Posts Tagged ‘white mold’

Managing Diseases of High Tunnel Tomatoes

Friday, June 1st, 2012

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu

I have received several questions about timber rot caused by Sclerotinia sclerotiorum, leaf mold caused by Fulvia fulva, and gray mold caused by Botrytis cinerea over the past week for greenhouse and high tunnel tomatoes in Maryland and Delaware.

Timber rot is common where tomatoes (or another susceptible host) have been planted in ground beds in the past. The fungus Sclerotinia sclerotiorum causes disease on hundreds of plant species. Therefore rotation is difficult. Even when a high tunnel is moved between seasons, the disease can be severe because the fungus overwinters both in and around the tunnels. Usually the primary source of inoculum is outside of a high tunnel. In the spring when the soil is moist, the fungal fruiting bodies emerge and spores (ascospores) are released. These ascospores will be released continually throughout the spring and are carried on wind into the doors or raised sides of nearby high tunnels. Ascospores are usually carried or dispersed less than 330 feet. Therefore it is important to use sanitation within 330 feet of a high tunnel. No plants, leaf clippings, potting mix, or soil from the tunnels should be discarded within this area.

There are some practices that will help reduce timber rot pressure, such as minimizing the length of time that the soil stays wet. The biocontrol, Contans has been effective in managing Sclerotinia diseases in the field. Contans, which is a formulation of the fungus Coniothyrium minitans, parasitizes the survival structures of S. sclerotiorum. If it is sprayed on the area around the high tunnel and watered into the soil, it may help reduce ascospore formation in future years. Because the product is a live organism, it must be handled carefully to preserve its effectiveness. Contans would be a good choice for fields or areas around high tunnels, which are used repeatedly for a susceptible crop. See the Contans label for additional information. Other products labeled for Sclerotinia timber rot are Endura, which is labeled for field use, and Botran, which is labeled for greenhouse use.

Leaf mold and gray mold are both favored by high humidity and therefore improving air flow can reduce the extent of disease spread. There are several fungicides that are labeled for greenhouse use that will help reduce disease. These include Scala for leaf mold, Mycostop and Decree for suppressing gray mold, mancozeb products such as Dithane F-45, and copper. In addition to timber rot, Botran has activity on gray mold.

Additional Information About Using Omega for Lima Bean Downy Mildew Control

Friday, August 27th, 2010

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

In last week’s article I went over the control measures for downy mildew on baby lima beans and recommended Omega as a new product labeled for lima beans that has excellent activity for downy mildew as well as white mold. The label is a little ambiguous about recommended application methods and it was clarified by the manufacturer that it is to be applied by ground only, not by air. I am in contact with the company concerning this issue, and they will be pursuing changing the label with EPA. Unfortunately nothing will happen in time for this season if downy mildew should appear later, but it can be applied by ground rigs now.

Timber Rot, White Mold, Sclerotinia Rot in Spring Greenhouses and High Tunnels

Thursday, May 6th, 2010

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu

The fungus Sclerotinia sclerotiorum along with other Sclerotinia spp. cause disease on hundreds of plant species, including most vegetables. Diseases caused by Sclerotinia, such as timber rot or Sclerotinia rot are becoming very serious problems in vegetables grown in greenhouses and high tunnels. The diseases overwinter in the soil as large resistant sclerotia, which multiply during years of susceptible crop production. However, even when a high tunnel is moved between seasons, the disease can be severe because the fungus overwinters both in and around the greenhouses and tunnels. The primary source of inoculum may originate inside as well as outside these structures. In the spring when the soil is moist, the fungal fruiting bodies emerge and spores (ascospores) are released. These ascospores will be released continually throughout the spring and are carried throughout the house if originating inside the structure. If the ascospores originate outside the house, they are carried on wind through the doors, vents or raised sides of nearby structures. Ascospores are usually carried or dispersed less than 330 feet. Therefore, it is especially important to use sanitation within 330 feet of a greenhouse or high tunnel. No plants, leaf clippings, potting mix, or soil from the greenhouse or high tunnel should be discarded within this area.

