 hours of effective chilling below 450F), I recommend using a 470 oil.

Reports from pistachio experts in Kern County suggest mid-January oil applications have been successful in their county. Replicated research at Parlier, Kettleman City and Madera County suggested that applications as close to February 15 as practically possible provided the most predictable rest-breaking response to oil. This research was performed between 1997 and 2007, when we had certain years of low chilling, but the frequency of unusually warm days was much lower than that of more recent winters. An oil timing study performed with Chris Wylie at Agri-World, over three winters, indicated that oil application became less valuable after February 21. Hence, Chris and I concluded that growers with large acreage needed to start around February 10 and finish by the 20th. The fact that you cannot pull this off on your ranch does NOT alter the conclusions of the experiment! To get the desired response from oil, one either has to treat the importance of timing like Gibberellin on table grapes, or do less acreage correctly.

I have been toying with treating only the Peters males in orchards with less than 46 chill portions, with the hope of improving bloom overlap, even if it is later than normal. Trials need to be conducted on treating Peters and Randy at different timings that Kerman or Golden Hills. It is possible that spraying Peters February 10-15, and then spraying Kerman February 20-25 might improve bloom synchronization. One never knows until one tries! I realize two sprays are costly and time consuming, but if it makes crop, it pays, no?

Presently, Helena Chemical and Britz-Simplot both have horticultural mineral oils registered on pistachio. Both companies market a 415 oil, the lightest one used in agriculture. In addition to its Omni 6E 415 oil, Helena also markets “Supreme Oil,” which is a 435 oil (i.e., 50 percent of it distills at 4350 F). Britz-Simplot is the only company I am aware of (meaning that I will get calls from companies telling me about theirs) that markets oil similar in weight to the old Volck®. It is called, “PHT 470 Supreme Spray Oil.” Britz-Simplot also has a 440 oil which is OMRI approved. During my years of oil research, I documented an average split nut increase in healthy mature trees of about five pounds per tree, and three to four pounds in seven-year-olds. An increase was also recorded in highly fruitful six-year-old trees (untreated produced 1700 pounds of split nuts per acre) but the response was more erratic than in the seven-year-old trees. I think treating six-year-old trees in a good chill year is pushing it, but it may be necessary to please the bank or investors in low chill years such as 2015.

Make sure your trees have good soil moisture before treating! I think we have had enough dew and fog to not worry about dry pistachio bark. As I have always stated, I have never burned any trees with oil in my experiments, including the registration trial where we applied 12 gallons of Volck® in 100 GPA. I have also told the story too many times about the grower whose PCO applied 20 gallons of 470 oil on sixyear-old trees by helicopter. No burn, but great rest-breaking. Salt stress is yet another factor that has to be considered in some orchards. I have no idea what effect high salinity has on a pistachio tree’s susceptibility to oil burn. Hopefully one of you with salty soil will apply oil at 6 and 12 gallons a half acre or so) and report back to us.

In years with reasonable chill accumulation, oil application can increase the risk of frost damage and Botrytis infections, especially on male trees, during wet springs. These infections can also predispose trees to BOT attack later in the year. However, I think this is the least of our worries in a year such as 2015 with such potentially low chilling. I would be thrilled to have you report your trees popped out uniformly and early from oil treatment with the winter we have had thus far. Oil also does not solve production problems associated with poor irrigation management, no pruning, insufficient fertilization, low infiltration and poor pest and disease management. It just helps overcome insufficient chilling!

Also, did your pruning crew report any trees with black shoots that cut dry? There are some orchards that may have suffered some limited cold damage this winter. If not found now, it will be considered oil damage during leaf out in the spring. Refer to last month’s task list for a detailed description of cold injury symptoms, but the clear sign of injury is a blackening of the bark tissue with white milky sap exuding from injured bark and cut tissue. Attempting to force these trees with oil may increase the risk of them being further damaged. I emphasized this statement because Mark Anderson, consultant, notified me of a grower who applied oil to six-year-old trees in 2013, and then reported dead trees randomly distributed in the orchard. Mark said they had blackened bark around the head of the tree, suggesting that they may have suffered cold injury prior to oil treatment.

I think the oil either finished them off, or the trees were already cold-damaged, but I do not believe that the random pattern suggests that oil was the primary cause for tree loss. Folks, I am not trying to defend my favorite child here! As mentioned above, when I registered Volck® oil, Chevron made me apply 12 gallons of it in 100 GPA on twenty trees, and we never saw any hint of injury. I have personally stood by trees only two years old, and emptied the spray tank on them with oil solutions from my test plots. The only thing they did was break bud 10 days ahead of the untreated trees. Donnie Rose is my witness!

Am I saying oil damage cannot happen? Heaven’s no! I am not a crazy man, ANYTHING can happen! The question is, how many of the conditions I have told you to avoid have you ignored and treated anyway? Since I am spewing personal opinions, I also think the effects of inadequate chilling are increased in trees with low zinc levels. This is yet another known factor that causes delayed leaf out.

Coverage is critical! Sprayer speed must not exceed 2 mph! If necessary, pay the applicator more to insure this! I cannot believe there are still growers out there that do not believe this! Oil must be stored and handled with great care to avoid breaking the emulsifier off before application. I recommend you take delivery of the oil in a container from your supplier, and use it directly from this container. This eliminates the argument of contamination. Do not apply if the oil is milky. The emulsifier has broken off the oil, and you will BURN your trees. Oil is not registered for rest-breaking. It is registered for soft scale control at this time. Therefore you break rest at your own risk.