Cucumber Beetle, Management
Striped cucumber beetle is our most serious early-season pest in vine crops. These beetles spend the winter in plant debris in field edges, and with the onset of warm days and emergence of cucurbit crops, move rapidly into the field. High tunnel and greenhouse cucumbers draw beetles first, followed by early field crops. Densities can be very high, especially in non-rotated fields or close to last year’s cucurbit crops. Adult feeding on cotyledons and young leaves can cause stand reduction, delayed plant growth, and reduced yield. The striped cucumber beetle vectors (Erwinia tracheiphila), the causal agent of bacterial wilt, and this can be more damaging than direct feeding injury. Crop rotation, transplants, and floating row cover are cultural controls that help reduce the impact of cucumber beetles. Perimeter trap cropping gives excellent control with dramatic reduction in pesticide use.
For more detailed information on the identification, life cycle, crop injury, and cultural controls of this pest, please see our main Cucumber Beetle, Striped article.
Avoid early season infection with wilt. Cucurbit plants at the cotyledon and first 1-4 leaf stage are more susceptible to infection with bacterial wilt than older plants.
Cultural Controls and Prevention
- Crop rotation can reduce the impact of cucumber beetles, as can transplanting, and protecting young cucurbits with row covers. In addition to insect protection, row covers also provide extra early-season heat, though it is important to remove them during flowering to allow for pollination.
- Perimeter trap cropping is another cultural control that has been shown to reduce or eliminate main crop sprays while providing effective beetle control. Trap cropping exploits the fact that SCB are more attracted to Cucurbita maxima crops (e.g. buttercup and hubbard squashes and giant pumpkins) than C. pepo or C. moschata crops (e.g. pumpkins, summer squash, butternut squash, other winter squash). Note that some specialty pumpkin varieties are C. maxima types and very attractive to beetles. Plant 1 or 2 rows of a C. maxima variety in an unbroken perimeter around the field. Always use 2 rows near woods or last year’s fields, and space plants no wider than the between-row spacing that is used in the main crop. Do not use a crop that is highly susceptible to bacterial wilt (see next paragraph) in the border. Beetles must be killed in the border, either by applying foliar insecticide when beetles first arrive or using a systemic insecticide at planting. Scout both borders and main crop to assess beetle numbers regularly. Repeat perimeter-sprays if needed to prevent influx into the main crop, and spray the main field if thresholds are exceeded. Attractive crop types that are planted in rows within the main field also work as trap crops that draw beetles as they move around within the field. These trap crops can be selectively sprayed.
- Beneficial nematodes: Some growers have expressed recent interest in applying entomopathogenic nematodes to the soil in order to control SCB. These nematodes would target the soil-dwelling, larval stage of SCB. Significant research has not been done on this topic, but theoretically it would be difficult to successfully control SCB using nematodes because of the high populations of SCB in the environments surrounding a field—if the SCB larva in the soil in a field were successfully killed, more adults will continue coming in from field edges throughout the season.
- Insect netting in high tunnels: SCB can be especially damaging early in the season in high tunnels. An increasing number of growers are experimenting with covering high tunnel sides and doorways with insect netting to exclude SCB. We’ve heard some success stories with this tactic, and some frustrations about ripping expensive netting, reduced airflow in netted tunnels, and incomplete exclusion that leads to resident high tunnel SCB populations. One way to increase success with this tactic is to combine it with crop rotation out of cucurbits in a netted tunnel so that the beetles that do make it into your tunnel one year will be unable to find food the following year.
Scouting & Monitoring
Cucurbit plants at the cotyledon and 1-to 2-leaf stages are more susceptible to infection with bacterial wilt than older plants. Thus, it is especially important to keep beetle numbers low before the 5-leaf stage. Scout frequently (at least twice per week up to SCB emergence, and for two weeks after) and treat after beetles colonize the field. Scout at least 25 plants to monitor the number of beetles and damage. Use this UMass Cucurbit Scouting Form to help keep track of what you find. The economic threshold depends on the crop. To prevent bacterial wilt in highly susceptible crops such as cucumber, muskmelons, summer squash, and zucchini, we recommend that beetles should not be allowed to exceed 1 beetle for every 2 plants. Less wilt-susceptible crops (butternut, watermelon, most pumpkins) will tolerate 1 or 2 beetles per plant without yield losses. Spray within 24 hours after the threshold is reached. Proper timing is key.
There are a number of broad-spectrum conventional insecticides which can be used for foliar control, including carbamates, pyrethroids, and neonicotinoids. All are highly toxic to bees and should only be used before bloom. Avoid using foliar neonicotinoid sprays (Actara [thiamethoxam] or Assail 30SG [acetameprid]) if systemics in the same class were used (see below). See the cucurbit insect management section of the New England Vegetable Management Guide for more details.
Systemic insecticides. Two neonicotinoid products, imidacloprid (multiple trade names) and thiamethoxam (Platinum) are registered for use in cucurbits as an in-furrow, banded, drench, or drip irrigation application to the seed/seedling root zone during or after planting/transplanting operations. Note specific application methods and rates on label. Commercially applied seed treatments (e.g. thiamethoxam, Farmore) are also available for early season control. Organic insecticides
Kaolin clay (Surround WP), pyrethrin (Pyganic Crop Spray 5.0 EC), and Azera (mixture of pyrethrin and azadiractin) are labeled for SCB. Surround does not kill the beetles but instead acts as a physical deterrent. With direct-seeded crops, apply Surround as soon as seedlings emerge if beetles are active. Transplants can be sprayed or dunked before setting out in the field. As with other insecticides, Surround must be re-applied after heavy rain and on new growth. Pyganic is a contact insecticide that provides a short-term knock-down with no residual effect. Spinosad (Entrust) is not labeled for and is not effective against SCB.
The New England Vegetable Management Guide describes many steps that growers can take to protect honey bees and native pollinators when using insecticides. The issue of neonicotinoids in particular has received a great deal of attention in recent years. This is a group of insecticides that have a chemical structure very similar to nicotine. They have been widely used in agriculture because they are effective against a wide range of insects, have lower mammalian toxicity compared to older classes of insecticides, and because they can be absorbed by roots and moved through the entire plant, reducing the need for foliar sprays. This trait allows for applications to be made to soil or on seeds, with less exposure to humans and to natural enemies of insect pests. Neonicotinoids are highly toxic to bees, and label requirements prohibit use on blooming crops or where there are blooming weeds or borders. Additional concern about impact on bees arises because research has shown that detectable, low concentrations of neonicotinoids can move into pollen or nectar. These are present at sublethal concentrations but may affect the foraging behavior of bees or suppress their immune system. The long-term or colony effects of sublethal concentrations of neonicotinoids are difficult to assess in the field because bees from each colony travel long distances and forage in many different habitats and types of plants. In cucurbits, both native bees (e.g., squash bees and bumblebees) and honey bees visit flowers to gather both pollen and nectar and are essential to crop pollination. Research in cucurbits has shown that higher levels of neonicotinoids were found after foliar treatments and chemigated insecticides were applied during flowering. Lower levels were detected in treatment regimens that involved a single application at planting via seed treatment, a drench application to transplant trays, or transplant water treatment. Thus, growers should avoid high rates and multiple applications, especially through trickle irrigation as the crop approaches flowering.
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