Ash rust, caused by the fungus Puccinia sparganioides, is a disease which affects white and green ash in Delaware. Symptoms on ash appear in mid-May as small yellow to yellow-orange spots on upper leaf surfaces. About ten days later bright orange-yellow clusters of aecia (fungal spore producing structures) became apparent on leaf under surfaces. Leaves often become distorted and petioles may develop wart-like swellings which also bear clusters of aecia. Leaves with infected petioles wilt and die and severely affected trees appear scorched in June. Defoliation of heavily infected trees occurs, but in most cases, infected trees may push a flush of new growth. Repeatedly infected trees may be predisposed to winter damage and to secondary infection by wood decay organisms. 
The alternate host for ash rust is marsh and cord grass which is found in coastal areas. If the disease only occurs sporadically, chemical control is not needed, especially if the infected tree is otherwise healthy. It is very difficult to predict if the disease is going to occur and preventative fungicide applications would need to be applied at bud break. Spraying after infection has occurred will not result in control.
NFG 5/17/2017
Tag: ash
Emerald Ash Borer and Ash Tree Health
EMERALD ASH BORER has been found in several surrounding states, but has NOT been found in Delaware to date. An article appeared in the 6/20/15 Wilmington News Journal regarding trapping efforts and preparedness for the detection of the invasive emerald ash borer in the state: http://www.delawareonline.com/story/news/local/2015/06/19/firewood-carries-unwanted-travelers/289815.... This is one of many cooperative efforts in Delaware between Delaware Department of Agriculture, USDA, University of Delaware, and many municipalities. Traps are specifically designed to attract and detect nearby emerald ash borer, which only feeds on ash, and another related tree, Chionanthus. A trap will not lessen the damage, those traps are only put out in certain locations in an attempt to detect low populations of the insect should it arrive in Delaware. If we detect very low numbers, we have a better chance of eradicating the pest. Ash, however, is attacked by numerous other insects (lilac/ash borers) and several plant disease causing organisms such as those causing anthracnose, rust, heart rot, ash yellows and ash decline. In Delaware, if you suspect you may have EAB in your ash trees, contact the Delaware Dept of Ag's Plant Industries Section at (302) 698-4586.
Keeping ash trees free of insect pests, woodpecker damage and plant diseases is best done by keeping trees healthy and reducing stress on trees. Water during times of drought, have trees pruned by a reputable company if there is significant dieback of branches, and avoid wounding if possible.
NFG 6/23/2015
Fringe Tree Possible Host for Emerald Ash Borer
On October 14, 2014, the USDA Systematic Entomology Laboratory (SEL) at the Smithsonian confirmed partial adult and larval specimens recovered from a white fringetree (Chionanthus virginicus) as emerald ash borer (EAB) (Agrilus planipennis Fairmaire). EAB larvae and a partial adult specimen were collected from four white fringetrees up to 20 miles from one another in the Dayton, OH area. D-shaped exit holes and fully developed galleries in wood were identical to those caused by EAB.
Based on these findings, APHIS PPQ is conducting studies whether EAB is able to complete its lifecycle on white fringetree as a host, which will take several months. APHIS is also revisiting research on whether other members of the Olive family can serve as hosts of EAB and whether this is a local phenomenon. APHIS will engage national, state, and industry partners as part of the regulatory decision making process should APHIS officially declare white fringetree as an EAB host and the plant and its parts as regulated articles under the regulations, quarantine, and detection aspects of the EAB program.
White fringetree is in the olive family, as is the genus Fraxinus (ash). Other members of the olive family, including lilac and privet, were tested, and are not considered suitable hosts for EAB. Further study and evaluation of white fringetree’s suitability as a host will be undertaken. White fringetree is native to the United States and grows wild from New Jersey south to Florida and west to Oklahoma and Texas. It is a popular ornamental tree that has been planted in other parts of the country.
10/23/14 NFG