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Anthracnose
What is anthracnose?
Well, knowing what it is, is one thing but trying to explain it is another. Anthracnose, named from the Greek words anthrax (carbuncle) and nosos (disease), is a fungus disease. The confusion is that every plant affected by it has different signs and symptoms. Basically, however, there can be an abnormal change in the plant's structure, decay or death of tissue, or some other symptom, such as a raised edge around a sunken or depressed spot.

This parasitic fungus overwinters in seeds or debris as a thread-like structure (called a mycelium). Come spring, when rainy weather occurs, or when we start watering, spores form and are splashed onto or carried to a host plant where they penetrate the tissue. Spores have a special 'thorn' on them for this job. Any spores that form during the growing season will infect other plants right away.

The giveaway is the pinkish spore masses that seep out of lesions on plant material. Tomatoes get a sunken spot that is dark with a light center. On maples and some other trees, light brown spots appear on the leaves and then merge together, giving the leaf the appearance of being scorched. Just as the symptoms vary on each plant, so does the treatment.
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My eggplants have small sunken spots on them and some are falling off the plant. What is the matter?
It sounds like anthracnose fruit rot, a fungal disease. The fungus, Colletotrichum, overwinters in soil and when the plants receive moisture, either from overhead watering or from rain, it becomes active. This problem often occurs where tomatoes and eggplants have been planted in the same area a few years in a row. Try growing your eggplant in an area where they or tomatoes have not been planted for the last three years at least. Water the base of the plants around the roots instead of the entire plant and don’t let the soil dry out. Clean out and destroy all diseased plant material to keep the fungal spores from staying in the soil. So, with proper soil preparation, good fertility, and relocating the bed, you shouldn’t have any problem next year.
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Aster Yellows
I was told that aster yellows is spread by a small insect called a hopper. Can you give me information on this?
Aster yellows is spread by tiny insects called leafhoppers. They hop or fly when disturbed and suck sap from plants. Aster yellows is caused by phytoplasmas, which are microscopic organisms similar to bacteria. When an infected plant is visited by a leafhopper, the pathogen is sucked up with the sap. Once in the body of the leafhopper it multiplies, and after about ten days the leafhopper can pass the disease on to another plant. Infected plants typically are stunted and start yellowing. The stems are very spindly and often no flowers are produced or they remain green. Destroying infected plants and weeds, together with proper control of the leafhoppers, will help keep aster yellows in check.
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Bacterial Spot
Last summer many of my annuals had brown spots with a yellow edge on the leaves. Some of my four o'clocks didn't even flower. What is the problem?
It sounds like bacterial spot. If you cut the stems of the four o'clocks you will find an oozing, sticky secretion? That is a great way of ascertaining whether you have a bacterial problem. The brown spots on the leaves start small but soon spread and merge together. The yellow edge on the leaf is called a halo, but sometimes it doesn't appear even when there are spots. These spots will eventually fall out of the leaves, leaving holes.

The pathogens of bacterial spot overwinter in soil, seeds, and plant material, and can even be found on tools and flower pots. Try to find seeds or plants that are resistant to this problem. Clean up and destroy all infected materials from your gardens and tools and don't plant in the same space as last year. There are some copper sprays that can be used as a last resort and this might help if the soil is severely infected with the pathogens. Read the label before purchasing any spray product and follow the directions carefully.
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Bean Rust
The leaves on my pole beans are covered with brown and yellow spots that are ruining them. What is happening? I’ve grown these beans along the fence for years and never have experienced this.
Sounds like bean rust. This is a fungus (Uromyces phaseoli) that overwinters in debris and spreads rapidly by wind, tools, clothes, and other sources. It spreads so rapidly that a new generation of spores is created every ten days. High humidity and a lot of rain are just the conditions it wants.
Pole beans vines grow close together, creating shade and preventing air circulation, thereby further aiding the fungus. You mentioned growing along a fence “for years.” You need to move them to a different location each planting, avoid overhead watering, and plant the seeds far enough apart to avoid entanglement. Also, you could look for resistant varieties. As for now, destroy the diseased plants and clean up any debris to prevent further spreading.
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Black Knot
What is the hard dark knob on the wild cherry trees around my yard?
Your trees have black knot. Those swellings that you see are the second year knots, which may grow quite large and can cause infection of trees in other areas. The disease symptoms show up on infected trees in the fall.

