Master the Battle Against Whitefly: Expert Strategies for Thriving Cotton Fields

Whitefly adults and nymphs generally feed on the lower side of the leaves by sucking the sap from the underside and weakening the plants. This results in low fruiting with reduced yield. These excrete large amounts of honeydew which encourages sooty mold growth, thereby, adversely affecting the process of photosynthesis. The pest causes lint discoloration and stickiness. It also acts as a vector of the cotton leaf curl virus which adversely impacts the growth of cotton crops.

Whitefly has a very wide host range including vegetable crops and different species of weeds. Management of whiteflies requires a year-round Integrated Pest Management (IPM) approach as these are highly mobile, and can quickly build resistance to many insecticides and numbers rapidly. It may expand if natural enemies are reduced by insecticidal sprays.

Alternate Host Species in the Off-Season

Whiteflies pass the winter on weeds and alternate host plants. Thus, the removal of hosts and maintaining a host-free period during this time will reduce the inoculum for the next season. Control weeds in/near the farm all year round. Favoured host species include bhindi, mung, arhar, castor, dhaincha, kangi buti, peeli buti, tandla, gutputana, datura, makoh, congress grass, cucurbits, volunteer cotton, etc. Destruction of crop residue after harvest and field sanitation will help in reducing the inoculum/carryover of whiteflies to the next season's crop.

Management of Whiteflies

For the implementation of an effective management strategy in cotton crop following points should be considered:

Survey and Surveillance on Alternate Host Crops: Surveys should be carried out from February onwards. Management of whiteflies using various chemical and non-chemical methods on these crops must be done, so that their carryover to cotton crops is reduced.

Selection of Suitable Field for Cotton Plantation: Avoid planting cotton near orchards. Also, do not engage with cotton planting near/in other host crops of whitefly viz. brinjal, tomato, cucurbits, moong, etc. This will help in early population build-up in cotton crops. So, prefer to grow desi cotton varieties in fields having a higher incidence of whiteflies in earlier years.

Practice Clean Cultivation: Whitefly passes the winter on various weed species and alternate host plants, thus, maintaining a host-free period during this time. It will reduce the inoculum for the next season. Destruction of crop residue after harvest and field sanitation will help in mitigating the inoculum/carryover of whiteflies to the next season's crop.  

Maintain a Healthy Crop: To uphold a healthy crop and sow the recommended varieties/hybrids of cotton before May 15, the crop is more prone to attack by whiteflies. Hence, avoid moisture stress by following the proper irrigation schedule as it increases the severity of whiteflies.

Encourage Beneficial Insects: Good insect populations play a dominant role in maintaining ecological balance in nature. If their numbers and habitats are disrupted, pest populations build faster. The presence of natural enemies of whitefly such as ladybird beetles, encarsia, chrysopa, minute pirate bugs, spiders, etc. is important in the field which is sometimes overlooked and needs to be promoted and popularized among the farmers. The insects can be encouraged by using IPM approaches including sprays based on economic threshold levels. Thus, go for a spray of neem-based insecticides like homemade extract, achook, nimbecidine, etc in the initial crop stage of cotton.

The use of eco-friendly ways like the yellow sticky traps @40 traps per acre should be encouraged. Moreover, for conserving these natural enemies, there is a need for the careful selection of insecticides. Avoid early-season use of broad-spectrum insecticides, particularly synthetic pyrethroids and organophosphates group insecticides.

Practice Insecticide Resistance Management Strategies: Due to its fast multiplication rate, whiteflies can develop resistance to insecticides. Follow Economic Threshold Levels (ETL) (6 adults/leaf) to get effective control of the whitefly. By doing so, we can minimize the number of sprays/chemicals as well as it helps delay the development of resistance. Do not repeat applications of the same insecticides or the products with same mode of action. Also, avoid applying more than the maximum number of applications recommended for a particular chemical. With this, always follow label directions. The knowledge of the registered products can help to improve management decisions.

Insecticides recommended by PAU, Ludhiana:

Decision-making in the selection of insecticide:

1. If the adult whitefly population is higher on cotton, then use any adulticide followed by a nymphicide viz. pyriproxyfen 10EC/ spiromesifen 22.9 SC after 8-10 days of the first spray.

2. If the nymphal population of whitefly is more in the field, then spray pyriproxyfen 10 EC/ spiromesifen 22.9 SC followed by adulticide viz. ethion 50EC / afidopyropen 50 DC after 8-10 days of the first spray.

3. If both whitefly adult and nymphal populations are more in the field and the crop canopy becomes dense (after the first fortnight of August) spray diafenthiuron 50 WP.

4. Use economic threshold levels (6 whitefly adults/leaf) and clean cultivation to avoid unnecessary sprays. Conduct surveillance and monitoring for the whitefly population weekly right from the beginning. Randomly sample 10-20 plants per field and count for whitefly adults on fully formed upper 3 leaves/ plant before 10.00 AM.

5. At the beginning of crop season on the appearance of a whitefly, the first spray of cimetidine or Achook @1 liter per acre or homemade neem extract @ 1200 ml/acre should be given. Also, use yellow sticky traps @ 40 traps per acre in June- July.

6. Avoid repeated applications of the same insecticide. Go for alternate use of chemicals and do not apply it more than twice in a crop season.