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Missouri Produce Growers


Zelalem Mersha
Lincoln University Cooperative Extension
Plant Pathology

Two for the price of one: Enhancing Disease Control during Wet Weather using Copper and other Dual Purpose Products

Zelalem Mersha
Lincoln University Cooperative Extension

Published: May 23, 2016

Weather in the past few years (following the 2012 drought season) is pretty much dominated by wet summers with monthly precipitations exceeding the normal averages in Missouri. The record high precipitation in decades during some summer months in 2015 has challenged many growers in the state and beyond. Obviously, the impact of a nonstop rain at the peak seasons and the subsequent "little ponds" created on farms for long durations has not only delayed land prep and plantings but also gravely burdened growers by a huge task of frequent weed management. Setting aside these, the excessive precipitation accompanied by windy rain storms has led to increased incidence of diseases on many farms and unfortunately, to the detection of sporadic diseases. One such example was the surprise appearance of cucurbit downy mildew (CDM) after the Labor Day in 2015. CDM was first detected on the sentinel plots at Lincoln University's G. W. Carver farm (https://ipm.missouri.edu/meg/2015/10/Cucumber-Downy-Mildew/) and in few more high tunnels afterwards.

The most frequent diseases in 2015 were those caused by bacteria and the water-loving "fungus-like" organisms (also known as the water molds belonging to the Oomycetes in the Kingdom Protista). This is based on the annual report of the Plant Diagnostic Clinic, frequently asked questions from clientele, and as witnessed by many educators' farm visits in the extension systems of University of Missouri and Lincoln University. Expectedly, extended wet weather equates to a "feast" for this groups of microbes as their livelihood entirely depends on presence of water. Undoubtedly, the continuous warmth and extended periods of wet weather accompanied by an increased relative humidity has also exacerbated the situation and led to a great spike in incidence and severity of many fungal diseases.

The question that comes to everyone's mind is what can be done differently under such circumstances. Growers are highly advised to a) anticipate based on weather predictions, b) monitor in a timely manner, and c) acquire an accurate diagnosis and detection as early as possible before the pathogen infections devastate their crops. At many instances, diseases caused by bacteria and oomycetes could easily cause a total crop failure in a short duration, if left unabated in a timely manner. In addition, chasing each group of pathogen under such a high disease pressure during extended periods of rain becomes extremely challenging. First, it is difficult to get a time window that is enough to get dried plant surfaces prior to sprays and second, it is difficult to keep plants covered by the fungicides for long without being washed away by the frequent rains.

Responsible use of chemistries with dual fungicidal and bactericidal property, as part and parcel of an integrated disease management strategy, inevitably becomes a necessity to save crops during these situations. Understandably, alternating and/or tank mixing different fungicides with different modes of action is essential to avoid or delay pathogen resistance. The purpose of this article is to shed some light on the available chemistries that could simultaneously take care of diseases caused by more than one pathogen group, bacteria, fungi and water molds*.

*These are groups of organisms within the kingdom protista division oomycetes are known to have some sort of motile stages in their life cycles (zoospores) and hence phylogenetically different from true fungi. Common pathogen genera within the oomycetes that are known to cause serious damage on produce include Pythium, Phytophthora, and many others that are responsible for downy mildews. For a long time though, they were grouped under the kingdom fungi, hence the term fungicide is still used for those compounds that kill oomycetes.

The following are few examples of chemistries that are known to have fungicidal and bactericidal properties:

  1. Copper products or different formulations of copper are the first group of chemistries with efficacies reported on multiple pathogen groups. The following are examples of two major sub-groups.

