Prevention & organic management of onion maggots (Delia antique) in cold arid region of Ladakh

Leh, Mar 01, 2016
Leh :
Onion is one of the most market sensitive commodities that create ripples in Ladakh trade. India is the second largest producer of onion after China, with a production about 15 million tonnes. Among all the agricultural products, prices of onions are more volatile than those of the non-farm commodities. Particularly in Ladakh, farmers’ preferences towards selling their produce in the particular market provide us a good amount of information on constraints they face. In Leh, it is grown on 65 hectares of land out of 280 hectares allotted to all kinds of vegetables in Leh. At present, the total requirement of onion in Ladakh is 5400 mt per year but it grows or imports onion to the tune of 1080 mt per year. This gap of 4320 mt may be attributed that the traditional practices with poor weed and insect management under low fertility reduce the tuber yield by 40 per cent. This can only be met using suitably improved production measures over traditional practices for improving onion yield. Utilization of high yielding varieties of any crop especially onion responds only to improved production packages. 

Growing healthy and vigorous crop is an ultimate aim of all farmers because a poor crop simply deprives funds without output. At planting time, it is required to mix nitrogen with side dress at certain intervals until bulbing begins. Onions are sensitive to photoperiod. Long days are favorable to onion production as this enhances leaf development and formation which, in turn, is directly related to bulb size. Early varieties require 13 hours for bulb initiation while late varieties require 16 hours for bulb initiation.

 Generally, onions do not need consistent watering if mulch is used. About one inch of water per week (including rain water) is sufficient. Onions will look healthy even if they are bone dry, be sure to water during drought conditions. Make sure soil is well-drained. Mulch will help retain moisture and stifle weeds. Amongst the vegetables, onion crop is one of them which deserves especial care and is always a victim of several enemies each of which requires specific management strategies.

In addition to this, it thrives well in soils with well-drained, loose, and rich in nitrogen and requires full sun for its better development. As onion is a heavy feeder and need constant nourishment to produce big bulbs. Amongst the important insects (like head borders, onion thrips, onion maggots, mites, cut worms), maggots pose a serious threat to onion crop in temperate parts of India like Ladakh. 

Mode of damage 

Onion maggot (Delia antique) is a serious pest of onion in Ladakh region, similar to house flies which lay their eggs in groups on leaves, and shoots of host plant leaves and larva enters into soil and damage disc portion of onion bulb. The eggs are white and elongated. The larvae are white and cylindrical and hatch in three to eight days. More than fifty maggots may feed on one bulb. Infested plants turn yellowish brown and finally dry up and affected bulbs rot in storage as infestation leads to secondary infection. Maggots overwinter as pupae in soil. Adult emerge around mid-May to late June after which females start laying eggs at the base of plants. Eggs will hatch in three to eight days. 

Maggots crawl beneath the leaf sheath and enter bulbs for two to three weeks, after weeks of feeding they pupate and the next generation of adults emerges 3-4 weeks later. There are usually 3 generations per year, the 1st being the largest and often most damaging. A complete cycle takes about 45 to 65 days.       
It is likely to break just below the rooting stem of the seedling. Maggots burrow into developing onions, killing young plants and hollowing out older plants seedling dies before the maggots are fully-grown. 
Damage can be determined by pulling the plants and observing the maggot’s infestation. It can cause 100 percent losses in untreated onion fields. But growers need more options for their control than they currently have. Possible ways of preventing onion maggots are as under:

Organic Control and prevention Methods

•    Based on the activity of onion maggot adults in onion fields, strategies target on first-flight adults along field edges rather than across entire fields, especially in fields that border woods. As first-flight male and female adult activity is greater along onion field edges and was especially high along edges bordering 

•    Use of yellow sticky traps when onion adult flies emerge. 

•    Rotate crop. Grow onions and related plants in a different spot from previous seasons.

•    An effective way to control laying eggs on host crops is to use cover seedlings and plants with floating row covers. 

•    Deep ploughing to destroy pupating larvae, remove plant debris, remove all onions and culls. 

•    White onion varieties are prone to onion maggot attack. Grow red onions and Japanese bunching onions.

•    Sprinkle onion planted areas with ground cayenne pepper, ginger, dill or chili powder to repel females and prevent them from laying eggs.
•    If a small area is infected with onion maggots, change the soil. If the area is too large, drench the area.

•    Use of insect parasitic nematodes that control onion maggots in cool, wet weather.

•    Sand, wood ash and diatomaceous earth can be applied to the base of plants to deter adult flies and onion maggots.

•    Growing onions in raised beds with fresh soil or in containers is a good idea as onion maggots love poorly drained soil.

•    Cover emerging onion crop with a fine mesh netting. Seal it by mounding soil around the edges. 

•    Keep mulch away because the insects like decaying organic matter, and make sure you completely harvest your onions as the season progresses.

•    Delayed weeding control at 2-4 leaf stage decrease number of maggot as it finds difficulty in identifying suitable hosts.  

•    Increase vegetation diversity by intercropping. As intercropping allows for greater plant diversity, which reduces pests. Possible intercropping of onion.

This article is written by  M.S. Raghuvanshi, Jigmat Stanzin, Stanzin Landol under Regional Research Station, Central Arid Zone Research Institute, Leh-Ladakh and  J.C. Tewari  and R.K. Bhatt under Central Arid Zone Research Institute, Jodhpur.