Getting Ready for Spring Planting? Reduce Seed-borne Diseases with a Hot Water Seed Treatment!

As we head into March, we begin to prepare for spring gardening once again! This includes tasks like wrapping up any necessary winter pruning and ordering seeds to plant for the upcoming year. With internet shopping of seed catalogues being more accessible than ever, many people will find that they can purchase the exact crop and cultivar they want with the push of a button. Varieties can even be filtered by yield or disease resistance.

Other people however, may wish to use heirloom seeds from their own or a neighbor’s garden, or organic seeds that aren’t pre-screened or treated for seedborne diseases. Although gardeners may have grown to anticipate some losses with these seeds due to seedborne diseases, a solution exists for many in the form of a hot water seed treatment (HWST).

What is a hot water seed treatment (HWST)?

It is exactly what you might expect: hot water is used to kill pathogens present on the surfaces of seeds before they are planted. For some types of plant diseases, this is an effective means to reduce disease incidence and give young plants the opportunity they need to become established and grow well. Seeds are “prepped” for treatment by first being submerged in a lukewarm water bath of 100 degrees Fahrenheit for 10 minutes. The seeds can then be moved to a bath set at the “treatment temperature”, which varies by crop type. After treatment, the seeds are gently, but thoroughly dried-off so they do not germinate prematurely.

Pure distilled water is pumped into the water baths.

Our equipment can precisely regulate water temperature!

An aquarium air bubbler helps move water and decrease damage to seeds that may overheat by staying still

The bubbler is kept at the base of the water bath using some removable weights (washers!)

The seeds are ready for the plunge!

Quick, gentle drying using only a fan is important so seeds are not damaged.

HWST process in photos. Photo credit: Nick Goltz, DPM

What types of seeds can undergo HWST?

Many types of seeds can undergo HWST for disease mitigation, but generally it is performed on small and hardy seeds. Large, fleshy seeds such as beans or pumpkin seeds may benefit from HWST in terms of disease reduction, but are more sensitive to damage from the hot temperatures and may have accordingly lower germination rates. Therefore, we only recommend HWST with seeds whose germination rates have been shown to be minimally impacted by the high temperatures. Additionally, seeds that have already been treated with HWST or fungicides, or those that have seed coatings (often these are a different color than uncoated seeds), should not be treated.

What diseases will HWST target?

There is ongoing research into what diseases can be successfully mitigated with HWST. Treatment efficacy varies by crop, but generally the diseases are those that will show up shortly after germination, while the plants are still seedlings. The UConn Plant Diagnostic lab and other university extension services that offer HWST will list the types of plants recommended for treatment and the diseases that can be controlled. Visit https://plant.lab.uconn.edu/hwst/ to find out more. The UConn PDL is funded, in part, by the state of Connecticut and the USDA through IPM Extension Implementation and National Plant Diagnostic Network grants.

Nick Goltz, DPM

 

Powdery Mildew: a Perennial Problem that I Don’t Usually Mind

I have to admit I get somewhat excited when I see the first fuzzy powdery mildew spots of the season appear. It’s almost like playing the plant pathology lotto, betting when the environmental conditions (warm, dry days followed by cool, humid nights) are just right for the fungi to cause disease. This year, I saw the first spots on roses in mid-June. I had just received a photo from a client with a strange white growth on her rosemary transplant, and I initially thought it was too early for a powdery mildew diagnosis. But alas, I was wrong.

Powdery mildew on rose. Photo by A. Beissinger.

Powdery mildew is a disease caused by several different species and genera of fungi. Though you may see powdery mildew on herbaceous perennials, vegetables, and woody ornamentals, each species of powdery mildew fungi is usually host specific. The powdery mildew on your cucumber plant is not causing powdery mildew on your maple tree. Instead, you hit the powdery mildew jackpot and happen to have more than one species in your yard. In the lab, we identify the fungus to genus based on characteristics of their chasmothecia, or overwintering structures.

