Insect pest management in cotton文档格式.docx

1、WhitefliesMinor pests ThripsSucking bugsBeetlesMinor caterpillar pestsOther pestsUntil the introduction of genetically modified （GM） cotton, the main insect pests of cotton were the larvae of Helicoverpa armigera and H.punctigera. These pests were generally controlled with synthetic insecticides, wh

2、ich also controlled the majority of other cotton pests.Now, over 90% of the cotton area is planted with varieties that have been genetically modified to produce highly specific toxins that kill Helicoverpa larvae and most other caterpillar pests when they feed on the cotton plant. However, sucking i

3、nsects may require more management on Bt cotton compared to conventional cotton.The genes used to produce the toxin in GM cotton are obtained from a naturally occurring bacterium calledBacillus thuringiensis（commonly known as Bt）. Insect-resistant or genetically modified cotton is often called Bt co

4、tton. The introduction of Bt cotton has resulted in a significant reduction of insecticide use by growers.A resistance managementplan （RMP） is essential to ensure that these valuabletraits remain effective. Visit the Cotton Cooperative Research Centre （CRC） website for more information.Major pestsHe

5、licoverpaHelicoverpa remains a major pest on conventional （non-genetically modified） cotton. The two species - Helicoverpa armigera and H.punctigera - are very similar in both appearance and the damage they cause to cotton. However, correct identification of the species is important because H.armige

6、ra has developed high levels of resistance to insecticides.Species composition in the crop will be influenced by the time of year and location. In temperate regions, the majority of the H.armigera population overwinter from mid-March onwards and emerge during September/October. Helicoverpa punctiger

7、a is usually the dominant species through September, but seasonal variation can lead to early infestations of H.armigera in some years, particularly in northern districts.Helicoverpaadults are mobile and produce large numbers of eggs,leading to rapid build-up of populations under favourable conditio

8、ns. Survival is influenced by the number of predators present as well as other mortality factors such as wind, rainfall and temperature extremes.DamageIn cotton, all stages of plant growth may be attacked but reproductive tissue is preferred. Seedlings can be tipped out when terminal buds are eaten.

9、 Chewing damage to squares and small bolls may cause them to shed, and chewing damage to maturing bollsmay prevent normal development and can lead to secondary fungal infections such as boll rot.Monitoring and thresholdsRegular monitoring of the crop for the presence of larvae and/or damage is neces

10、sary in order to make timely decisions on control. This is especially important when targeting small and possibly insecticide-resistant larvae.Visual sampling is the recommended method. Check at least 30 plants or 3 separate metres of row for every 50ha （larger samples give more accurate estimates）.

11、 Eggs are notnecessarily a good basis for thresholds as not all hatch and very small larvae have high mortality rates. Assess beneficial insect numbers and note parasitised eggs and larvae.When making pest management decisions in cotton, insect numbers alone may not be sufficient. Plant monitoring （

12、fruit load, yield and maturity） assists in decision making when pest levels are just below threshold or when there are combinations of pests.Thresholds for conventional cotton depend on crop stage and are:Seedling to flowering:2larvae/m or 1larvae （8mm）/m.Flowering to cut-out:mm）/m or 5brown eggs/m.

13、Cut-out:15% open bolls - 315%-40% open bolls:5larvae/m or 2Thresholds for Bollgard II cotton are the same for the entire season at 23mm）/m in 2consecutive checks or 1ResistanceHelicoverpa armigera developed resistance against most insecticides in the late 1990s. However, with the introduction of gen

14、etically modified cotton, biopesticides and more selective insecticides, insecticide resistance to older chemistry has decreased in recent years. Helicoverpa punctigera has no known resistance to any insecticides but the use of more selective options is encouraged to help preserve natural enemies.In

15、 order to prevent insecticide resistance, the cotton industry has developed the Insecticide Resistance Management Strategy （IRMS）. This strategy is reviewed annually to delay development of resistance of H. armigera to conventional insecticides. The core IRMS principles include:rotation between chem

