Occurrence regularity and Control of Cotton pests under drip Irrigation

With the large-scale application of drip irrigation cotton technology, its irrigation mode has been improved, and it transports water and nutrients uniformly and continuously to the vicinity of cotton root system, and the matching techniques of cotton cultivation are changed. as a result, the ecological environment and occurrence law of pests in cotton field have changed accordingly. Therefore, it is necessary to find out the occurrence regularity and control measures of cotton pests under drip irrigation under plastic film, so as to ensure a sustained and balanced yield increase of cotton.

1. Cotton bollworm

1. Occurrence degree

Compared with previous years, moderate bias occurred in 2005, in which the first and second generation occurred moderately, and the third generation occurred slightly, which was the first time in Xinhu reclamation area.

two。 Cause of occurrence

The temperature and humidity related to the change of ① and irrigation mode are the main factors affecting the growth and development of cotton bollworm. Compared with flooded irrigation, cotton drip irrigation under plastic film is characterized by less irrigation volume, shorter irrigation cycle, more irrigation times and shallower water infiltration depth, thus changing the ecological microclimate of cotton field.

The suitable temperature is 2528 ℃ and the relative humidity is 70% 80%. Drip irrigation under plastic film can always maintain the moist state of cotton field, which is beneficial to the pupation of mature larvae in 5 cm soil of cotton field. The investigation of pupation of the first and second generation in the field shows that the pupation of Helicoverpa armigera in the soil near the dry and branch pipes is more than that in other parts of the cotton field.

② is related to farming system, according to the data, the overwintering mortality rate of autumn ploughing and winter pupae filling is more than 60%; the overwintering mortality rate of no ploughing and no pupae is only 6%, the difference is 10 times, the soil water content is 30%, and the overwintering mortality of pupae can reach 70% to 90%.

③ is related to cultivation and management. increasing the number of seedlings in a certain range of density is an important means to achieve high yield, but it is dense and uneven, which leads to inconsistency in cotton management, such as water and fertilizer management, chemical regulation, topping sooner or later, and so on, which provides good conditions for the occurrence of cotton bollworm.

④ is related to climate warming in recent years, the temperature in autumn and winter is obviously higher than that in previous years, the temperature in spring rises faster, the opening period of spring is 5-7 days earlier than that of previous years, and the first frost period is 9 days later than that of previous years and 13 days later than that of 2004, which makes the occurrence of Helicoverpa armigera changed greatly, with large overwintering base, low mortality and early emergence of overwintering generation.

⑤ related to control methods the irrigation area in autumn and winter has been reduced by less than 30% year by year, resulting in a large overwintering base and low mortality, and some effective agricultural control techniques have not been implemented. For example, digging ridges and removing pupae in autumn and spring is the best control measure to eliminate the overwintering generation, and corn trapping belt is only planted without prevention.

⑥ is related to the investigation of insect pests in the field. Not enough attention has been paid to the investigation of insect situation in cotton fields, and it is too late to control insect pests in cotton fields.

⑦ is related to geographical environment. The occurrence of overwintering adults is related to the surrounding environment of cotton fields. According to the investigation, the occurrence of overwintering adults in 2005 is heavy, one is cotton fields near sand bags, the other is cotton fields on sandy land, the third is cotton fields with poplar forest belts but no winter irrigation, and the fourth is cotton fields with serious damage caused by cotton bollworm last year.

⑧ is related to dripping emergence in general cotton field sowing ends on April 18 and dripping emergence ends on April 25. During the sowing period, the wind is strong in spring, the soil moisture runs fast, the soil relative humidity is small, and the pupa overwinters in a 7-8 cm soil chamber, while the 8-10 cm soil is basically a dry soil layer. Dripping increases the soil moisture, which is beneficial to pupation in advance.

(3) occurrence regularity and harm characteristics.

In the overwintering generation of ①, female Helicoverpa armigera and male Helicoverpa armigera were trapped on May 11 and May 15, respectively. The female was 3 days later than the male, and the male / female ratio was 1 ∶ 2.4.The Eclosion lasted 21 days from May 11 to 30, and the peak period of Eclosion lasted 6 days.

The first generation of ② eggs: the peak period was May 25-30 and lasted for 6 days. Larvae: from May 22 to June 15, it lasted 25 days. In the early stage, it mainly harmed the top and tender leaves of cotton, resulting in many heads of cotton, while in the later stage, it mainly harmed cotton buds and caused a large number of inner buds to fall off. Pupa: the calendar period is from July 17 to 31, lasting 15 days. Adults: the Eclosion period lasted 34 days from June 7 to July 10, and the peak period lasted 16 days from June 18 to July 3, with a male-female ratio of 1 ∶ 1.3. From June 11 to 20, 10 poplar branches and one insecticidal lamp were placed in each company to observe the occurrence of adults. On June 14, 70% of the company lured adults. Since June 21, workers have placed a large number of poplar handlebars, and all insecticidal lights have been turned on to trap and kill. From June 22nd to July 7th, a total of 177067 poplar trees have been placed, with an average of 11804 poplar trees per day.

The oviposition in cotton field was observed on June 11. It took 2.5-3 days from egg to first instar larva hatching. At that time, the average temperature was 26.5 ℃, and the highest was 33.4 ℃. After the emergence of cotton bollworm, it takes 3-4 days for adults to mate and lay eggs.

