Bagworm Prevention Requires Proper Timing

Brian Jervis: Ask a Master Gardener

Sunday, July 19, 2020

Q: I have bagworms all over my arborvitae. What can I do to get rid of them? JG

A: Bagworms seem to be everywhere this year. Getting rid of them can be a challenge, but it is possible if you are up to the task. First, let us talk about the bagworm life cycle because understanding their life cycle is key to controlling them.

To begin, let’s go back a couple of months. Bagworm larvae overwinter in the bag and begin to emerge in late April or early May. Once emerged, these larvae begin to feed and construct the bags with which we are familiar. Initially, these bags may be only ¼ of an inch in length. But, as the larvae feed and begin to grow, they increase the size of the bag. This feeding is what can cause damage to the host plant. You mentioned arborvitae, but they also like eastern red cedars and junipers. However, in peak seasons, they can make their homes on pines, spruce, bald cypress and others.

For the female bagworms, the bag is their forever home. They do not develop wings, legs, eyes, or antennae and are almost maggot-like in appearance. Adult females can grow to about 1 inch in length. Males on the other hand grow to become small black moths that have a wingspan of about 1 inch.

Pupation occurs within the bag, and in the late summer or early fall, the males emerge from their bags in search of females. Adult males and females have a short lifespan — the female, a couple of weeks; the male, only a couple of days so the search is on. Neither the adult female nor male feeds. After mating, the adult female lays several hundred eggs within her bag and then dies. The eggs overwinter within the bag only to start the cycle all over again the following year.

So back to your question of what to do about them. With bagworms, timing is everything. When they are in their bags, about the only thing you can do is to remove them by hand, and you can do this any time of year. If your shrub is of an appropriate size, this is a good strategy, one the kids might enjoy helping with as well. Once the bags are collected, they need to be destroyed or placed in a sealed bag in the trash.

About the only other time you have a shot at control is in April and May when the larvae are feeding. During this time, you can spray with an organic pesticide called Bacillus thuringiensis or Bt for short. This organic pesticide only affects feeding caterpillars. You spray the pesticide on the infested plant, they ingest the pesticide while eating and die. Spraying this time of year while the bagworms are in their bags will not be an effective strategy as the bag does a great job of protecting them from harm.

Typically, damage is minimal from bagworms. However, infestations that build up over time can be detrimental to the health of your plant. So taking appropriate action at the appropriate time is key to bagworm control.

Get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th St., or by emailing mg@tulsamastergardeners.org.

Garden tips

·        When watering your lawn, ornamentals, or vegetables, always do so in the morning if possible. If watered in the evening, plants will go into the night still being moist. Most disease-causing organisms need moisture, and because they grow best at night, leaving leaves wet in the evening will promote many plant diseases.

·        Bulb onions are ready to harvest when the tops fall over. They should be removed and allowed to dry in a well-ventilated, shaded area. After the tops are completely dry, they may be stored in a cool, dry area.

·        Tall, spindly tomato plants with scarce fruit are usually due to either too much nitrogen fertilizer or too much shade.

The Many Myths of Epsom Salts

Tom Ingram: Ask a Master Gardener

Monday, July 6, 2020

Q: I keep seeing posts online that recommend adding Epsom salts to the soil when planting tomato plants. Is this something I should be doing? JE

A: The internet seems to be abuzz with many near-miraculous claims attributed to Epsom salts. Before we talk about those, let’s talk about Epsom salts and a bit of soil chemistry.

Epsom salts is magnesium sulfate. Magnesium is one of the secondary nutrients found in healthy soil, and Epsom salts can be utilized as a soil additive if you have a magnesium deficiency. However, magnesium deficiencies are not common in home gardens.

Magnesium deficiencies can be found in soil that has been under intensive production over an extended period or in soil that has experienced a great deal of nutrient leaching due to excessive rainfall or irrigation. In this instance, adding magnesium would be an appropriate strategy to remedy a magnesium deficiency.

Potassium is one of the big three soil nutrients (nitrogen, phosphorus and potassium), and high levels of potassium in soil can interfere with magnesium uptake, but adding additional magnesium to the soil will not overcome the problem created by an abundance of potassium.

On the flip side, adding magnesium to soil that is not deficient in magnesium can interfere with potassium uptake, which may result in a potassium deficiency in plants even if the soil has adequate potassium supply.

Rather than continue to dig deeper into soil chemistry, let’s look at some of the claims we often see associated with adding Epsom salts to your gardens.

1. Epsom salt helps with seed germination.

Seeds have all the nutrients they need to germinate within the seed and can germinate in a wet/damp paper towel. Epsom salts does not aid in this process.

2. Put a scoop of Epson salts into each hole when planting tomatoes to prevent blossom end rot.

Blossom end rot is a common malady in tomatoes that is caused by a calcium deficiency. Adding Epsom salts when planting tomatoes not only does not help prevent blossom end rot but also can contribute to its occurrence because magnesium and calcium compete for uptake into the plant. An abundance of magnesium present in the soil will encourage less calcium uptake, thus increasing the potential for blossom end rot.

