Biological Update

Xanthomonas on ranunculus was reduced with applications of Cease under field conditions.

Any way you look at it, growers must use every tool available to produce crops. This includes biological control products. But don’t expect the same results from biological control products as from standard synthetic products. Some good ideas — and some bad ones — still seem to plague use of these products.

To be successful, you must agree to look at biological control products without preconceptions about what they do. I have read over many trials conducted on vegetables and other agronomic crops in order to get a more complete picture of how well the biological control products that have the same active ingredients as ornamental products have worked. I am going to review a few of the biological control products for diseases of ornamentals in this article.

Success with Cease
The active ingredient in Cease (BioWorks) is Bacillus subtilis (QST 713). This bacterial product works on a wide variety of diseases, with the best results on some foliar diseases. Good control is possible on downy mildew, powdery mildew, bacterial leaf spots (like Pseudomonas and Xanthomonas), Botrytis, Cercospora leaf spot and Colletotrichum leaf spot. We have not seen successful control of Erwinia soft rot, fire blight (E. amylovora), or crown gall (Agrobacterium) with Cease.

A 2011 trial including Cease was conducted by Dr. D. M. Ingram (Mississippi State University) on gray mold (Botrytis blight) affecting greenhouse tomatoes. It is very interesting to see how these products worked to control gray mold on these tomatoes (see Table 1).

Cease is compatible with a wide range of fungicides and bactericides. For a complete list, visit www.bioworksinc.com/products/cease/compatibility-chart.pdf.

It is especially interesting to me that Cease (a bacterium) is compatible with copper products, although we have not seen any benefits of combining the two in overall efficacy against bacterial leaf spots. I also have not seen any research supporting the combination of MilStop and Cease to achieve higher levels of disease control.

RootShield Plus
RootShield Plus (BioWorks) is a combination of two fungi: Trichoderma harzianum T-22 and T. viride G41. The trials I performed were mainly against Pythium root rot, but some trials on Phytophthora, Rhizoctonia, Fusarium, and even Thielaviopsis (black root rot) were included. I also reviewed IR-4 trials on fungicides for control of Pythium diseases on ornamentals. The average control in the 11 IR-4 trials on Pythium diseases was 23 percent control.

We also performed trials on P. aphanidermatum root rot on poinsettia and saw excellent control. Two trials on celosia with damping-off by either P. irregulare or P. ultimum yielded results with no control in either trial.

Strangely enough, the stem rot trials with Phytophthora parasitica on vinca showed no control in one trial and excellent control in another trial. The first trial had very severe stem and crown rot, while the second trial showed root rot only. The product may work better under low disease pressure. When applying a biofungicide as a drench, it is also more challenging to control a soil-borne pathogen that is able to move up into the foliage.

Pythium root rot on poinsettia (plant on left) can be effectively prevented with RootShield (plant on right).

Rhizoctonia damping-off on celosia was also tested with RootShield Plus. Results confirmed that using a root-inoculating fungus does not help on a stem-rotting pathogen (like Rhizoctonia), with no control at all in one study. In one trial on black root rot on pansy (Thielaviopsis basicola), no control was seen with RootShield Plus.

For Fusarium diseases, I performed one trial on lisianthus (F. oxysporum) with no control. IR-4 trials showed the following results for Fusarium diseases:

• Dracaena stem rot caused by F. solani — very good control
• Delphinium crown rot caused by F. oxysporum — some control
• Douglas fir damping-off caused by F. commune — no control in two trials

Many other trials have been conducted by Dr. Ramon Georgis of AgroSci R&D in Palo Alto, Calif., in 2010 and 2011. His results were overwhelmingly good in contrast to the average results obtained in the IR-4 (or my) trials.

Vermicompost tea
Dr. Neil Mattson (assistant professor and floriculture extension specialist, Cornell University) and Margery Daughtrey (senior extension associate, LIHREC, Cornell University) have been working on quite a few biological control agents, including vermicompost tea. The research was performed on Pythium root rot in seed geranium ‘Pinto Classic White.’ Treatments included a nontreated control and several incorporated biocontrols: a Streptomyces (Actino-Iron); a T. harzianum (RootShield G); and a T. harzianum + T. virens combo (RootShield Plus G); 10 percent vermicompost (by volume as incorporated into the substrate); and a 100 mL/pot vermicompost tea drench. The vermicompost tea drench was prepared using a non-aerated 1:40 (W/W) solution at transplant, repeated in 48 hrs. Plant growth and mortality was scored five weeks later, and plants were collected at the soil line for dry-weight analysis.

When assessed five weeks after inoculation, the inoculated control plants showed 10 percent mortality and some stunting, while noninoculated controls showed no symptoms. Geraniums given RootShield and ActinoIron treatments exhibited less mortality (about 5 percent) and less stunting than inoculated controls, whereas geraniums in RootShield Plus and vermicompost incorporation treatments showed greater mortality than the controls. The experimenters hypothesize that storage issues related to the RootShield Plus and vermicompost explain why they performed poorly versus controls, highlighting a relevant consideration when utilizing biological materials.

Interestingly, all 24 of the plants given the vermicompost tea treatments were vigorous at the end of the trial, with no mortality. Dry weights were reduced in comparison to controls by all treatments except the vermicompost tea.

Keep in mind that vermicompost tea is not a controlled product in that it may differ from source to source or even batch to batch, thus giving differing results. Further trials will be conducted to determine whether the miscellany of microorganisms in the vermicompost tea can provide this level of biocontrol consistently.   

On the horizon
One of the most interesting things I have been hearing about is a new species of Trichoderma asperellum being tested for remediation of nursery sites with Ramorum blight. The completed research trials have been very positive, with no Phytophthora ramorum detectable after treatment of contaminated soil with this species of Trichoderma. Dr. Tim Widmer, USDA-ARS, is conducting research at the North American Ornamental Research Site at Dominican University of California.

Conclusions
The conclusions we made 30 years ago about how well biological control products worked are no longer valid. Many new products have been developed and brought to market, and they work far better than some of us thought they could. On top of that, the market for biologicals is expanding with the change in societal attitudes toward agricultural production throughout the world.

The only thing that has not changed is that disease control is still difficult, and the products we use must work. Biological control products are still more difficult to use than standard chemistries. This is primarily due to the fact that when a living organism is employed, whether it is a fungus or bacterium, you have to be concerned with its welfare.

Using a biological control agent for disease management means understanding the plant and its needs, the pathogen that causes the disease, and the biological agent and its needs. Using biological products for disease control successfully will end up making us better growers.

Ann R. Chase is a well-known plant pathologist and expert on diseases of ornamental plants throughout the United States. She is a widely published author, teacher and speaker.

Photos courtesy of Ann R. Chase

Ideas Wanted
Editor’s Note: Greenhouse Management is always reporting on the latest research on the products that growers use every day. If you have an idea for future articles focused on experts’ field trials and related product research, contact astankiewicz@gie.net, 216-236-5960.