Rose rosette and microscopic mites

A writer from the News Journal heard about invasive microscopic rose bud mites in Delaware that are killing plants.  She became concerned and wanted to learn more about this situation.  These are very small eriophyid mites that spread rose rosette disease, also known as witches’-broom of rose, which is caused by a virus (Emaravirus sp.). The disease is limited to plants in the genus Rosa but some roses are believed to be resistant. Its main host is the multiflora rose, which is considered an invasive plant in Delaware. Multiflora rose has a small white flower in early spring and has taken over many natural areas in Delaware.  It can grow as a shrub or a vine and become intertwined with other shrubs and trees in the woods.  Interest in rose rosette has been generated by the threat to garden roses and also its possible use as a biocontrol for multiflora rose.

Rose rosette disease starts as a red color on the underside of leaf veins and quickly progresses to sharply increased growth at branch tips.  The growth is more succulent than normal and colored in various shades of red. Leaves often become deformed, crinkled, and brittle with yellow mosaics and red pigmentation. As the disease progresses, leaves become very small, petioles are shortened, and most lateral buds grow, producing short, intensely red shoots (witch’s broom). The disease causes the plant to be exceptionally susceptible to freeze damage. Symptoms on cultivated roses are typically less severe than on multiflora rose. Symptoms can be confused with some forms of herbicide damage.

The disease is transmitted by an eriophyid mite, a wingless mite that can travel passively in the wind as well as on contaminated clothing and equipment. The mites feed and reproduce in the tips of rose shoots. Females overwinter under bark or on bud scales of living roses. The females move to newly developing shoots where they lay one egg a day for about 30 days. The young hatch in 3-4 days. They can reach adulthood in about a week depending upon temperatures. Multiple generations occur each year until fall when females seek overwintering sites.  The mites are hampered by low humidity and can only survive about 8 hours without being on a host plant.

The virus is transmitted most readily between May and mid-July when plants are actively growing. Symptoms from new infections usually start appearing in mid-July. In general, smaller plants go through the disease stages more quickly than larger plants. Small plants are usually killed in about 2 years, while a large plant may survive for five years in a deteriorated condition.

To control this disease, you can:

  1. Remove ornamental roses with symptoms. Remove and destroy the entire plant including the roots by burning or placing in a plastic bag. Take care when working with diseased plants as you can spread the mites that spread the disease. Bag the plant before removal, cut it at ground level and then dig out the plant’s roots. Soil need not be removed. Clean tools and put on fresh clothing before moving to a disease-free plant or area.
  2. Plant ornamental roses as far away as possible from known stands of multiflora rose. Maintain at least 300 feet between your roses and any stands of multiflora rose. Even greater distance is preferred especially if they are upwind of your desirable rose plants.
  3. Control the disease by controlling the mite. Start mite control early by pruning your roses hard in late winter (back by 2/3) to remove as many overwintering mites as possible and then spray with horticultural oil to kill any remaining mites. Use horticultural oil or soap, which are less harmful to natural predators that feed on the problem mites. Apply weekly during the months of June and July paying particular attention to the new growing tips where the mites will congregate. Refrain from using leaf blowers around roses as they can spread mites.
  4. Help to isolate your roses. Do not plant roses too close together. With extra space between the plants mite movement can be reduced. Also, consider interplanting roses with other ornamental plants.
  5. Using rose rosette disease as an IPM strategy. The multiflora rose is an exotic invasive species that is responsible for the degradation of millions of acres of farmland and recreational areas. Using the disease to control this invasive weed can cut costs and be considered environmentally friendly for reducing the amount of synthetic chemicals used. However, the disease also affects cultivated roses. One should be extremely cautious and good neighbor-minded when it comes to rose rosette disease.

    Multiflora rose growing at the edge of the woods. It would be great if this virus killed multiflora rose without harming our desirable garden roses, but that does not seem to be the case.

    Multiflora rose growing at the edge of the woods. It would be great if this virus killed multiflora rose without harming our desirable garden roses, but that does not seem to be the case.

Weed Control in the Vegetable Garden

With July 4th approaching many Delawareans are anxiously awaiting the first home-grown tomato from the vegetable garden.  You probably have most of your summer crops planted, so now is the time to focus on weed control.  Weeds steal moisture, nutrients, sunlight and growing space from crop plants.  Their presence can reduce crop growth, quality and yield.  They can also make harvest difficult and they provide cover for diseases, insects and animal pests.

