What are the agricultural control measures for rice pests?
In recent years, as the severity of rice pest outbreaks has continued to increase, the use of some highly toxic pesticides with large residual amounts on rice has also gradually increased, which has brought hidden dangers to rice safety. In response to this situation, starting in 2004, the author purposefully carried out agricultural control research in demonstration areas. Through two years of practice, the results showed that: agricultural measures applied to rice pest control have unique and superior effects compared with chemical pesticide control, biological control and physical-mechanical control, and have played a positive role in improving the control effect on rice pests and ensuring high and stable rice yields. Several agricultural measures are described below.
1 Rational fertilization
Fertilization can improve the nutritional conditions of crops, enhance the insect resistance of crops, increase the total volume of crops, reduce the degree of loss to crops caused by pests, promote crop growth and development, accelerate the healing of insect wounds, improve soil properties, worsen the living conditions of soil pests, and directly kill pests. If, when fertilizing rice, sufficient base fertilizer is applied, seedling fertilizer is applied early, and topdressing is applied appropriately, it can promote early growth and rapid development of rice, with tillering and heading neat and uniform, enabling early rice to avoid the damage of the second generation of the second-generation striped stem borer. Applying silicate fertilizer to rice can promote firm rice stems and reduce the damage of stem borers. In years when the rice leaf roller occurs severely, rational fertilization can prevent excessive early growth and vigorous growth of rice and prevent late-season delayed ripening due to excessive greenness, which has a good effect on reducing pest damage. If too much nitrogen fertilizer is applied to paddy fields, or applied too late, it often causes the rice leaves to be tender and green, with rows closed and shaded, thereby attracting severe damage from stem borers, rice leaf rollers, leafhoppers and planthoppers.
In 2005, when the fifth (3rd) generation of the rice leaf roller broke out in Mingguang City, the author compared the damage of the rice leaf roller in fields where formula fertilization was carried out by the soil and fertilizer station and in fields where farmers used their own customary fertilization. It was found that the damage in formula-fertilized fields was significantly lower than in conventionally fertilized fields. In formula-fertilized fields, the highest leaf-rolling rate was 27.6%, the average leaf-rolling rate was 12.8%, the highest number of larvae per 100 hills was 410, and the average was 185, while in conventionally fertilized fields the highest leaf-rolling rate was 41.3%, the average was 23.9%, the highest number of larvae per 100 hills was 660, and the average was 290. Therefore, timely and rational fertilization, with attention to the combination of cyanide, phosphorus and potassium, is of great significance in reducing the damage of rice pests.
2 Rational close planting
Close planting is an important agricultural measure for achieving high and stable crop yields. Rational close planting can reduce the waste of nutrients caused by ineffective tillering of rice, make plants develop robustly, with neat heading, and greatly improve the resistance of rice to pests, especially reducing the damage of stem borers. If planting is too dense, it can cause excessive growth of rice plants, thin and weak stems, poor root systems, and create a relatively high humidity in the field microclimate with insufficient light, creating favorable conditions for the occurrence of pests such as stem borers and rice planthoppers; moreover, excessive close planting causes early row closure, which also brings difficulties to chemical pest control, and if rice lodging occurs, chemical pest control will be even more difficult.
3 Deep plowing and soil improvement
Plowing the soil can turn the original underground pests to the soil surface and turn aboveground pests deep into the soil layer, causing a large number of underground pests to die and preventing surface pests from emerging from the soil; in addition, plowing weeds into the soil can cut off the food supply of pests and can also eliminate pests and eggs parasitic on weeds; deep plowing can also cause some pests to be killed by agricultural machinery or have their nests and pupal chambers destroyed, thereby increasing the mortality rate. For example, the larvae of the rice weevil and the rice root leaf beetle spend their entire life period under the soil feeding on rice roots, and cannot survive away from the soil; the second-generation striped stem borer and the third-generation striped stem borer overwinter as larvae in rice stubble below the soil surface. For these pests, changing the soil environmental conditions will affect their growth, development and survival.
4 Selection of improved varieties
The insect resistance of rice varieties generally manifests as non-preference and tolerance. Before sowing seeds, promptly remove mixed weed seeds and insect-carrying seeds, and select plump, uniform, disease- and pest-free improved seeds for sowing, which can ensure full and strong seedlings, neat growth and rapid development. Studies have shown that in paddy fields where selected rice seeds have a purity of over 90%, the heading duration is only about 9 d, and the rate of white heads damaged by stem borers is about 0.4%; in paddy fields with a purity of about 60%, the heading duration is about 32 d, and the white head rate is about 8%; in paddy fields with a purity below 50%, the heading duration is about 33 d, and the white head rate is as high as about 15%. The reason is that low seed purity makes rice growth uneven, thereby prolonging the damage period of stem borers.
5 Timely irrigation and drainage
Irrigation and drainage can rapidly change the environmental conditions in the field and often achieve significant control effects on many rice pests. For example, when the overwintering third-generation striped stem borer larvae are about to pupate, timely irrigation can cut off their oxygen supply and kill them in large numbers. The second-generation striped stem borer mostly pupates in rice bases or leaf sheaths not far above the water surface; when the larvae are mature and pupating, draining the field water to lower the pupation position, then irrigating with 20 cm of water to soak the field, has a good effect on killing stem borers. Draining and drying the field during the occurrence period of rice planthoppers to reduce field humidity can effectively suppress the occurrence of rice planthoppers and reduce the degree of damage.
6 Cropping system
A rational cropping system can artificially control the occurrence and damage of pests. For example, rational crop rotation and stubble changing are not only beneficial to rice growth and enhance insect resistance, but also have an inhibitory effect on pests with a single feeding habit and weak activity ability, and can even achieve the purpose of direct elimination. For example, some areas of Mingguang City practice rice-wheat rotation, which effectively suppresses the occurrence of rice stem borers; compared with fields planted with only one season of rice, the degree of stem borer occurrence is significantly reduced.
7 Weed control
Weeds are places where many rice pests reproduce, spread and proliferate. First, weeds are transitional bridges for pests; many pests live on weeds before rice sowing or after harvest, and only later migrate to rice to cause damage. For example, before rice is planted, the large stem borer first lives on grasses and other weeds in the field or at the field edges. Second, weeds are also overwintering sites for pests. For example, stem borers, leafhoppers and rice thrips all partially, or even entirely, overwinter on weeds. In addition, many weeds are places that provide nectar for certain pests. For example, adult rice skipper butterflies feed on the nectar of weeds such as yellow vitex and wild chrysanthemum. Therefore, eliminating weeds and changing plant communities is one of the important measures for preventing and eliminating rice pests.