Black chasmothecia, overwintering structures on English oak. Photo by A. Beissinger

 

Powdery mildews are identified based on the morphology of chasmothecia. Pictured here is Microsphaera sp. Photo by A. Beissinger.

One of the most common questions we get in the Home & Garden Education Center is about chemical treatments for powdery mildew. Due to the biology of powdery mildew fungi, we don’t usually recommend spraying anything for woody and herbaceous perennials and here is why: powdery mildew only causes aesthetic damage and will not jeopardize the health of your plants. The fungi are obligate parasites, meaning they require a living host plant to grow, obtain nutrients, and thrive. As such these fungi have a biological incentive to keep their host plant alive; if they kill their host plant, they would not survive. It’d be more useful for you to save money and not spray a product  into the environment that will have very little success at controlling the disease.

The answer about chemical controls is a bit different for fruit and vegetable crops such as apple, grape, and cucurbits. While powdery mildew doesn’t necessary kill the host plants, the disease can present challenges for fruit quality, consistency, yield, and taste. Fruit can be deformed, have blemishes, or other markings that render them unmarketable, and produce far less than normal. In these cases, we may recommend a sulfur, neem oil, triforine, or potassium bicarbonate product. Always read the pesticide label before applying any product, and please note that chemical controls are usually only effective when appropriate cultural controls are taken as well.

Apple powdery mildew. Photo by J. Pscheidt

So, what are these cultural controls?

• Start off with resistant cultivars. Selecting plant varieties that have resistance to powdery mildew is one of the most important strategies to help prevent infection. There are many options to choose from, and require you to plan ahead before you begin planting. Garden centers and seed catalogues can be very helpful.
• Space plants adequately. Dense plantings can increase humidity, which can in turn increase disease development. Remove plants to improve airflow.
• Avoid overhead watering. Using a soaker hose, drip irrigation, or watering plants only at the base can help decrease humidity in the planting.
• Thoroughly clean up all infected plant parts at the end of the season. Many herbaceous perennials are left by gardeners to maintain fall habitat for pollinators. However, removing all infected plant parts at the end of the season will decrease the inoculum able to overwinter and infect plants the following year. Do not compost infected plants as at-home compost systems do not reach temperatures high enough to kill the fungus.

One other note about diseases in the garden: powdery mildew mycellium (a mat of fungal growth; the “fuzzy” growth you see) typically grow on the upper leaf surfaces of plants, and unlike other fungi, will not grow when a film of water is present on the leaves. Occasionally mycelium will grow on the lower leaf surface, but that is less common. If you’re seeing powdery white-grey spots only on the lower leaf surface, more than likely you’re seeing downy mildew, which is a far more serious disease. These diseases are often confused for each other because of their name and appearance. Downy mildew is caused by an oomycete rather than a fungus, and spreads when water is present. Early action is required to save your plants.

Downy mildew on grape. Note the spores are present only on the lower leaf surface. Photo by A. Beissinger.

For more information on powdery and downy mildew, visit our website for fact sheets.

-Abby Beissinger

 

What a Little Rain Can Do

This summer has been, as they say, one for the books. High temperatures that went on for weeks and limited rainfall certainly did a number on our gardens, containers, and flower beds. Many calls to the Home & Garden Education Center were from gardeners bemoaning the sad state of affairs. Plants were stunted, didn’t set flowers or dropped them early when they did, leaves were scorched looking, and in general plants just performed poorly.

What a relief when the temps dropped into the 80s and rain actually fell in measurable quantities. Plants rebounded, lawns revived, and gardens began to produce once again. My window boxes and some hanging containers did not quite survive though and I refilled most of them this week with some beautiful flowering vinca and a plant that is new to me, evolvulus, a member of the morning glory family that produces tiny, bright blue flowers that last just a day.

