Relevance of squash vine borer and squash bugs as pests of cucurbit crops
The squash vine borer, Melittia cucurbitae - a clear wing moth, and the squash bug, Anasa tristis - a true bug, are two significant pests of cucurbit crops. These two insect pests can cause serious economic losses to cucurbit farmers if populations are left uncontrolled. Commercial vegetable farmers and gardeners often find themselves scratching their heads to find effective ways of controlling them. Insecticides can be an effective control option; however, harvest interruption due to pre-harvest intervals, and the potential impact on beneficial/pollinator species must be considered. Many of these insecticides will also be "restricted-use", requiring private pesticide applicator training and licensing. This article discusses trap cropping as an Integrated Pest Management (IPM) strategy to control squash bugs and squash vine borer with little or no insecticides applied to the cash crop.
Squash vine borer: The adult squash borer may be mistaken for a wasp. The front wings are a metallic green and the rear wings are transparent with black or brown margins and veins. The body is orange and black. The adult moths are active during the day, so they can be spotted relatively easily. Soon after emerging from cocoons in the ground around June (in mid-Missouri), squash vine borers lay eggs singly at the base of susceptible plants. Approximately one week after they are laid, the eggs hatch and the resulting borers, which are a type of caterpillar, drill into stems to feed. At this moment the plant is destined to die. The larvae feed through the center of the stems, blocking the flow of water to the rest of the plant. The larvae feed for four to six weeks, then exit the stems and burrow about one to two inches into the soil to pupate. They remain there until the following summer. There is one generation per year.
Squash bug: Adults overwinter in sheltered places. In spring (around late May and June in mid-Missouri) they mate and lay small masses of shiny, oval, copper-colored eggs beneath leaves. Hatchlings are pale green. They grow and molt through various immature stages (nymphs). Older nymphs are gray with dark wing buds. Often a mixture of stages congregates together on the same plant. Upon the final molt, they emerge as winged, sexually mature adults. There are at least two broods per year.
What is trap cropping?
Just like most animals do, insects have a preference for certain types of foods. Given a choice, insects will likely select their preferred food. If no option is given, they will be happy feeding on the type of plants that are available. Trap cropping means using very attractive plants growing in the perimeter of the garden or cucurbit field. These attractive plants pull the pest away from the cash crop. Insects congregated on trap crop plants can be more easily killed with insecticides or by other means. Research conducted by the Lincoln University (LU) IPM program since 2011 indicates that Blue Hubbard squash is very attractive to squash bugs and to squash vine borer, and therefore it is an excellent trap crop plant. In addition, Blue Hubbard squash is also very attractive to spotted and striped cucumber beetles, so farmers and gardeners can actually control four insect pests using Blue Hubbard as a trap crop.
Benefits of trap cropping
By using trap cropping, farmers can reduce inputs (fuel, labor, time, and insecticides) resulting in increased income while protecting pollinators and other beneficial insects. As an example, one producer from St. Peters has not sprayed any insecticides to his cucurbit cash crop since 2011. He only applies a small amount of insecticide to the Blue Hubbard seedlings shortly before transplanting them to the corners of his fields. He currently sells his cucurbit produce as insecticide-free.
Implementing trap cropping in gardens and small farms
With some planning, using trap crop plants can be easy and inexpensive. Blue Hubbard squash can also be used as a monitoring tool. For example, start growing Blue Hubbard squash transplants in mid- or late-April, and set one tray with Blue Hubbard squash seedlings out in the field. As soon as squash bugs (and/or cucumber beetles) are seen, then it will be time to transplant the trap crop plants to the field. The key is to transplant 2- week old Blue Hubbard seedlings (trap crop plants) to the field at the same time you sow the seeds of your cucurbit cash crop. If you grow your cash crop from transplants, then you will need to transplant the Blue Hubbard seedlings at least 2 weeks before your cash crop. The bottom line is that, to be most effective, Blue Hubbard squash plants need to be bigger than cash crop plants.
