Thursday, June 16, 2005

Reports of Blackleg in Potatoes

Some growers in Michigan are reporting 40 – 50% of plants with stem blackleg and seed piece decay caused by Erwinia carotovora ssp atroseptica (Eca). That amount of seed piece decay and post-emergence blackleg usually indicates that the seed was frosted at some point, which can happen during transportation. All potato tubers carry the pathogen on their surfaces but normally problems develop only after infection occurs through wounding, frosting or other physical damage. The bacterium is a facultative anaerobe which means it thrives both with and without oxygen. Eca gets into the sprout and develops rapidly after emergence resulting in a lower stem and root rot. The stem is left with no anchoring and the stem pulls easily out of the ground. Typically, plants affected by Eca are stunted, with yellow necrotic leaves and black stems. The stems can also have a characteristic acidic odor after other saprophytic bacteria invade the stem. Some cultivars are more susceptible than others and usually early maturing cultivars such as Red Norland, Onaway and other colored cultivars are prone. Other sprouts on the tuber seed piece can compensate but if the temperature reduction was at the surface of the pile of seed in transit then the damage can be extensive and kill all the sprouts on the seed piece. This disease can be particularly important in seed crops as there is a tolerance of 0.5% incidence in the growing crop. Generally, in lighter infestations the crop can compensate but when fields have up to 15% plant loss, compensation is inadequate. There are no recommendations for controlling blackleg other than rouging out affected plants or post-harvest disinfestations. In severe cases and when wet conditions prevail there is risk of movement of inoculum form plant to plant in the soil.


Wednesday, June 15, 2005

New domain name acquired

In line with the name of the website (Michigan Potato Diseases) we have just acquired the new domain name It may take a couple of days for the name to become active and when it does it will become the default address for the website. However, you will still be able to to reach the website via or for those interested just in lateblight

Thursday, June 09, 2005

Website Updates

There have been several major changes and additions to the website today. Firstly, I have redesigned the Publications pages to make it easier to find extension publications and research articles. I have split the publications page into two parts, one page for extension bulletins and related publications and another for research publications. We have several new extension bulletins on Rhizoctonia diseases, Pink Rot, Early Blight, and White Mold, due to be published in the next couple of months and as they come out they will be added to the extension bulletins page. New publications will also be listed on the Recent Publications page.

Secondly, the Fungicide Rates page has been updated with some new compounds for use in the control of potato diseases, and a new article on Fungicide resistance management is available for download.

Wednesday, June 08, 2005

Storms increase chances of disease outbreak

The thunderstorms that were widespread throughout the state on Sunday (June 5) created ideal conditions for potential late blight outbreaks in many locations. Check the Stations Comparison webpage for the station nearest to your location to see if you are at increased risk for a disease outbreak. Stations with a total of more than 3 DSV's for the past 7 days are at increased risk.