The squash plants that I thought were done for have now taken over their areas and are producing copious blossoms and fruit. I am happy to see that the Powdery mildew resistant variety (Success PM) has proven its worth as there are very few signs of the disease.

The squash bugs however have yet to give up the fight. There are still egg masses every few days and the odd grouping of nymphs that I am not sorry to say do not last long once I have spotted them.

The cucumbers and the eggplants are loaded with blossoms and have started bearing fruit. The tomatoes, which hadn’t suffered as much as some of the other plants, have been slow to ripen but they can continue to produce into October if they are covered at night.

I had moved some potted basil plants into a shady area a few weeks back and they have shown their appreciation by filling out nicely. I detect pesto in our near future! A second planting of arugula looks great as does the kale.

 

 

And we are not the only ones that are enjoying the kale. This differential grasshopper was munching away happily, not even caring that I was filming him. This species of grasshopper (Melanoplus differentialis) has been known to do some substantial damage to crops such as grains, hay, and alfalfa, especially during hot, dry periods which increase the likelihood of survival of the nymphs and adults. They will also feed on annuals such as sunflowers and perennials including one of their favorites: ragweed. Maybe they are not all bad. They don’t cause enough damage in a home garden to warrant insecticidal control.

 

A striped cucumber beetle (Acalymma vittatum) was also enjoying the kale even though the cucumber plants were not far away. The adult feeds on the foliage and the larvae feed on the roots but the biggest problem that they bring with them is the bacterial wilt known as Erwinia tracheiphila which can be fatal to cucurbits. The feeding of the adult beetle opens wounds in the plant but it is through the frass (excrement) that the bacteria enter the vascular tissues of the plant. As the bacteria multiply they block the xylem and prevent water and nutrients from reaching the shoots and leaves. The striped cucumber beetle is definitely a bigger concern than the grasshopper or squash bugs as they move so quickly that it is hard to just squish them out of existence like I do with the squash bug nymphs.

Over on the asparagus fern a red milkweed beetle (Tetraopes tetrophthalmus) stood out brightly against the delicate ferns. As with other insects that also feed on milkweed the red milkweed beetle accumulates alkaloid toxins in their flesh that protect it from predators. The black spots against that bright red-orange background are the insect equivalent of a large ‘Do Not Eat” sign. These can be picked off and dropped into a container of soapy water. Don’t use a spray or systemic insecticide on the milkweed as it will harm the beneficial insects that also visit, especially the Monarch butterfly.

The Asian lady beetle has that same bright coloring and also uses a defensive chemical to deter predators. Some humans are allergic to this foul-smelling liquid that can be exuded from their legs. But this one was very busy doing what ‘ladybugs’ do best, munching on some aphids that were on the underside of a squash leaf.

 

The lady beetles may start to congregate both inside and outside of houses and can be a nuisance. Visit our fact sheet for information on the Asian lady beetle if you experience an infestation and consider the non-lethal ways to remove them, keeping in mind how beneficial they will be in next year’s garden. Although the nighttime temperatures can start to dip into the 50s as we progress into September the garden will enjoy the still warm days into October.

Susan Pelton

All images and videos by S. Pelton

 

 

Tomato Troubles: Blossom End Rot, Yellow Shoulders and Cracking

 

Cracks in tomatoes, black rotten spots on the bottom of tomato fruit, and a hard yellow or white area on the inside walls of ripe tomatoes are all physiological problems, not caused by insects or disease.  It is a sad sight for gardeners investing so much time and energy to see the actual fruits of their labor turn into less than perfect tomatoes.

 

Cracked Tomato

Let’s start with why tomatoes crack. Higher moisture levels after a dry period, such as lots of rain after a time of drought, will cause the inside cells to swell and grow faster than the outside skin will grow, resulting in splitting of the skin. To prevent cracking, keep soil evenly moist by watering, and use a mulch to prevent evaporation and keep soil cooler. Cracked tomatoes are still very edible, but not so pretty. Sometimes the cracks are deep, allowing rot to happen inside the meat of the fruit. Plan to use split tomatoes before rotting happen.

