Re: [apple-crop] Late summer drop and fruit size
Hello Vincent, I usually am not an active participant in post but I thought that I might weigh in on your comment since I have been doing preharvest drop research for a number of years. Jim Krupa our technical assistant has been involved and he expressed an interest in doing an experiment to find out a little more about why fruit drop? The experiment was done on McIntosh and Delicious over two seasons. Briefly, 6 to 10 trees were selected. Half were designated to be drop trees and half were designated to be harvest trees. The experiment was carried out from the time the first fruit dropped until most of the fruit were on the ground. Each morning fruit under the drop tree were picked up and taken to the lab where they were weighed and internal ethylene was determined on each fruit. Red color, flesh firmness, soluble solids and starch rating were determined and seed number counted. This was repeated for fruit that dropped at 3:00 pm. Three times a week 10 fruit were harvested from the harvest trees and similarly processed. Seed number was not associated with fruit weight or drop although this has been documented in the literature. I suspect that this may be an issue when there are 0, 1 or 2 seeds per fruit but that was not the case here. The conclusion that we came to was all fruit that dropped were climacteric and showed signs of ripening (internal ethylene greater than 1 ppm, increased red color and reduced starch content). The appropriate question to ask then may be why did the fruit that drop ripen early? We know from research done here in the 1980s that fruit with very low seed number are also low in calcium. Fruit low in calcium may ripen earlier. I offer another explanation. Many of you know that recent reserach has indicated that a carbohydrate balance deficiency in trees druing June drop is a factor that infouences thinner response as well as the severity of June drop. This is based on the original work of Alan Lakso and taken to the field by Terence Robinson. The model is good and the practical application for thinning is important. However, if one looks at the carbon balance in Alan's model over the growing season you will note two things. First, there is likely to be a deficit during the June drop period and this has been highly publicized. A second period of deficit occurs at harvest time and this has been largely ingnored. It makes perfect sense since as fruit ripen there is a large increase in respiration (climacteric) which fuels the synthesis of enzymes involved with ripening. Vincent mentioned that were might be a shelf shedding mechanism in trees. When trees have a carbohydrate deficit they must respond. In some instances this response is shedding of fruit. Even with fruit it is survival of the fittest. This occurs at June drop, why not at harvest? Drop is frequently controlled by spurs. If spurs are shaded or leaf area is small then the fruit on these spurs are most likely to drop early. Mite damaged trees also show early drop. We have followed drop from McIntosh over the course of the season which often occurs over a 7 week period. Fruit increase in size about 1% per day they are on the tree. Consequently, it is not surprising that average fruit sized will increase over the harvest season. This is one of the attributes of using drop control compounds. I am not sure if I have helped in this discussion but drop can be precipitated by several events (seed number, heat, lack of light, reduced leaf area, damaged leaves, etc) but I do believe it comes right back to any factor that stimulates ripening will lead to increased drop. Duane On 1/13/2014 12:12 PM, Vincent Philion wrote: Hello, I'm analyzing some data and I have seemingly contradictory results. I'm hoping someone can comment and make sense of this: For a number of randomly selected trees, fruit drop was recorded starting late summer until harvest. For each tree, we recorded total fruit drop (and weight), harvested fruit (and weight) and the total (drop + harvest). As I was looking at the data, I noticed average harvested fruit size (weight/number) was related to Total fruits per tree... Nothing strange, until I realized harvested fruit size INCREASED with Total fruit number on tree. As if the fruit dropping left more energy for the remaining fruits to grow? I was expecting harvested fruit size to be smaller on trees that had more total fruit, not the other way around. I'm not sure this late natural fruit drop can be compared to very late hand thinning, but does anyone know if fruit size increase can be linked to late thinning (notwithstanding total yield that can go down)? Maybe this is normal? Any comment welcome! Vincent http://www.irda.qc.ca/assets/client/img/logo.png *Vincent Philion*,M.Sc. agr. Microbiologiste Phytopathologiste pomiculture *Institut de recherche et
Re: Apple-Crop: For Discussion: Pesticide Applications Rates and Tree Row Vol...
