Do you remember the saying “when the cats away the mice will play?” Well I believe the saying should go: “When the gardeners away the bugs will have a party!” Not only will they party, play and invite friends, but they will devour a garden in just a few days, as I learned in taking a mini-vacation. I came home to find squash vine borers abundant, tomato hornworms to boot and stink bugs making themselves at home. So what am I going to do to destroy them? I choose to use nature or physical means to combat garden pests without Agent-Orangeing my entire garden. In order to use these methods you must first become skilled at identifying their favorite ways to gain access. The more you know about your enemy the better you are in combat and let’s face it, this is combat.
Enemy #1: Squash Vine Borers-The squash vine borer, Melitta curcurbitae, is a common clearwing moth that can cause devastating results in home gardens. It is a serious pest of vine crops, commonly attacking summer squash, zucchini, winter squash, and pumpkins. Yellow crookneck is less susceptible than zucchini. Cucumbers and melons are less frequently affected. Butternut and cushaw are resistant. Beginning in late June or early July, squash vine borer adults emerge from cocoons in the ground. (This season I noticed them in early June).
There are two methods for detecting squash vine borer adults. The first is observation of adult activity in the garden. These moths are unusual because they are conspicuous when flying and fly during the day while nearly all other moths fly at night. These moths are about 1/2 inch long with a bright orange abdomen with black dots. The first pair of wings is metallic green while the back pair of wings is clear, although that may be hard to see as the wings are folded behind them when they at rest. In addition, the adults make a very noticeable buzzing sound when flying. Watch and listen for them when you’re in your garden (and catch and squash them if you can). If despite of your diligent monitoring you miss the adult moth, it will quickly lay its eggs singly at the base of susceptible plants. Approximately one week after they are laid, the eggs hatch and the resulting larvae bore into stems to feed. The larvae then feed for four to six weeks. You will start to notice a squash plant looking a little “off.” From its sudden wilted appearance you will begin to think that it hasn’t had enough water, when in actuality it’s the larvae feeding through the center of the stems, blocking the flow of water to the rest of the plant. After the larvae finish feeding they will exit 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 vine borers are challenging to prevent or manage because many larvae can attack one plant. Most management options are limited to controlling (i.e. squashing) the hatching larvae before they enter the plant. Once the larvae invade the stem, it is difficult to treat squash vine borers.
If the plant begins to wilt despite watering, closer observation often will reveal holes near the base of the plant filled with moist greenish or orange sawdust-like material called frass. If left unattended, over time, the base may become mushy or rot away altogether. To help save the plant, slit the stem above the hole with a razor and remove the larva. Then mound soil around the injured stem. Dust lower stems with rotenone or pyrethrum or wrap them with aluminum foil. Till soil at season’s end to kill/expose squash vine borer cocoons.
The best way to break the life cycle of the squash vine borer is to promptly pull and destroy affected plants. This can be easily done by placing pulled plants in a black plastic bag and disposing of them. Then, plant a second round of summer squash in early July; these will mature after adult borers have finished laying eggs.
Enemy #2: Tobacco Hornworm-Manduca sexta is native to the United States and is the larvae form of the “sphinx,” “hawk,” or “hummingbird” moth, which is large and heavy-bodied with narrow front wings. It is mottled gray-brown with yellow spots on the sides of the abdomen and a wing spread of 4 to 5 inches. The moth deposits its eggs on the lower bottom leaves of the tomato plant; the eggs hatch in six to eight days depending on weather conditions. The caterpillar reaches maturity in three to four weeks. This insect does not usually cause extensive economic damage in commercial operations. However, large numbers of larvae can cause significant damage in home gardens. Tobacco hornworms are most commonly seen feeding on tomato plants, but will feed on eggplant, pepper and potato plants as well. Tobacco hornworms are voracious eaters and will consume leaves, stems and pieces of immature fruit. The first signs are usually the partially defoliated stems of the tomato plant. They are difficult to spot because they are virtually the same shade of green as the plant foliage. After spotting, you can toss them in a bowl of soapy water. The horns, which are on the back of the hornworm,will not hurt you. The caterpillar may try to nibble on your finger, but this will not hurt either.
If you see a hornworm covered with white egg sacs, leave it be. The egg sacs are those of a parasitic wasp called the Braconid wasp. Let the eggs hatch and you’ll have an army of beneficial wasps ready to defend your garden against all types of pests. These wasps will not sting you, and they are so small that you probably will not even notice them. If fully grown hornworm larvae are left on the plant and are not infected by the Braconid wasp then they will drop off the plant and burrow into the soil beneath the tomato plant to pupate. During the summer moths will emerge from the pupae in about two weeks. After emerging from the soil the cycle begins again. By early fall, the pupae will overwinter in the soil and will emerge the following spring as a moth.
