Dutch Elm Disease is Devastating for American Elm Trees

Tom Ingram: Ask A Master Gardener

Sunday, August 2, 2020

Q: I have an American Elm that started looking like it had a problem and then died a few weeks later. What in the world happened? JA

A: The culprit was likely Dutch elm disease. I was speaking with Jen Olson of the OSU Plant Disease & Insect Diagnostic Lab recently and she said she was seeing more Dutch elm disease this year than in recent years, which is too bad because it’s one of the most destructive tree diseases in North America.

Dutch elm disease was first discovered in the Netherlands in the early 1900s, but it didn’t take long for it to make its way to the U.S. It arrived around 1930 on beetles who were hitching a ride on some logs headed our way to make furniture.

Quarantine helped control the disease until 1941, but the nation then became more focused on fighting a war. Some estimates suggest there were approximately 77 million elms in North America in the early ’30s. By 1989, more than 75% of those trees were lost.

Dutch elm disease grows in the xylem of the tree. The xylem is the tissue that helps bring water up from the roots throughout the entire tree. You typically start to see evidence of Dutch elm disease in the upper branches with leaves gradually browning, then yellowing and eventually getting dry and brittle.

When adult elm bark beetles emerge from under the bark of infected trees in the spring, they are covered with the Dutch elm disease fungal spores. They look for tender young bark on healthy trees to feed upon. Their feeding leaves wounds that become great places for the Dutch elm disease to take hold.

If you suspect your elm may have Dutch elm disease, you can cut off a branch about 1 inch in diameter from an actively wilting section, peel back the bark and look for discoloration similar to that in the photo (the dark strips). To be sure, you can bring a sample to your local Extension Office, and we will send it off to OSU for positive diagnosis.

If you catch the disease early, the infected areas can be pruned out, but you will need a minimum of 8 to 10 feet of un-infected, streak-free wood below the infected areas.

Fungicides and insecticides are available to help prevent Dutch elm disease; however, these chemical treatments should be applied by a licensed arborist because a fungicide may need to be injected into the tree. You can find a licensed arborist for our area at treesaregood.org.

There are a variety of elm species that are resistant to Dutch elm disease, but none is immune. Resistant varieties include Siberian elm, Chinese or lacebark elm, “Valley Forge,” “Princeton,” “New Harmony” or “American Liberty’.”

Garden tips

• Now is the time to divide and replant crowded hybrid iris (bearded iris). 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.

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.

Good Garden Practices Prevents Problems

Good Garden Practices

Tom Ingram: Ask a Master Gardener

Tuesday, June 23, 2020 

Q: It seems like there is always something wrong in my garden. If it’s not insects, it’s some sort of disease. What am I doing wrong? JK

A: It can seem like that sometimes but let us talk a little bit about disease prevention rather than just how to deal with disease once it happens.

Resistant plants and seeds:

If you start your vegetables from seeds, purchase disease-resistant seeds. If you are like most people, you will say, “How the heck do I do that?” Well, most vegetables have varieties that are more disease resistant than others. Heirlooms (for example) are typically traditional cultivars that have been passed down from generation to generation that remain true to their heritage. As such, they can be more susceptible to disease because they do not have the advantage of having disease resistance bred into them via hybridization. Hybrids are not GMOs; they are varieties that have been cross-pollinated with other varieties to either increase production, increase disease resistance or both. For example, seed packets for tomatoes indicate their disease resistance with the letters V, F and N. Seeds with those disease-resistance indicators would be naturally resistant to Verticillium Wilt, Fusarium Wilt and Nematodes. So right from the start, you are ahead.

Also, try to purchase healthy plants. As gardeners, we all know that the bargain table with the sickly looking plants can be tempting. But try to remember these plants are there for a reason. The reason might be disease. If you cannot resist (and many of us can’t), try to keep them away from your other plants until you nurse them back to health.