A second piece of advice is to kill the insect pests on the trap crop plants. Remember, having 1-2 squash bugs on your cash crop doesn't mean that you need to spray. Our research has demonstrated that for a small garden of 100 or so cucurbit plants, you can be successful at controlling squash bugs (and cucumber beetles) using 6-8 Blue Hubbard squash plants. The trap crop plants can be planted at the corners, at some distance (3-8 ft.) from the cash crop.
On a commercial farm, for cucurbits grown using plastic mulch and drip irrigation then we recommend you transplant 2-4 Blue Hubbard squash seedlings to both ends of each row.
Blue Hubbard squash can also be grown in large pots. Some farmers have implemented trap cropping outside high tunnels to protect cucumbers by placing potted Blue Hubbard plants treated with a systemic insecticide early in the season, with good results. If temperatures at night are expecting to drop potentially injuring the Blue Hubbard squash seedlings, then pots can be moved indoors.
Removing / killing insect pests congregating on trap crop plants
Insect pests (e.g., squash bugs) congregating on trap crop plants need to be eliminated. Otherwise, they are likely to reproduce on those plants, and then they can move to the cash crop. Not killing the squash vine borer means that the trap crop plants will succumb. Therefore, for both squash bug and squash vine borer control insecticides applied to the Blue Hubbard squash are recommended. Whether using organic or synthetic insecticides, make sure to apply them thoroughly, especially near the base of trap crop plants.
Synthetic insecticides: Foliar applications of insecticides listed in the Midwest Vegetable Production Guide for Commercial Growers for use in cucurbit crops will result in effective control of squash bugs and squash vine borer. Some producers have opted for using small amounts of systemic insecticides (examples of trade names: Admire Pro®, Alias 2F®) applied to the trap crop plants only. When applied to the roots, systemic insecticides are absorbed by plant tissue, producing plants that will be toxic to insects that feed on them. Imidacloprid-treated plants will continue to kill insect pests for about 3-4 weeks, depending on weather conditions.
Organic insecticides: Pyrethrins-containing insecticides such as AZERA® and Pyganic® represent good options to kill cucurbit pests. Because squash bugs are hard to kill, then use the high label rate if you are targeting the adult stage. If sprays are targeting the nymphs (immature stages), then a low or medium application rate will be effective. Timing of application is important particularly in the case of the squash vine borer, as again, once the caterpillar hatch from eggs and bores into the stem, no control method will be effective.
During bloom, sprays should be made early in the morning or later in the evening to reduce the effect of insecticides on honeybees or other pollinators. ALWAYS follow label instructions and safety procedures, and check to make sure the chemical you are using is registered for use in your crop. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. If you are an organic certified producer make sure that the substance, including its brand name and formulation, is listed in your organic system plan, reviewed, and approved by your USDA-accredited certification agency.
Evaluating the success of trap cropping
Factors influencing the efficacy of trap cropping include (1) having Blue Hubbard squash under water / nutrient stress, (2) having cash crop plants bigger in size than the trap crop plants, and (3) not removing the pest from trap crop plants. Provide the Blue Hubbard squash with enough water and nutrients - in the same way you manage the cash crop.
One way to determine the success of trap cropping is by scouting both the trap crops and the cash crop at least once a week. For squash bugs, apply insecticide to the cash crop if cash crop plants are in the seedling stage, squash bugs are present, and some wilting is observed. At the early flowering stage, cash crop plants can tolerate an average of 1 egg mass per plant.
As a result of research and outreach conducted since 2011, some Missouri farmers that have increased production of high-quality vegetable crops using more sustainable IPM methods such as trap cropping. This has led, for some producers, to increased profits and less negative impact on pollinators and other beneficial insects while decreasing pesticide use, labor and other farm inputs.
Funding for trap cropping research was provided by the Ceres Trust: An Organic Initiative (http://cerestrust.org/), and by the USDA/National Institute of Food and Agriculture (NIFA) Capacity Building Award No. 2011-38821-30867. Funding for mass trapping research was provided by the North Central Region IPM Center through Sub-Award # 2007-04967-35 and by the USDA/NIFA Capacity Building Grant program, Award No. 2011-38821-30867.
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REVISED: February 21, 2017