May 2021 Horticulture Tips

Saturday, May 1, 2021

Pecan Topics for May

Becky Carroll, Associate Extension Specialist, Fruit and Pecans

Pecan Topics zoom series continue May 7 at 1 p.m. The meeting will cover timely topics for pecan growers and homeowners. Dr. Phil Mulder will discuss control of pecan insects. Training young pecan trees will be explained by Charlie Graham with Noble Research Institute. Four-flap grafting technique will be presented as well as a discussion about recent freeze damage to the state’s pecan crop.

The program is offered to anyone and at no charge. Extension educators who participate will receive in-service credit. Please feel free to promote to your pecan audience.

Information and recordings of previous sessions are available on the Oklahoma Pecan Management webpage or the Oklahoma Pecan Management Facebook page - @okpecans.

Questions can be emailed to becky.carroll@okstate.edu.

Pecan Graftwood Sources

Becky Carroll, Associate Extension Specialist, Fruit and Pecans

The updated 2021 Pecan Graftwood Source List is available on the pecan webpage.

For information on variety selection or grafting techniques, check out the webpage for fact sheets or videos showing different grafting techniques.

Pruning and Feeding Azaleas

Casey Hentges, Oklahoma Gardening Host and Laura Payne, Oklahoma Gardening Field Producer

The Azalea is a true plant for the south. They come in an array of colors and can range from one foot to ten feet tall. With their large, showy blooms, southern landscapes are painted with color in late spring.

Because azaleas are typically spring blooming shrubs, they need to be pruned immediately after they have flowered, to prevent cutting off any new flower buds that develop going forward. Azaleas do not need to be pruned each year, instead it is typically just to maintain the shape or size of the plant and to remove any damaged or diseased tissue. If pruning azaleas to maintain a more appropriate size make sure to take out any of the taller stems by cutting them back to a side branch. For a bit more modest pruning just cut back the tips a couple of inches.

After your azaleas have finished blooming make sure to fertilize. After all, they just spent a lot of energy to create a beautiful floral display, so it is time to reward them. Because azaleas prefer a slightly acidic soil, get a fertilizer that is for azaleas or one that is acid based and apply about 1/4 to 1/2 cup in a circle starting about 1 foot away from the base of the plant. Don’t apply any fertilizer after August because this can cause possible winter damage. Azaleas prefer a slightly acidic, organically rich, moist but well drained soil and thrive in Eastern Oklahoma.

While pruning is not necessary each season, applying an acidic fertilizer is necessary in order to maintain that true southern garden with colorful azaleas.

Rehabilitation or Removal?

David Hillock, Consumer Horticulturist

The decision to save or remove a storm-damaged tree is usually a subjective one, with the choice relying more on opinion than fact. Emotions often are the overriding factor in the decision process, especially when the damaged tree is a very large, old or ‘heirloom’ tree. Here are a few points to keep in mind when deciding whether to rehabilitate or remove your storm-damaged tree:

Use common sense and ask yourself if the damage has perhaps rendered this tree hazardous? In other words, does it now look vulnerable to any additional wind or ice event that could cause it to fall in its entirety or at least “drop” one or more large branches that could damage nearby property or prove fatal to people and pets?
Educate yourself as to the potential growth rate and commercial availability of replacement trees.
Even if the tree can be salvaged, assess whether it will ever look “right” again with some semblance of symmetry.
If significant bark has been ripped or loosened from the trunk, be realistic about the tree’s potential for attack from opportunistic microorganisms and damaging insects outlined later.

Transplanting Tomatoes

David Hillock, Consumer Horticulturist

Tomatoes are one of the most popular vegetables for homeowners to grow and now is the time to get them planted if you have not done so already.

Two main types of tomatoes are available, determinant and indeterminate types. Determinate types set all their fruit at one time, while indeterminate types produce fruit over a longer time. We typically grow indeterminate types in the home garden; however, determinate tomatoes are ideal for small spaces and containers or if you plan to can your tomatoes for later use.

When selecting tomato cultivars for the vegetable garden one consideration is disease resistance. Consider selecting varieties resistant to Fusarium wilt and nematodes since these are problems in all areas of Oklahoma.

The ideal tomato transplant should be six to eight inches tall and dark green, with a stocky stem and well-developed root system. Normally, six to eight weeks are required to produce this type of plant from seed. When selecting plants at the garden center, do not be fooled into to buying the biggest, tallest tomato plants, a short, stocky plant is a better choice.

The number of plants needed, will depend on your planned use. If your family is interested in having only fresh fruit, plant three to five plants per person. If you intend to can or freeze fruits, then five to ten plants per person should be grown.