Blossom End Rot, photo by Joan Allen.

Blossom end rot is expressed by a black, sunken area on the bottom, the blossom end, of the tomato. It is caused by a lack of calcium reaching the fruit. The soil could be lacking calcium which can only be determined by having a soil test done for nutrient levels. UConn does a basic soil test for $12.00 at soiltest.uconn.edu. New England is not usually lacking calcium in its soil, it is more likely the cause of blossom end rot is an interruption in the delivery of calcium from the soil to the fruit via water uptake. This is caused by irregular watering, letting the soil dry out, then watering or having a big rain event. Occasionally, high levels of potassium or magnesium fertilizers will compete with calcium uptake by the plants. Only use a balanced fertilizer to avoid an excess of individual nutrients and provide even water levels to the soil to avoid blossom end rot. Portions of the tomato not rotted are also still edible if you cut away the bad part.

Yellow Shoulders, hort.purdue.edu

Yellow shoulders disorder occurs on the top part of the tomato when areas never turn red, but stay yellow. The flesh underneath can be tough and corky. It can occur only on the top portion or can occur as a grey or white wall just under the skin around the whole fruit.This problem is caused by a number of different circumstances or combinations of them. We do know it is a problem at the cellular level that happens very early as the fruit is forming.  Cells in the area are smaller and not aligned normally, and the green chlorophyll areas do not develop red pigment. Causes are thought to be high temperatures over 90 degrees F at time of fruit formation, and possible pH levels over 6.7, and potassium, magnesium and calcium competition among each other. Again, a balanced fertilizer is needed.

Tomato with white walls, yellow shoulders, photo by Becky M.

 

The take away message for all of these physiological problems are to have an adequate soil fertility and soil pH without over fertilizing, and have even soil moisture. Hope for summer temperatures to stay at or below 90 degrees F and your harvest baskets will be full of beautiful, delicious tomatoes.

-Carol Quish

 

 

A Blight of Pachysandra

The Home & Garden Education Center has received an abundance of inquiries related to Japanese pachysandra, (Pachysandra terminalis) during the last few weeks. Homeowners all over Connecticut are experiencing difficulty with this groundcover. It first becomes noticeable as other things around it start to green up in the spring and we see that the leaves are remaining a sickly shade of yellowish-green.

Affected bed of pachysandra

As it catches our attention we notice that the plantings in general look a bit sad and sparse. A closer look at the leaves will reveal that there are areas of irregular brown blotches that have concentric line patterns within the affected area and pretty sharply defined darker brown edges. The center of the spots will can appear much lighter if the salmon-pink fungal spores are present.

Pachysandra leaves showing signs of Volutella blight

The browning areas will continue to spread and darken and can encompass the entire leaf as it dies. The cankers that can develop on the stems and stolons can girdle the stem and cause the plant to wither and die by disrupting the transport of water and minerals through the plants vascular system.Unfortunately this can happen in as little as two weeks, especially if the weather is wet and humid. It has certainly been wet over the last week and although the total precipitation is around the average 1” needed for growing plants it has come in a slow but steady sprinkle allowing plants little time to dry out between the showers.

This is all the work of the fungus called Volutella pachysandricola, or Volutella Leaf and Stem Blight. This fungus is considered an opportunistic pathogen that attacks weak plants. It can infect leaves, stems, and stolons and is considered the most destructive disease of pachysandra. The pink spores that appear in the spring will darken to reddish-orange in the late summer and fall when a second type of spore is produced.

