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Ask the Master Gardener: Salvaging summer squash from insect attacks

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Examples of summer squash. Photo illustration by Metro Newspaper Service

Dear Master Gardener: Last year at this time something attacked and killed my summer and winter squash. Can I do something to prevent it from happening this year?

Answer: It sounds like the very damaging moth called the squash vine borer. They commonly attack summer squash, winter squash, and pumpkins. The adult borer, which looks more like a wasp than a moth, is approximately one-half inch long and has an orange abdomen with black dots. Beginning in late June or early July the adults emerge from cocoons in the ground, then lay eggs at the base of susceptible plants. About one week later the eggs hatch and the white or cream-colored larvae, approximately one-inch long with brown heads, start feeding on squash stems, continuing for 4-6 weeks. The first symptom is wilting of the affected plant and you may see holes near the base of the plant filled with moist greenish or orange material (frass) that looks like sawdust. Squash vine borers are difficult to prevent and manage. They make a buzzing sound, fly around, and are easy to spot. They are attracted to yellow so you could set out yellow-colored pans of water, which they will fly into and drown. It is important to pull up and destroy any plants killed by squash vine borers. You can plant a new crop of summer squash now because these plants will mature after the adult borers are finished laying eggs and will not suffer any damage. Another option is to plant vine crops that are usually not attacked by squash vine borers, such as melons, cucumbers, or butternut squash.

Dear Master Gardener: I have a Siberian Peashrub and was wondering if I can cut it back now.

Answer: Siberian Peashrub (Caragana arborescens) is an invasive species and in Minnesota it’s a Restricted Noxious Weed. Although Restricted Noxious Weeds are not required to be controlled or eradicated by law, landowners are strongly encouraged to manage these invasive plants on their properties in order to reduce its spread into other areas. A Siberian Peashrub grows as a large shrub or small tree up to 18 feet tall. It has fragrant, yellow, tubular flowers that bloom in May and June then produce one to two-inch-long seed pods that are green in summer then turn brown, curl, open, and release seed in the fall. Rather than cut it back, I encourage you to cut it out.

Dear Master Gardener: I have a row of blueberry bushes but have never gotten any blueberries. My friend’s blueberry bushes have lots of blueberries. What could be the problem?

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Answer: The most likely explanation is you do not have two or more varieties, which is necessary for successful pollination. If all your plants are the same variety, you will need to plant another blueberry bush of a different variety nearby. Blueberries need full sun and acidic soil (pH 4.0 to 5.0), so if those criteria are not being met, this may also be the cause.

Hot July Weather Gardening Tips

  • It is best to water in the morning to allow the soil to absorb the water and reduce evaporation. Water at the base of plants whenever possible to reduce the chance of diseases. This is applicable for both garden beds and container plants.
  • Don’t apply an herbicide in hot weather. When temperatures are in the upper 80s and 90s, the volatility of some products increases. The vapor can drift and harm desirable plants (yours and your neighbor’s). Read the product labels, which will indicate safe temperatures for application. Always follow the label of any pesticide — it’s the law!
  • Continue to deadhead flowers.
  • During these high temperatures in July, our cool-season lawn grasses become dormant. Mow your lawn at a height of three inches or more. The grass plants will be less stressed and the likelihood of burn-out reduced.
  • Don’t fertilize your lawn in this heat. It will force grass plants into active growth, which is something you want to avoid during hot weather. Wait until cooler weather — August or September.
You may get your garden questions answered by calling the new Master Gardener Help Line at 218-824-1068 and leaving a message. A Master Gardener will return your call. Or, emailing me at umnmastergardener@gmail.com and I will answer you in the column if space allows.
University of Minnesota Extension Master Gardeners are trained and certified volunteers for the University of Minnesota Extension. Information given in this column is based on university research.
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