The second generation eggs of ③ lasted for 10 days from June 25th to July 4th. It was found that the number of eggs laid by one hundred plants was 60.8 at 11:00 on June 25th. Larvae: it lasted 22 days from June 28 to July 19, mainly harming cotton buds, causing a large number of buds to fall off, causing long and serious damage. Pupa: the calendar period is from July 17 to 31, lasting 15 days. Eclosion takes 6-9 days. Adults: Eclosion lasted 24 days from July 25 to August 17, and the peak period lasted 13 days from July 27 to August 7, with a male-female ratio of 1 ∶ 1.4.

The eggs of the third generation of ④ lasted for 4 days from July 28 to 31. Bt powder was sprayed during the peak spawning period from July 24 to 31, and the eggs were observed. 8 eggs laid on July 26th to July 29th did not hatch. Cotton fields without spraying Bt powder laid eggs on the morning of July 27th and hatched on July 28th morning. Larvae: it lasted 24 days from July 30 to August 22, and the field investigation did little harm to cotton. Adults: Eclosion lasted 18 days from August 25 to September 11, the peak period was not obvious, and the occurrence regularity was very irregular. From the observation points, 27 females were attracted from August 25 to September 11 and September 22-26, and 10 males were attracted in September 6-9, September 24-26, 7 days, with a male-to-female ratio of 1 ∶.

4. Prevention and control technology

① strengthens the field pest investigation. Before the initial period of adult emergence, each company carries out poplar handles and insecticidal lamps to monitor the peak period of adult emergence (to determine the time of placing poplars), and special attention should be paid to egg investigation (determining the time of biological control). The combination of fixed-point investigation and non-fixed-point investigation can be combined with regular investigation and irregular investigation to form a measuring and forecasting network with the forecasting station as the center and each company as the forecasting point, so as to provide a reliable basis for scientific prevention.

② agricultural control is the most economical and effective measure in the control of cotton bollworm. For autumn ploughing and winter irrigation, it is necessary to increase winter irrigation. In early spring, ridges were comprehensively carried out to remove pupae, especially for heavy cotton fields, corn fields and forest belts, so as to depress the population base of overwintering generations. Early sowing and early management, comprehensive realization of April seedlings, advance the growth process, the current ploughing destroys the pupa chamber, pulls out field weeds, especially abutilon, and makes chemical control of Elaeagnus angustifolia trees in the edge forest. Strengthen the management of each growth stage of cotton field to achieve uniform water, fertilizer and seedlings. Reasonable regulation and control of water and fertilizer to achieve balanced cotton growth, prevent prosperous growth and late maturity, and achieve timely and early topping and pruning. At the same time, during the peak period of adult Eclosion, uniform spraying of potassium dihydrogen phosphate of 150g / 667 square meters is conducive to repelling oviposition, promoting egg calcification, reducing the number of eggs laid in cotton fields and reducing the hatching rate of effective eggs.

③ trapping and killing control. In order to plant and manage the corn trap belt well and adopt the large net format, in order to sow and drip seedlings synchronously with cotton, the corn trap belt must be prevented in time during the peak spawning period. In the initial stage of adults, poplar handles and insecticidal lamps should be placed in sufficient quantity, and the method and position should be correct.

④ biological control. Grasp the period of prevention and control, and achieve scientific and rational prevention and control. Bt powder was sprayed evenly within 2-3 days during the peak spawning period to avoid strong light. It can be mixed with other insecticides in the morning and evening, and biological agents were used before the 3rd instar larvae. The main control object is the first generation Helicoverpa armigera.

Timely forecast, find out the insect situation, do not blindly use drugs; chemical control of the first generation, the number of eggs per 100 plants is 810 or 2 larvae, the second generation can not be chemical control; improve the quality of control; the amount of spray should be sufficient, the amount of liquid should not be less than 30 kg / 667 square meters. Investigate the prevention effect, and those with poor effect should make up in time.

Chemical control of ⑤. The use of broad-spectrum pesticides is prohibited.

⑥ captures larvae and controls pupae artificially.

Cotton leaf mite and cotton aphid

1. Red spider is a perennial pest. It is the key to make a good forecast, observe frequently, spot the occurrence and cure thoroughly, and insert a good mark. Acaricides are used alternately throughout the process.

two。 Cotton aphid is a phased pest, biological control is the key, sweeping the ground, the edge of the ground.

Three new pests in cotton field

1. Truncated spider mites were mainly Turkestan spider mites in Xinhu reclamation area, but a large number of truncated spider mites occurred in cotton fields in 2005, and the harmful symptoms were not obvious and difficult to find.

two。 The double-spotted firefly beetle, which mainly harmed cereal crops in the past, has now entered the cotton field to harm cotton. Adults are clustered and belong to chewing mouthparts, which mainly feed on cotton leaves to form leaf holes and withered spots, which affect the normal growth of cotton leaves.

3. The yellow-bellied lamp moth, the adult has black spots on the forewings, the abdomen is yellow on the back, the abaxial and ventral sides of the mature larvae are yellow, and there are dark longitudinal bands on the back. The larvae are mainly distributed in the weeds around the cotton field near the sandbag. Cotton is harmful to cotton field when it emerges, and the larvae are clustered in cotton cotyledons, true leaves, centers and young stems, resulting in lack of seedlings and broken ridges, and internal absorption insecticides such as monocrotophos are selected to control them.