Tomatoes should be set in the garden when the weather has warmed and the soil temperature is above 60°F. These conditions usually occur about April 5 in southern Oklahoma and about April 25 in northwestern Oklahoma. Temperatures below 50°F impair tomato growth. Tomatoes will produce roots along portions of the buried stem. So, to help increase the root system, plant your tomatoes fairly deep. Pull off the lowest set of leaves or even two sets if the stems are very compact, and then set the plants to the depth of the lowest set of remaining leaves. This is much different than the way we plant most other plants but is very beneficial for establishing a strong root system.

Sometimes the only tomato transplants we can find are long and leggy. To plant these, we will dig short trenches about four inches deep and lay the plants down in the trench. Set the plant in the trench and turn the top upward, leaving the top six inches of the plant exposed above the soil line as you fill the soil back in. This will allow roots to develop along the buried portion of the stem and you will end up with a much stronger plant than if you left the long leggy stem above ground. Tomatoes are set two feet apart. Planting them in a line will make it easier to stake the plants later. A stake and weave system works very well in holding up the plants.

It is best to set out tomato plants in the evening or on a cloudy day to keep the plants from wilting and getting too dry. Mulching tomatoes is very important to provide even moisture and prevent fruit from cracking. Place a two- to three-inch layer of organic material such as compost, leaves or hay around the growing plants. Compost, which is dark, will help keep the soil warm. Once the temperatures rise, cover the compost with straw, which has more of a cooling effect.

How to Produce High Quality Tomatoes

Select or prepare soil high in organic matter and sufficiently loose to allow for extensive vigorous root growth.
Apply needed fertilizers and mix into the soil prior to planting.
Obtain husky plants of recommended nematode and wilt resistant varieties. Set them into the garden as early as weather and recommended planting dates permit.
Water in newly set plants with a starter solution.
Provide protection from cutworms and other possible pests of the transplanting season.
Use mulching materials around plants within one month following planting.
Apply supplemental water as needed, drip irrigation being preferred.
Control insects and spider mites as well as leaf and fruit diseases if numbers are increasing week to week.
Windbreaks may be especially desirable as hot, dry weather develops.
Maintain the identity of different varieties to evaluate their qualities and thus determine the more appropriate kinds for future plantings.

For more information on growing tomatoes refer to Extension Fact Sheet, HLA-6012 Growing Tomatoes in the Home Garden.

Powdery Mildew

David Hillock, Consumer Horticulturist

Powdery mildew is a common foliage disease in late April and May. This disease causes a white, powdery-like covering on the upper portions of the leaf. Powdery mildew starts off as small circular areas, but soon covers large portions of the leaf surface. Plants commonly attacked by powdery mildew include apple, crabapple, crapemyrtle, honeysuckle, lilac, oak, pecan, phlox, photinia, rose, willow, and zinnia. Powdery mildew is sometimes found on catalpa, euonymus, quince, privet, and sycamore.

When choosing new plants for the landscape, look for species and cultivars that are resistant to powdery mildew. Newer cultivars of many shrubs and flowers have been selected for powdery mildew resistance.

Lime-sulfur and copper fungicides are organic products that can be used for powdery mildew control. Do not use sulfur or oil within one month of each other or plant damage can occur. Some cultivars of roses are sensitive to sulfur products and may have leaf damage after an application. Some species and cultivars may be sensitive to copper sprays, discontinue use if plant phytotoxicity occurs.

Other plant protection products available for powdery mildew include synthetic fungicides such as Funginex®, Halt®, Immunox®, Fung-Away®, and Fungi-Fighter®. These products are systemic fungicides and provide 10-14 days of control.

Oklahoma's Weather Affects Fruit and Pecan Crops

Becky Carroll

Once again, Oklahoma’s unpredictable weather has hit many of our state’s fruit and pecan growers. If the negative February temperatures did not affect the fruit buds and, in some cases, mature wood, the late April spring freeze may have wreaked havoc on the upcoming crop.

I have heard from many that their peach trees did not bloom this season. For early blooming fruit trees like peach, nectarine, and especially almond and apricots, the loss of the fruit crop is usually the result of a late spring freeze event. This year for many peach and nectarine growers, the winter temperatures in February were just too cold and damaged the fruit buds prior to bud swell. When the trees began to push buds, only leaf buds were seen. The fruit buds or blooms did not break because they were severely damaged. I was amazed to see several apricot trees flowering in March. Apparently, apricot dormant buds are more cold hardy than peach. Now, that does not indicate that we will have apricots but there is a chance unless they were damaged by the recent April 21 freezing temperatures. Some pictures surfaced on Facebook of peaches that were flowering but most that I have observed were not. Why the difference? Well in some cases, those peaches that did flower were seen in towns and neighborhoods where the trees were in warmer micro-climates that protected the buds.