Close-ups of the Volutella damage and spores

Close-ups of the Volutella damage and spores

This winter may have provided the perfect storm needed by Volutella to thrive. Drying winds and winter sun can desiccate pachysandra if there is not an adequate cover of snow to provide protection. Also, many beds of pachysandra are near roads and sidewalks where salts may dry them out further. A cover of mulch could provide just enough needed winter protection for plantings in these areas but it should be removed in the early spring. Some symptoms of winter injury or sunscald such as tan or scorched leaves may initially appear to be Volutella but they will not exhibit the characteristic concentric lines of the disease.

Those same pachysandra beds that are near sidewalks or roads or are used as edgings can receive damage from mowers, clippers and weed whackers (Or as they are called in Australia, ‘whipper snippers’. I just love that!). Cuts from lawn equipment can provide an opening in plant tissue and when the plant is wet the fungal spores are able to infect it easily and travel to the stems where they will cause the girdling mentioned earlier.

Good sanitation practices can be helpful when dealing with pachysandra blight. It is too late for a good fall cleanup now but you can still remove any plant debris that remains. During dry weather remove and bag (not compost) any diseased plants to reduce the inoculum. Thinning out beds will also help improve the air circulation that can speed up drying. Fungicides can be used as preventives for new growth or when wounds occur and systemic curatives can be used when symptoms first appear although they will not correct damaged tissues. Allegheny pachysandra (Pachysandra procumbens) can be less susceptible to the disease or you could consider another groundcover such as creeping myrtle or vinca.

Vinca major, also known as variegated greater periwinkle

Another source of wounds to pachysandra that should not be overlooked in insect damage. Scale insects such as Euonymous scale, two-spotted spider mites, and root knot nematodes have been found on plant samples that have come in to the Center. Horticultural oils and insecticidal soaps applied now can help control scale, just be sure to thoroughly coat the pests with the product. A miticide can be used on the spider mites but there is currently no control chemical treatment for the nematodes.

Euonymous scale image by Joan Allen

If you are experiencing these symptoms in your pachysandra beds you can get additional information from the Connecticut Agricultural Experiment Station fact sheet entitled Volutella Blight of Pachysandra, on our website at Pachysandra Leaf and Stem Blight, or by contacting us at the UConn Home & Garden Education Center.

-Susan Pelton

 

 

 

 

 

 

 

 

Tobacco Growing in Northern Connecticut

 

A weathered tobacco barn in Enfield, CT

In northern Connecticut along the Connecticut River a quintessential image of winter is a tobacco barn in the snow. It may be bright red or a lovely weathered wood but either way it is an image of New England that many may think represents a time gone by. Although tobacco has been condemned as a health hazard the growing of tobacco is still a viable agribusiness in many towns in Connecticut, Enfield among them.

Tobacco was already being grown by the native populations when the European settlers arrived in the early 1600s. Within seven years of the town of Windsor’s founding in 1633 tobacco was being produced for both personal use and profit although the majority grown was a variety that originated in the Virginias. The rich sandy soil by the river and the short, hot summers yielded an excellent crop. By 1820 Connecticut Valley tobacco leaves were being used for cigars as the two outside layers, the binder and the wrapper.

The late 19^th century saw a variety from Sumatra that began to replace the wrapper from this area. Local farmers created the ‘shade’ conditions that mimicked the sunlight and humidity of Sumatra. 1920 saw a cultivation height of 20,000 acres in the Connecticut River Valley although it is currently just over 2,000 acres. My husband’s great-uncle, Frank Burton, farmed tobacco in South Windsor during the 1930s and 40s. The following images are from a 1938 booklet that he used called ‘Hubbard’s Handybook for Growers’ from the Rogers & Hubbard Co. of Portland, Connecticut:

 

Tobacco is part of the genus Nicotania from the Solanaceae (nightshade) family, a family that includes tomatoes, potatoes, eggplant, and peppers. Tobacco mosaic virus is a disease that affects tomatoes and peppers in addition to tobacco. It can be transmitted through the debris of infected plants in the soil or through contamination of smoking materials on workers hands. It has been known to survive up to 50 years in dried plant parts. Avoid using tobacco products while handling or transplanting plants in the solanaceous family. Tomatoes will have foliage that has mottled yellow and green areas, reduced fruit set, dwarfing, and distortion. There is currently no control for TMV.