The disease process begins in the spring on the current year's shoots with a swelling that will split the bark and become a soft, greenish blob. By the second year, the hard knot appears where the swelling was located. The fungus Apiosporina morboba produces spores during warm spring rains which are ejected and then carried by water or blown by the wind to infect other trees.
To control this disease on cherry and other ornamental trees of the same family (i.e., plums) remove the knots and swellings by pruning with a cut just below them while the tree is dormant; sometimes an entire branch will have to be removed. Burn this wood, if possible, or have it removed from the area. The infected wild cherries may have to be removed to stop the spread of disease unless it can be successfully pruned out. Some species and cultivars of Prunus are disease resistant.
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Carrot Foliage Disease
My carrot tops have black spots with yellow edges. Some plants are dying. I was told it is caused by the heat wave we had. Is this true?
Someone was on the right track. We just went through a spell of temperatures in the 90 – 100 degree range plus the humidity was up and there was a lot of rain. You may have either Alternaria leaf spot or Xanthomonas leaf spot. The two are so similar it takes a microscope to distinguish them.  One, Alternaria, is a fungus and the other, Xanthomonas, is a bacterium. These are seed- and soil-borne diseases; Alternaria is spread by wind, Xanthomonas is spread in splashing and running water. Alternaria infects leaves only when they are wet. Pull the carrots and if they are healthy harvest and destroy all the foliage and clean up the bed they were grown in. Plant carrots in a different location next season.
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Cedar Apple Rust
We were told to forget planting crabapples in our yard because of the cedar trees in the neighborhood. What is the connection?
Cedar apple rust, a fungal disease, is the problem. However, you don't have to give up on planting those crabapples because there are many resistant varieties available. In fact, there are too many for me to mention here, but they can all be found in our Sustainable Plants list. You can also ask your nurseryman about them.

Do you recall seeing what are often described as oozy, orange, slimy things with horns, on the Eastern red cedar (Juniperus virginiana) trees after a warm spring rain? These are cedar apple galls produced by cedar apple rust. This is a fungus and it spreads to within a mile of the infected cedar tree, creating rust spots on leaves and this can lead to leaf drop. If you check any cedar trees around your yard, look for brown, shriveled up, nut-like galls called telia, these will become the orange ball-like fungus. When the temperature is right and moisture is available, the telia absorb water and swell. Then long "horns" appear that dry to a dark color. These contain thousands of spores that germinate and are discharged into the air. Within a couple of months, the rust appears on the leaves or fruits of the apple trees, creating a fungal structure that produces spores that are released during dry weather in late summer and go back to the cedars.
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Cherry Tree Leaf Spot
Our cherry tree has a problem.  There are holes in the leaves and some of the leaves are folding back from the center and have turned purple. Now the tree is dropping leaves. What is going on?
The tree has cherry leaf spot, a fungal disease. The fungal spores remain on fallen leaves over the winter and when spring rains arrive the spores will be splashed or blown onto new leaves. The fungus thrives in mild wet weather, like a rainy spring. When this fungus is present you will see purple spots on the tops of leaves and clumps of cream-colored spores beneath. The centers of these spots will darken and fall out, leaving holes. In bad cases, the tree looses too many leaves and is weakened as the fungus reduces the amount of nutrients the tree can take in. Also, infected trees often suffer from cold injury during the winter months.

Clean up all litter from beneath the tree in the fall and next spring, right after the tree has bloomed, an antifungal spray can be applied, following directions on the label. 
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Damping Off Disease
My seedlings suddenly got thin and fell over and died. Help!
Your seedlings have succumbed to damping off disease! It strikes without warning, causing the seedlings to wither away at the soil line and collapse. A combination of microorganisms causes this problem, but most often it is Rhizoctonia. Once a seedling is attacked, it's done for.

