The significance and methods of thinning male flowers (male flower thinning) on walnut trees

  Walnut trees produce a large number of male flowers, far more than needed for pollination, and the development of male flower buds consumes large amounts of water, sugars, amino acids and so on. Removing excess male flower buds from walnut trees is called male flower thinning. Thinning male flowers can save large amounts of water and nutrients for the development of female flowers, thereby improving the nutritional conditions during female flower development, increasing nut yield and quality, and also favoring the growth of new shoots and flower bud differentiation, ensuring the following year's yield. According to measurements by the Analysis Center of the Chinese Academy of Forestry, the dry weight of one male flower bud is 0.036 grams, and by the time it reaches a mature inflorescence the dry weight increases to 0.66 grams, a gain of 0.624 grams, of which it contains 4.3% nitrogen, 1.0% phosphorus, 3.2% potassium, 1l.1% protein and amino acids, 4.3% crude fat, 3l.4% total sugars and 11.3% ash. If 9o% of the male flower buds are thinned from a walnut tree, about 50 kg of water can be saved and 1.1~1.2 kg of dry matter conserved. In a sense, thinning male flower buds is a measure of reverse irrigation and fertilization. Male flower thinning has a very obvious yield-increasing effect on walnut trees: the fruit-setting rate can increase by 15%~20%, and the yield can increase by 12.8%~37.5%.

  In addition, excessive male flowers not only consume large amounts of nutrients, but more importantly cause the female flowers to be over-pollinated and stimulated, leading to shedding and affecting nut yield.

Pictured: walnut

  Timing and methods of male flower thinning

  In principle, male flowers should be thinned as early as possible; generally it is best to do it within the 20 days before the male flower buds sprout, that is, when the male flower buds begin to swell; during the dormant period the male flower buds are firmly attached and handling is troublesome, while thinning during the male flower bud elongation stage gives no obvious effect. The ratio of female inflorescences to male inflorescences in walnut is 1:5 plus or minus 1, and the amount thinned should preferably be 90%~95% of the male inflorescences on the whole tree, so that the ratio of female inflorescences to male flowers (florets) reaches l:30~60; however, for trees planted in scattered locations and trees with fewer male flower buds, and for young trees that have just begun to bear fruit, thinning may be reduced appropriately or not done at all. According to relevant reports, one male inflorescence has 117 plus or minus 4 florets, each floret has l2~26 stamens, the anther has 2 locules, and each locule has 900 pollen grains; calculated this way, each male inflorescence has 1.8 million pollen grains. Although the pollen germination rate is only 5%~8%, the male inflorescences left behind can fully meet pollination needs. For superior cultivars, the male flowers of the pollinizer cultivar should be thinned less, while the main cultivar can be thinned more.

  When thinning male flowers, use a 1~1.5 m wooden pole with a hook, pull the branches down, and simply twist them off by hand; this can also be done in combination with pruning. Chemical male flower thinning agents are also used, but the effect is unstable.