Apples, pears and cherries seem to have fared better. These types of fruit trees have higher chilling requirements and do not normally bloom as early but are also better adapted during dormancy for cold winter temperatures. The fruit development in some areas may be affected by the mid-20 temperatures experienced on April 21. Cell damage to the fruit can cause misshapen fruit but it is too early to tell just yet.

Wind machines, helicopters, propane heaters, and burning haybales were being used in different areas of the state on April 21 to try to protect different fruit crops. Some growers were successful and protected the crop and some methods did not produce the results that they had hoped. Mixing the warm layers of air with the colder layers near the ground when using wind machines and helicopters can raise the temperatures a couple of degrees. Two to three degrees may be enough to save a crop of peaches or pecans. In pecan orchards, it is not uncommon to see the lower half of a tree lose the crop and the upper half produce a large crop due to the radiational freezes settling near the ground. Mixing the air can give some protection when the right air inversions in place.

Frequently I receive questions about using sprinklers for freeze protection. Watering the ground underneath the trees a few days prior to a spring freeze will allow the soil to stay warmer. Wet ground can hold more heat while dry ground will cool off more quickly. Plants in areas with sandy soils may have more damage than clay soils due to water holding capacity and heat storage. Spraying the trees once prior to a freeze really will not give much protection. The energy or heat released is made possible due to the water freezing. So, for sprinkler freeze protection, the water must be continuously freezing during the critical temperatures until the temperatures warm above freezing. This can be difficult to accomplish due to the amount of water needed or the amount of ice building up on the trees. Once the water stops sprinkling and freezing, the heat protection stops.

Site selection and surrounding areas can make a big difference in how much damage may be received due to cold temperatures. Higher elevations and sloping areas will benefit in that cold air, like water, flows downhill and collects in the lowest areas. If your pecan orchard or vineyard is at the bottom of a valley or hill, there is nowhere for the cold air to go and it will fill up the site with cold air. If the site is on a hillside or at the top of a hill, the cold air can settle away from the planting site and can protect the plants. Be aware that even though the plants are on a hill, something impeding the cold air can have the same effect as being at the bottom of the hill. An overgrown fence row, brush pile, building or anything that slows down the cold air from draining can cause it to pool on the side or top of the hill which can result in cold injury. This was recently observed at the Cimarron Valley Research Station where brush piles kept cold air up on the higher pecan orchard causing more damage than the lower orchard that had air drainage available.

Many vineyards reported freeze damage from both winter and spring freeze events. Those vines with severe winter injury (many European grapes) may need to be replaced or if new growth sprouts from own-rooted vines, they can be re-trained. Those vines that lost new shoot growth may have an opportunity to still produce a crop. Some varieties will produce on secondary buds but not all types.

Pecan growers will need to assess their damage. If female flowers were killed, the potential crop will be lost. Careful observation for an upper crop should be made. Continued zinc applications when new growth begins will help with replacing new healthy foliage. If the 2021 crop is lost, trees should continue to be managed with reduced inputs since next year’s crop can be affected by management this season.

Grape shoots showing freeze injury at Cimarron Valley Research Station on April 21, 2021.

Photo 1 – Grape shoots showing freeze injury at Cimarron Valley Research Station on April 21, 2021

Pecan growth on lower limbs received injury from freezing temperatures on April 21, 2021.

Photo 2 – Pecan growth on lower limbs received injury from freezing temperatures on April 21, 2021.

Pecan grower North of Tulsa employing helicopters in the orchard to try to save pecan crop during spring freeze event.

Photo 3 – Pecan grower North of Tulsa employing helicopters in the orchard to try to save pecan crop during spring freeze event.

Selecting Evergreen Trees for the Landscape

David Hillock, Consumer Horticulturist

“Evergreen” refers to plants that normally retain most of their foliage through the winter. When evergreen trees are mentioned, the pines, plants belonging to the genus Pinus with needle-like leaves often are thought of, but there are other types of evergreen plants such as junipers with scale- or awl-like leaves and cherrylaurel with broad leaves.

Even though evergreen trees retain their foliage year-round, they do not retain all their leaves indefinitely. For example, southern magnolia, a broadleaf evergreen, and loblolly pine, a needle-leaf evergreen, usually drop leaves that are three years old each year. These older leaves are the innermost ones toward the main trunk. Younger leaves, further out on the branch, are retained until they are three years old. This annual browning and drop of innermost, older needles can cause concern, but it is a natural process.

