When is the best time to pollinate walnut trees? A detailed explanation of pollination methods
1. Collecting pollen. Select robust adult trees locally or elsewhere, and collect male inflorescences whose bases are about to shed pollen (the inflorescences turning from green to yellow) or that have just begun to shed pollen. In a dry, ventilated indoor space without direct sunlight, place the inflorescences on clean sulfuric acid paper or newspaper to dry. At a temperature of 20-25°C, after 1-2 days, once most of the male flowers have shed pollen, sieve out the pollen. Then collect the pollen in finger-shaped tubes or small penicillin bottles, seal them tightly, and place them under low-temperature conditions of 2-5°C for later use. At room temperature, pollen viability can be maintained for about 3-5 days, and in a refrigerator at 3°C it can be kept for more than 20-30 days. Note that bottled pollen should be properly ventilated (plug the bottle mouth with cotton) to prevent mold and reduced pollination effectiveness. To meet the needs of large-area pollination, the pollen can be diluted; generally, adding starch or talcum powder at 1:10 is sufficient. Diluted pollen can also achieve good pollination results.
2. Optimal pollination period. According to the opening characteristics of female flowers, when the stigma of the female flower splits and opens in an inverted splay shape, and the stigma has feathery protrusions and secretes a large amount of mucus with a certain luster, this is the best period for female flower pollination. At this time, it is generally the peak period for female flowers, lasting 2-3 days; for protandrous plants, this period lasts only 1-2 days. When the stigma reverses or changes color and the secretions decrease, pollination effectiveness drops significantly. Therefore, pollination should be carried out promptly to avoid missing the optimal pollination period. Sometimes, due to poor weather conditions, the female flowering period on the same tree can differ by 7-15 days. To improve the fruit-setting rate, pollination can be carried out twice when conditions permit.
3. Pollination methods
(1) Pollinator pollination method. For precocious walnut young trees with smaller tree bodies, a pollinator can be used for pollination, and a "medical laryngeal powder sprayer" can also be used as a substitute. Put the pollen into the glass bottle of the powder sprayer and spray it over the middle and upper parts of the canopy (note that the nozzle should be more than 30 cm away from the stigma). This method pollinates quickly, but uses a large amount of pollen.
(2) Manual spot pollination method. Dip a new writing brush with a small amount of pollen and gently tap it onto the stigma. The brush tip must not touch the stigma; keep it above the stigma at a distance of 1-2 cm, and flick the brush handle with your finger to shake the pollen onto the stigma. Be careful not to apply it directly onto the stigma, so as to avoid excessive pollination or damage to the stigma, which can lead to flower and fruit drop.
(3) Pollen bag shaking pollination method. For adult trees or tall late-fruiting walnut trees, the pollen bag shaking pollination method can be used. The specific method is: mix male and female inflorescences that have just shed pollen, or pollen and starch, at a ratio of 1:10 and stir evenly, then put the mixture into a 2-4 layer gauze bag, tie the bag mouth tightly, tie it to a bamboo pole, and then gently shake it on the windward side above the canopy to release the pollen.
(4) Hanging inflorescences in the canopy method. This involves collecting male inflorescences that have begun to shed pollen, tying every 4-5 into a bundle, and hanging them in the upper part of the canopy to let them shed pollen freely. This method is also very effective and can also save the trouble of collecting pollen.
(5) Liquid pollen spraying method. Prepare the pollen into an aqueous suspension (ratio of pollen to water is 1:5,000) for spray pollination. When conditions permit, 10% sucrose and 0.2% borax (acid) can be added to the water to promote pollen germination and fertilization. Spray at 9-10 a.m. or 3-4 p.m. This method both saves pollen and can be carried out together with foliar fertilizer spraying, and is suitable for mountainous areas or areas lacking water sources. The pollen liquid must be used immediately after preparation and cannot be left for long periods or overnight.