Bacterial blight alert

According to the Compendium of Cotton Diseases, Bacterial Blight has been around for over 100 years. This disease is caused by the organism (Xanthomonas axonopodis pv. Malvacearum).

I have seen this disease in the past but I have never seen it cause economic yield loss. I learned earlier this week that Arkansas cotton was being affected by this disease that I have not seen for 10-15 years. This disease was reported earlier in Mississippi in the Mississippi Crop Situation by plant extension plant pathologist, Tom Allen on July 15. This report can be found at

http://www.mississippi-crops.com/2011/07/15/alert-bacterial-blight-of-cotton/.

It was reported in reported in Arkansas by Terry Kirkpatrick on their extension website at http://www.arkansas-crops.com/2011/07/20/alert-bacterial-blight-of-cotton-found-.... It has been reported in Desha and Mississippi Counties. At the present time, I know of no cases in Missouri, but that could change rather quickly.

Bacterial blight was historically a major cotton disease across the U.S. Cotton Belt, but the discovery and use of resistance to the pathogen in most cotton cultivars and modern seed processing and handling procedures, particularly the use of acid-delinted seed, lowered incidence of this disease substantially for the last two decades. In 1976, The Cotton Disease Council estimated that 73,000 bales were lost as a result of the foliar and stem phases of this disease. Since this organism can cause boll rot, additional losses were probably included in this category.

Bacterial Blight can occur on all parts of the plant. It can be part of the seedling disease complex, but the first visible symptoms are the leaf spots. This disease is also called angular leaf spot because the leaf spots are angular shaped and they are found along the main veins of the leaf. The disease can be found on the leaves, bracts, squares, and bolls. Lesions on bolls will appear as if hot oil splashed on the boll.ˇ Some people have described the boll lesions as having the appearance of a cigarette burn depending upon the stage of the disease as well as the stage of the bolls.

Bacterial Blight is most prevalent at high temperatures and high humidity. Temperatures in the 86-97 degrees and humidity of greater than 85 percent provide the right conditions for development. Since the disease is bacterial it is easily spread by windblown moisture and water splashing on the plants.

Since this is a bacterial disease, spraying fungicides will not help. It the disease is present, workers or equipment can spread the disease by moving through the field. So growers should walk their fields after the dew has dried. Look for the leaf and square symptoms and excessive leaf shed. Non-irrigated fields have more stress and might show the symptoms first.

So what can producers do now if they find it in the field? The Arkansas Alert recommends the following: 1)ˇ?Continue to manage the crop for yield.ˇ While the disease may hurt, it will not likely hurt nearly as bad as abandoning the field or cutting back on inputs.ˇ 2)ˇˇRecognize that the disease can be spread by equipment or people moving through the field when the leaves are wet.ˇˇ Avoid running ground rigs through or scouting fields when the foliage is still wet from rain, dew, or irrigation. 3)ˇˇBe realistic regarding irrigation.ˇWhile overhead irrigation may contribute to the spread of the pathogen, lack of irrigation will be of much greater concern.ˇ Continue to irrigate as needed to meet crop demands, but do not over-irrigate. 4)ˇˇThere are no chemical control methods for control of bacterial blight in the field.ˇ Maintain good insect control to minimize the possibility of infection through wounds created by insect feeding.

5)ˇˇDo not over fertilize.ˇ Lush, rank foliage will contribute to higher humidity in the canopy, a longer period of leaf wetness, and will enhance infection.ˇ In fields or cultivars where the crop tends toward rank growth, consider using plant growth regulators to maintain an open canopy.?

If this disease does appear in Missouri, growers can contact their local extension specialists for assistance in collecting samples for diagnosis. I can be contacted at 573-888-4722. Sam Atwell in New Madrid County can be contacted at 573-748-5531 and Anthony Ohmes in Mississippi County may be contacted at 573-683-6129. This disease may originate from debris or transmitted by planting seed. The University of Arkansas is recommending that the planting seed be tested.

University of Missouri Extension programs are open to all

Dr. Michael R. Milam is an agronomy specialist and county program director with University of Missouri Extension in Dunklin County.