Evergreen trees lend year-round interest, color, and texture to the landscape. They can help define your garden space by providing structure, which can serve as the backdrop for other plants. This structure is the secret to a beautiful winter garden. Evergreen trees are versatile and can be used as specimens, hedges, privacy screens or windbreaks. They also can be used for sound-reducing purposes, wildlife shelters and shade.

Because there are so many evergreen trees for use in landscaping, carefully select plants appropriate for your needs. Selection should be based on several different factors such as intended purpose, environmental conditions, and maintenance requirements.

The intended purpose should influence selection of plants with appropriate shape, size and other physical characteristics. Consider the size of mature trees and where they are to be used. Trees that grow tall, such as the loblolly pine, are suitable for larger buildings and spaces. They tend to dominate or hide one-story buildings. For attractive and proper balance with one-story buildings, choose trees more in scale with the building size. Careful consideration of mature size will reduce the need for pruning.

Environmental conditions also should influence the selection of plants. Site characteristics such as sunny or shady, wet or dry, exposure to winter winds or pollution are important. Plants selected should be tolerant of existing conditions and be cold and heat hardy in the Oklahoma climate.

Finally, consider how much maintenance the plant will require and any possible disadvantages including susceptibility to attack by disease and insect pests, soft or brittle wood that is easily damaged by wind and ice, fruits and seeds that are large, messy or otherwise obnoxious and abundant shedding of twigs and small branches. Plants that may exhibit these types of characteristics can still be used but should be carefully placed.

For more information and a comprehensive list of suggested evergreen species for Oklahoma see our fact sheet HLA-6463 Selecting Evergreen Trees.

Planting Trees

David Hillock, Consumer Horticulturist

To ensure successful tree establishment, the following planting techniques and methods should be used.

When to Plant

The best time to plant most trees is spring or fall; however, many trees can be planted any time if handled properly. Plants installed during the growing season are susceptible to high transpiration rates leading to desiccation of plant tissues.

Early fall - best time for container - grown and balled & burlapped (B&B) trees.
Mid-February through mid-April - bare-root.

Handling Trees before Planting

Avoiding unnecessary damage and stress to trees prior to planting will ensure better success.

Keep root-ball moist
Handle tree by the container, not by the trunk.

Preparing the Hole and Planting the Tree

Preparing the planting hole properly before planting is very critical. When working with heavy clay or sandy soils, organic matter such as composted manure, etc., can improve soil properties.

Add soil amendments to entire planting area prior to digging the hole. Do not apply amendments to backfill only.
Dig planting hole 2-3 times the diameter of tree’s rootball and no deeper than the root ball itself.
Plant trees at original grade OR plant trees 1-3” above grade if soil is poorly drained.
Do not put crushed stone or gravel in bottom of hole!
Remove all bags, containers, strings and wires. Burlap of B&B trees may be left on to decay but be sure to lay burlap back away from trunk and cover with soil. Synthetic burlap is used by some growers and should be removed.
If roots are excessive and circling inner walls of pot, shave about ¼ to ½ inch off all edges of root ball. Inspect for girdling roots and remove if possible.

Backfilling the Planting Hole

Fill in the planting hole (backfill) with native soil and tamp lightly. Soil amendments are not necessary and may result in further complications such as root rots.

Fertilizing: A new tree has a very limited capacity for utilizing fertilizer until it starts to establish itself. Do not overfertilize the new tree. If fertilizer is needed based on a soil test:

Incorporate fertilizer into entire bed area.
Do not dump fertilizer into bottom of planting hole.

Watering the New Tree

Apply at least one inch of water weekly during the growing season. Water should not stand longer than 20 minutes. In some soil types, surrounding soil may be moist while the root-ball itself is dry. Be sure to occasionally check the root-ball for adequate moisture.

Mulching the New Tree

New trees should be mulched using an organic mulch 1-2” deep; keep mulch at least 1-2” away from trunk of tree. Benefits of mulching to create a weed and turf-free area about 5-6’ in diameter include:

Reduced plant competition for water and nutrients.
Even soil temperature and moisture.

Pruning the New Tree

Avoid overpruning new trees. Leave lower limbs intact if possible. Remove injured or diseased branches only. Overpruning may result in sunscald and overall depressed growth.