    1. Copper sulfates which come in different trade names. Just to mention three: 1) Basicop™ whose active ingredient (a.i.) is tribasic copper sulfate monohydrate, 2) Cuprofix® Ultra 40 Dispress® (a.i. basic copper sulfate), and 3) Tri-Base Blue® (a.i. tribasic copper sulfate in the form of a suspension concentrate). For instance, Tri-Base Blue® is registered for a number of bacterial (spot, speck, canker), fungal (early blight, septoria leaf spot) and oomycetous (late blight/phytophthora blight) diseases.
    2. Copper hydroxides which also comes in different trade names as Kocide 2000®, Kocide 3000®, Champion®, Champ® etc. Copper products such as Kocide®, Champ®, Cuprofix® are labelled for bacterial spot of pepper in greenhouses. They also give a fair protection in field applications of pepper for bacterial spot. Similar copper products such as Badge®, Champ®, Cueva®, Cuprofix®, Kentan®, Kocide®, and Nordox® are labelled for greenhouse use to manage bacterial spot and speck on tomatoes. Copper products also reduce spread of bacterial diseases under field conditions. In both cases, however, bacterial strains that are copper-resistant have been detected in the Midwest. To mitigate this and improve efficacy, growers are highly encouraged to use Mancozeb products (e.g. Dithane, Manzate, and Penncozeb) with copper products.
  2. Some watermelon growers in boot-heel area have hinted the use of Kocide® alongside chlorothalonil containing products (Bravo®, Equus® or Echo®) as an early preventative spray against most fungal and bacterial diseases of watermelon. In addition to its primarily bactericidal properties, Kocide® is registered for a number of fungal pathogens in cucurbits.

    Recently, there are also products such as ManKocide® that contain active ingredients of both Kocide® (46% Copper Hydroxide) and Mancozeb® (15% Manzoceb, a product of zinc ion and manganese ethylene-bis-dithiocarbamate). ManKocide® is labelled for a range of crops and pathogen groups including but not limited to fungi, bacteria and oomycetes.

  3. The second groups are those which have a proven efficacy as Plant Defense Inducers. For example, acibenzolar-S-methyl (ASM), also known as Actigard® as a commercial product, belongs to the group P1 according to the 2016 Fungicide Resistance Action Committee (FRAC) mode of action classification (http://www.frac.info/docs/default-source/publications/frac-code-list/frac-code-list-2016.pdf?sfvrsn=2). This is a group known to have a host plant defense induction. On cucurbits, it has a good efficacy against bacterial leaf and fruit blotch but it has to be combined with copper applications for the best outcome. It has a poor efficacy on other fungal diseases (powdery mildew and scab) and downy mildews. On tomatoes, this product has been reported to show a fair efficacy for bacterial spot and speck diseases. In other herbs, such as basil, Actigard® has shown a good control of the recently emerging downy mildew disease in greenhouses.
  4. The third group is products with broad spectrum, multi-site actions that are used to manage the two major groups of pathogens, water molds and fungi. One amongst many other examples for this group is Gavel® which contains mancozeb and zoxamide, for instance, has a good efficacy against downy mildew and phytophthora blight as well as the fungal disease alternaria leaf blight of cucurbits as shown on the 2016 Midwest Vegetable Production Guide. Tanos®, a product which combines cymoxanil and famoxadone as active ingredient, has a wide spectrum of activity on many fungal (good performance against Alternaria and Anthracnose), oomycetous and bacterial diseases. The production guide can also be accessed online (https://ag.purdue.edu/btny/midwest-vegetable-guide/Pages/default.aspx) for free.

Overall, products that could simultaneously thwart diseases caused by multiple pathogen groups are economically beneficial as long as the labels are followed. In any case, however, compatibility should be checked if any tank mixing of products is planned. Such a use in both cases not only saves money and time by half but also makes planning and implementation of sprays very efficient.

N.B. Trade names in this publication are used solely for the purpose of providing specific information. Such use herein is not a guarantee or warranty of the products named and does not signify that they are approved to the exclusion of others. Mention of a proprietary product does not constitute an endorsement nor does it imply lack of efficacy of similar products not mentioned. Do not use any of the products unless registered for the given crop in the state.

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REVISED: January 4, 2017