Mad about Maggots?

Have you visited your vegetable field lately and come back disappointed because you were met with wilted, drooping plants? You are not alone. Recently, we have had an uptick in reports of maggot damage in vegetable crops. The insect culprits in question are most likely either onion maggot, seedcorn maggot or cabbage maggot. These maggots are very similar, and even belong to the same fly genus, Delia. These cream-colored maggots are small (0.5-1.5 cm) and have between 3-5 generations per year. These fly species will overwinter as pupae in the soil and emerge as adult the following year to find suitable host plants. Maggot will feed on seedlings and either kill the plant before it can successfully mature or injure the plant, thus giving entry to soil pathogens (secondary infections). This past season, you may have noticed more damage from maggots than normal. And that’s not surprising; maggot damage is typically greater in cool, wet seasons and in fields with high organic soil types.

There are some differences between these species that may point to one being the cause over another. Onion maggots love alliums, and are most problematic in onion, garlic, and leek. Cabbage maggot has an affinity for brassica crops including cabbage, cauliflower, Brussel sprouts, and turnips. Seed corn maggots love just about everything and can be found in as many as 40 different plant hosts. Notable crop hosts for seed corn maggot include soybeans, corn, beans, peas, cucumber, melon, pepper, potato, and even onion. As a general rule, seedcorn maggots typically damage the seed, whereas onion/cabbage maggots often feed on seedling roots.

The bad news is that if you are facing maggot damage there is little you can do to “rescue” your planting. Your best bet is to wait it out and replant if possible. You can drench with Diazinon (Diazinon AG500), but this product won’t ultimately save you from the damage that has already been afflicted. If you decide to use this product, make sure you use enough water. Diazinon doesn’t move easily through the soil and is best applied with adequate water.

Avoid “chasing” adult flies. You may see adult flies (figure 1) in your field but using foliar insecticides to kill adult flies is not an effective option for any species. Keep in mind the damage is in the soil, so make sure you target your management decisions to strategies that will protect the below-ground tissues of the plant (I.e., seed treatments or in-furrow applications at planting/transplanting).

If you are dealing with maggot damage on your farm, consider some of the options below.

  1. Prevention is key. If you know you have a history of either seed corn maggot or onion maggot, make sure you take action by preventing an infestation before it starts.
    • Rotate your crop. Flies will show up when they know food is available. So do your best to confuse the flies by rotating your crops, especially alliums and brassicas. If you want to limit future infestations, consider planting a non-host crop to decrease the likelihood of subsequent maggot problems. If you are rotating your crop to a non-host, make sure you rogue out any volunteers from the previous year. (Maggots love volunteers!)
    • Use a seed treatment (Table 1). Insecticide treated seed is one of the most effective tactics to manage maggot populations. A number of efficacious products are available including thiamethoxam+ spinosad (FarMore FI500), cyromazine (TRIGARD), and clothianidin and imidacloprid (SEPRESTO) for many vegetable seeds (table 1). Rotate products between years so you are not exposing multiple generations to the same active ingredient. For example, if you are using FarMore in year 1, rotate to a different seed treatment like Trigard or Sepresto in year 2. WHY DOES THIS MATTER? Reports from the Northeast and MidAtlantic suggest that some maggot populations may become resistant to these seed treatments.
      Table 1: seed treatment options to manage  maggot infestations in vegetables. Please note that efficacy of these products may differ based on maggot infestation and/or soil type.
      Product OMRI listed? Active ingredient Relative control of maggot IRAC codes
      FarMore FI500 No. thiamethoxam+ spinosad Excellent. 4A, 5
      Trigard OMC No. cyromazine Excellent. 17
      Sepresto 75 WS No. clothianidin+ imidacloprid Good. 4A, 4A
      Regard SC Yes. spinosad Excellent/Good. 5
  2. Exclude flies from the crop. One viable management approach is to keep female flies from finding your crop. You can isolate your crop either in space (row cover) or time (degree day modeling).
    • Consider using row covering over your susceptible crops to stop adult oviposition (egg-laying). Multiple studies have found that this is a highly effective method at limiting damage.
    • Avoid maggot damage altogether by planting later in the season to bypass peak infestation. Maggots have predictable phenological patterns, and you can use degree day models to accurately predict times in the season when maggot risk is high. The first peak of seedcorn maggot occurs earliest in the season when 200 degree days has been accumulated, followed by cabbage maggot (250 degree days) and then onion maggot (250-300 degree days).
  3. Monitor, monitor, monitor. While there is little you can do to manage maggot infestations within the immediate growing season, it’s important to identify problem areas so you can plan accordingly for the following year.
    • The best way to tell if you have Delia maggots on your farm is to scout early and often. Fields with poor plant emergence or wilted seedlings (figure 1, video) should be inspected for maggot damage. Make sure you cull any infested plants.