Another disease that can attack tobacco is blue mold, Peronospora tabacina, a downy mildew disease caused by a fungus-like organism that is highly destructive to seed beds, transplants, and fields.  Initially it can be confused with cold injury, malnutrition, or damping off. According to an Enfield tobacco farmer they did not have an issue with blue mold in 2015.

Insect pests of tobacco include aphids, cutworms, flea beetles, snails, slugs, wireworms, budworms, hornworms, and thrips. Many of these insects are common pests of tobacco’s relatives in the solonaceous family. Tomato spotted wilt virus (TSWV) is vectored by tobacco thrips. Tobacco and tomato hornworms are large caterpillars of the Manduca species that can strip a plant of foliage in a short period of time. As with tomato hornworm, tobacco hornworm can also be parasitized by wasps.

The end of the tobacco growing season is not the end of farmer’s work. Little has changed over the centuries in the way that tobacco is harvested. The entire plant is cut off the stalk at ground level and brought to curing barn by way of slow-moving tractors.

In our neighborhood following a wagonload of newly cut tobacco is a common occurrence.

When the harvested plants reach the barns they are speared through the base in groups of four to six and hung to cure. The curing process allows for the slow oxidation and degradation of the carotenoids in the tobacco leaf that give it the aromas such as sweet hay, tea, rose oil, or fruits when smoked. Starch is converted to sugar which oxidizes into advanced glycation endproducts (AGEs), the inhalation of which during smoking contributes to atherosclerosis and cancer.

Air-cured tobacco is allowed to dry in well-ventilated barns over a period of four to eight weeks. Fire-curing takes three days to ten weeks. The tobacco barns used for these methods have openings along the long sides that can be adjusted to control the heat and humidity in the barn during the curing process.

Cured leaves are then sorted for use as filler or wrapper based on their appearance and overall quality and sent on to cigar manufactures.

For over 350 years tobacco has been omnipresent in this area. Many a Connecticut teenager worked on a local tobacco farm and although I never had that experience personally I understand that it was not pleasant work. Currently most tobacco work is done by seasonal employees although their numbers may also dwindle in the future as the land is turned over to more economically viable pursuits such as real estate development. The tobacco barns that dot our landscapes may be no more than curiosities to future generations.

A beautiful red barn in winter.

 

Susan Pelton

(all images by Susan Pelton)

 

Blossom End Rot of Tomatoes

August is supposed to be the month of non-stop tomatoes. Occasionally things go awry to interrupt those carefully laid spring visions of bountiful harvests, sauce making, and endless tomato sandwiches. Blossom end rot can appear to put an end to the crop production by damaging the ripening and developing fruits. We are seeing and receiving calls in a  higher number than more recent years from backyard gardeners complaining about black rotten spots on the bottom of their tomatoes. The spots start as a thickened, leathery spot which sinks in, always on the bottom of the fruit.

Blossom end rot on tomato, ohioline.osu.edu

Blossom end rot can also occur on peppers.

Blossom end rot on peppers, photo taken by client

Blossom end rot is a physiological condition due to lack of calcium. Calcium is needed by plants for  proper growth in all functions of cell making, but is most important for cell walls. Without enough calcium either in the soil, or if delivery of uptake of dissolved calcium in soil water is interrupted, cell division stops in the fruit. Tomatoes are especially sensitive to a lack of calcium.

Interruptions in uptake of calcium can happen by repeated cycles of soil drying out, receiving water, then drying out again. Times of drought and hot, humid weather make the problem worse. Plants lose water through their leaves through a process called transpiration, similar to the way we sweat. They then pull up water through their roots. If there is not enough soil moisture, plants wilt. This break is water delivery also limits calcium delivery. Tomato, and to a lesser degree pepper fruits, respond by developing rot on the bottom, the end where the blossom was before the fruit started growing.

