Now is the time when a small pest that has the potential to do a large amount of damage will be hatching. I am speaking of the Squash Vine Borer, the larval stage of the clearwing moth Melittia cucurbitae, an insect so synonymous with the squash family that it has cucurbit in its name.

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The adult clearwing moth, unlike many other moth species, is diurnal and is therefore active during the day. With its orange abdomen and clear wings it is often is mistaken for a wasp. The adults are now emerging from the soil where they have over-wintered as pupae. Anecdotally it is said that the squash vine borer lays its eggs when the blue chicory is in bloom and a drive along any of our major interstates will confirm that it is indeed blooming now. (image by Chris Evans, University of Illinois, Bugwood.org)

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The eggs, which are very small, are laid singly at the base of the stalks near the soil. This will make it easier for the newly-hatched larvae to enter the stalk. Seven to ten days later the larvae, which are white with a brown head, will emerge from the reddish-brown eggs and within hours instinctively burrow into the stem to begin feeding.(image by Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org)

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At this point symptoms will begin to appear starting with a wilting of the plant that recovers in the evening but progressing to a plant that does not revive in the evening or after watering. There may also be small entry holes visible at the base of the stem and sawdust-looking frass (waste). The larvae feed inside the stem for a little over two weeks, reaching 1” in length, at which time they exit the plant, burrowing 1-6” into the soil where they will pupate until next spring. I plant my cucurbits in upside-down coco coir liners that have a 2″ diameter hole in the bottom (now the top).

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The small opening and the protective coco coir make it easier to cover the base of the plant with row cover cloth and harder for the larvae to get to the soil to pupate. In warmer climates there may be two generations per year so we are fortunate that Connecticut only experiences one generation each summer.

It is almost impossible to control the larvae once they have entered the stems. If Bt (Bacillus thuringiensis) is applied to the plant tissue that is near the area where the larvae will hatch then they will feed on the residues prior to entering the stalk. Bt is a common soil-dwelling bacterial organism that forms crystals of insecticidal toxins called Cry proteins or crystal proteins. When consumed by the larvae, the Cry proteins undergo a series of chemical changes to the point that they paralyze the intestinal tract and the insect starves to death. Also good to know is that mammals have no toxic or allergic reactions to Bt, it only affects species in the orders Coleoptera, (beetles), Diptera (flies), Hymenoptera (ants, bees, sawflies, and wasps), Lepidoptera (moths and butterflies, and nematodes. Bt can also be injected into the stem where squash vine borer activity is suspected making it the only treatment that may work once the borer is inside. Additionally, normal exposure rates of Bt will not harm bees so that is good news for our pollinators.

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Butternut squash, cucumbers, and melons are not as susceptible to the squash vine borer as summer squash, pumpkins, and Hubbard squash, so plant the former varieties if you don’t want to deal with the borer. There are some practices that can be used if, like me, you can’t imagine a summer without freshly picked and grilled summer squash or a winter without home-canned ratatouille.

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The best protection is to prevent the clearwing moth from laying its eggs in the first place. Row covers placed during the egg-laying period starting in mid-June can be highly effective, just be sure to remove when the blossoms are ready for pollination (or leave them on and hand-pollinate). If possible, don’t plant in the same location as the prior year. If it’s not possible to rotate, at least turn over the soil at the end of the season to expose the pupae to the freezing temperatures of winter.

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For more information and control measures please check out our: Squash Vine Borer fact sheet.

Susan Pelton

 

Lots of happenings in the vegetable garden this week as things start to take off. Yellow summer squash and zucchini are starting to produce fruits. The first flowers that appeared were male, identified by their long stems holding the blossom. Female flowers have a small squash shaped ovary at the blossom base, that if becomes pollinated, will grow into a full-sized squash.If the pollination of the female flower does not happen, the tiny squash will drop off. Female flowers appear about a week after the first male flowers are put out by the plant.

Female squash blossoms with a fruit behind it. Photo by C.Quish

Female squash blossoms with a fruit behind it. Photo by C.Quish

Male squash blossom is on the long stem. Photo by C.Quish

Male squash blossom is on the long stem. Photo by C.Quish

At the first appearance of blossoms, the squash vine borer also was seen. The adult is a clear winged moth that lays her eggs on the hollow stems both varieties. The egg hatches into a larva tunneling into the center of the vine, feeding on the inside of the stem and blocking the transmission of water to the leaf and all plant material above their feeding site. The result will be wilting of the plant.

