Determination of an Economically Optimal Organic Control of Onion Maggots in Allium Crops

Final Report for FNC04-497

Project Type: Farmer/Rancher
Funds awarded in 2004: $1,405.00
Projected End Date: 12/31/2005
Matching Non-Federal Funds: $245.00
Region: North Central
State: Illinois
Project Coordinator:
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Project Information


Our farm is currently approximately 17 acres. Lisa does most of the hands-on work, Eric does most of the mechanical work, and son Maxwell (age 11) puts in a fair amount of time choring animals and helping with harvest and weeding. Maxwell has expressed serious interest in taking over the farm at some point. Our financial goal is to make the farm profitable enough that he can join us as a partner when he is old enough. Our current outlets are mainly farmers market, on-farm sales, and CSA (Community Supported Agriculture). These are all about equal parts of our farm income. We try to do a lot of outreach to various school groups, environment groups, etc. about sustainable agriculture and organic farming methods. We have also organized organic community gardens for a local homeless/transitional housing ministry.

We have two acres in vegetable production. This is split into four fields and crops are rotated on a broad basis through this. Our rotations are: 1) allium crops, 2) sweet corn and squash, 3) beans and peas, 4) all other vegetables and annual flowers. Currently, we plant clovers or vetches into the allium field immediately following harvest. Sweet corn is under seeded with clover. We intensively plant vegetables – as soon as they are harvested, new ones take their place, with an application of compost or organic fertilizer. We have two acres in tree fruit and two acres in small fruits. We hay crop between the rows of younger trees. Animals are allowed to graze among mature trees. We have four acres in row crop. Our current rotation is through four fields 1) wheat and flax under seeded with clovers, 2) calypso, kidney, or other bean, 3) corn, 4) soybeans. When conditions are favorable, the corn is under seeded with nitrogen fixers after the first couple of tillages. Beans and wheat are marketed direct to consumers through farmers markets, CSA, and on-farm sales. Corn and soy are used here for animal feed. The balance of our area is either grass/tree buffers or rotationally grazed. We raise chickens (meat and eggs), geese, ducks, heritage turkeys, sheep, goats (dairy), and veal calves. We also keep two beehives for fruit pollination. Putting honey on our roadside sign is a surefire way to draw customers in so we may add more hives.

We do have one acre planted into forest trees, which will hopefully start growing this year. We also keep two beehives for fruit pollination. Putting honey on our roadside sign is a surefire way to draw customers in so we may add more hives.

The main sustainable practice from this project is to hopefully get away from floating row covers, which are decidedly unsustainable.

Several organic methods to control onion fly (Delia antiqua), damage were tested. The three methods that showed the most promise were spraying of parasitic nematodes (S. feltiae), application of organic cinnamon, and application of kaolin clay (Surround). Trap crops of mature leeks showed an apparent effect, however none of the trap crops became infested, so this was an anomaly. This year had an abnormally low incidence of early season damage, so these results are not conclusive. It was seen, at the small scale done on this farm, in this year that these methods were not particularly economically feasible, mainly due to sprayer difficulties and associated labor costs. It should be emphasized that on a larger scale they may be extrapolated to be practical to organic farmers.

Severe onion fly damage at our farm ranges from 10 to 50 percent of our onion crops. Leeks are typically much higher. Severe damage is defined as damage that impacts marketing. Smaller blemishes are considered mild damage. The flies seem to prefer leeks first, softneck garlics second, and onions third.

Onion flies locate their host both through visual and olfactory cues. Eggs are deposited on the ground near the host plant. It was hoped to deter oviposition through the methods of row cover, cinnamon, mulch, and kaolin clay. Trap crops were tried in one bed in an attempt to concentrate oviposition in one area. Parasitic nematodes were applied to one bed to control the larvae. The expectation was that the control patch would sustain much higher than normal damage due to the oviposition deterrence in other beds.

While important to plant healthy, crop rotation on a small scale is not practical since the flies will travel over 1 km to find allium crops. (Martinson 1988) The previous year’s crop was located to the west of this study by only a hundred feet.