The first line of defense is to plant crops in combination, using sprawling crops like squash, pumpkins, cucumbers, potatoes, etc. to shade the ground around taller crops like corn, pole beans, peppers and tomatoes.  This is the concept between the native American planting of the three sisters—corn, beans and squash.  Corn provides structure for beans to climb.  Beans fix nitrogen from the air and put it back into the soil and squash covers the ground to reduce weeds.
Fall planted cover crops that you till in prior to spring planting, like winter wheat, will reduce winter annual weed germination and as a bonus, improve soil by adding compost.

Use mulch to suppress weeds in the vegetable garden.  Many annual weeds require light to germinate, so a relatively thin covering a mulch can reduce many weed problems.  For tougher weeds, use a thicker layer of mulch (3-4 inches).  Organic mulches, like grass clippings, yard waste, shredded newspaper or straw provide some flexibility because they can be raked around existing plants.  Do not use straw with weed seeds.  Salt hay is a good alternative that will not contain seeds.  If you use grass clippings, know their source and make sure the grass has not been treated recently with an herbicide.

Landscape fabric that allows water penetration is an excellent inorganic mulch to use in the vegetable garden.  Install the sheets of fabric at the time of planting.  Landscape fabric can be used for many years if you carefully remove it in the fall and store it indoors over the winter.  Be sure to by good quality, name brand landscape fabric. You can also use black plastic to cover areas of the garden you are not currently using.  Don’t put black plastic around growing crops because it will exclude water.  If you have a fallow section of the garden, even for a few weeks prior to the next successional crop, black plastic can kill existing weeds by excluding light and raising the soil temperature, so that section of the garden is ready for planting when you are ready to use it.

Tilling is another important method of vegetable garden weed control.   It is easier to kill weeds by tilling when they are young.  Seedlings can be dug up and their roots exposed to air with a hoe.  Once weeds get to be 3 inches tall, they cannot be easily tilled and should be hand pulled, using a trowel to get the entire root system.  Once you have hand weeded an area of the garden, cover it quickly with mulch to reduce the need to continue weeding all summer long.

Herbicides can be used with great care in a vegetable garden.  Before a crop is present, glyphosate (commonly sold as Roundup or other generics) can be applied to kill all the present green growth.  Once you have crops in the ground, avoid using glyphosate in your garden.  Treflan can be used to control germinating weed seedling before the crop emerges.  Poast is a grass herbicide that will kill grass plants without harming broadleaf crops.

Weeds are best controlled preventatively in the garden.  Once you have a lush stand of weeds, you will spend many hours removing them.  But, a few hours spent applying mulch or tilling seedling weeds will prevent problems later on.  Never allow weeds to go to seed in the garden.  That increases your weed pressure for later in the season or the following year.

Tomatoes and peppers planted with weed control fabric are completely weed free.

Tomatoes and peppers planted with weed control fabric are completely weed free.

Enjoy those first ripe, red tomatoes!

Container Gardens are HOT

Container gardens are “in” and have been for several years.  Planting in a container allows you to grow plants where you can’t otherwise.  Containers allow apartment dwellers to grow tomatoes, but they also brighten the deck or patio of any home.  Combination planters achieve the look of a “bouquet with roots” providing color all season long.  Even where there is ample room for a garden, well-placed containers provide seasonal accents.

Choose a container that fits your décor or style.  Containers can be amusing, valuable, clever, loud, quiet, classy, creative, solid, sophisticated, stylish, primitive, homespun, friendly, understated, matched or anything you want them to be.  But, they MUST have a drainage hole.

Soils for containers must be well aerated and well drained while still being able to retain enough moisture for plant growth.  Don’t use garden soil in your containers, it is too heavy and won’t drain properly.  Purchase a soilless mix designed for use in containers.  For succulents, herbs and perennials, select a coarse soilless mix with more bark, perlite or sand because these plants need good drainage and you don’t want the mix to retain moisture over long periods of time.  For tropical and foliage plants, choose a media with more peat and less coarse material as these plants tend to prefer moister growing conditions.  Moisten your media slightly before planting by filling a tub with media, adding water and mixing.