To avoid damping off, start by sowing seeds in a sterile growing mix formulated for just this purpose. Keep the soil line high in the starting flat, this creates good air circulation. Don't go overboard with watering and water from the bottom. Keep the seedlings somewhat cool; once seeds have germinated the temperature can be lowered a few degrees. This also stops seeds from growing too fast, stretching and becoming leggy. Temperatures that are too low will also cause problems but the upper 60s or low 70s seem to work fine. Avoid overcrowding by thinning out the seedlings. Keep a light about and inch or two above the seedlings as they grow. Stretching for light can stress seedlings, making them vulnerable to other problems.
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Hawthorn Rust
Our hawthorn tree is beginning to develop yellow spots on the leaves with dark centers in each spot. We sprayed for insects but the spots are still there. 
Are you familiar with cedar apple rust?  Have you seen orange balls on cedar trees in the spring? These masses produce spores that are carried by wind to apple trees, causing spots on the leaves and fruits. Well, the same thing is happening with your hawthorn tree. It’s hawthorn rust and it is caused by a fungus. When it is wet the spores germinate and attack leaves. This is what you are seeing now. Other than making the leaves, and sometimes fruits, look bad, this fungus does little damage.
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Leaf Galls
What are galls on tree leaves?
Depending on the type of gall, they can be an insect, a fungus, or a bacterium. An insect gall occurs when an insect injects a toxin into the plant tissue while feeding and this irritates and blisters the plant tissue, creating odd shapes on the leaves. The roots and stems will swell and the buds and flowers will look odd. Fungal galls, also called stem galls, create large swellings on stems and leaves; some of these turn brown as they age. Stem galls are generally a problem when it is wet in the spring. Both insect and fungal galls look ugly but seldom damage plants. However, bacterial crown gall enters plants through the roots or trunk where there has been damage and it chokes off the flow of water and other nutrients in the plant, creating stunted growth and weakening the plant considerably.
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Lily Leaf Scorch
The tips of my lily plant leaves have turned brown but the stalk and the rest of the leaves are okay.  This looks very strange and I would like to know what is causing it.
The cause is low pH (that is, soil is too acidic) and the problem is leaf scorch. Lilies need a pH of 6.5 or higher. What happens is that toxic amounts of salts, mainly aluminum and manganese, are being drawn into the plant due to the low pH, resulting in burned tips. This occurs during a rapid growth spurt associated with changes in temperature. The plants need more nitrogen and calcium, but have the soil tested for pH first to see how much of what is needed. 
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Oak Anthracnose
The leaves of our white oak tree are all splotchy. Some are shriveled while others are multi-colored like someone splashed yellow and green paint on them. Is this the deadly disease that's killing the oaks in California?
No, it is oak anthracnose, caused by the fungus Apiognomonia quercinar. These infestations seem to be heaviest in southern New England when there is a long spell of cold and then a wet spring. This fungus attacks in cycles, so different symptoms will appear on the leaves at different times. If the leaves manage to mature they are resistant to the disease. Clean up any dead twigs beneath the tree to minimize overwintering of the fungus. Chemical control is not recommended.
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Oak Leaf Blister
What is wrong with the oak leaves this year? They’re covered in what looks like blisters.
It’s called Oak leaf blister. This is a caused by the fungus Taphrina caerulescens that make the leaves look horrible but rarely does any damage otherwise. This fungus winters over in the bud scales and during cool wet spring weather it enters emerging leaves and forms blisters as it gets into the tissue. The leaves will eventually die and turn brown but may stay on the tree. The fungus produces spores in the fall which will overwinter and if the next spring is cool and wet, it starts all over again.
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Onion Rot
My onions are big but the leaves are wilting and some are dying. There is also some white slimy stuff all over the bottom of the onion…actually the onions are soft and rotted. What is causing this problem?
This is fusarium basal rot and it is caused by a soil-inhabiting fungus that likes onions, garlic, leeks, shallots, and chives.  Something wounded the onion allowing this fungus to enter where it spreads through the plant, resulting in leaves turning yellow and dying. The problem is worse as the bulbs approach maturity. Often this infection doesn’t show up until after the onions are harvested and in storage. There is no chemical control for this problem. Dig out and destroy infected plants and bulbs and plant onions in an entirely different location next year. 
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Powdery Mildew
What exactly is powdery mildew? 
Powdery mildews are one of the most widespread and easily recognized plant diseases. They are caused by fungi and are characterized by spots or patches of white to grayish, talcum-powder-like growth. Powdery mildew will invade dry and wet leaves while most fungi attack only wet ones, and it’s the only fungal disease that is severe in warm, dry climates. However, the relative humidity of the air does need to be high for spore germination. Therefore, the disease is common in crowded plantings where air circulation is poor and in damp, shaded areas. Incidence of infection increases as relative humidity rises to 90 percent. Leaves may eventually turn yellow and dry up; the entire plants can be killed.
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Red Thread
What can you tell me about treating red thread in the lawn. I have checked the internet and only found chemical controls. 
Red thread (Corticium fuciforme) remains dormant in the soil until favorable conditions prevail; in hot, humid weather the fungus (Laetisaria fuciformis) grows visibly on the infected grass blades and leaf sheaths. The fungus produces thread-like strands or web-like areas of coral-pink to blood-red hyphae on the tips of brown grass blades. It favors older varieties of Kentucky blue grass, red fescue, ryegrass, and sometimes bentgrass. It thrives on soils that are low in nitrogen, so treat with a high nitrogen fertilizer, but it would be wise to have the soil tested for pH.
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Scab
My potatoes and beets had warts on them last year. What caused this?
A bacterium called Streptomyces scabies, better known as scab. This is a strange bacterium in that it grows as a mycelium and develops spores, just as a fungus would. Scab is soil-borne and can live a long time in soil without a host to feed on. It is the causative agent on all the root crops with warts, scabs, or brown sunken depressions on the skin. The bacterium doesn't hurt the inside or change the flavor of the root crop but you shouldn't store root crops with scab because other organisms can enter through those scabby spots.

