Impatiens Downy Mildew – Dr. Margery Daughtery from The Cornell Extension Agency on Long Island spoke to us about Impatiens Downy Mildew. Prior to 2011 this disease had been isolated in a few pockets of the U.S. including the Midwest and New England. The unusually wet and stormy summer and fall we had helped to spread the disease to near outbreak symptoms in some areas across the eastern U.S. Dr. Daughtery’s research is showing that preventative sprays of Adorn+Protect DF, Heritage, Subdue, Pageant, Stature, Segway, and Vital work well. She is also recommending to landscapers not to replant Impatiens in locations that had infected Impatiens in 2011.
Boxwood Blight – Across most of the mid-Atlantic and Northeastern U.S. Boxwood Blight still continues to be on the minds of growers and landscapers alike. Researchers and Boxwood growers continue to feverishly work on this pathogen. Some new findings include Sarcocca also being a host plant to this Cylindrocladium strain. Also, there are a couple of chemical classes that are showing promise in controlling this disease when used preventatively including; Chlorothalonil (Daconil), Strobilurins (Heritage, Pageant, Cygnus, and Compass O), Fludioxonil (Palladium, Medallion, Hurricane WDG) and the DMI class (BannerMaxx, Stature, Strike, Terraguard). The following is a link to an interview put out by NMPro Magazine that addresses the topic of Boxwood Blight, steer your customers to this link for more information regarding this disease.
Last fall during mum production, Mum Brown Rust started to show up in nurseries across much of the northern states. Mum Brown Rust is not quarantinable like the Chrysanthemum White Rust. Mum Brown Rust first appears on the undersides of the leaves as orange to yellow zits. These reproductive organs of the fungi, if left untreated, can grow to become large pustules. Preventative sprays once a month thru the course of the growing season offer the best strategy for controlling this disease. Strobilurins like Heritage and Pageant work the best for rust control, Mancozeb or Protect and Daconil also are effective. Some growers also suggest that Ni helps to inhibit rust sporulation, Harrell’s MAX® Ornamental 9-3-6 has a small concentration of Ni in it and would be a good candidate to spray once a month at a rate of 64oz/100 gals. Always spray Harrell’s MAX® products during the cooler hours of the day when the plant is more actively respiring for quicker uptake.
Sansevieria anthracnose was addressed by Dr. Dave Norman from the U of FL. This plant is especially susceptible to new diseases because so much of the propagules come from offshore sites. When shipped into the U.S. these plants could be harboring harmful plant pathogens, like Colletotrichum sansevieriae, or Sansevieria anthracnose. This pathogen is host specific to Sansevieria and will not infect other crops. This disease first appears as small brown spots that often looked water soaked. As the disease progresses these spots will become increasingly larger and have the ability to completely stretch across the entire leaf. Dr. Norman’s research is showing that preventative sprays of these chemicals are effective at controlling Sansevieria anthracnose: Pageant, Heritage, Torque, Concert, thiophanate methyl, Affirm, Palladium, Disarm, Cease and Milstop. This typically isn’t a crop that needs to be sprayed and might present an opportunity to pick up some extra chemical sales in the south. There is no cure for this disease, prevention only so staying on top of this disease is key.
I also chatted with Dr. Norman about a disease that has been around for a while now, the Myrothecium leafspot. Myrothecium roridum has again started to show up in nurseries and propagation houses across the southern U.S. This pathogen is opportunistic and usually uses a wound site to enter into the plant, infecting a wide range of host plants including tropicals, bedding and floral crops, woody ornamentals and even vegetables. The spores of this disease can be seen with a hand lens and are usually flat white domes with black caps on them. This disease does best in warm humid environments making it a serious problem in the propagation setting. Over time the disease will continue to progress and can lead to complete necrosis of the leafspot and the tissue may fall out in some species, making them unsightly. Spray rotations of Pageant, Medallion, Affirm or Veranda, Segway, Heritage, and Iprodione at 14-21 day rotations work well at controlling this pathogen.
Ceratocystis Blight was also mentioned at the conference because it is now being found in Anthurium and Aspidistra. Ceratocystis fimbriata has long been document on mango, cocoa, chocolate, cassava, taro, sycamore, aspen, Caladium, Diffenbachia and sweet potato, but has just only recently been document on Anthurium and Aspidistra. This pathogen first infects the axillary petioles of the plant, and they quickly become chlorotic which eventually leads to dieback. Rotations of Pageant and thiophanate methyl at monthly intervals should keep this disease at bay.
For the southern growers, Xanthomonas Bacterial Blight seems to be getting a lot of attention because it has now been documented on Rubber Tree (Ficus elastica) and on Zebra plant (Aphelandra squarrosa). Xanthomonas first appears as small chlorotic spots on the leaves. As the pathogen progresses it leads to large watersoaked spots and eventually complete leaf necrosis will occur if left untreated. Warm and humid conditions favor disease development. Sanitation is very important in controlling this disease, promote good air circulation and clean up old leaf litter. Copper products such as Phyton27, CuPro, and Kocide are still the best curative option for this bacterium. Follow this spray up with an application of Protect or Mancozeb. Then apply a biological such as Cease or Regalia.