Crop rotation

If you plant tomatoes in the same spot every year, disease pathogens can build up in the soil, becoming a bigger problem each year. To counteract this, you can rotate your crops. Some people rotate every year, but for sure, it’s good practice to rotate at least every three years. But here is the trick; you need to learn about the vegetable families because vegetables in the same family are usually susceptible to the same diseases and you might be surprised by who is in the same vegetable family. Tomatoes are in the solanaceous family, so are potatoes, eggplant and peppers. So if you are going to rotate your crops, don’t plant potatoes where the tomatoes were. Brassicas include broccoli, cauliflower, Brussels sprouts, kale, radishes, etc. Legumes include the bean family. And the others kind of make sense. So rotate by family, not just vegetable.

Garden practices:  You need to be aware of how your garden practices might be contributing to plant disease. First, you should water in the morning. When you water in the morning, the water can evaporate off the plant and soak into the soil before the heat of the day. Watering at night can leave the leaves of your plants wet, and wet leaves are more prone to disease. Also, be sure to water the roots, not the leaves. The roots need the water, the leaves do not.

And clean your tools. If you have been trimming or pruning infected branches or leaves, wash your tools with a 10% bleach solution to prevent spreading the disease to other plants.

If these habits become part of your garden practices, you will be well on your way to minimizing plant disease and being a happier gardener.

Garden tips

·        White grubs will soon emerge as adult June Beetles. Watch for high populations that can indicate potential damage from grubs of future life cycle stages later in the summer.

·        Fertilize warm-season grasses at 1 pound Nitrogen per 1,000 square feet. Do not fertilize fescue and other cool-season grasses during the summer. Because nitrogen is soluble in water, much of it may have been lost due to percolation and runoff if you fertilized before recent rains.

Squash Vine Borers

Brian Jervis: Ask a Master Gardener

Sunday, June 21, 2020

Q: My squash plant was big and beautiful, and then one day, the leaves started turning yellow and in a few more days it was dead. What happened? RW

A: The culprit was likely the squash vine borer. These insects can be a problem for all cucurbit plants and are the reason many of us no longer grow squash but grow cucumbers instead. Yes, I know cucumbers are cucurbits too, but they don’t seem to bother cucumbers like they do the squash.

Squash vine borers overwinter in the soil as either larvae or pupae. Adult moths begin to emerge in June (possibly sooner if we have a mild winter like we have had) and remain active through August.

During this time, they find a mate. The female deposits her eggs, usually about a dozen or so at a time, on the stem of the squash plant near ground level. The eggs hatch and the larvae enter the stem to begin feasting on your beautiful squash plant. They essentially eat out the inside of the stem, destroying the plant’s ability to draw up nutrients into the rest of the plant.

Signs of this not only include the yellowing and wilting of the leaves on your squash plant, but you will also see something that looks like wet sawdust on the stem of the plant. This is the excrement (frass) of the borer inside of the stem.

These larvae continue to feed for four to six weeks and can migrate to other plants if their host plant dies or ceases to become suitable for their needs.

These borer larvae are white or cream colored and can be easily seen by slicing open the vine in the affected area. The fully grown moth is primarily black and orange and is easily mistaken for a wasp.

Squash vine borers are worthy adversaries and controlling them can prove difficult. The first line of defense will require diligence on your part. This entails visually inspecting your plant stems near the soil line for eggs. If eggs are found, they can be destroyed.

If you missed the eggs and are seeing evidence of the squash vine borer (frass), you can gently slit the stem and remove the larvae. Once removed, you should cover the damaged part of the stem with soil. With any luck, you will continue to get production from your plant.

Weekly preventative applications of an organic insecticide during the active months can also help. An organic pesticide like spinosad should be applied to the stalk of the plant near the soil level during their period of activity. But be careful to only spray the base of the stalk and spray late in the evening, as you don’t want to harm any of the pollinators working on your behalf to get you some squash.

As an alternative strategy to weekly pesticide spraying, pheromone traps can be placed in your garden near your squash plants. When the squash vine borer moth shows up on your trap, you know it is time to begin spraying the stalks near the soil with spinosad.

