This month’s articles

§ Check for Hosta Virus X in Your Greenhouse

§ Sumagic plant growth regulator now registered for use on several vegetable transplants

§ Managing crown gall

Check for Hosta Virus X in Your Greenhouse
Thomas A. Dudek, Extension Horticulture and Marketing Educator

March 30, 2009 -- Growers need to be on the lookout for this important virus pathogen of Hosta. Look over plants that are flushing out their leaves. Over the last few years this problem has been on the increase. The following information was provided from the publication: A Pocket Guide for IPM Scouting in Herbaceous Perennials by Jan Byrne and Raymond A. Cloyd. Purchase this in a pocket-sized guide for reference in the greenhouse or nursery from MSU Extension (publication E-2981).

If you suspect this problem contact your local greenhouse extension educator or send samples in to the MDU Diagnostic Services Lab.

Pathogen: Hosta virus X (HsVX).

Hosts: Hosta.

Symptoms: Cultivars vary in their susceptibility, symptoms vary as well. Mottling or mosaic patterns on the foliage are common. Foliage may be puckered or distorted. Severely affected foliage may become necrotic. Blue-flowered cultivars may have color breaking.

Spread: The most significant source of disease spread is through movement of infected plant material. The virus is sap transmissible and therefore, can easily be spread during plant propagation. This virus is not spread by insect vectors.

Management: Infected plants can not be treated and should be removed and destroyed. Carefully inspect all incoming plant material, particularly that coming in from outside the United States, to be sure it is free from symptoms. Material to be used for propagation should be tested prior to propagation. Contact your local plant diagnostic lab to see what testing options are available. The MSU Diagnostic Services lab offers HsVX testing by ELISA. Regularly disinfest equipment used during propagation or trimming to avoid sap transmission of the virus.

Mottling on hosta foliage caused by hosta virus X. Plant infected with hosta virus X Leaf infected with hosta virus X
This information was developed from A Pocket Guide for IPM Scouting in Herbaceous Perennials by Jan Byrne and Raymond A. Cloyd. Purchase this in a pocket-sized guide for reference in the nursery from MSU Extension (publication E-2981).

Sumagic plant growth regulator now registered for use on several vegetable transplants

Erik Runkle, Horticulture

March 16, 2009 -- The Plant Growth Regulator Sumagic from Valent Professional Products is now labeled for use on several vegetable transplants grown in commercial greenhouses. Sumagic, which contains the active ingredient uniconazole, is the first and only plant growth retardant that can legally be used on fruiting vegetable crops. This is a significant milestone, as growers have had to use a variety of environmental techniques and low levels of fertility to help maintain compact vegetable plugs.

Sumagic is specifically registered for use as a foliar spray on tomato, pepper, eggplant, groundcherry, pepino and tomatillo. The recommended label rate is 2 to 10 ppm at a volume of 2 quarts per 100 sq ft of crop. Experiments performed with Sumagic at Michigan State University in cooperation with Valent Professional Products, showed that as little as a single 1.0 ppm spray application had a noticeable effect on inhibiting extension growth of tomato seedlings. Therefore, as with all plant growth regulators, small-scale trials by growers are encouraged to determine appropriate rates for your growing conditions, crops grown and desired responses.

According to the supplemental label, the total amount of Sumagic applied to vegetable transplants may not exceed that from a single 10-ppm spray application at 2 quarts per 100 sq ft. In addition, the final application may not occur later than 14 days after the 2 to 4 true leaf stage. Sumagic is registered for use on vegetable transplants in all states except California and New York. Finally, the supplemental label must be in the possession of the user at the time of application.

Managing crown gall
Jan Byrne, Diagnostic Services

March 10, 2009 -- Agrobacterium tumefaciens is the bacterial pathogen that causes crown gall. Crown gall is well known as a disease of woody ornamentals and tree fruits, but it can also affect herbaceous perennials. Producers of perennials, especially those propagated by cuttings, should be aware of the disease and the symptoms it causes. The bacterium typically induces plants to produce an abnormally large number of cells that make up the gall. Galls range from pea-size to larger than one foot in diameter and are produced on roots, stems and foliage.

Agrobacterium tumefaciens is soil borne and can survive in soil without a host for several years. The bacterium enters plants through wounds, often those made by cultural practices such as grafting, pruning or taking cuttings. Once inside the host plant it induces gall formation. Larger galls may destroy vascular tissue of the plant, causing dieback or plant death. With time gall tissue breaks down, releasing A. tumefaciens back into the soil or onto other host material.

Good sanitation is an important component of crown gall disease control. Equipment used to prune plants or to take cuttings should be thoroughly disinfested. Symptomatic plants should be removed and destroyed. Greenhouse plants that are in close proximity to those with galls should also be removed and destroyed; these may be infected although they are not yet showing symptoms.

There are several disease control products available for crown gall control; these contain a strain of Agrobacterium that is antagonistic toward the gall causing pathogen. The efficacy of these products varies somewhat with the type of plant material being treated. These products are meant to protect healthy plant material; they do not eradicate current infections. Copper-based fungicides can be used to help limit spread, but again these will not eradicate current infections.