Enemy #3: Brown Marmorated Stink Bug (BMSB) – Halyomorpha halys, an insect native to China, Japan, Korea and Taiwan, was apparently accidentally introduced into eastern Pennsylvania in the late 1990’s. It was first collected in September of 1998 in Allentown, but probably arrived several years earlier. As of September 2010, Halyomorpha halys has been recorded as a severe agricultural and nuisance pest in Pennsylvania, Maryland, New Jersey, Delaware, Virginia and West Virginia. As many Marylanders may recall this insect was a huge nuisance in the fall of 2010 and this has continued into the present growing season. The adult BMSB measures at 5/8” and are dark mottled brown. The last 2 antennal segments have alternating light and dark bands. The exposed edges of the abdomen also have light and dark banding. Females lay clusters of 27 to 28 light green, barrel-shaped eggs on the undersides of leaves from June to August. The young bugs (nymphs) are yellowish and mottled with black and red. Older nymphs more closely resemble the adults. There are 5 stages or instars. In Maryland we can have over 2 or more generations a year depending on environmental conditions (temperature, rain, humidity). One female BMSB can produce 400 to 500 eggs per lifetime depending on the stress level, nutrition and environmental conditions. 1st instar nymphs will began feeding 10 days after hatching. BMSB reach adulthood in 50 to 60 days.
BMSB can feed on more than 300 different plant hosts, but their prime choices are plants with high nutritional values such as crops, fruits and vegetables. Unlike the squash vine borer and the tobacco hornworm, the BMSB’s have a sucking mouth part which makes them particulary devastating to agriculture crops and home gardens. They inject their sucking mouth part into many areas on fruits and vegetables. The nymphs or young stink bugs tend to feed shallowly, while the adults feed deeply into plant tissue causing more damage. On leaves damage can appear as small stippled areas and/or necrotic areas. On fruit there may be water-soaked lesions, pitting, dimples, catfacing, and/or depressed areas.
Adult stink bugs can cause deep feeding injury in fruit such as apples making them unsalable. Damage on vegetables such as peppers and tomatoes appears as cloudy whitish areas in the fruit. On beans and okra there will be wart-like growths and deformation or shriveling of the pods. Early stink bug feeding on corn results in incomplete kernel formation, while later feeding causes kernel collapse and brown discoloration.
Since this is a recently introduced insect pest it is NOT recommended to use a pesticide. Most are ineffective in causing mortality and can actually harm other beneficial insects. The best methods currently shown to reduce the BMSB populations in the garden are knocking them off into a cup of soapy water or squishing them. Additionally, there is an all natural product called Surround or Kaolin Clay, which can be sprayed onto the entire plant to help reduce BMSB damage.
If you have a floundering vegetable garden or an unidentifiable garden pest, you can bring a sample or pictures to the University of Maryland Extension-Queen Anne’s County Master Gardener booth at the Queen Anne’s County 4-H fair starting on Monday, August 8, 2011 to August 13, 211. At this booth University of Maryland Extension Master Gardener Volunteers provide information to home gardeners. Master Gardeners will be available to look at samples of ailing plants to make diagnoses, give recommendations, answer questions, and provide printed information on a variety of gardening subjects. All information at Master Gardener booths are free and open to the public. Also check out the Maryland Food Gardening Network/Grow It Eat It program at http://growit.umd.edu , for more tips on growing great gardens.
by Rachel Melvin, Queen Anne’s Co. Master Gardener Coordinator
For information contact: Rachel Melvin, (410) 758-0166 or email@example.com; or visit Queen Anne’s County Extension, 505 Railroad Avenue, Suite 4,Centreville, MD 21617; our booth at the Queen Anne’s County Fair at the 4H Park, August 8-13; or http://queenannes.umd.edu/QACMG/index.cfm
University of Maryland Extension programs are open to all citizens without regard to race, color, gender, disability, religion, age, or national origin.
Grow It Eat It- July & August Tips
- Sow seeds of broccoli, cauliflower, turnips, beets and other fall crops in late July.
- Sow seeds of squash, beans and cucumbers through the end of July.
- Harvest onions when tops die back; let them dry in the garden after digging them up, or tie the stems together and hang them up in a garage or attic with good air circulation. Store onions in a cool, dry place.
- Hand-pick pest insects and their egg masses.
- Remove badly diseased leaves or plants.
- Plant a late crop of basil, cilantro, and dill.
- Plant a last crop of snap beans the first week of August.
- Plant cool season crops, including spinach, lettuce, carrots, beets, broccoli, cauliflower, Chinese cabbage, turnips, kale and mustard. Keep seedlings moist and mulched.
- Order garlic, walking onions, and shallots for fall planting.
- Harvest leaves of herbs before they flower. Pick individually, and dry indoors, or hang the stems a dry, semi-shady room. Store dry leaves in air-tight jars. Fresh basil leaves freeze well in plastic bags that can be sealed.
- Keep weeding and watering