3. Use Epsom salts as a foliar spray to help tomato plants grow and enable a larger harvest of better-tasting fruit.

Again, this is unnecessary unless you have a magnesium deficiency.

4. Epsom salts are highly soluble so you can’t overuse it.

Epsom salts are in fact highly soluble; however, unnecessary nutrients applied in excess typically become a pollutant as they will be washed out, landing in unwanted areas.

5. Epsom salts can help plants grow bushier.

This would be true if you have a magnesium deficiency but not true as a general all-purpose additive.

So how can you tell if you have a magnesium deficiency? Magnesium helps with the production of chlorophyll so plants grown in magnesium-deficient soil will lose their deep green color and their ability to photosynthesize. Therefore, if you are seeing yellow leaves with stunted growth, you may have a magnesium deficiency. But remember, this is not common in home gardens.

If you have concerns about a magnesium deficiency in your garden soil, before you start adding Epsom salts, you should get your soil tested by the OSU Extension (be sure and say you want your secondary nutrients tested also) but know, we rarely find a magnesium deficiency in residential soil tests. Best strategy … save your Epsom salts for your bath.

Garden tips

• Vigorous, unwanted limbs should be removed or shortened on new trees. Watch for forks in the main trunk and remove the least desirable trunk as soon as it is noticed.

• Most varieties of mums are more productive if “pinched back” now. Either pinch off with fingers or cut to remove an inch or so of limb tips above a leaf. This results in the growth of new limbs and a fuller plant. Do not pinch after mid-July or it will interfere with fall blooming.

• Watch for tiny, sap-sucking insects called aphids on roses, perennial flowers, shrubs and vegetables (especially tomatoes). They produce a sticky substance called “honeydew”. Many can be dislodged with a hard spray from your garden hose or 2 applications of insecticidal soap will usually greatly reduce any aphid damage to your plants.

• Crapemyrtles are one of the few shrubs that should be planted in the middle of summer. Growth of new roots of these plants occurs best with summer soil temperatures.

Now is the Time to Start A Fall Vegetable Garden

Fall Vegetable Gardening

Brian Jervis: Ask a Master Gardener

Sunday, July 5, 2020

Q: I have heard good things about fall gardening but know nothing about it. When can I start and what can I plant? JP

A: For many gardeners, gardening is a year-round adventure, not just something we do in the spring and summer. And as summer is starting to hit full steam, now is the time to start planning and getting ready for your fall garden.

When we talk about fall gardens, we split fall garden vegetables into two categories: tender and semi-hardy. Tender vegetables will not make it past the first frost. Semi-hardy vegetables can endure several frosts and keep producing.

Tender varieties, such as pole beans, bush beans, cilantro, eggplant, peppers, pumpkin, squash and tomatoes, among others, can be planted starting around mid-July.

Semi-hardy crops can be planted a little later. These would include beets, broccoli, Brussels sprouts, cabbage, potatoes, etc.

Fall gardening has several advantages. One of those is that you can get some of the best quality vegetables from your plants due to the warm days and cool nights later in the season. Another advantage comes from the fact that some of the insects we have been battling won’t be as much of a problem due to the timing of their life cycle. But it’s not all fun and games because we still have July and August to deal with.

In the spring, we are challenged with cold soil temperatures so many of us start our seeds indoors and move the plants outdoors when the soil has warmed up. In the fall, we do the same thing but for opposite reasons: We start our seeds indoors so they can germinate in cooler conditions and then move the plants outdoors.

Direct seeding becomes problematic for fall gardens and may require extra effort on your part due to high soil temperatures. Exposed soil on a hot day in July and August can warm up to 140 degrees. This presents challenges to direct seeding as these high temperatures will prevent germination. If you do direct seed, you will need to protect those tiny seeds by using a thick layer of mulch or perhaps covering them with shade cloth to help keep the soil cooler.

We have a great fact sheet on our website that gives you a list of veggies you can grow in your fall garden, as well as information on when to plant, how to plant and number of days before harvest. You can find it in our Hot Topics section on our homepage.

Also, if you are new to gardening or just want to learn more, you can sign up for our Online Urban Gardener classes and learn about soil, vegetable gardening, pollinator gardens, trees and shrubs, and turf management. Info on these classes can be found by clicking on the Urban Gardener link on our homepage at tulsamastergardeners.org.

Good luck and happy gardening.

Get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th St., or by emailing mg@tulsamastergardeners.org.

Garden tips

• Divide and replant crowded hybrid iris (bearded iris) after flowering until August. When planting, take care not to plant the rhizomes too deeply. Cover them with an inch of soil or less. Do not mulch iris.
• Water all plants deeply and early in the morning. Most plants need approximately 1 to 2 inches of water per week. Rather than watering daily, water less often and more deeply.
• Some trees, such as sycamores and river birches, lose large numbers of leaves in the heat of summer. Trees do this to reduce water loss from their leaves. It is a coping action by the tree; it is not dying.