Allium crops, including onions and leeks were planted in 8 separate beds between April 9th and 15th. Each bed included 9 varieties of onions and a mix of two leeks. The varieties, amount planted, and the order they were placed was as follows (from west to east):

Alisa Craig-- 125 (softer, mild yellow onion)
Red Long of Tropea-- 125
Candy-- 125 (hard, sweet, white/yellow onion)
Greek salad-- 91 (red)
Copra-- 91 (yellow storage)
Mars-- 91 (red)
Varsity-- 91 (yellow storage)
Lincoln & King Sieg leek—312
Redwing-- 91 (red)
Scallions-- succession plantings of 14 bunches per week for 6 weeks (evergreen hardy white)

Layout of plantings:

Control(former turkey area)/ Cinnamon spray
Trap crop/ Early season row cover
Mulch/ Control
Parasitic nematodes/ Kaolin clay

Attempts to use heritage turkeys in pens adjacent to the beds as a method for fly control were abandoned in early June when a particularly nasty predator attacked nightly. Heritage turkeys were chosen since they are much more active than either commercial turkeys or chickens. The remaining birds were moved closer to the house.

Similarly, the row cover was abandoned in mid-June (post first generation) after if kept getting ripped and flies were found (of some sort, they were never caught and identified) inside. Additionally, the tops of onions and leeks were getting damaged.

Parasitic nematodes (S. feltiae) were applied twice during the year, once during the first generation of flies, and once during the second cycle.

Kaolin clay was applied as a spray on a weekly basis.

Ground organic cinnamon was applied as a spray on a biweekly basis. The sprayer was cleaned out well between each spraying – a task that took longer than the spraying itself. The cinnamon itself was difficult to get into suspension and clogged the sprayer. Sprinkling it might be a better option.

The mulch used was a layer of partially composted stable shavings and was applied after the first several weedings. (Compost was heated fully to destroy pathogens, but the wood shavings were not fully decomposed).

Trap crops of large over-wintered leeks were planted in early June. These were removed prior to leek harvests in August and were not infested.

The first three onions (Ailsa Craig, Red Long, and Candy) as well as scallions were mainly harvested weekly as fresh onions beginning in late June and marketed with their tops on. Other types of onions were harvested just as the tops were falling over and drying. The dirt was brushed off and they were checked over for damage and allowed to cure in the greenhouse (our only dry covered structure suitable for messy crop storage). Approximately 60 percent of the leeks were harvested before mid-September, and the others were harvested between mid-September and early October.

There was no real difference in the size or quantity of onions harvested from each bed, with the exception of the ‘turkey’ bed. This was due (entirely) to the bed being situated on newly reclaimed pasture – so it was quite a bit trashier and weedier. Onions in this bed were half the size of others. The mulched bed had very slightly larger onions (5 percent) overall.

There was a difference in appearance. The kaolin clay was extremely difficult to wash off the fresh onion greens completely without damaging the tops. They looked clean when wet, but had a film when dry! Onions from the row cover bed had damage to their tops.

Onion maggot damage in onions was predominantly superficial and no live maggots were observed pre-storage. While the first actual maggot seen was in a leek on July 22nd, the number of leeks damaged prior to mid-September was quite small (Table 1).

[Editor’s note: the tables submitted with this project report and the entire report are available on the author’s website at:]

In Table 1, M refers to mild damage. Often, this was just a small hole/nick that may or may not have been caused by an onion maggot. This could be easily ignored or stripped away with one layer of skin. S refers to severe damage. This was definitely due to onion maggots and would affect several layers of the onions or leeks. This type of damage is also a problem since the maggots migrate to different locations between layers so a hole that looked relatively small could not be ignored. Mild damage also is more apparent in fresh onions than dried.

Post storage damage and late season leek damage were fairly extensive. Post harvest onion damage was not quantified since the onions were inspected before going in to storage. Much of the damage was sustained several weeks after harvest so it was assumed that it was new egg laying activity.

Costs incurred in treating the area were:
Parasitic Nematodes: These were sprayed twice at a cost of $45 for each treatment plus two hours of labor. ($16)

Mulch: This was on-hand at the farm. The cost was two hours of labor ($16) since it was applied post planting and needed to be placed carefully. Weed pressure in that area of the field was high early on, so the mulch was unable to help much and was disturbed when weeding was done. In a more controlled weed environment, the mulch could go on sooner.

Trap Crop: No additional cost.