High humidity and multiple cloudy days reduces transpiration, thereby reducing water uptake. This leaves plants not able to bring up new calcium rich water to the site making new cells of the fruit. Another interruption of delivery of calcium resulting in blossom end rot. This means that even if you have enough calcium in the soil and you water the soil regularly, the plants still may not be able to move enough calcium to where it is needed to produce a fruit.

Have a soil test done to make sure soil has enough calcium and that pH levels are around 6.5 so nutrients are most readily available. Water regularly so plants receive 1 to 2 inches of water per week for optimum growth. Feel the soil around the root zone to make sure water is soaking in and reaching the roots. Humidity and cloud cover are not obstacles we can help the plant with, so monitor the fruit for rot spots and remove. There are calcium foliar sprays which claim to deliver calcium to be absorbed by the leaves for use by the plant. This won’t help after the rot has already developed, but may help deter future spots on still developing tomatoes.

-Carol Quish

 

 

 

 

August in the Vegetable Garden

Late summer in the vegetable garden can be a time of great harvest and a time of disappointment. The spring planted lettuce, spinach and radishes have all gone to seed, and insects and disease are taking their toll on crops that have lasted til now. Tomatoes, peppers and eggplants are producing their bounties in large amounts and cleaned out beds hold the promise of another round of seed planting for greens. Try kale, winter lettuces and chard. Below is a visual tour of what is happening in my garden.

– Carol Quish

Eggplant ready to be picked. photo by Carol Quish

Sweetie Cherry Tomato plant with brown leaves stripped off of the bottom of the plant to reduce fungal spores in the tomato bed. photo Carol Quish

Red Onions beginning to have their tops fall over. Harvest after tops die back. Photo Carol Quish

Peas plants have been removed making room for Bright Lights Swiss Chard to grow. Photo Carol Quish

Pole Green Beans are in need of picking! Photo Carol Quish

Zinnia’s are keeping the pollinators happy so they continue to visit the garden. Photo Carol Quish.

Every garden needs some blooming flowers. Keep up with dead heading to the the flowers coming. Photo Carol Quish

Zucchini leave attacked by powdery mildew. I should remove this so the unaffected plants might be protected. Photo Carol Quish

Waltham Butternut Squash vining its way over the potato plants. Photo Carol Quish

Red Kuri Winter Squash pitiful harvest. Vines were killed by the Squash Vine Borer. Photo Carol Quish

Late ripening blueberry variety keeps the fruit season coming. Photo Carol Quish

 

 

Galls & Burls Explained…Sort of

Trees and other woody plants often have large or interesting swellings on their trunks or branches.   The cause is often difficult or impossible to determine.  Possible causes include fungi, bacteria, insects, mechanical or environmental injury, or genetic mutation.  The terms gall, tumor and burl are commonly applied to describe these abnormal swellings. 

Galls and tumors can be any size or shape and may occur on both woody and herbaceous plants and plant parts.  The swelling occurs as cells divide more rapidly than normal (hyperplasia) and/or due to excessive cell enlargement (hypertrophy).  Burls are generally considered to be large woody swellings that are basically hemispherical in shape.  They often bear many buds and sometimes sprouts.   The burls of black walnut, coast redwood, sugar maple and black cherry are highly prized by woodworkers for their beautiful swirling or ‘bird’s eye’ grain.   This relatively small burl from an apple tree (cause unknown) has an interesting surface pattern and interior grain showing bud traces.

Burl from an apple tree trunk.

 

Tiny brown lines are bud traces.

An individual tree may have one or many swellings.  On this maple tree, the many swellings are of unknown origin.  Often, a tree with large or numerous galls will decline earlier than a tree without them. 