Inside the greenhouse or high tunnel, improve air flow in and around the plants by increasing in-row spacing and trellising plants to reduce disease incidence. Conversely, the proliferation of leaves near the soil will increases disease. The biocontrol Contans has been effective in managing Sclerotinia diseases in the field. The active ingredient of Contans, Coniothyrium minitans, parasitizes the overwintering (or surviving) sclerotia. If Contans is sprayed on the area around the high tunnel and watered into the soil, it may help reduce ascospore formation in future years. Contans must sprayed long before disease development occurs (2 months) to be effective within a crop year. Because the product is living, handle it carefully prior to use. Contans would be a good choice to try in fields or areas around greenhouses and high tunnels that are used repeatedly for a susceptible crop. See the Contans label for additional information.

Other fungicide products labeled for Sclerotinia in the greenhouse are Botran and Terraclor. Maximizing fungicide coverage to plants during application is important. Apply fungicides prior to disease development for greatest efficacy. Keep in mind that the fungus becomes established on senescing tissue first and then colonizes the plant. See the Botran and Terraclor labels for information on individual vegetable crops.

The black sclerotina on the small tomato fruit will overwinter and result in ascospore formation in future years. The fruit should be either buried or discarded more that 330 feet from the high tunnel.

Lima Bean Disease Update

Friday, August 14th, 2009

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Downy Mildew and Lima Bean Pod Rot
Two more fields were identified with downy mildew this week so it is important to keep scouting. Phytophthora capsici was also identified on pods from a field close to harvest. This disease we have named lima bean pod rot. It is found most commonly in low spots in the field. I had talked about it in the article titled Downy Mildew Identified on Lima Beans in WCU 17:20 and have included another picture to help you identify it in the field. There is no effective fungicide control for this disease at the present time. Copper applications may help, but have not been very effective on Phytophthora capsici on other crops. Some field populations of this fungus may be resistant to Ridomil Gold/Copper as we discovered several years ago, so that product cannot be depended on to provide control unless the fungus population is susceptible to Ridomil (mefanoxam).

P. phaseoli on upper pod, P. capsici on lower podDowny mildew on the upper pod and lima bean pod rot on the lower pod. Note the granular appearance of the fungus on the lower pod and the lack of a reddish brown border on the pod infected with lima bean pod rot or Phytophthora capsici.

White Mold
We have yet to see white mold in limas but there is a new fungicide labeled for white mold in lima and snap beans. Omega 500F (fluazinam) from Syngenta, an excellent white mold fungicide that has been labeled in potatoes and peanuts for a long time, is now labeled on beans (snaps and limas). The good thing is that this fungicide is also very effective against downy mildew on limas if applied preventatively although downy mildew is not on the label. I have one year’s test results under heavy disease pressure and it performed very well at the 5.5 fl oz rate. This label was granted after the recommendations book was printed so it is not in the recs. It is the only product that provides control of both white mold and downy mildew. I am going to get another look at it this fall for downy mildew control so I can have two years of data.

Timber Rot, White Mold or Sclerotinia Rot in High Tunnels

Friday, May 8th, 2009

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu

The fungus Sclerotinia sclerotiorum causes disease on hundreds of plant species. Timber rot or Sclerotinia rot is becoming a very serious problem in tomatoes (and other crops) grown in high tunnels. Even when a high tunnel is moved between seasons, the disease can be severe because the fungus overwinters both in and around the tunnels. Usually the primary source of inoculum is outside of a high tunnel. In the spring when the soil is moist, the fungal fruiting bodies emerge and spores (ascospores) are released. These ascospores will be released continually throughout the spring and are carried on wind into the doors or raised sides of nearby high tunnels. Ascospores are usually carried or dispersed less than 330 feet. Therefore it is important to use sanitation within 330 feet of a high tunnel. No plants, leaf clippings, potting mix, or soil from the tunnels should be discarded within this area.

The biocontrol Contans has been effective in managing Sclerotinia diseases in the field. Contans, which is a formulation of the fungus Coniothyrium minitans, parasitizes the survival structures of S. sclerotiorum. If it is sprayed on the area around the high tunnel and watered into the soil, it may help reduce ascospore formation in future years. Because the product is living, it must be handled carefully prior to use. Contans would be a good choice to try in fields or areas around high tunnels, which are used repeatedly for a susceptible crop. See the Contans label for additional information.

Other products labeled for Sclerotinia timber rot are Endura, which is labeled for field use, and Botran, which is labeled for greenhouse use.

The black sclerotia on the small tomato fruit will overwinter and result in ascospore formation in future years. The fruit should be either buried or discarded more that 330 feet from the high tunnel.

 Sclerotinea rot on a small tomato fruit.

Tomato fruit infected with Sclerotinia sclerotiorum.