Detailed Explanation of Key Citrus Cultivation Tasks in April
April (Qingming to Guyu) is the spring shoot emergence period, flower bud period, and flowering period. In late March, there was mostly cloudy and rainy weather with little sunshine, especially in the early part of the month with consecutive rainy days and relatively low temperatures, which affected the emergence of citrus spring shoots. According to meteorological forecasts, rainfall in early April will be lower than normal, and the average temperature will be higher than normal. Spring rain in citrus orchards...
April (Qingming to Guyu)
Spring shoot emergence period, flower bud period, flowering period
In late March, there was mostly cloudy and rainy weather with little sunshine, especially in the early part of the month with consecutive rainy days and relatively low temperatures, which affected the emergence of citrus spring shoots. According to meteorological forecasts, rainfall in early April will be lower than normal, and the average temperature will be higher than normal. With excessive spring rain in citrus orchards and suitable temperature and humidity, pests and diseases are prone to breeding, and it can also easily cause abnormal flower and bud drop. This is one of the key periods for citrus production this year, and the following work needs to be done well:
(1) Fertilizer, water and soil
Due to the cloudy and rainy weather in late March, it is necessary to clean and dredge the drainage ditches around the citrus orchard, do a good job in drainage and soil conservation, and ensure normal flowering and fruiting of the plants. For mature trees with weak vigor and many flowers, it is advisable to supplement flower bud fertilizer to promote the maturation of new shoots. Compound fertilizer 0.2-0.3 kg or dilute human manure 10-20 kg can be applied. For young trees, continue to topdress quick-acting fertilizers such as urea and human manure every month to promote branch and shoot growth. Generally, apply 0.1-0.2 kg urea or 5-10 kg dilute human manure per plant. Adult orchards without intercropping may consider sod culture, that is, selecting and retaining beneficial weeds in the orchard, which not only saves labor but also has soil and water conservation effects, and can increase soil organic matter and improve the orchard ecological environment, such as Ageratum conyzoides, white clover, Chinese milk vetch and soybean, etc. Spring green manure should be deeply plowed and incorporated from late April to late May. Returning the freshly cut grass to the field and renewing grass roots each year can increase soil organic matter year by year, activate the soil, and improve the vitality of the citrus root system.
(2) Flower bud (flower) thinning and shoot control
For citrus trees that bore many fruits last year and were harvested late, there are relatively many plants with fewer flowers. When spring shoots grow to 2-4 cm, adopt the method of thinning strong shoots and retaining weak ones, removing part of the spring shoots according to "remove one out of three" and "remove two out of five", which is beneficial for preserving flowers and reducing bud and flower drop; if there are many flowers and the tree vigor is weak, part of the flower buds or flowering branches should be appropriately thinned. For varieties with serious flower and fruit drop or relatively low fruit-setting rate, such as navel orange and Benzao mandarin, spray boron-based foliar fertilizer at the initial flowering stage (no need to use it year after year), and spray 50 x 10-6 gibberellin once when 3/4 of the flowers have faded (Yuhuan pomelo should be reduced to 25 x 10-6) to preserve flowers and fruits; supplement foliar fertilizer during the flower-fading period, choose 0.3% urea plus 0.2% potassium dihydrogen phosphate, or other fruit tree nutrient solutions for canopy spraying, which can effectively reduce fruit drop after flowering.
(3) Pest and disease control
For citrus orchards with many flower bud midges, cover with plastic film before adults emerge from the soil to prevent adults from climbing the trees. Alternatively, when the calyx begins to crack and show white, broadcast 50% phoxim 150-200 g mixed with 15 kg fine soil per mu to kill them; for scab, use Bordeaux mixture and other agents when 2/3 of the flowers have faded. For orchard blocks where the disease incidence on autumn shoot leaves last year was above 5%, spraying is required both when spring shoots grow 0.2-0.3 cm and when 2/3 of the flowers have faded; for blocks with incidence below 5%, focus mainly on spraying when 2/3 of the flowers have faded; when 2/3 of the flowers have faded, choose 78% Kobo wettable powder 600-fold solution, 80% Bibei wettable powder 500-fold solution, 77% copper hydroxide wettable powder 600-fold solution, 0.5% equal-amount Bordeaux mixture, or 70% thiophanate-methyl wettable powder 800-fold solution, etc.; for varieties sensitive to canker such as sweet orange, use Bordeaux mixture and other agents about 10 days after flowering, and also control scab, black spot, gummosis, anthracnose, etc. When there is fresh frass from longhorn beetle larvae, use a steel wire hook to kill them. Before adults begin to lay eggs (late March to early April), wrap or whitewash branches and trunks within 1 m of the ground with woven bags to prevent egg laying. For citrus orchards with many scale insects, mites and sooty mold, etc. As temperatures rise, citrus red mites reproduce faster. When there are more than 3-4 mites per leaf, promptly choose 0.3-0.5 Baume lime sulfur mixture, 5% hexythiazox (Nissorun) 1500-fold solution, 15% pyridaben 1200-2000-fold, 20% clofentezine 1500-2000-fold solution, etc.