The most common bacterial gall disease is crown gall caused by the bacterium Agrobacterium tumefaciens.   This soil-borne bacterium enters the roots of the host plant through wounds caused by planting, cultivation, frost heaving, insects or nematodes.  The bacteria, upon attaching to the plant cell walls, send DNA that causes production of plant growth hormones into the plant cell where it is incorporated into the plant cell chromosome.  Affected cells begin to multiply at an uncontrolled rate, resulting in visible tumors within 2-4 weeks.   More than 600 plants are susceptible to crown gall.  One of the most common, where galls occur on both roots and stems, is Euonymus, shown in the photo. 

Crown gall of Euonymus.

 

Examples of galls caused by fungi include azalea gall (Exobasidium vaccinii), black knot of plum and cherry (Apiosporina morbosa), and Fusiform rust of pine (Cronartium quercuum).    More information on these diseases is available by clicking on the name of the disease. 

 A close up of a leaf gall on azalea . (Plant Disease Diagnostic Clinic, Cornell University)

Black knot of plum and cherry.

 

 Fusiform rust (USDA Forest Service – Region 8 – Southern Archive, USDA Forest Service, Bugwood.org)

Insects and mites cause some very interesting galls on leaves as shown in the photo.  These usually cause little damage to the host plant or tree and control measures are not normally recommended.  A new theory is being explored by scientists that the swellings associated with these arthropods may in fact be caused by bacteria transferred to the plant tissue during feeding.   Fascinating! 

Hickory gall phylloxera.

 

Galls can be caused by cultural, mechanical and environmental factors including graft incompatibility, wounding, and freeze injury.   Galls on some conifers that vary from small to huge (several times wider than the trunk) are thought to originate when the trees are young seedlings from a single cell and enlarge for many years.  Low temperature injury is suspected, but not proven, as the cause. 

J Allen

 

What causes ringspots on Pachysandra?

Pachysandra is a relatively problem free plant and is widely grown as a ground cover in shady areas.  The most common disease is Volutella blight caused by the fungus Volutella pachysandrae.  Dark blotches form on the leaves and the stems.  These increase in size until the plant is killed.  Plants may be killed in patches within a bed.  This disease is most common when plants are stressed by winter injury, insects, transplanting, mowing, drought or exposure to full sun. 

A relatively new disease of Pachysandra in the northeast is caused by a virus known as alfalfa mosaic virus (AMV).  The virus was first reported on Pachysandra in 1982 in New Jersey and is the only virus known to occur on Pachysandra.  Symptoms include chlorotic ring spots and blotches on the leaves.  This virus is transmitted by a number of aphid species including the green peach aphid and others.  It is also transmitted via seed or infected sap. 

Alfalfa mosaic virus has a broad host range that includes over 600 plant species in 70 families.  Symptoms vary quite a bit depending on the host and can include wilting, white spots, stunting, ringspots, mottling, mosaic patterns or necrosis.  Symptom expression is also affected by the weather, strain of the virus and the age of the plant when infected.   Alfalfa plants can be infected without showing any symptoms.  Plants growing near alfalfa fields are at the highest risk of infection. 

Control of this disease is not always necessary.  Prevention by avoiding planting hosts near alfalfa fields is the most effective.  Managing this virus by controlling the aphid vector population has not been successful.  In the case of Pachysandra, removal of symptomatic plants as they appear is the best approach.   Avoid wounding adjacent healthy plants to prevent sap transmission of the virus. 

Scorch can also occur on Pachysandra and is caused by environmental factors including winter injury or drying.  No treatment is necessary; the plants should recover once new growth appears in the spring.

Scale insects may infest Pachysandra.  The three most common are Euonymus scale, San Jose scale and Oystershell scale.  Control measures for these insects include insecticidal soaps, horticultural oils and conventional insecticides.  Another option for severe infestations is to mow the Pachysandra and collect the clippings to physically remove the scales.  New growth will develop from the stolons. 

JA