Hello, I have tried not to get into the TRV discussion. However, we have had some rather good discussion among individuals working on the New England Pest Control Guide. Glen has been a key player here, and in his presentation at the New England Vegetable and Fruit Conference he made some very good points. I work with plant growth regulators, and as Dave Rosenberger pointed out this concept was born and developed because of variable results with chemical thinning. Plant hormones differ from pesticides since their response is linear or curvilinear based upon dose applied. The goal is to apply an appropriate amount of hormone (thinner) to get the appropriate amount of abscission, and the correct amount is somewhere in the middle or lower portion of the dose response curve. The margin of error is not great so a mechanism is needed to apply an appropriate and needed amount of chemical to all leaves and fruit for proper thinning. I had the privilege of interacting many times with authors of the two most-commonly cited papers on TRV, Dick Unrath ( Sutton and Unrath) and Ross Byers. Both researchers did their work in the mid Atlantic and the Southeast. Tree vigor was high and tree grew on semi dwarf rootstocks. Terminal growth in many places was measured in feet not inches and trees were very thick. This was confirmed when I toured North Carolina orchards with Dick in the 1980s.Therefore, it is easy to see why they used the relatively high water volumes for a minimum. Trees look a whole lot different now. Trees are smaller and they are more open. Blocks now with a TRV of 100 gal/min are common. All plant growth regulator researchers that I know use only TRV in developing data that leads to the recommendations that appear in our pest guides. Initial screening and early observation of new plant growth regulators involves the use of dilute hand gun sprays. However, once efficacy has been established and an appropriate amount of material is made available, all researchers on the east coast apply research sprays based upon TRV. There have been discussions that the calculated TRV that is published does not wet the foliage. Most of use use the published procedure for calculating TRV. The major value of this is that it gives us a tree volume that we are spraying and it gives us a volume of water in which we put our hormone sprays. This then gives us a number of molecules of hormone that we are applying in the volume of foliage and based upon efficacy data. The molecules are distributed somewhat equally on leaves and fruit if the sprayer is calculated correctly. This system is not perfect but I would prefer to have an imperfect system that appears to work reasonably well rather no system. I offer government as a modern day example. Do we need to revisit TRV, as has been suggest, and how to calculate it more accurately on different systems? That is a great idea. However the topic of TRV in the past has been spurned as either being too difficult or not terribly relevant. Perhaps there is interest and this is a viable research topic that if revisited can provide information for more efficient and effective application and use of materials that we apply to our trees. Best regards, Duane Dave Rosenberger wrote: Hi, Glen -- 1. Yes, as a general rule, I do want growers to believe that, except for crop load adjustment, the safest bet will be to apply the recommended amount of product/A regardless of tree size. The 5-10% of growers who actually grasped and properly applied TRV will continue to do so (at their own risk), whereas the rate/A recommendations will avoid losses for the other 90% of tree fruit growers and will also bring us into compliance with EPA label writing and, for the most part, manufacturer recommendations. 2. I agree that using a minimum rate/A of 150-200 gpa increases the safety of TRV recommendations, but I still go back to the fact that, after 20 years of hearing the TRV gospel, the vast majority of growers (and probably the majority of research/extension folks) don't know how to make TRV work on large farms with a variety of tree sizes and spacings. 3. I'm not certain about leaf density on modern trees compared to old standards. However, spur-type trees are relatively new, and there can be no argument that leaves are closer on spur-type trees than on non-spur types. Also, large old standard trees, and even many mature trees on MM.106 or M.7 rootstocks tended to have umbrella canopies whereas the areas within the TRV in modern training systems tends to be more fully occupied with leaves and fruit. 4. Concerning your question about why a large tree should need more captan than a smaller tree: I don't disagree with your analysis. However, my point is that our application systems (as currently used by most growers) are so inaccurate that the only
