| VOLUME 6. # 7&8 | July-August, 1998 |
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Texas Produce Convention & Expo Sept. 9-12
This year's state Produce Convention will be held at the South Padre Island Convention Centre beginning on Wednesday September 9th and ending on Saturday September 12th. In order to avoid late registration fees you'll want to register prior to the August 21st early registration deadline. Hotel reservations need to be in by August 9th.
The Convention will begin on Wednesday with registration and TPA business meetings on shipping and international trade and a TVA board meeting. Thursday's program will include a morning general session and concurrent afternoon sessions on citrus, vegetable and watermelons. Friday's program includes concurrent sessions on production and member meetings for both the Texas Vegetable Association and Texas Produce Association. For more information on the meetings and how to register contact TPC registration headquarters at (956)584-1772.
1998 National Pepper Conference
If you're in the pepper business and would like a great place to learn more about this fascinating crop, the National Pepper Conference is the place to be. The 14th biennial National Pepper Conference will be held
at the San Antonio Marriott Rivercenter on October 13 through the 15th, 1998. Registration will begin at 4:00 p.m. Tuesday October 13 at the Marriott Rivercenter with a welcome reception to follow. The conference will include an all day tour on Wednesday the 14th of the San Antonio area featuring area pepper trials and processing plants. Formal conference sessions will feature sections on pepper genetics, pest management and cultural management. The sessions will be on Thursday the 15th and will run during the entire day. The conference will conclude with a San Antonio style banquet on Thursday evening.
If you would like more information about the conference please contact Ben Villalon or Lynn Brandenberger at (956) 968-5581 or contact us through the Pepper Conference web-site at http://extension-horticulture.tamu.edu/southtex. Hope to see you at the conference.
Diagnosis and Control of Watermelon Diseases in South Texas
Our Extension Plant Pathologist Tom Isakeit has done a fantastic job on a new World Wide Web publication that features both text and pictures of watermelon diseases that are found in South Texas. The article describes 24 different pathological problems of watermelon and several physiological problems. There are 44 different clickable images in the document ranging from Anasa Wilt to Southern Blight to pimples on the fruit. Diagnosis and Control of Watermelon Diseases in South Texas should provide an excellent diagnostic tool for producers and crop advisors alike.
We would encourage you to take a closer look at this Web publication which can be found in the information and reports section of the South Texas Vegetable Web. The World Wide Web address for the South Texas Vegetable Web is http://extension-horticulture.tamu.edu/southtex/.
Herbicides for Fall Vegetables by Lynn Brandenberger
Many of the vegetable crops that we depend upon for our livelihoods come in a distant second place when competing with weed species that can and will, out compete these crops. Weed control is an important part of the production system that vegetable growers need to pay attention to, particularly during the dry spell that we are currently experiencing. Poor weed control wastes water and can result in serious problems, i.e. low yields, poor quality, increased costs, and weeds also act as reservoirs for plant disease.
Identification of past and potential problem weed species is important. By knowing what we're up against we have a better chance of selecting cultural practices and herbicides that will successfully control the weeds. Included in this newsletter is a table of several herbicides that are labeled for use on fall/winter vegetable crops.
Once you have selected the right material for controlling weeds, the next important step is proper application. Even if you've done a great job of picking a fantastic herbicide that will control all your problem weeds in a field, if you mess up the application, chances are it won't be effective. So, where to begin? First and always first, read the label and heed the label. If it says that you should use a certain nozzle or sprayer configuration use it! When it tells you to apply so many gallons of spray solution using a specific rate of herbicide per acre, do it! Don't assume that your sprayer is set properly, even if you set it last week, check it again. All this sounds time consuming and tedious and it is, but checking the sprayer's nozzles, settings and making sure it's calibrated correctly will ensure that you have the best possible application to ensure good weed control and will prevent you from wasting money and herbicide.
Diagnosing Foliar Diseases of Vegetables by Tom Isakeit
Often, a grower will refer to photographs in books and bulletins for guidance in determining the cause of abnormalities on leaves. However, such materials depict more common symptoms of infectious diseases and usually the variation in symptom appearance caused by the pathogen is not depicted, nor are many common and uncommon non-infectious causes of similar symptoms. Thus, such material does not depict many commonly encountered symptoms. They should, however, be considered a useful starting point for disease diagnosis. Although it would be preferable to know the cause of a symptom, if the symptom isn't getting worse over time (i.e. more of the leaf affected or appearance on other foliage), for practical management purposes, it is sufficient to rule out an infectious cause. In this article, I will present some general points for deciding whether a symptom is caused by an infectious agent or something else. In making generalizations, I will use watermelons as examples, although these generalizations will also apply to most other vegetable crops.