Think of your container garden as a living flower (and foliage) arrangement.  Include a tall plant in the center or back of the container.  Select filler plants to provide interest and use cascading plants to soften the edges.  Consider plant requirements when planning combination containers.  Use all shade plants for shady locations and sun-loving plants on a sunny patio.  If you use a combination of sun-loving and shade-loving plants in a single container, there will be no appropriate exposure for the container.  Also, think about moisture requirements.  Don’t combine plants that like it moist with plants that require good drainage.  You can combine shrubs, perennials and annuals, but the annuals will need to be replaced the following year.  Depending on the size of the container and exposure, the shrubs and perennials may overwinter in the container.  Tropicals are fun to add in a combination container, but they will need to be brought indoors to survive the winter.  If you combine a shrub and a tropical, you will have a conundrum—bring it in and the shrub will suffer; leave it outdoors and the tropical will die.

Once you have selected your container, growing media and plants, fill the container (almost full) with media.  Arrange the plants on the surface and play with the design until you are happy with the combination.  Remove each plant from its plastic pot and loosen the roots, especially if they are circling within the container in which it was grown.  Add a bit more media and water thoroughly.  Watering after planting settles the media and eliminates air pockets.  You may need to water several times to insure the media is thoroughly moist.  Make sure water drains out of the hole in the bottom of the pot.  A waterlogged container will not thrive unless you are growing water plants.  Remember to water container plants frequently throughout the summer.  Soilless media dries out more quickly than garden soil.  Fertilize containers a few times during the summer.  Annuals and tropical will need more frequent fertilization than shrubs and perennials.

Evergreen and deciduous shrubs are combined with perennials and annuals in this sumptuous planter combination at Longwood Gardens.

Evergreen and deciduous shrubs are combined with perennials and annuals in this sumptuous planter combination at Longwood Gardens.

Striking architectural container set by the pool at Chanticleer.

Striking architectural container set by the pool at Chanticleer.

If you want inspiration for designing container plantings, visit a local public garden.  Longwood Gardens in Kennett Square, PA and Chanticleer in Wayne, PA have spectacular planted containers throughout the gardens.  You can also buy combination containers already planted and ready to place on your deck or patio from most local garden centers.

Pears on the roadside – Beauty or Beast?

Sue Barton

Roland Roth, retired Entomology and Wildlife professor from the University of Delaware, wrote a short piece in the New Journal on Friday highlighting the invasive callery pear that is so prominently blooming on Delaware’s roadsides this April.  He said while they may seem pretty, they are crowding out native plants that once existed on natural land in Delaware.  He went on to suggest that everyone do their part to cut down invasive plants (especially pears, but also burning bush, barberry and butterfly bush) on their properties and replant with native plants that support native wildlife.

A few days later another article appeared in the News Journal.  It seems Patricia Dougherty took a ride downstate and never enjoyed it so much.  “The white trees that were blooming on both sides of the road were beautiful.  Some even looked like white Christmas trees.  I do not know what kind of trees they are.  I would love to know.”  Those trees are callery pears

Pears along Delaware's roadside in April.

Pears along Delaware’s roadside in April.

In fact, callery pear is spreading like wildfire on Delaware roadsides.  Once we just planted the cultivar ‘Bradford.’  This tree has a nice conical habit, white flowers in the spring and attractive maroon fall color.  What is not to like?  Well, Bradford pears have a nasty habit of branch splitting when the trees reach about 15 years of age.  Large limbs can break out of trees and fall on cars, even pedestrians.  This became such a problem that about 10 years ago, Newark removed all the Bradford pears on Main Street and replaced them with other tree species.  The nursery industry responded to the problem of weak branches by breeding other callery pear cultivars that have better branch structure.  Some examples include ‘Aristocrat’, ‘Chanticleer’ and ‘Redspire’.  While Bradford alone produced a small amount of fruit, the fruit production of callery pears skyrocketed with all these new cultivars for cross pollination.  That is when callery pears started escaping into disturbed areas along our roadways and crowding out native species.  At one time, not too long ago, when you drove past a wooded stretch in Delaware and saw a white tree blooming at the edge of the woods, you could be pretty sure it was a serviceberry (Amelanchier canadensis), a beautiful native trees sometimes also called shad bush; and you knew the shad would be running on the Susquehanna. Now, there are few serviceberries remaining and LOTS of callery pears.