16、ical groups with different modes of actionlimiting the time period during which an insecticide can be usedlimiting the number of applications of one particular insecticide.Visit the Cotton Cooperative Research Centre （CRC） website for more information.Cultural controlPost-harvest cultivation （pupae

17、busting） to reduce the overwintering stage of Helicoverpa is one of the most important cultural control practices available. Cultivation to a depth of at least 10cm will damage or disturb pupae, seal their emergence tunnels and trap emerging moths. Cultivation also leaves survivors open to attack by

18、 birds, mice, earwigs, and wasp parasites.Natural enemiesBeneficial insectscan affect allHelicoverpa life stages:PredatorsEgg:red and blue beetle,damsel bug,green lacewing,brown lacewing,nightstalking spiders, andvarious antsLarvae: glossy, brown and predatory shield bugs,bigeyed bug,assassin bug,co

19、mmon brown earwig, andspidersPupae: common brown earwigand wireworm larvaeMoth: spidersParasitoids Trichogramma spp. and Telenomus spp. Microplitis demolitorand tachinid flies banded caterpillar parasiteBack to topThetwo-spotted mite （Tetranychus urticae） is the most numerous mite species on cotton.

20、 Other speciesthat may occur are bean spider miteand strawberry spider mite. Mites live on the underside of leaves and are difficult targets for aerial sprays. Mites prefer more mature leaves and the highest populations are usually found near the top of the plant on main stem nodes 3-5 below the ter

21、minal. Heavy mite infestations on cotton can originate from adjoining fields of early sown corn from where they are carried by air currents.Mite infestations in seedling cotton rarely justify control but may be a useful indicator of potential problems and should be monitored closely.The first sign o

22、f damage is bronzing of the upper leaf surface near the petiole or leaf fold. As numbers increase, theleaves turn red and become covered in fine webbing, and affected leaves may dry and fall off. High mite populations can significantly affect yield and quality of cotton. The earlier in the season th

23、at infestations develop, the greater the potential of yield loss and quality downgrades.Start sampling at seedling emergence andcontinue at least weekly. At low numbers, mites are difficult to find. Mites are often too numerous to count individually, so infestations can be rated on a presence/absenc

24、e system. In Australia, the leaves on the third to fifth main stem node （down from the plant terminal） are the best to sample.The general threshold for mites for most of the growing season is 30% of plants infected. The threshold depends more on when mite populations begin to increase and how quickl

25、y they increase rather than the number of mites. To estimate the percentage of yield reduction caused by mites, a chart has been developed by the cotton industry for the different cotton growing regions.ManagementUnder Australian conditions, mite populations increase less rapidly on the okra leaf va

26、rieties than broadleaf varieties.Mite infestations increase after the application of some broad-spectrum insecticides for control of other pests.Control weeds within fields and along field boundaries that serve as over-wintering sites for mites.For chemical options to control mites see the latest Co

27、tton CRCs pest management guide.Thrips are the major mite predator in cotton. Others include damsel bug, bigeyed bug,ladybird beetles,brown smudge bug,apple dimpling bug,brown lacewing adults, andtangle web spiders. Mirids （Creonitiades spp）An important sucking insect pest of cotton, mirids are abun

28、dant in cotton from early to mid season and occur throughout the cotton growing regions of Queensland and New South Wales.Green mirids are more common than brown mirids but both cause similar damage.Adults and nymphs feed by piercing plant tissue and releasing a chemical that destroys cells in the f

29、eeding zone, resulting in the following symptoms:localised leaf damageterminal wilting of young plantsdeformity （broom shaped）shedding of squares and small bollsdamage to bolls （up to 15days old） by causing warty growths inside carpel which causes discoloured lintmalformed bolls, delay of maturityreduced lint and fibre quality.Mirids are a very mobile pest and populations can fluctuate rapidly so sampling needs