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Fire Blight Symptoms Occurring Now

July 31, 2015
Yolanda Schmidt - County Agent , Pierce County Tribune

Now is the time to be on the lookout for fire blight, a serious disease of apples, crabapples and pears. When blossoms, blossom spurs and branch tips are infected, they turn brown and die rapidly. The tips of branches often curl to form what resembles a shepherd's crook, or the curved end of a walking cane. The dead leaves remain brown to almost black, and may remain on the branch all winter. The disease is caused by a bacterium that lives in the conducting or vascular tissues of the plant. It progresses down the diseased shoots and spurs and sometimes reaches a larger branch, where a dark or discolored area is formed. This discolored area is called a "canker". The bacterium lives over the winter in young cankers with smooth, indefinite margins. In the spring, bacteria ooze from the canker, forming a sticky, thick liquid that insects feed on. These insects transmit the bacteria to blossoms, where new infections start. Later, the disease may spread from infected blossoms and old cankers to the shoots. Rain, wind and hail help spread the disease.

Successful fire blight control requires a combination of actions. First, overwintering cankers should be pruned away by cutting at least eight to 12 inches below the edge of the canker. Smaller diseased branches should be pruned about twelve inches below the edge of the diseased area. Pruning is best done in late fall after leaf drop - when the diseased shoots can be readily seen, since they retain their leaves - or in late February to early March. Dormant-season pruning is the best option for treating fire blight. Pruning tools should be sterilized between each cut, Lysol diluted 3/4 cup per gallon of water, or household bleach diluted 1 cup in each gallon of water. Household bleach works very well but corrodes tools, which must be carefully washed and oiled after use to prevent rusting.

Second, apple or pear trees can be sprayed with streptomycin at blossom time. Use streptomycin at 50-100 parts per million every three to five days during blossoming. It can also be used every 14 days after blossoming, but it is not as effective for control of shoot blight as it is for control of blossom blight. After a hail storm, it can be sprayed immediately to reduce infection in the hail-induced wounds. Uptake of streptomycin is improved if applied during the evening. It should not be applied within 50 days of harvest for apples or within 30 days of harvest for pears. It is not registered for use on crabapple, cotoneaster or mountain ash.

Fire blight is most severe on succulent shoots. Avoid over-fertilizing trees and do not fertilize in late spring or early summer.

Source: Joe Zelenik, NDSU Extension Horticulturalist

NDSU Ditch Hay Project

With the Ditch Hay harvest season well underway, I would to take this opportunity to ask for your assistance in a project with which county agents across the state are assisting NDSU researchers. Our Animal Science Specialists are working on a Ditch Hay program. The main goals of the program are to determine quality and quantity of ditch hay, along with costs associated with putting up ditch hay so that program content can be developed for local county agents to share with producers at meetings/workshops in their counties later this fall/winter.

I have agreed to collect up to 10 samples each in both Pierce and McHenry county (or until a new agent is secured in McHenry). Producers will receive nutritional data on the ditch hay samples collected. So what I need from you at this point is to let me know if you'd like to participate, and if so I will need you to let me know when the ditch hay has been harvested and where it is located so that I can come sample it. Project organizers have asked that all samples be submitted by early September, as they wish to have results compiled to share with agents at our annual fall conference in October.

Thanks for your time and consideration in helping with this project! For questions or information about this project please call the Pierce County Extension office at 776-6234.

 
 

 

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