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.