Squash vine borer adults, Jeff Hahn photo, UMN.edu

Squash vine borer adults, Jeff Hahn photo, UMN.edu

Control measures are trapping adults, preventing egg laying, and killing larva once stem is invaded. Trap adults by placing a yellow bowl or container filled with soapy water in the garden. Adults are attracted to the color yellow, will fly to the container where they become trapped in the soapy water. Check for eggs on the stems daily and crush any you find. Some folks wrap stems with aluminum foil to create a barrier to egg laying. If larva are found inside the stem, use a hat pin to poke through the stem into the larva to cause death of the insect while the stem will not be harmed much. Another way is to use a knife to slice lengthwise into the stem, dig out the larva, put the stem sides back together and cover with soil. The plant often recovers. Chemical control includes applying insecticide to the base and stems of the squash plant. This will kill the larva before it has a chance to burrow into the stem. Registered insecticides again the squash vine borer are neem, Surround, permethrin and pyrethrins. Always follow pesticide label directions.

Kale, bok choi and Swiss chard are keeping us in greens. The dreaded small caterpillars are starting to appear. Imported cabbage moth, crossed striped caterpillar and the cabbage looper are all common in Connecticut. Insecticidal soap, Bt and spinosad are organic control measures that work well on the early stages of the caterpillar. Apply at recommend label times to keep up with any new hatchings. Be aware of any white moths flitting around the cole crops to alert you to egg laying and the subsequent caterpillar presence.

Cross-striped cabbagworm larva (Evergestis rimosalis). Clemson University USDA Cooperative Extension Slide Series, www.insectimages.org

Cross-striped cabbagworm larva (Evergestis rimosalis).
Clemson University USDA Cooperative Extension Slide Series, http://www.insectimages.org

Cabbage looper larva (Trichoplusia ni) and feeding damage. David Cappaert, Michigan State University, www.insectimages.org

Cabbage looper larva (Trichoplusia ni) and feeding damage.
David Cappaert, Michigan State University, http://www.insectimages.org

Tomatoes, peppers and cucumbers were planted late as my garden had to wait for other responsibilities to happen before planting took place this year. All seem to be slow due to the colder spring soils, so maybe this is a blessing in disguise and I will have an extended harvest. I plan on planting spinach, lettuce, kale and carrots during August for later season crops. Colder hardy varieties will be selected and I will use row covers later to protect from frosts.

– Carol Quish

Male squash blossoms, C.Quish photo.

Male squash blossoms, C.Quish photo.

Where are all my summer squash? Why do my plants have many blossoms and not squash? These are a few of the questions I hear about yellow and zucchini squashes when the squashes look like they should be setting fruit. Be patient, gardeners, squash will come.

Squash plants produce separate male and female flowers on the same plant. The male flowers contain the pollen, the male part the reproduction process.  The female flowers have the ovary at their base. The ovary looks like a very small squash. This ovary will not develop and will be aborted,(dropped off), of the plant if pollen is not moved from the male flower to female. The process is called pollination, resulting in fertilization, then the ovary will develop into the fruit, the squash. The male flowers are produced and open a few days before the female flowers open. So the males are ready before the females. (I am not going to comment on this.)

The male flowers are on a long stem with no little squash at the flower base.

Male Squash Blossom, photo by C.Quish

Male Squash Blossom, photo by C.Quish

Male squash blossoms, C.Quish photo.

Male squash blossoms, C.Quish photo.

The female shows the small squash.

Female squash ovaries at base of flower. C.Quish photo.

Female squash ovaries at base of flower. C.Quish photo.

 

Insects such as bees are the common pollinators of squash plants. They feed on the nectar in the flower, and in the process pick of pollen from the male flowers, dropping some in the female flower when the move into it. If all goes well, fertilization happens and the squash will develop.

A common pest insect of summer squash is the squash vine borer which lays eggs on the stems of the squash. The eggs hatch into a larva which tunnel into the stem to feed. Their feeding damages the inside of the stems and the water conducting vessels of the plant, causing part or entire collapse and wilt of the plant. The squash vine borer is a clear winged moth with 1/2 inch long orange abdomen with black dots. It flies during the day and rests at night. The SVB is attracted to the color yellow. A trap can be made by filling a yellow bowl with with soapy water. The SVB will fly into the bowl and drown. Place trap near squash plants. Other management options are to plant a second crop of summer squash in early July that will mature after adult borers have finished laying eggs. Pull and destroy any plants killed by squash vine borers to keep the larva from overwintering after feeding for four to six weeks. They exit the stems and burrow a few inches into the soil to pupate  where they stay until the following summer. There is only one generation per year..

I use a row cover as a physical barrier that keeps out all insects. The row cover is a poly spun fabric similar to mosquito netting placed over all of the squash plants in the bed, then held down with weights to exclude all insects. The row cover also excludes the pollinators, so I have to either hand pollinate each female blossom or remove the cover once the female blossoms appear to allow insects in to do their job of pollinating. If hand pollinating, do it in the morning as the pollen is most available then.

Row cover protecting squash from insects reaching the plant. C.Quish photo

Row cover protecting squash from insects reaching the plant. C.Quish photo

Squash vine borer adults, Photo UMN.edu

Squash vine borer adults, Photo UMN.edu

 

Squash vine borer larva and damage. Photo UMN.edu

Squash vine borer larva and damage. Photo UMN.edu

 

-Carol Quish