QUICK SURVEY: Do you use the OSU insect pest scouting network?


We are in the process of reevaluating and determining the monitoring needs of fruit and vegetable growers in the state. For awhile now, OSU extension educators and specialists have monitored for specialty crop pests.  We know there are a lot of different crops in Ohio and many different insect pests, but we’d like to know which pests are the most important to monitor.  This survey should only take 5 minutes and your thoughts and opinions are very important to us.

Click here for the survey link.

Thank you,

Ashley Leach and Jim Jasinski

What’s that on my cucurbit?

As noted by Sally Miller last week, bacterial wilt and yellow vine decline are being found in cucurbit fields across the state. There are two primary insects responsible for these outbreaks, the Striped cucumber beetle (Acalymma vittatum) and squash bug (Anasa tristis). I was just scouting some of my pumpkins this past week and counted 20 beetles in one flower! But sometimes looks can be deceiving as we can encounter as many as 4 different types of beetles in our cucurbit fields. It’s important to know what’s in your cucurbit since it could be the difference between making an insecticide application (or not). Below, I have included an image of different beetle species you may encounter in your cucurbit fields. As a reminder, we generally want to make an insecticide application when the striped cucumber beetle density exceeds 1 beetle/plant in a field. If you want information about specific products, check out my former post here.

Squash bugs are arguably easier to scout for since there aren’t many other insects that resemble them. However, we need to keep track of different squash bug life stages (shown below). Squash bug eggs are fairly diagnostic with a bright amber coloring. They are typically found along the midribs on the undersides of leaves. Those egg masses eventually give rise to nymphs which are powdery blue. Adults have a flattened appearance and are typically brown with alternating white and orange spots along their abdomen. Insecticide applications are warranted when squash bugs exceed a cumulative threshold of 1 egg mass, nymph or adult bug/ plant in a field.

Insecticide options and reminders for cucurbit pest control this summer

As you create your pest management programs for the rest of the season, make sure you keep pollinators and natural enemies in mind. Most cucurbits are obligately reliant on pollinators to set fruit and secure high yields. Further, many common cucurbit pests are controlled by natural enemies. For example, aphid infestations are often curbed by parasitoid wasps (pictured below). Ideally, non-chemical options should be prioritized (e.g., exclusion netting, trap cropping) but we don’t always live an ideal world. If you need to make an insecticide application, choose compounds with reduced toxicity to beneficial insects (options are shown below in Table 1).

  • Scout your field. Try to only spray when you need to spray. Use thresholds (described below in Table 1) to determine when an insecticide application is necessary. It’s possible that your preventative pyrethroid application is doing more harm than good. Pyrethroids in particular have a high “flaring potential” since they can disrupt natural enemies that provide FREE pest control.
  • Rotate chemistries. Take the IRAC code into consideration before you make an insecticide application and limit the number of sprays with the same insecticide class. This will prolong the efficacy of insecticide materials for the future.
  • Pollinator protection. While many insecticide products are safe to apply during the bloom period (although you still can’t apply during pollinator foraging), there are a fair number of neonicotinoids and pyrethroids that are not safe to apply during the bloom period at all (listed in Table 1 as ‘Highly toxic’). If you plan to use these products, make sure you position them well before or after bloom to limit negative effects on pollinators.

– Ashley Leach (OSU Entomology) and Jim Jasinski (OSU Extension)

Thresholds triggered across state for Codling moth control

Codling moth is on the move! In the graph below, we have degree day models for 4 different sites across Ohio (Piketon, Columbus, Wooster, and Ashtabula). As expected, the southern sites (Piketon, Columbus) show higher Codling moth activity compared to our more northern sites (Wooster, Ashtabula). Make sure to time first or second cover sprays in line with egg-laying hatch. Generally, the first cover spray can be applied when eggs are at 3-5% hatch and then a second application around 10-14 days later.

Degree day model of Codling moth activity across 4 sites in OH. Data was taken from NEWA.

Depending on the insecticide product you want to apply, you can use the following table to determine when applications are needed based on the development of Codling moth in your area. For example, if you are looking to target Codling moth populations with insect growth regulator like Rimon, make sure you make your first application between 50–75 degree days. However, if you are planning to use Exirel wait until 150-250 degree-days. As you consider your insecticide program for the second generation of Codling moth, make sure you rotate your chemistries or IRAC codes. Please note that there are other products to control Codling moth, and this is not an exhaustive list of insecticides that can control Codling moth. Consult your Midwest fruit pest management guide for more options and information.

Please note that this DOES NOT include all options to control codling moth in apple.