Proper watering

Overall, we’ve had a great rainfall year for plants in most of the state, but that doesn’t mean you can forget about watering. I have received a number of questions about failing plants and often the answer to the question or solution to the problem has something to do with watering. Let’s start with the lawn:

In Delaware, you do not need to water your lawn to keep it alive, even when we have a drought; UNLESS you have new seed or new sod. Then you must keep the soil moist until the seed or sod becomes well established. But, if we forget about new lawns for a moment, the only reason to water a lawn in our climate is to keep it green throughout the summer. That may be important if you are a golf course and make your money based on the playability of your course. But, if you have a regular home lawn, does it really make sense to spend one of our valuable resources, water, on keeping a lawn green all summer long? If you don’t water, your lawn will go dormant. The grass will turn brown, but as soon as normal rains return in the fall, the grass will green up again. If there are a few spots on your lawn that don’t green up, they are indicators of a more serious stress on the lawn that should be corrected, such as compaction, insect infestation or inappropriate high traffic use. Those spots should be fixed before the problem spreads to the rest of the lawn.

If you are establishing a new lawn or renovating an existing lawn, it is critical to water your new seed or sod properly. Supply enough water at a slow enough rate to soak at least one inch of soil and ideally 3-4 inches. With new sod, you may need to water daily for the first week or so. Then as the sod starts to root into the soil, slow the watering to weekly. For newly planted seed, keep the soil moist. Since the soil is exposed or covered in straw mulch, it is easy to monitor soil moisture. For windy, sunny, open areas of lawn, that may require daily watering. When applying water to a newly seeded or sodded lawn, use a sprinkler or soaker hose and water in the morning so you don’t lose too much to evaporation. Avoid evening watering. If the grass stays moist all night, it is easier for fungal diseases to spread.

Shrubs and trees, once established, rarely require watering, but there is a misconception about how long it takes for a plant to become established. We usually say it takes one year for every inch of caliper on a tree. Thus, a four-inch caliper tree, will take 4 years to become established. That means if we don’t get enough rainfall during the spring, summer or fall, the tree will require supplemental watering, for the next four years. If you planted a landscape in the early spring, most of the shrubs will be established by that summer, but you should still check soil moisture around those plants to make sure they are getting enough water. There are some trees that don’t tolerate drought well. Katsura (Cercidiphyllum japonicum) is one example; it will lose most of its leaves in August /September if we have a dry spell. It may be appropriate to provide some supplemental water during dry periods to specimen or special plants.

When you water a landscape shrub or tree, apply the water slowly. Especially with heavy clay soils, water will start to run off after the first minute or so. Water is not getting to the roots, where it is needed, if it is running down the hill. Gator bags (those green plastic bags that zip up around the tree trunk) or simply a 5 gallon bucket with holes punched in the bottom, will allow you to fill the container all at one time and then the water can seep into the soil slowly.

Container plants on your patio or deck require frequent watering. In most cases they are planted in a porous soilless container mix that is light but doesn’t hold much water. Also, as we near the end of the season, roots have started to fill those containers so there is even less soil volume available for absorbing water. In a hot, sunny location a container plant, especially a hanging basket, may need daily watering. But, it is always best to check moisture in the soil or container mix before adding water.

In fact, overwatering can be as big a problem as under-watering. Surprisingly, the symptoms of too little and too much water are often the same. When a plant is under-watered, it doesn’t take up enough water through its roots so there is not enough water to be carried through the stems out to the leaves. Leaves start to brown on the edges, eventually turn crispy and finally die. When plants are overwatered, their roots can rot, which means they aren’t taking up water and the plant looks like it is suffering from drought. Well-meaning gardeners just water more, which makes the problem worse. Always check the soil to make sure it is no longer moist before you apply more water.

Watering may seem like a mindless task but in fact the person in charge of watering is one of the most important people at a plant production nursery. He or she can make or break the success of a crop by the way it is watered. So, pay attention to how you water your plants at home. Let’s hope we get consistent fall rains, and nature can take over the task of watering. But, it is always a good idea to check for yourselves and make sure your container plants, newly planted shrubs and trees, new lawns and special specimen plants have the RIGHT amount of water.

Gator bag used to slowly water this newly planted tree.

Gator bag used to slowly water this newly planted tree.

