Key Technical Points and Application Methods of Flower Spraying in Greenhouse Tomato Cultivation
Tomato (scientific name: Lycopersicon esculentum Mill.) is an annual or perennial herbaceous plant of the genus Lycopersicon in the Solanaceae family, with a plant height of 0.6-2 m, covered all over with sticky glandular hairs, with a strong odor, stems prone to lodging, leaves pinnately compound or pinnately deeply lobed, inflorescence peduncle 2-5 cm long, usually with 3-7 flowers, calyx radiate, corolla radiate, berry oblate or nearly spherical, fleshy and juicy, seeds yellow, flowering and fruiting period in summer and autumn.
In overwintering greenhouse cultivation of tomato, the first half of the entire flowering and fruiting period occurs under relatively low temperature conditions, and at the same time the humidity inside the greenhouse is relatively high, so tomato pollen is not easily shed naturally for pollination; therefore, tapping the flowers at noon on sunny days or releasing bumblebees for assisted pollination can be adopted to increase the fruit-setting rate. At present, farmers still use growth hormones——4-chlorophenoxyacetic acid treatment to promote and ensure fruit setting, but the correct method of use must be strictly mastered.
1. Choose 4-chlorophenoxyacetic acid for treatment
The use of 2,4-D is not advocated. 2,4-D was originally a herbicide, with strong medicinal properties, and is prone to causing phytotoxicity. There have been many experimental reports abroad that it is harmful to humans, and it has long been banned internationally. Using 4-chlorophenoxyacetic acid is relatively safe. The chemical name of 4-chlorophenoxyacetic acid is p-chlorophenoxyacetic acid, also known as “Tomato Spirit”. Adopting flower spraying technology can save labor and time and also promote fruit setting. Members of the tomato group of the Vegetable Research Institute of the Wenzhou Academy of Agricultural Sciences conducted experiments on the effects of several different types of hormones on tomato in experimental fields from January to March 2009. From Table 1 it can be seen that, compared with 4-chlorophenoxyacetic acid, 2,4-D takes effect quickly and has a good effect on preserving flowers and fruits, but is prone to producing deformed fruits; 4-chlorophenoxyacetic acid is relatively safe and not prone to producing deformed fruits, but takes effect more slowly. The use of 4-chlorophenoxyacetic acid can greatly reduce the rate of deformed fruits, and the concentration used is also significantly lower than the concentration used for 2,4-D.
2. Concentration for using 4-chlorophenoxyacetic acid
The concentration for using 4-chlorophenoxyacetic acid is generally 14-16 mg/L. If the concentration is too low, the effect is not significant; if too high, deformed fruits and hollow fruits are likely to appear. The concentration should also change with changes in external temperature. Generally speaking, at high temperatures use the lower limit of concentration, and at low temperatures use the upper limit of concentration. Before application, it is best to first conduct a dipping test: select and dip a few normal flowers. If the ovary of the dipped flowers begins to swell within 4~5 days, it indicates that the concentration is suitable, and this concentration can be used for general application. Swelling too early indicates the concentration is too high, and swelling too late indicates the concentration is too low.
3. Suitable period for flower spraying and the part to spray
4-chlorophenoxyacetic acid products seen on the market now are everywhere. In terms of use, some say that when using 4-chlorophenoxyacetic acid, the concentration should be reduced as much as possible, which is good, but at the same time they also say that the part for spraying flowers with 4-chlorophenoxyacetic acid is the whole plant, which is completely wrong and is a misleading guide to the use of 4-chlorophenoxyacetic acid.
① Flower spraying period. Use a small sprayer to spray flowers. It is best to spray when 2~3 flowers in an inflorescence are open. Do not use the flower-smearing style of spraying when the first flower bud of an inflorescence is about to open, as this will affect the flowering and fruiting of the several flowers behind it and is also prone to causing phytotoxicity. When spraying flowers, never spray the 4-chlorophenoxyacetic acid solution onto the young leaves and growing points (brain tips) of the plant, otherwise phytotoxicity will also occur.
② Flower spraying part. When spraying flowers, spray the back of the flower, that is, the pedicel and calyx, and do not spray the petals. This is because the fundamental cause of tomato abscission is the increase in abscisic acid concentration at the junction of the calyx and pedicel. When abscisic acid reaches a certain concentration, it causes separation of the pedicel and calyx, that is, flower and fruit drop. The fundamental cause is an imbalance in the concentration ratio of abscisic acid and auxin. In this way, as long as we inhibit the increase of abscisic acid at the junction of the calyx and pedicel, we can promote tomato fruit setting, and spraying 4-chlorophenoxyacetic acid at the junction of the calyx and pedicel can effectively inhibit the formation of abscisic acid and promote the formation of auxin. Generally, spraying once per inflorescence can set more than 2 fruits.
③ When spraying flowers, temperature is mainly based on the weather and the temperature inside the greenhouse. Choosing a time with a temperature of 20—25℃ gives the best flower spraying effect. Therefore, in autumn from September to October or in early summer from May to June when the temperature is very high, generally after 5:00 p.m. is the most suitable time for spraying; in late autumn and spring from March to April, 9:00-10:00 a.m. or 3:00-4:00 p.m. is best. In the low-temperature period of winter, choose cloudy or sunny days from 10:00 a.m. to 2:00 p.m. as the most suitable; when the greenhouse temperature is around 15℃, flowers can also be sprayed. However, do not spray on cloudy and rainy days in winter and early spring, because after spraying 4-chlorophenoxyacetic acid, the solution is not easy to dry on cloudy and rainy days, and the residual liquid will be conducted to the growing point and cause phytotoxicity.
④ Interval between flower sprayings. For the interval in days between sprayings of 4-chlorophenoxyacetic acid, in spring and autumn seasons and periods of high humidity, generally the interval is 3~4 days; in early spring when temperatures are low, every 5~6 days. Generally, when in the previous spraying you can see the flowers wilting and the fruits beginning to swell and set, then spray the next time, so that repeated spraying can be avoided. If consecutive cloudy and rainy days occur, wait until the weather clears before spraying; spraying already-open tomato flowers again is also effective.
4. Field management after flower spraying
In order to improve economic benefits, promptly remove inferior fruits with no value or low value (diseased fruits, deformed fruits, cracked fruits, small fruits) during the young fruit stage. Because some tomato varieties have strong growth vigor and fruit-setting ability, such as FA-189, FA-516, Haoweisite, Beiying, FA-1420 from abroad, and the Zheza and Ouxiu series from China, after treatment with 4-chlorophenoxyacetic acid, sometimes a single truss sets too many fruits, so appropriate fruit thinning should be adopted. For plants in normal growth condition, generally leave 2-3 fruits on the first truss, and thereafter leave 3-4 per truss, at most 5; do not let a single truss set too many fruits. It is required that every truss can set fruit, and especially for each truss, the fruits are required to be uniform in size. When a truss has already set 3-4 small fruits, the flowers or small fruits that open afterward must be removed promptly. In short, all harvested fruits are required to be high-quality commercial fruits of uniform size.