Claude Mellan’s tour de force is one of the great achievements of printmaking. The entire print consists of a single engraved line. To begin, Mellan placed the point of his burin at the center of Christ’s nose and spiraled outward, swelling and tapering the line as needed to create this celebrated curiosity. His seemingly miraculous feat mirrors the very image it represents-the imprint of Christ’s face on Saint Veronica’s cloth, or sudarium. The inscription, which reads, “It is formed by one and no other,” alludes both to the power of the divine and to the virtuosity of Mellan’s masterful hand.
This is 1649 engraving by Claude Mellan, The Sudarium of Saint Veronica. Christ’s face is rendered as a single spiral line of varying width.
The basic sound source for this CD is the copper engraving ‘The Sudarium of St Veronica’, cut by the French artist Claude Mellan (1598-1688) in Paris 1649. A portrait of Christ engraved through a continuous spiral line that starts at the tip of his nose. An old heliogravure (a 19th Century reproduction of one of the original prints) was used to make a photo etching in copper to get a replica as close as possible to the original plate. This plate was played back with a specially constructed record player and recorded at Firework Edition, Stockholm, July 17, 2007.”
Apparently there is a message in this engraving that is at the National Gallery of Art, Washington D.C.
- Knobby swollen black growths called galls grow parallel along the length of stems and branches.
- In early summer, young galls or new areas of growth on the edges of older galls are covered with velvety olive green spores.
- These galls mature by the end of the summer; turning black and hard.
- Black knots are most noticeable during winter because all the leaves are gone and the black knots stand out against the blue sky or white snow.
- Infected branches may distort and bend due to the one-sided growth happening within the gall.
- When galls completely girdle a branch, leaves on infected branches do not emerge or wilt and die in early summer.
- A few galls to hundreds of galls can be within the canopy.
- Large rough black galls that are often cracked can occur on the main trunk of the tree and may ooze sticky liquid.
M. Grabowski, UMN Extension
Dead leaves and wilting caused by a black knot gall that has girdled the branch
The fungus overwinters in the galls. During wet periods in the spring, spores are expelled and windblown to infect young green shoots or wounded branches.
Once spores germinate, the fungus grows between the plant cells with no outward signs visible on the plant for several months. During this time the parasite starts growing within the tree and releases chemicals that cause the plant to initiate excessive cell growth and enlargement that results in swollen black galls. Galls are made up of both plant and fungal tissue.
It is not uncommon for the gall to completely encircle and girdle a branch. When this happens the leaves beyond the gall wilt and die. In some cases, the branch and the gall die after spores are released in early spring. If the branch lives, the knot becomes perennial and continues to enlarge, producing new spores every spring. Although the black knot fungus will not cause trunk decay itself, the cracks formed by a trunk infection can provide an entry point for other wood rotting fungi.
M. Grabowski, UMN Extension
Large black knot gall on the main trunk of a Prunus tree.
Site and tree selection
- In areas where there are many wild Prunus sp. infected with black knot, avoid planting landscape and edible Prunus sp.
- If only a few infected wild Prunus sp. are present, prune out existing galls or completely remove infected plants to reduce the amount of fungal spores present before planting landscape and edible Prunus sp.
- Choose Prunus spp. that have some tolerance to black knot (Table 1).
- Thoroughly inspect ornamental as well as edible trees and shrubs to ensure they are disease free before purchasing them from the garden center.
Pruning out galls
The black knot fungus does not systemically infect the tree, but rather only infects the branch at and around the galls. Black knot galls can be removed from infected trees through pruning. This will improve the look of ornamental plants and reduce the amount of fungal spores produced within the tree canopy each spring. Unfortunately, black knot is a common disease of wild and landscape Prunus species in Minnesota. Even with diligent pruning, spores can be blown from infected plants far away and result in new infections. In addition, galls remain very small until a full year after infection. Therefore it may take 2 years of pruning to completely remove all existing infections as young galls are often overlooked.
- Because black knot is common throughout Minnesota, galls in landscape trees can be tolerated if the disease does not result in wilt and death of leaves and branches.
- In late winter remove all branches with swellings, cracks in the bark or black knots.
- Remove at least 4 inches of healthy wood beyond the black knot.
- Bury, burn or dispose of all branches from a site as spores can still be produced on pruned branches and spread to new areas.
- Cracked and oozing galls on trunks or large branches should be inspected by a certified arborist to determine the structural stability of the tree. Black knot itself will not rot wood but secondary fungi can enter through cracks and result in wood rot and structural instability.
Fungicides can be used to protect young or highly susceptible Prunus trees from infection. Sprays must be applied in early spring to protect young green shoots. Begin fungicide treatment when flower buds are just beginning to open. Repeat sprays according to label instructions (typically every 7-10 days) until shoots mature or weather is consistently warm and dry. Sprays are most effective when applied before a rain event when temperatures are warmer than 60°F. In order to greatly improve the efficacy of the fungicide application it is important to prune out any existing galls in late winter before applying fungicides in spring.