August – Time to Renovate

It is hard to believe, but August is right around the corner.  That means it is time to start thinking about renovating the lawn.  We have had such a moist summer, that lawns have not really gone dormant.  But, your lawn may have dead spots or weedy areas you want to fix.  Maybe your lawn is a complete disaster and you want to undertake a complete renovation.  The first step is to decide where you want lawn and where you can choose a different type of landscaping.  Just because you have always had a one acre lawn in your front yard, doesn’t mean you have to keep that area in lawn.  Think about how you use the lawn—for recreation, for circulation through your landscape, and as a gathering space.  Make sure your lawn is actually useable space.  What you plant instead of lawn is a topic for another column (one that I have covered before but it can’t be said to much so stay tuned).

For the area you want to be lawn, evaluate its current condition.  Is it full of crabgrass?  If so, is that because you are mowing the lawn too close?  A lawn maintained at 3” usually doesn’t develop crabgrass because the crabgrass seed doesn’t receive the light it needs to germinate.  Or do you have weeds because the turfgrass is so patching it isn’t providing any competition against weed incursion.  Maybe the soil is so compacted only weeds can grow.

Kill competing weeds before you try to renovate the lawn.  This can be accomplished with a non-selective herbicide, like glyphosate or by covering the area with black plastic and smothering the weeds.  Black plastic is only practical for small areas and takes longer than using an herbicide.  Plants must be actively growing for the herbicide to work.  If you use glyphosate, wait 10 days to 2 weeks to make sure the glyphosate gets translocated throughout the root systems of the existing vegetation.

Take this opportunity to correct soil problems.  Take a soil sample to find out if your soil is deficient in nutrients or if the pH is too low.  Correct a low pH by adding lime.  Add nutrients as recommended by your soil test results.  Core aerate the soil if it is compact.  Core aeration will also facilitate good seed soil contact once you reseed.  Also, consider adding some type of organic matter, such as mushroom soil, manure, composted yard waste to improve the soil structure.  Add a starter fertilizer (containing no more than ½ pound of nitrogen per 1000 square feet of lawn). Once the site if fully prepped, you are ready to seed.

Only seed that contacts soil will germinate, so having open soil or compost is critical for a successful lawn renovation.  Select a turfgrass that works well in your location.  In Sussex County, Delaware, we recommend using only tall fescue cultivars.  In New Castle County, you can also grow perennial ryegrass and Kentucky bluegrass, but tall fescue is the toughest and most drought tolerant of our cool season grass species.  If your lawn is shady (too much shade means you should select a groundcover other than turf), choose red fescue in a blend.  Spread seed using a slit seeder and by simply broadcasting seed over the site.

Add a light layer of straw or salt marsh hay as mulch on top of the seed.  This will help keep the soil moist and control some of the weeds that might compete with your newly establishing turf.  Keep newly seeded lawn moist with a sprinkler, soaker hoses or irrigation system.  If you have perennial ryegrass in the mix, expect germination in 4 to 5 days.  Tall fescue can take up to 10 days to germinate.  You can cut the grass for the first time when it reaches 4 – 4 1/2 inches.  Cut off 1 – 1 1/2 inches to bring it back to 3 inches.  Be sure to use a sharp mower blade when cutting newly seeded grass.  Once you have cut the grass a few times, you can add about one pound of nitrogen per 1000 square feet.  Don’t forget to keep the new grass moist.  By this time we should be into September and nights should be getting cooler.

If you only have a few bad patches in a lawn, you may not need to undertake a complete renovation.  Kill perennial weeds if they are a problem and rake out the area so soil is exposed.  Spread the seed and continue as above with straw mulch and watering.  Spreading grass seed on top of existing vegetation with no soil exposed is a waste of time. Late summer and early fall is the best time to renovate the lawn because soil temperatures are still warm enough to promote good germination, but air temperatures are beginning to cool, promoting growth of cool season turfgrasses.

Be sure to follow me on Instagram (sbartonhort) for gardening tips and interesting horticultural news.

This attractive combination of lawn and meadow at Chanticleer Gardens in Wayne, PA, shows lawn used as a means of circulation and as a gathering space.

This attractive combination of lawn and meadow at Chanticleer Gardens in Wayne, PA, shows lawn used as a means of circulation and as a gathering space.