And last but not least, because squash vine borers overwinter in the soil, tilling the soil at the end of the season can help disrupt their life cycle.

Good luck!

Garden tips

·        Remain alert for insect damage. Add spider mites to the list. Foliage of most plants becomes pale and speckled; juniper foliage turns a pale yellowish color. Shake a branch over white paper and watch for tiny specks that crawl. Watch for first-generation fall webworm.

·        Some pests can be hand-picked without using a pesticide. Do not spray if predators such as lady beetles are present. Spraying insecticides early in the morning or late in the day will avoid spraying honeybees and other essential pollinators.

Soil Tests Help Select a Fertilizer

Tom Ingram: Ask a Master Gardener

Sunday, June 7, 2020

Q: With all the different fertilizers out there, how do I know which one I should be using? AR

A: Fertilizers can be confusing. They come in a variety of strengths with a variety of numbers and for the beginner or novice, it can be overwhelming. So let’s break it down.

The fertilizers you find at the store have a series of numbers on the bag. These numbers can be something like the following: 10-20-10, 19-19-19, 3-17-17, 31-0-4, 46-0-0, etc. Those numbers coincide with the percentage of nitrogen, phosphorus, and potassium in each particular product. So, if a product says it is 10-20-10, that means it contains 10% nitrogen, 20% phosphorus and 10% potassium. If it says 46-0-0, that means that it contains 46% nitrogen, 0% phosphorus and 0% potassium.

So how do you know which one you should use?

The best way to know for sure is to have your soil tested. This may sound a little intimidating, but it is a simple process.

First, you will need to collect the soil sample. You can collect this sample using a specialized soil sampling tool or just use a garden trowel. A bulb planter works well also. The trick is to get between 15-20 samples from the area you want tested. These samples need to contain soil to a depth of 6 inches. If this is your yard, get 15-20 samples from various points in your yard, put them in a bucket, mix it up, remove the twigs and fill something about the size of a sandwich bag from the soil in your bucket. If you are wanting a soil test for your vegetable garden or your flower bed, get your 15-20 samples from those areas.

Once you get your soil sample in a bag, bring it to the OSU Extension office, 4116 E. 15th St. Even though the office is closed, there is a black mailbox on the south side of the building (in the back) where you can fill out a form and leave your sample. There is a $10 charge for a soil test. We will pick it up and forward it to OSU, where they will test for pH, nitrogen, phosphorus and potassium. Once tested, you will get a recommendation on what nutrients are needed for your situation. These recommendations will vary depending on what area you are sampling and what you are growing.

Once you have the results of your soil test, you will know how much of each nutrient you need to add to your soil for best results.

So back to the fertilizer. Let us say the test revealed your soil only needed nitrogen, and it was recommended that you add 1 pound of nitrogen for every 1,000 square feet. In this case, you could purchase some 46-0-0 fertilized because it is 46% nitrogen and does not contain phosphorus or potassium. This means that if each pound of fertilizer is 46% nitrogen, you would need about 2 pounds of fertilizer to give you 1 pound of nitrogen. If you purchased 10-20-10, you would need 10 pounds of this fertilizer to give you the 1 pound of nitrogen. Plus (in this case) you would be purchasing phosphorus and potassium that you didn’t need and which might also be harmful to your growing environment.

Yes, you may need to use a calculator, but odds are that getting a soil test will not only be good for your soil but also will ultimately help you save money by not having to purchase nutrients you don’t need.

Garden tips

•Do not work soil if it is too wet. Tilling it while wet will cause damage to the structure and it will take a long time to recover.

•Thatch is a layer of dead and living stems, shoots and roots which pile up on top of the soil at the base of lawn grasses. If it is over ½ thick it should be removed with either a core-aerator or power-rake. Now is the time to de-thatch Bermuda and zoysia. De-thatch fescue, if needed, in the fall.