Trunk Protective Materials

Protective wraps can provide physical protection against equipment, animals, insects, people, herbicides, etc. Protective wraps also provide protection by modifying temperatures and bark moisture for thin-barked trees such as ash, birch, linden, and maple.

If misused however, damage may occur in the form of trunk girdling or constriction, insects, diseases, and excessive moisture.

Protective wraps may not be necessary at planting time. Use based on type of protection needed.
Wrap loosely from base up to first branch by overlapping for shingle affect.
Do not use plastic twine.
Plastic guards should fit loosely and include holes or slits.
Plastic lasts longer and is quite resistant to rodents.
Inspect for damage and insects and spray for borers when necessary.

Staking Trees

Stake young trees sparingly and briefly when possible. Stake when top-heavy or planted in windswept areas. Always allow for sway. Too tight or prolonged staking results in an overall weaker tree. Remove stakes after one growing season or as soon as tree is sufficiently rooted.

Bagworms

David Hillock, Consumer Horticulturist

Bagworms can be a real nuisance on many plants. In Oklahoma, the most common hosts are eastern redcedar, other junipers, and arborvitae. Other hosts sometimes damaged include pines, spruce, bald cypress, maple, boxelder, sycamore, willow, black locust, oaks, and roses. The bagworm has been recorded on 128 different plant species in various parts of the United States.

Symptoms

Bagworm larvae damage their hosts by feeding on the foliage. Heavy infestations can completely defoliate small plants. Defoliation usually kills hosts such as redcedar and other junipers. Broadleaf hosts are not killed but are weakened and become more susceptible to borers and diseases.

Life Cycle

The overwintered eggs (in the year-old female bags) begin to hatch in late April or early May and the young larvae begin to feed and construct bags immediately. The first evidence of an infestation is normally a small bag, about 1/4-inch long, standing almost on end. As larvae grow, silk and fragments of the host plant foliage are added to the bag until it reaches 1 1/2 or 2 inches long. When larvae are mature, they fasten the bag to a plant stem with silk. Pupation occurs in the bag in August and males emerge in late August and September. They engage in a mating flight in search of the wingless females still inside their bags. After mating the female lays several hundred white eggs inside her old pupal case, drops from the bag, and dies. There is one generation per year.

Description

Adult males are small, clear winged moths with a black, hairy body and a wingspread of about 1 inch. Adult females are wingless, have no functional legs, eyes, or antennae, and are almost maggot-like in appearance. The female’s body is soft, yellowish white, and practically naked except for a circle of woolly hairs at the posterior end of the abdomen. Mature larvae have a dark brown abdomen, and the head and thorax are white, spotted with black. They are about 1 inch long. Both larvae and adult females are found in silken bags on the host plants.

Cultural control

Infestations can be reduced by handpicking bags (and overwintering eggs within bags) during fall, winter, or spring before eggs hatch. Eggs remain viable within bags so be sure to destroy bags upon removal by crushing or burning them. When larvae become active, bagworms can still be removed by hand if the numbers are small and the affected host plants are small enough to reach the canopy. Again, take care to destroy the bags once they are removed.

Biological control

There are several naturally occurring parasitic wasps and predatory insects that attack bagworms. The activity of these natural enemies apparently explains the fluctuation in bagworm populations observed from year to year.

Dothistroma Needle Blight of Pine

David Hillock, Consumer Horticulturist

Dothistroma needle blight is a serious disease of pine trees in Oklahoma that causes premature needle drop. The disease affects both landscape plantings and pines in windbreaks. Austrian (Pinus nigra) and ponderosa (P. ponderosa) pines are highly susceptible while Scots or Scotch (P. sylvestris) pine is resistant to this disease. When Dothistroma needle blight is left uncontrolled, trees may be weakened and eventually killed.

Symptoms

Although needles are infected in the spring, the symptoms do not develop until the fall. Early symptoms consist of yellow and tan spots that may be bordered by a water-soaked band. As the spots enlarge, the tips of the needles will die while the needle bases remain green. The dead portion of the needle may break off leaving a blunted tip. Needles may be prematurely shed or cast from the tree, especially needles on lower branches. Winter desiccation injury causes symptoms similar to Dothistroma needle blight. However, needles damaged by winter desiccation will show browning of tips to roughly the same point on the needle. The amount of tip browning caused by Dothistroma needle blight is variable.

Disease Cycle

In late winter, fruiting structures are visible as small, erumpent black dots along the blighted needles. Fruiting structures mature in mid to late spring and conidia (spores) are spread by rain splash through the growing season (May to October). Although infections occur throughout the growing season, symptoms are not evident until fall. Two seasons are required for the pathogen to complete its lifecycle.