The cost of the heritage turkey poults was $48.60. Portable coops were on hand and are part of the general farm operation. However, due to predation in the field, most of these were lost.

Cinnamon: Two pounds of organic cinnamon were used, plus eight hours of labor to spray. ($72) The amount of cinnamon could probably have been reduced.

Row Cover: Abandoned. The labor for this farm would amount to about one extra hour per week since onion harvest occur twice per week, but expectation would be zero damage with some deficiencies in fresh appearance of leaves and possibly size.

Control: No extra cost.

Kaolin clay (Surround): This was sprayed weekly. The costs were one bag of clay ($30) plus 16 hours of work ($128). Spraying frequency could be reduced if a spreader sticker was used, or drip irrigation instead of overhead in a dry season. Stickers would make cleaning of onion greens more difficult but would be suitable for leeks and dried onions.

Table 2 summarizes these results. The extra crop harvested relative to control is shown. Because early season damage was so low, and the late season leek damage is more typical here in a given year, an extrapolation is shown that assumes early season damage to everything would occur that is equal to late season damage in these beds. The figure used is 312 leeks and 739 total onions.

Typically, organic onions here sell for $1.25 per pound and leeks for between $1 and $1.50 a piece. Average onion size this year was around ½ pound.

This year’s early season allium crop sustained much lower than normal damage in both the control and experimental test plots. This may be due to the weather, especially the dryness and fluctuating temperatures in spring/early summer. Early season rain totals were below normal, with rains frequently totaling less than .2 inches at time. This was interspersed with deluges (over 7 inches of rain received over the third week in July). Applications of control methods may have been negated or delayed due to these heavy rains.

The applications of Surround, cinnamon, and to a lesser degree, parasitic nematodes, seemed to protect leeks. However, in absence of choice, onion flies will lay eggs despite deterrence measures, and the highest damage areas were adjacent to the cinnamon and Surround beds. Therefore, an important part of organic control would likely involve a carefully managed trap crop with other control methods.

A standard lightweight row cover was used. A heavier row cover would be beneficial since onions and leeks are relatively long season so the row cover is removed more often. These crops also get quite tall and need a higher system than was used.

A third nematode spraying should be added into the season for the leeks as well as more aggressive control tactics during the latter part of the season.

Hot peppers have shown promise with trap crops (Cowles 1989) – this would be a useful tactic if the problems of skin burning could be addressed. (Around 90 percent of the time, the author manages to get hot pepper in her eye when working with powders, or the peppers themselves.) They would have the advantage of being free if hot peppers are already produced on the farm.

Repeating the study in a more normal year would be beneficial as well. There was not enough fly activity early in the season to determine effectiveness in onions. Also, having a larger stand of leeks would allow more accurate data and give a better idea of the economics of control methods late season.

It was also apparent that due to post harvest infestation, a better system of curing and storing onions is needed. A pungent spice might be useful here as an oviposition deterrent.

It is hoped to repeat this study with above changes in the 2006 season.

For outreach, we posted the results on our website, and hosted three field trips. Two of theses were University of Illinois classes (approximately 24 people), and one with visiting farmers through Oxfam (8 people). [Oxfam America is a non-profit organization that works to end global poverty. For more information see:] Several other area farmers wanted these results as they noticed very serious late season damage as well, so I sent copies out to them. In the future, I am planning to pass this on to the local park district organic garden coordinator since they have noticed leek damage.

This program really helped get this work done. It definitely helped with motivation to follow it through as the season became chaotic with the usual things and lack of rain. It completely helped to be able to hire people to do part of the work, freeing up my time to do other things as well.

Partial funding for the work reported here was provided by a grant from the USDA Sustainable Agriculture Research and Education (SARE) Program. I would also thank Joe Spencer (Illinois Natural History Survey) for generously supplying me with advice and a large body of onion fly literature.

Cowles, R.S, Keller, J.E., Miller, J.R, Pungent Spices, Ground Red Pepper, and Synthetic Capsaicin as Onion Fly Ovipositional Deterrents, J.Chem. Ecol, Vol 15 No 2, 1989. pp719-730

Martinson, T.E., Nyrop, J.P., Eckenrode, C.J., Dispersal of the Onion Fly and Larval Damage in Rotated Onion Fields, J. Econ. Ent. 81:508-514


Participation Summary
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.