Generally, leaf-spots caused by fungi tend to be circular (reflecting the pattern of fungal growth) and the affected tissue tends to be dead. Such tissue is either black or brown in color. Furthermore, the discolored tissue is not collapsed in relation to surrounding tissue. This is in contrast to physical or chemical causes of leaf injury, which tend to cause affected areas to become dried up and shrunken.
Sometimes, leaf-spots caused by fungi have very distinctive symptoms and a photograph is sufficient for making a diagnosis . An example is Cercospora leaf-spot of watermelon. In contrast, photographs of leaf-spots caused by Alternaria or by the gummy stem blight fungus are just not distinctive enough for diagnostic purposes. Additionally, photographs of advanced symptoms of downy mildew, gummy stem blight and anthracnose that depict extensive leaf blight are not useful either.
To determine if these particular diseases are present, I recommend that growers remove suspicious leaves and place them in a "moist chamber" at room temperature for 12-24 hours. The moist chamber is a small, sealed container (or even a sealed plastic bag) in which a wet paper towel is present to generate a humid atmosphere. Under these conditions, spots will expand, or at least, pathogenic fungi will produce spores on them. The presence of spores can be determined with a good hand lens or a "pocket" microscope. Of course, the identification of these spores does require previous training, but for the purposes of a watermelon grower, that training need not be extensive. I have done such training by simply having infected plant tissue on hand and taking five minutes to show the grower what to look for with a hand lens. The results of a moist chamber incubation are usually conclusive for diagnosing a fungus disease or ruling it out.
Additional diagnostic clues can be determined by the pattern of symptom appearance in the field. Uniformity suggests a non-infectious cause, for example, leaf-spots that occur over most of field caused by foliar fertilizer burn. Infectious diseases tend to have a clustered distribution in a field. The timing of symptom appearance can also offer a clue. The sudden appearance of similar symptoms suggest a non-infectious cause. If the advanced symptom of an infectious disease is found in a portion of the field, earlier symptoms can also be found. For example, if downy mildew is the cause of a blighted leaf (i.e. dead) , leaves with yellow spots - an early symptom - will be found on leaves in close proximity. Finally, the pattern of symptom appearance should be compared to recent weather patterns. A leaf blight occurring when day temperatures are in the 90's with no rain occurring does not have downy mildew or gummy stem blight as a cause. In fact, leaf miner insects can be the cause of such blight in different areas of Texas and they can easily be diagnosed by the presence of serpentine, hollowed-out trails on non-blighted leaves.
Diseases caused by bacteria and viruses will also tend to occur in clusters in the field and result in a range of symptom stages on plants in that area. So, if the distribution of symptomatic plants is clustered and fungi are ruled out with a moist chamber, these other infectious agents need to be checked out. Unfortunately, this is not always a "do-it-yourself" proposition for growers. There are some diagnostic kits for specific bacterial and viral diseases that are "grower-friendly". For example, STA Laboratories has an excellent bacterial fruit blotch testing kit, while Agdia has numerous kits for bacterial and virus diseases on various crops. Another option is to bring samples to a plant disease diagnostic clinic.
One other consideration is that wilting and yellowing symptoms on the leaves may be caused by infectious agents working on the roots. Be ready to dig up and examine the whole plant.
The grower should strive to quickly identify the presence of foliage-infecting fungi if they occur on the crop. Under the right weather conditions (i.e. moist conditions), these fungi can cause significant yield losses, but if they are diagnosed quickly enough, they can be readily controlled with fungicides.
Farewell to Tom Isakeit
If you haven't heard the sad news, you're about to hear it. Tom Isakeit has taken a new position with the Extension Service at College Station as a state-wide plant pathologist working primarily on field crops, but will still do some work on vegetables.
In Tom's tenure in South Texas he has done a great job as our Extension Plant Pathologist. His work in diagnosing crop disease problems and being available to help the vegetable industry with it's many and varied problems has earned him our greatest respect. Tom, best of luck and please, don't become a complete stranger to South Texas.
Lynn Brandenberger/Editor
The information given herein is for educational purposes only. References to commercial products or trade names are made with the understanding that no discrimination is intended and no endorsement by the Cooperative Extension Service is implied.