Don't use lime or wood ashes in soil where you plant root crops. Also, if you are using manure make sure that it is composted completely. Plant your root crop area with a legume companion for a couple of years in a row. Also, scab doesn't like soils with high pH. The best thing is to establish a raised bed area with good compost for the root crops and use the old beds for other vegetables.
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Slime Flux
What is slime flux?
This is a bacterial (Ervinia nimipressuralis) problem characterized by the oozing of slimy liquid coming from cracks or wounds on trees, and this liquid may have a very sour odor. Often, the condition s called bacterial wetwood. As the ooze dries, it turns gray, creating streaks down the tree bark. Slime flux can affect a tree for years.

What happens is that the bacteria causes the heartwood of the tree to produce abnormally high sap pressure, which forces fermented sap, or flux, out of any wounds, cracks, or crotches of the infected tree. This process stresses the tree and makes it susceptible to other problems. For example, insects are attracted to the sap. Effected may have wilt or dieback on the branches. An arborist can often insert a tube to divert the oozing sap away from the tree.
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Snow Mold
What is snow mold? Does it happen because there is lots of snow?
Snow mold is a pathogen that occurs on turf grass. There is gray snow mold and pink snow mold, caused by different pathogens but occurring under the same conditions.

Gray snow mold, caused by a fungus that is found in most soils, is found in early spring after the snow has melted. It is common in areas where snow accumulation is greatest, such as along areas where it is piled up from plowing or from drifting. Gray snow mold becomes active beneath the snow when temperatures are very low but the soil is not frozen. Turf that is affected by gray snow mold has a bleached, grayish, packed-down look. The grass crowns and roots generally survive while the grass blades are killed.

Pink snow mold fungus is found in Midwestern soils and snow cover is not required for it to develop. It is active during the wet, cool weather, that is, during spring and fall. Like gray mold, it usually kills only the blades of grass unless extremely severe infestations occur.
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Sooty Mold
There is something black on my lilies. It looks like someone painted it with tar. What is it?
Sooty mold. Look for insects such as aphids, scales, whiteflies, or mealybugs on the leaves. They secret a sticky, sugary substance (called honeydew) that this mold grows on. The mold won't hurt the leaves by itself but does prevent sunlight from getting to the leaves. This interferes with the plant's metabolism and ends up reducing the size of your plant. Find the pest and dispose of it. Hint: The sticky honeydew could be dropped from something growing above the lilies, perhaps from the end of some tree branches. You can wipe this mold off your leaves, they would appreciate it very much.
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Tar Spot
What is Rhytisma acerinum?
This is the fungus that causes tar spot of maple. It can attack many maple species causing tar like spots to appear on the leaves. The fungus overwinters on fallen leaves and when the spring rains come, it re-infects the leaves on the trees. At first, the spots are yellowish, but by mid- to late summer a mix of fungal and leaf tissue develops inside the yellowed area and it resembles a spot of tar. Once in awhile, leaves will shrink and drop but this isn't a serious issue. The use of fungicides is not generally recommended. In the fall, rake up all leaves from beneath affected trees and remove from them the area to prevent this fungus infection.
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Tomato Bacterial Canker
My green tomatoes have gotten spots that look like little bulls eyes – white circles with a darker raised center. Some of them are all brown. Now the leaves are drooping. What disease if attacking the tomatoes?
They have bacterial canker, also known as bacterial blight, which is caused by Corynebacterium michiganense.  It’s a widespread and destructive disease that is made worse by warm, wet weather. The bacterium that causes this disease is carried on and inside the seeds and it lives on infected debris, plant stakes, and tools; it can live in the soil for almost three years.
If you cut open a stem, a yellowish slime can be squeezed out. There might also be light streaks on the stem that will eventually develop into cankers. There is no chemical cure for this so expect to lose some plants. Plant your tomatoes in a new location next year and don’t repeat locations for at least three years, preferably more. Wash all the tools you have used around the tomatoes in a bleach-water solution. The infected plants you have now should be removed and destroyed. Don’t put them in a compost pile.
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Tomato Late Blight
What causes late blight on tomatoes and can it harm them?
Late blight is caused by the fungus Phytophthora infestans, which can also infect potato and eggplant. This fungus doesn't show up every year but when it does, it is devastating as it attacks all parts of the plant - fruit, stems, and leaves. Late blight is most virulent in wet weather where the nights are cool and the days warm.

The symptoms are dark blotches that look like water stain on the leave, stems, and fruit. When these spots occur on fruit, it looks greasy at first and then corklike, usually starting at the stem end of the tomato.

When the weather is really wet, a mold will grow on the under surface of leaves and they become blighted. Often the fruit will be covered and the plant has a very foul odor. Remove any diseased plants from your garden right away, including all dropped leaves, fruit, and the entire root system…and don't put them in your compost pile.
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