Before application make sure to read the label carefully! The plant to be treated MUST BE listed on the label or the fungicide cannot be used on that plant. Not all fungicides registered for use ornamental Prunus spp. can be used on edible Prunus spp. For large trees, high-pressure spraying equipment is needed in order to get complete coverage; therefore hire a professional arborist who can safely operate all necessary equipment.
Chemical treatments effective against black knot include fungicides with one of the following active ingredients:
- Thiophanate- methyl
- Lime sulfur
Vegetable or Canola OilBasic liquid vegetable or canola oil is a key element in a homemade pesticide for your fruit trees. Vegetable or canola oil works by suffocating small insects, insect larvae and eggs, thus preventing infestation. One cup of vegetable or canola oil is mixed in one gallon of water.
Cinnamon OilWhile its mechanism isn’t fully understood, cinnamon repels and kills many kinds of insects including ants, aphids, mealybugs and other problem pests. One tablespoon of pure cinnamon oil is mixed into the water and vegetable oil mix. However, too much cinnamon oil could potentially harm the tree’s leaves; a one tablespoon dose of cinnamon oil will keep insects at bay and keep your tree healthy and robust.
Hot PeppersHot peppers, such as cayenne and red chili, will keep bugs off your fruit trees because insects do not like the spicy taste or feeling of hot peppers. Adding some hot peppers to your homemade pesticide will keep the bugs away while keeping your trees and fruit healthy. Two tablespoons of cayenne or chili pepper powder is steeped one cup of hot water for 24 hours.Strain the solids from the liquid through a cheesecloth or heavy paper towel, then add the liquid to the main mixture.
GarlicInsect pests are repelled by the odor of the sulfur compounds in garlic. Two tablespoons of garlic powder and one cup of hot water, stirred occasionally, steeps for 12 to 24 hours to make a garlic tea. The solids are strained from the liquid by pouring the tea through a cheesecloth or thick paper towel. The remaining liquid is then added to the mixture.
Liquid Dish DetergentA liquid dish detergent works as an emulsifying agent to bind together the oils and liquids in the homemade pesticide. It can also work in a fashion similar to oil to suffocate small insects, larvae and eggs. One-quarter cup of any kind of liquid dish detergent is added to the mixture and stirred gently.
ApplicationTo apply the homemade pesticide to your fruit trees, you will need to use a pesticide sprayer made specially for trees. These are available at garden centers everywhere. If you’re applying the mixture to very young or dwarf trees and you can reach the top of the tree, a simple spray bottle will suffice. Wearing gloves and protective eye goggles keeps over-spray from getting in your eyes or on your skin. The mixture is applied evenly to the leaves on the tree using the wand attachment on the sprayer. The liquid should be visible on the leaves, but not dripping. The pesticide will dry in about an hour in full sun, or within two hours on a cloudy day. The organic pesticide is reapplied to your fruit trees every two weeks or after heavy rains during the growing season.
Homemade Oil-Soap Spray
Gardening stores often sell insecticidal soap sprays, but you can make your own. Experts at Oregon State University recommend mixing 1 teaspoon of vegetable oil and 1 teaspoon of dishwashing soap per cup of water. This spray will help with aphids, mites, scales and other insects that have very small breathing holes. To use it, spray the fruit tree leaves thoroughly, and then wash the soap away after a few hours. You can also use 3 tablespoons of dishwashing soap or 2 tablespoons of baby shampoo per gallon of water.
Peppermint Oil Spray
Peppermint oil spray repels ants and gets rid of other hard-bodied insects. Oregon State University recommends mixing one part peppermint oil with 10 parts water to produce a spray that gets rid of ants. Experts at the University of Hawaii suggest a similar mixture containing 2 tablespoons of liquid soap, 2 tablespoons of peppermint oil and 1 gallon of water to get rid of insects with hard bodies, such as weevils. The peppermint oil helps the mixture penetrate insect shells, while the soap reduces surface tension and helps the mixture smother insects.
Many insects will avoid hot peppers. To produce a spray that wards off Japanese beetles, boil 1/2 cup cayenne pepper and 1/2 cup jalapeños in a pot of water. Strain out the peppers, and spray the trees with the remaining water to repel the beetles. A spray made from 1 teaspoon of soap, 1 tablespoon of hot pepper, six cloves of garlic, 1 minced onion and 1 gallon of water blended together will repel a variety of insects. It will affect aphids and other insects killed by soap sprays, as well as caterpillars, hornworms, cabbage worms and other insects that avoid pepper.
Soap may burn fruit tree leaves, so check them for damage and wash away soap sprays after a few hours without rain. It is also important to keep in mind that some recommended homemade insect control methods can be effective but potentially hazardous. For example, cooked rhubarb leaves release oxalic acid, which works well to control aphids. Rhubarb leaves, however, are toxic to humans. If you choose to use a homemade insecticide containing rhubarb, do not spray it where children may consume it and wash fruit thoroughly before consuming it. Solutions containing tobacco and chrysanthemum flowers can also be toxic.